Dave, if your receiver system (including feedline loss effects) is not perfectly quiet, then you do stand to gain *something* in performance by using a quiet LNA at the antenna. But in doing so you will suffer some loss in receiver dynamic range. In order to make a wise decision, you need hard numbers for the performance of your receiver, and you need to find out for sure what noise level comes out of your antenna when it's pointed in the quietest direction, which is where the most benefit from an LNA will accrue. Dana K8YUM On Tue, Jun 30, 2020 at 4:59 PM Dave Sublette via mvus-list < mvus-list@lists.febo.com> wrote: > Thanks Trevor, > > I found that graph, but it stops at 30 MHz. In the meantime, I think I > have answered my own question IF the info I found is correct. > > I found an article by a Dutch amateur that stated "the noise figure on 50 > MHz is >6dB. " If this is true, then the noise figure of my receiver plus > loss in the feedline can be as high as 6 dB and it won't do any good to put > a preamp at the antenna. > > The total loss of 100 feet of LMR400 is .9 dB. The loss of 250 feet of > 1/2" superflex is 1.825 dB. The sum of the two in 2.7 dB. My Rx front end > is surely less than 3 dB (Elecraft K3s). So I don't think I need a preamp > for my proposed installation. > > But it all hinges on the statement that the atmospheric terrestrial noise > figure at 50 MHz is 6 dB. Anybody got any better number for this?? > > 73, > > Dave, K4TO > > On Tue, Jun 30, 2020 at 5:29 PM Trevor Clarke <retrev@csh.rit.edu> wrote: > > > > https://en.wikipedia.org/wiki/Radio_noise#/media/File:Atmosphericnoise.PNG > > > > > > On Tue, Jun 30, 2020 at 5:19 PM Dave Sublette via mvus-list < > > mvus-list@lists.febo.com> wrote: > > > >> I know that ambient noise drops as frequency increases. That is why we > >> strive for ever lower noise figures in our preamps as we operate higher > >> bands. > >> > >> What I am looking for is a chart, or graph that shows this noise level > >> from > >> about 30 MHz up. > >> > >> At this moment I am particularly interested in 50 MHz. The reason is I > am > >> putting a yagi for six meters out on the tower behind the house. I > >> will have 100 feet of LMR 400 and 250 feet of 1/2 inch superflex between > >> me > >> and the antenna. I want to know if I need a preamp. > >> > >> I went through this exercise when I mounted the yagi at 50 feet right by > >> the house and had only 75 feet of 1/2 inch hardline feeding it. It did > no > >> good to put a preamp at the antenna. > >> > >> I have been googling and evidently haven't used the proper terms > because I > >> don't get the results I need. Any link to this info would be greatly > >> appreciated. > >> > >> Thanks & 73, > >> > >> Dave, K4TO > >> _______________________________________________ > >> mvus-list mailing list > >> mvus-list@lists.febo.com > >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > >> > > > > > > -- > > Trevor R.H. Clarke > > Computer Science House > > Rochester Institute of Technology > > retrev@csh.rit.edu > > http://www.csh.rit.edu/~retrev/ > > > _______________________________________________ > mvus-list mailing list > mvus-list@lists.febo.com > http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >

Well my receiver will be the K3s, which has a built in whiz bang preamp and attenuator options to manage dynamic range. The Antenna allegedly has 15 dBd gain and is very quiet due to the loop driver. The feedline loss will be 2.7 db and I could lower that 0.17 dB by going to 1/2 inch superflex on the tower. So what else do we need to know? BTW I have an Agilent N8973A Noise Figure Measuring System to measure with. 73, Dave, K4TO On Tue, Jun 30, 2020 at 7:12 PM Dana Whitlow <k8yumdoober@gmail.com> wrote: > Dave, if your receiver system (including feedline loss effects) is not > perfectly quiet, then you do stand to gain *something* in performance > by using a quiet LNA at the antenna. But in doing so you will suffer > some loss in receiver dynamic range. In order to make a wise decision, > you need hard numbers for the performance of your receiver, and you > need to find out for sure what noise level comes out of your antenna > when it's pointed in the quietest direction, which is where the most > benefit from an LNA will accrue. > > Dana K8YUM > > > On Tue, Jun 30, 2020 at 4:59 PM Dave Sublette via mvus-list < > mvus-list@lists.febo.com> wrote: > >> Thanks Trevor, >> >> I found that graph, but it stops at 30 MHz. In the meantime, I think I >> have answered my own question IF the info I found is correct. >> >> I found an article by a Dutch amateur that stated "the noise figure on 50 >> MHz is >6dB. " If this is true, then the noise figure of my receiver plus >> loss in the feedline can be as high as 6 dB and it won't do any good to >> put >> a preamp at the antenna. >> >> The total loss of 100 feet of LMR400 is .9 dB. The loss of 250 feet of >> 1/2" superflex is 1.825 dB. The sum of the two in 2.7 dB. My Rx front >> end >> is surely less than 3 dB (Elecraft K3s). So I don't think I need a preamp >> for my proposed installation. >> >> But it all hinges on the statement that the atmospheric terrestrial noise >> figure at 50 MHz is 6 dB. Anybody got any better number for this?? >> >> 73, >> >> Dave, K4TO >> >> On Tue, Jun 30, 2020 at 5:29 PM Trevor Clarke <retrev@csh.rit.edu> wrote: >> >> > >> https://en.wikipedia.org/wiki/Radio_noise#/media/File:Atmosphericnoise.PNG >> > >> > >> > On Tue, Jun 30, 2020 at 5:19 PM Dave Sublette via mvus-list < >> > mvus-list@lists.febo.com> wrote: >> > >> >> I know that ambient noise drops as frequency increases. That is why we >> >> strive for ever lower noise figures in our preamps as we operate higher >> >> bands. >> >> >> >> What I am looking for is a chart, or graph that shows this noise level >> >> from >> >> about 30 MHz up. >> >> >> >> At this moment I am particularly interested in 50 MHz. The reason is >> I am >> >> putting a yagi for six meters out on the tower behind the house. I >> >> will have 100 feet of LMR 400 and 250 feet of 1/2 inch superflex >> between >> >> me >> >> and the antenna. I want to know if I need a preamp. >> >> >> >> I went through this exercise when I mounted the yagi at 50 feet right >> by >> >> the house and had only 75 feet of 1/2 inch hardline feeding it. It >> did no >> >> good to put a preamp at the antenna. >> >> >> >> I have been googling and evidently haven't used the proper terms >> because I >> >> don't get the results I need. Any link to this info would be greatly >> >> appreciated. >> >> >> >> Thanks & 73, >> >> >> >> Dave, K4TO >> >> _______________________________________________ >> >> mvus-list mailing list >> >> mvus-list@lists.febo.com >> >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >> >> >> > >> > >> > -- >> > Trevor R.H. Clarke >> > Computer Science House >> > Rochester Institute of Technology >> > retrev@csh.rit.edu >> > http://www.csh.rit.edu/~retrev/ >> > >> _______________________________________________ >> mvus-list mailing list >> mvus-list@lists.febo.com >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >> >

When in doubt, build the preamp and make it remotely switchable so you can compare with real reception. If you don't ever need to use it you'll find another use... Maybe when you install that 250' tower Trevor R.H. Clarke, K8TRC On Tue, Jun 30, 2020, 7:23 PM Dave Sublette via mvus-list < mvus-list@lists.febo.com> wrote: > Well my receiver will be the K3s, which has a built in whiz bang preamp and > attenuator options to manage dynamic range. The Antenna allegedly has 15 > dBd gain and is very quiet due to the loop driver. The feedline loss will > be 2.7 db and I could lower that 0.17 dB by going to 1/2 inch superflex on > the tower. > > So what else do we need to know? BTW I have an Agilent N8973A Noise > Figure Measuring System to measure with. > > 73, > > Dave, K4TO > > On Tue, Jun 30, 2020 at 7:12 PM Dana Whitlow <k8yumdoober@gmail.com> > wrote: > > > Dave, if your receiver system (including feedline loss effects) is not > > perfectly quiet, then you do stand to gain *something* in performance > > by using a quiet LNA at the antenna. But in doing so you will suffer > > some loss in receiver dynamic range. In order to make a wise decision, > > you need hard numbers for the performance of your receiver, and you > > need to find out for sure what noise level comes out of your antenna > > when it's pointed in the quietest direction, which is where the most > > benefit from an LNA will accrue. > > > > Dana K8YUM > > > > > > On Tue, Jun 30, 2020 at 4:59 PM Dave Sublette via mvus-list < > > mvus-list@lists.febo.com> wrote: > > > >> Thanks Trevor, > >> > >> I found that graph, but it stops at 30 MHz. In the meantime, I think I > >> have answered my own question IF the info I found is correct. > >> > >> I found an article by a Dutch amateur that stated "the noise figure on > 50 > >> MHz is >6dB. " If this is true, then the noise figure of my receiver > plus > >> loss in the feedline can be as high as 6 dB and it won't do any good to > >> put > >> a preamp at the antenna. > >> > >> The total loss of 100 feet of LMR400 is .9 dB. The loss of 250 feet of > >> 1/2" superflex is 1.825 dB. The sum of the two in 2.7 dB. My Rx front > >> end > >> is surely less than 3 dB (Elecraft K3s). So I don't think I need a > preamp > >> for my proposed installation. > >> > >> But it all hinges on the statement that the atmospheric terrestrial > noise > >> figure at 50 MHz is 6 dB. Anybody got any better number for this?? > >> > >> 73, > >> > >> Dave, K4TO > >> > >> On Tue, Jun 30, 2020 at 5:29 PM Trevor Clarke <retrev@csh.rit.edu> > wrote: > >> > >> > > >> > https://en.wikipedia.org/wiki/Radio_noise#/media/File:Atmosphericnoise.PNG > >> > > >> > > >> > On Tue, Jun 30, 2020 at 5:19 PM Dave Sublette via mvus-list < > >> > mvus-list@lists.febo.com> wrote: > >> > > >> >> I know that ambient noise drops as frequency increases. That is why > we > >> >> strive for ever lower noise figures in our preamps as we operate > higher > >> >> bands. > >> >> > >> >> What I am looking for is a chart, or graph that shows this noise > level > >> >> from > >> >> about 30 MHz up. > >> >> > >> >> At this moment I am particularly interested in 50 MHz. The reason is > >> I am > >> >> putting a yagi for six meters out on the tower behind the house. I > >> >> will have 100 feet of LMR 400 and 250 feet of 1/2 inch superflex > >> between > >> >> me > >> >> and the antenna. I want to know if I need a preamp. > >> >> > >> >> I went through this exercise when I mounted the yagi at 50 feet right > >> by > >> >> the house and had only 75 feet of 1/2 inch hardline feeding it. It > >> did no > >> >> good to put a preamp at the antenna. > >> >> > >> >> I have been googling and evidently haven't used the proper terms > >> because I > >> >> don't get the results I need. Any link to this info would be greatly > >> >> appreciated. > >> >> > >> >> Thanks & 73, > >> >> > >> >> Dave, K4TO > >> >> _______________________________________________ > >> >> mvus-list mailing list > >> >> mvus-list@lists.febo.com > >> >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > >> >> > >> > > >> > > >> > -- > >> > Trevor R.H. Clarke > >> > Computer Science House > >> > Rochester Institute of Technology > >> > retrev@csh.rit.edu > >> > http://www.csh.rit.edu/~retrev/ > >> > > >> _______________________________________________ > >> mvus-list mailing list > >> mvus-list@lists.febo.com > >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > >> > > > _______________________________________________ > mvus-list mailing list > mvus-list@lists.febo.com > http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >

Some comments on 6M noise figure. Back in the late 60s, Drake designed and sold 6M converters and the TR6 transceiver. During the design phase, the engineer that designed the front end stages found that data that showed 6 dB NF equivalent was the thermal noise floor or sky temp at the horizon, whatever you want to call it. But does that mean you should be happy if your radio has a 6 dB noise figure (the Icom 7610, Icom 7300, Flex 6600 are all about at that number - 5 to 7 dB) ? There are a couple of other things to be considered - one is coax loss that will add to the rx NF as mentioned in this thread, and don’t forget some insertion loss if your radio is connected through an amplifier whose relays may add a dB. So if you have say 3 dB of feedline and other insertion loss, then you need your rx to have a 3 dB NF to get back to 6 dB NF at the antenna. But your rx might not be 3 dB NF, so you may want to add a preamp. The president of Flex claims that 6 dB NF is good enough for 6M but he is not considering feedline and other losses so I disagree with his statement. Also, I don’t think people are looking at that 6 dB NF goal exactly right. If your rx system NF is 6 dB at the antenna connector and you are in the middle of nowhere where the sky temp is not increased by human added noise, then you have two equal noises, the rx front end generated noise and the sky received noise. So both are contributing equal noise. If you lower the rx NF to say 2 dB NF you will reduce that component and the sky noise will be dominant. No one seems to ever mention this and I wonder what some of you guys think about that ? Is that a valid conclusion ? But, regardless of any of the above, at your QTH, compare the noise, when your antenna is connected, to the noise when a 50 Ohm resistor is connected and if the noise comes up maybe 5 dB when the antenna is connected, in your quietest direction, then manmade noise is high enough that you don’t need to try to lower you NF any more. This is the true test and you don’t even need to know any of the theory and you don’t need to know what your NF is. That is my situation at home as my noise will come up 10 to 15 dB on the antenna vs 50 Ohms. But at our contest site in Urbana, using an Icom 7610 or 7300, if the line noise is quiet, I here no increase in noise with the antenna. So I use a 0.5 dB Down East Microwave 24 dB gain preamp in the preamp loop of the 7610. With that much preamp gain, the internal Icom preamp is left off and the radio NF measures about 2 dB at the antenna terminal with preamp this way. There is some loss in the Icom switching. With this improvement, some increase in noise is noted when the antenna is connected vs 50 Ohm resistor. 73 Steve K8DZ > On Jun 30, 2020, at 7:32 PM, Trevor Clarke via mvus-list <mvus-list@lists.febo.com> wrote: > > When in doubt, build the preamp and make it remotely switchable so you can > compare with real reception. If you don't ever need to use it you'll find > another use... Maybe when you install that 250' tower > > Trevor R.H. Clarke, K8TRC > > On Tue, Jun 30, 2020, 7:23 PM Dave Sublette via mvus-list < > mvus-list@lists.febo.com> wrote: > >> Well my receiver will be the K3s, which has a built in whiz bang preamp and >> attenuator options to manage dynamic range. The Antenna allegedly has 15 >> dBd gain and is very quiet due to the loop driver. The feedline loss will >> be 2.7 db and I could lower that 0.17 dB by going to 1/2 inch superflex on >> the tower. >> >> So what else do we need to know? BTW I have an Agilent N8973A Noise >> Figure Measuring System to measure with. >> >> 73, >> >> Dave, K4TO >> >> On Tue, Jun 30, 2020 at 7:12 PM Dana Whitlow <k8yumdoober@gmail.com> >> wrote: >> >>> Dave, if your receiver system (including feedline loss effects) is not >>> perfectly quiet, then you do stand to gain *something* in performance >>> by using a quiet LNA at the antenna. But in doing so you will suffer >>> some loss in receiver dynamic range. In order to make a wise decision, >>> you need hard numbers for the performance of your receiver, and you >>> need to find out for sure what noise level comes out of your antenna >>> when it's pointed in the quietest direction, which is where the most >>> benefit from an LNA will accrue. >>> >>> Dana K8YUM >>> >>> >>> On Tue, Jun 30, 2020 at 4:59 PM Dave Sublette via mvus-list < >>> mvus-list@lists.febo.com> wrote: >>> >>>> Thanks Trevor, >>>> >>>> I found that graph, but it stops at 30 MHz. In the meantime, I think I >>>> have answered my own question IF the info I found is correct. >>>> >>>> I found an article by a Dutch amateur that stated "the noise figure on >> 50 >>>> MHz is >6dB. " If this is true, then the noise figure of my receiver >> plus >>>> loss in the feedline can be as high as 6 dB and it won't do any good to >>>> put >>>> a preamp at the antenna. >>>> >>>> The total loss of 100 feet of LMR400 is .9 dB. The loss of 250 feet of >>>> 1/2" superflex is 1.825 dB. The sum of the two in 2.7 dB. My Rx front >>>> end >>>> is surely less than 3 dB (Elecraft K3s). So I don't think I need a >> preamp >>>> for my proposed installation. >>>> >>>> But it all hinges on the statement that the atmospheric terrestrial >> noise >>>> figure at 50 MHz is 6 dB. Anybody got any better number for this?? >>>> >>>> 73, >>>> >>>> Dave, K4TO >>>> >>>> On Tue, Jun 30, 2020 at 5:29 PM Trevor Clarke <retrev@csh.rit.edu> >> wrote: >>>> >>>>> >>>> >> https://en.wikipedia.org/wiki/Radio_noise#/media/File:Atmosphericnoise.PNG >>>>> >>>>> >>>>> On Tue, Jun 30, 2020 at 5:19 PM Dave Sublette via mvus-list < >>>>> mvus-list@lists.febo.com> wrote: >>>>> >>>>>> I know that ambient noise drops as frequency increases. That is why >> we >>>>>> strive for ever lower noise figures in our preamps as we operate >> higher >>>>>> bands. >>>>>> >>>>>> What I am looking for is a chart, or graph that shows this noise >> level >>>>>> from >>>>>> about 30 MHz up. >>>>>> >>>>>> At this moment I am particularly interested in 50 MHz. The reason is >>>> I am >>>>>> putting a yagi for six meters out on the tower behind the house. I >>>>>> will have 100 feet of LMR 400 and 250 feet of 1/2 inch superflex >>>> between >>>>>> me >>>>>> and the antenna. I want to know if I need a preamp. >>>>>> >>>>>> I went through this exercise when I mounted the yagi at 50 feet right >>>> by >>>>>> the house and had only 75 feet of 1/2 inch hardline feeding it. It >>>> did no >>>>>> good to put a preamp at the antenna. >>>>>> >>>>>> I have been googling and evidently haven't used the proper terms >>>> because I >>>>>> don't get the results I need. Any link to this info would be greatly >>>>>> appreciated. >>>>>> >>>>>> Thanks & 73, >>>>>> >>>>>> Dave, K4TO >>>>>> _______________________________________________ >>>>>> mvus-list mailing list >>>>>> mvus-list@lists.febo.com >>>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>>>> >>>>> >>>>> >>>>> -- >>>>> Trevor R.H. Clarke >>>>> Computer Science House >>>>> Rochester Institute of Technology >>>>> retrev@csh.rit.edu >>>>> http://www.csh.rit.edu/~retrev/ >>>>> >>>> _______________________________________________ >>>> mvus-list mailing list >>>> mvus-list@lists.febo.com >>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>> >>> >> _______________________________________________ >> mvus-list mailing list >> mvus-list@lists.febo.com >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >> > _______________________________________________ > mvus-list mailing list > mvus-list@lists.febo.com > http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com

Good discussion about the noise figure. Steve - So in the case for the Urbana location (very little urban generated noise), where using the low-noise Down East preamp is better than what’s in the Icom 7610, moving the preamp up to the antenna would not improve the situation any more. Is that correct, since you’ve now reached the point where additional noise improvement would not help? That leads to the next question. On 144 MHz, how much improvement is gained by moving a preamp from the shack to the antenna, if you use a .3 dB NF preamp for terrestrial (non-EME) use? For 144 MHz terrestrial work, is a preamp in the shack fine unless one had several dB of redline loss? For EME, it seems like serious operators go after every tenth of a dB possible from antenna gain. Joe - WA8OGS > On Jul 1, 2020, at 10:21 AM, Steve Koogler via mvus-list <mvus-list@lists.febo.com> wrote: > > Some comments on 6M noise figure. Back in the late 60s, Drake designed and sold 6M converters and the TR6 transceiver. During the design phase, the engineer that designed the front end stages found that data that showed 6 dB NF equivalent was the thermal noise floor or sky temp at the horizon, whatever you want to call it. But does that mean you should be happy if your radio has a 6 dB noise figure (the Icom 7610, Icom 7300, Flex 6600 are all about at that number - 5 to 7 dB) ? There are a couple of other things to be considered - one is coax loss that will add to the rx NF as mentioned in this thread, and don’t forget some insertion loss if your radio is connected through an amplifier whose relays may add a dB. So if you have say 3 dB of feedline and other insertion loss, then you need your rx to have a 3 dB NF to get back to 6 dB NF at the antenna. But your rx might not be 3 dB NF, so you may want to add a preamp. The president of Flex claims that 6 dB NF is good enough for 6M but he is not considering feedline and other losses so I disagree with his statement. > > Also, I don’t think people are looking at that 6 dB NF goal exactly right. If your rx system NF is 6 dB at the antenna connector and you are in the middle of nowhere where the sky temp is not increased by human added noise, then you have two equal noises, the rx front end generated noise and the sky received noise. So both are contributing equal noise. If you lower the rx NF to say 2 dB NF you will reduce that component and the sky noise will be dominant. No one seems to ever mention this and I wonder what some of you guys think about that ? Is that a valid conclusion ? > > But, regardless of any of the above, at your QTH, compare the noise, when your antenna is connected, to the noise when a 50 Ohm resistor is connected and if the noise comes up maybe 5 dB when the antenna is connected, in your quietest direction, then manmade noise is high enough that you don’t need to try to lower you NF any more. This is the true test and you don’t even need to know any of the theory and you don’t need to know what your NF is. That is my situation at home as my noise will come up 10 to 15 dB on the antenna vs 50 Ohms. But at our contest site in Urbana, using an Icom 7610 or 7300, if the line noise is quiet, I here no increase in noise with the antenna. So I use a 0.5 dB Down East Microwave 24 dB gain preamp in the preamp loop of the 7610. With that much preamp gain, the internal Icom preamp is left off and the radio NF measures about 2 dB at the antenna terminal with preamp this way. There is some loss in the Icom switching. With this improvement, some increase in noise is noted when the antenna is connected vs 50 Ohm resistor. > > 73 Steve K8DZ > > > > > >> On Jun 30, 2020, at 7:32 PM, Trevor Clarke via mvus-list <mvus-list@lists.febo.com> wrote: >> >> When in doubt, build the preamp and make it remotely switchable so you can >> compare with real reception. If you don't ever need to use it you'll find >> another use... Maybe when you install that 250' tower >> >> Trevor R.H. Clarke, K8TRC >> >> On Tue, Jun 30, 2020, 7:23 PM Dave Sublette via mvus-list < >> mvus-list@lists.febo.com> wrote: >> >>> Well my receiver will be the K3s, which has a built in whiz bang preamp and >>> attenuator options to manage dynamic range. The Antenna allegedly has 15 >>> dBd gain and is very quiet due to the loop driver. The feedline loss will >>> be 2.7 db and I could lower that 0.17 dB by going to 1/2 inch superflex on >>> the tower. >>> >>> So what else do we need to know? BTW I have an Agilent N8973A Noise >>> Figure Measuring System to measure with. >>> >>> 73, >>> >>> Dave, K4TO >>> >>> On Tue, Jun 30, 2020 at 7:12 PM Dana Whitlow <k8yumdoober@gmail.com> >>> wrote: >>> >>>> Dave, if your receiver system (including feedline loss effects) is not >>>> perfectly quiet, then you do stand to gain *something* in performance >>>> by using a quiet LNA at the antenna. But in doing so you will suffer >>>> some loss in receiver dynamic range. In order to make a wise decision, >>>> you need hard numbers for the performance of your receiver, and you >>>> need to find out for sure what noise level comes out of your antenna >>>> when it's pointed in the quietest direction, which is where the most >>>> benefit from an LNA will accrue. >>>> >>>> Dana K8YUM >>>> >>>> >>>> On Tue, Jun 30, 2020 at 4:59 PM Dave Sublette via mvus-list < >>>> mvus-list@lists.febo.com> wrote: >>>> >>>>> Thanks Trevor, >>>>> >>>>> I found that graph, but it stops at 30 MHz. In the meantime, I think I >>>>> have answered my own question IF the info I found is correct. >>>>> >>>>> I found an article by a Dutch amateur that stated "the noise figure on >>> 50 >>>>> MHz is >6dB. " If this is true, then the noise figure of my receiver >>> plus >>>>> loss in the feedline can be as high as 6 dB and it won't do any good to >>>>> put >>>>> a preamp at the antenna. >>>>> >>>>> The total loss of 100 feet of LMR400 is .9 dB. The loss of 250 feet of >>>>> 1/2" superflex is 1.825 dB. The sum of the two in 2.7 dB. My Rx front >>>>> end >>>>> is surely less than 3 dB (Elecraft K3s). So I don't think I need a >>> preamp >>>>> for my proposed installation. >>>>> >>>>> But it all hinges on the statement that the atmospheric terrestrial >>> noise >>>>> figure at 50 MHz is 6 dB. Anybody got any better number for this?? >>>>> >>>>> 73, >>>>> >>>>> Dave, K4TO >>>>> >>>>> On Tue, Jun 30, 2020 at 5:29 PM Trevor Clarke <retrev@csh.rit.edu> >>> wrote: >>>>> >>>>>> >>>>> >>> https://en.wikipedia.org/wiki/Radio_noise#/media/File:Atmosphericnoise.PNG >>>>>> >>>>>> >>>>>> On Tue, Jun 30, 2020 at 5:19 PM Dave Sublette via mvus-list < >>>>>> mvus-list@lists.febo.com> wrote: >>>>>> >>>>>>> I know that ambient noise drops as frequency increases. That is why >>> we >>>>>>> strive for ever lower noise figures in our preamps as we operate >>> higher >>>>>>> bands. >>>>>>> >>>>>>> What I am looking for is a chart, or graph that shows this noise >>> level >>>>>>> from >>>>>>> about 30 MHz up. >>>>>>> >>>>>>> At this moment I am particularly interested in 50 MHz. The reason is >>>>> I am >>>>>>> putting a yagi for six meters out on the tower behind the house. I >>>>>>> will have 100 feet of LMR 400 and 250 feet of 1/2 inch superflex >>>>> between >>>>>>> me >>>>>>> and the antenna. I want to know if I need a preamp. >>>>>>> >>>>>>> I went through this exercise when I mounted the yagi at 50 feet right >>>>> by >>>>>>> the house and had only 75 feet of 1/2 inch hardline feeding it. It >>>>> did no >>>>>>> good to put a preamp at the antenna. >>>>>>> >>>>>>> I have been googling and evidently haven't used the proper terms >>>>> because I >>>>>>> don't get the results I need. Any link to this info would be greatly >>>>>>> appreciated. >>>>>>> >>>>>>> Thanks & 73, >>>>>>> >>>>>>> Dave, K4TO >>>>>>> _______________________________________________ >>>>>>> mvus-list mailing list >>>>>>> mvus-list@lists.febo.com >>>>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>>>>> >>>>>> >>>>>> >>>>>> -- >>>>>> Trevor R.H. Clarke >>>>>> Computer Science House >>>>>> Rochester Institute of Technology >>>>>> retrev@csh.rit.edu >>>>>> http://www.csh.rit.edu/~retrev/ >>>>>> >>>>> _______________________________________________ >>>>> mvus-list mailing list >>>>> mvus-list@lists.febo.com >>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>>> >>>> >>> _______________________________________________ >>> mvus-list mailing list >>> mvus-list@lists.febo.com >>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>> >> _______________________________________________ >> mvus-list mailing list >> mvus-list@lists.febo.com >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > > _______________________________________________ > mvus-list mailing list > mvus-list@lists.febo.com > http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com

Joe, it can make a huge difference if there's feedline loss- much more than one might think at first glance. The reason is that feedline loss does more than simply attenuate the signal. It also adds a new noise source to the picture, namely "blackbody radiation" from the distributed loss in the line. To give the most extreme possible example, suppose the receiver were entirely noiseless and you were pointing the antenna at things of interest in the sky in the frequency regime where the sky can be quite quiet. Now introduce feedline loss where the feedline's sole effect was signal attenuation. With a noise-free receiver, the sole effect of noiseless feed- line loss is signal amplitude reduction, easily corrected in any amount at at the receiver end. Consider, for example, a feedline loss of 3 dB. But now consider that the feedline (hence its loss mechanism) is sitting at 300K (comfortable room temperature for me). Now the feedline is not only losing half the signal power- it is also "radiating" noise into the receiver in the amount of half the feedline's physical temperature, namely 150K. In low noise situations such as radio astronomy, this effect is dominant and devastating. It has the effect of raising the actual receiver's input- referred noise temperature by 150K. The only real mitigation is to either cool the feedline itself to cryogenic temperatures (rarely if ever practical), or to put a good LNA right at the antenna's feed point (or as close thereto as is physically manageable). By so doing you can raise the signal level entering the feedline to the point that it dominates over that 150K contribution from the feedline itself at the receiver end. This is why radio astronomers s go to the considerable expense of putting cryogenic LNAs at the antenna end. This expense includes not only the physical HW (at about the cost of a new car), but operating costs as well [continuous electrical power to the tune of up to several kW, plus makeup refrigerant (very high purity helium) to replace loss due to diffusion and/or gross leaks, plus manpower to monitor the system and perform fairly frequent maintenance tasks to keep it all running, etc]. Cheers, Dana On Wed, Jul 1, 2020 at 10:43 PM Joe via mvus-list <mvus-list@lists.febo.com> wrote: > Good discussion about the noise figure. > > Steve - So in the case for the Urbana location (very little urban > generated noise), where using the low-noise Down East preamp is better than > what’s in the Icom 7610, moving the preamp up to the antenna would not > improve the situation any more. Is that correct, since you’ve now reached > the point where additional noise improvement would not help? > > That leads to the next question. On 144 MHz, how much improvement is > gained by moving a preamp from the shack to the antenna, if you use a .3 dB > NF preamp for terrestrial (non-EME) use? For 144 MHz terrestrial work, is a > preamp in the shack fine unless one had several dB of redline loss? > > For EME, it seems like serious operators go after every tenth of a dB > possible from antenna gain. > > Joe - WA8OGS > > > On Jul 1, 2020, at 10:21 AM, Steve Koogler via mvus-list < > mvus-list@lists.febo.com> wrote: > > > > Some comments on 6M noise figure. Back in the late 60s, Drake designed > and sold 6M converters and the TR6 transceiver. During the design phase, > the engineer that designed the front end stages found that data that > showed 6 dB NF equivalent was the thermal noise floor or sky temp at the > horizon, whatever you want to call it. But does that mean you should be > happy if your radio has a 6 dB noise figure (the Icom 7610, Icom 7300, Flex > 6600 are all about at that number - 5 to 7 dB) ? There are a couple of > other things to be considered - one is coax loss that will add to the rx > NF as mentioned in this thread, and don’t forget some insertion loss if > your radio is connected through an amplifier whose relays may add a dB. So > if you have say 3 dB of feedline and other insertion loss, then you need > your rx to have a 3 dB NF to get back to 6 dB NF at the antenna. But your > rx might not be 3 dB NF, so you may want to add a preamp. The president of > Flex claims that 6 dB NF is good enough for 6M but he is not considering > feedline and other losses so I disagree with his statement. > > > > Also, I don’t think people are looking at that 6 dB NF goal exactly > right. If your rx system NF is 6 dB at the antenna connector and you are in > the middle of nowhere where the sky temp is not increased by human added > noise, then you have two equal noises, the rx front end generated noise and > the sky received noise. So both are contributing equal noise. If you lower > the rx NF to say 2 dB NF you will reduce that component and the sky noise > will be dominant. No one seems to ever mention this and I wonder what some > of you guys think about that ? Is that a valid conclusion ? > > > > But, regardless of any of the above, at your QTH, compare the noise, > when your antenna is connected, to the noise when a 50 Ohm resistor is > connected and if the noise comes up maybe 5 dB when the antenna is > connected, in your quietest direction, then manmade noise is high enough > that you don’t need to try to lower you NF any more. This is the true test > and you don’t even need to know any of the theory and you don’t need to > know what your NF is. That is my situation at home as my noise will come up > 10 to 15 dB on the antenna vs 50 Ohms. But at our contest site in Urbana, > using an Icom 7610 or 7300, if the line noise is quiet, I here no increase > in noise with the antenna. So I use a 0.5 dB Down East Microwave 24 dB gain > preamp in the preamp loop of the 7610. With that much preamp gain, the > internal Icom preamp is left off and the radio NF measures about 2 dB at > the antenna terminal with preamp this way. There is some loss in the Icom > switching. With this improvement, some increase in noise is noted when the > antenna is connected vs 50 Ohm resistor. > > > > 73 Steve K8DZ > > > > > > > > > > > >> On Jun 30, 2020, at 7:32 PM, Trevor Clarke via mvus-list < > mvus-list@lists.febo.com> wrote: > >> > >> When in doubt, build the preamp and make it remotely switchable so you > can > >> compare with real reception. If you don't ever need to use it you'll > find > >> another use... Maybe when you install that 250' tower > >> > >> Trevor R.H. Clarke, K8TRC > >> > >> On Tue, Jun 30, 2020, 7:23 PM Dave Sublette via mvus-list < > >> mvus-list@lists.febo.com> wrote: > >> > >>> Well my receiver will be the K3s, which has a built in whiz bang > preamp and > >>> attenuator options to manage dynamic range. The Antenna allegedly has > 15 > >>> dBd gain and is very quiet due to the loop driver. The feedline loss > will > >>> be 2.7 db and I could lower that 0.17 dB by going to 1/2 inch > superflex on > >>> the tower. > >>> > >>> So what else do we need to know? BTW I have an Agilent N8973A Noise > >>> Figure Measuring System to measure with. > >>> > >>> 73, > >>> > >>> Dave, K4TO > >>> > >>> On Tue, Jun 30, 2020 at 7:12 PM Dana Whitlow <k8yumdoober@gmail.com> > >>> wrote: > >>> > >>>> Dave, if your receiver system (including feedline loss effects) is not > >>>> perfectly quiet, then you do stand to gain *something* in performance > >>>> by using a quiet LNA at the antenna. But in doing so you will suffer > >>>> some loss in receiver dynamic range. In order to make a wise > decision, > >>>> you need hard numbers for the performance of your receiver, and you > >>>> need to find out for sure what noise level comes out of your antenna > >>>> when it's pointed in the quietest direction, which is where the most > >>>> benefit from an LNA will accrue. > >>>> > >>>> Dana K8YUM > >>>> > >>>> > >>>> On Tue, Jun 30, 2020 at 4:59 PM Dave Sublette via mvus-list < > >>>> mvus-list@lists.febo.com> wrote: > >>>> > >>>>> Thanks Trevor, > >>>>> > >>>>> I found that graph, but it stops at 30 MHz. In the meantime, I > think I > >>>>> have answered my own question IF the info I found is correct. > >>>>> > >>>>> I found an article by a Dutch amateur that stated "the noise figure > on > >>> 50 > >>>>> MHz is >6dB. " If this is true, then the noise figure of my receiver > >>> plus > >>>>> loss in the feedline can be as high as 6 dB and it won't do any good > to > >>>>> put > >>>>> a preamp at the antenna. > >>>>> > >>>>> The total loss of 100 feet of LMR400 is .9 dB. The loss of 250 feet > of > >>>>> 1/2" superflex is 1.825 dB. The sum of the two in 2.7 dB. My Rx > front > >>>>> end > >>>>> is surely less than 3 dB (Elecraft K3s). So I don't think I need a > >>> preamp > >>>>> for my proposed installation. > >>>>> > >>>>> But it all hinges on the statement that the atmospheric terrestrial > >>> noise > >>>>> figure at 50 MHz is 6 dB. Anybody got any better number for this?? > >>>>> > >>>>> 73, > >>>>> > >>>>> Dave, K4TO > >>>>> > >>>>> On Tue, Jun 30, 2020 at 5:29 PM Trevor Clarke <retrev@csh.rit.edu> > >>> wrote: > >>>>> > >>>>>> > >>>>> > >>> > https://en.wikipedia.org/wiki/Radio_noise#/media/File:Atmosphericnoise.PNG > >>>>>> > >>>>>> > >>>>>> On Tue, Jun 30, 2020 at 5:19 PM Dave Sublette via mvus-list < > >>>>>> mvus-list@lists.febo.com> wrote: > >>>>>> > >>>>>>> I know that ambient noise drops as frequency increases. That is > why > >>> we > >>>>>>> strive for ever lower noise figures in our preamps as we operate > >>> higher > >>>>>>> bands. > >>>>>>> > >>>>>>> What I am looking for is a chart, or graph that shows this noise > >>> level > >>>>>>> from > >>>>>>> about 30 MHz up. > >>>>>>> > >>>>>>> At this moment I am particularly interested in 50 MHz. The reason > is > >>>>> I am > >>>>>>> putting a yagi for six meters out on the tower behind the house. I > >>>>>>> will have 100 feet of LMR 400 and 250 feet of 1/2 inch superflex > >>>>> between > >>>>>>> me > >>>>>>> and the antenna. I want to know if I need a preamp. > >>>>>>> > >>>>>>> I went through this exercise when I mounted the yagi at 50 feet > right > >>>>> by > >>>>>>> the house and had only 75 feet of 1/2 inch hardline feeding it. It > >>>>> did no > >>>>>>> good to put a preamp at the antenna. > >>>>>>> > >>>>>>> I have been googling and evidently haven't used the proper terms > >>>>> because I > >>>>>>> don't get the results I need. Any link to this info would be > greatly > >>>>>>> appreciated. > >>>>>>> > >>>>>>> Thanks & 73, > >>>>>>> > >>>>>>> Dave, K4TO > >>>>>>> _______________________________________________ > >>>>>>> mvus-list mailing list > >>>>>>> mvus-list@lists.febo.com > >>>>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > >>>>>>> > >>>>>> > >>>>>> > >>>>>> -- > >>>>>> Trevor R.H. Clarke > >>>>>> Computer Science House > >>>>>> Rochester Institute of Technology > >>>>>> retrev@csh.rit.edu > >>>>>> http://www.csh.rit.edu/~retrev/ > >>>>>> > >>>>> _______________________________________________ > >>>>> mvus-list mailing list > >>>>> mvus-list@lists.febo.com > >>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > >>>>> > >>>> > >>> _______________________________________________ > >>> mvus-list mailing list > >>> mvus-list@lists.febo.com > >>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > >>> > >> _______________________________________________ > >> mvus-list mailing list > >> mvus-list@lists.febo.com > >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > > > > _______________________________________________ > > mvus-list mailing list > > mvus-list@lists.febo.com > > http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > > > _______________________________________________ > mvus-list mailing list > mvus-list@lists.febo.com > http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >

Joe, yes you are correct as to 6M. 2M is quieter though and we do use a preamp at the top of the tower for 2M even though we have a fairly large hardline going out there. You can do the same test on 2M - compare noise floor with 50 Ohm load on rcvr to noise heard when antenna is connected. If you don’t ‘hear’ the sky when connecting to the antenna, then you likely can improve by moving preamp closer to the antenna. My experience has been that you can always use a better NF, as low as practical, on 2M if you have a quiet location. Remember, once the S/N has degraded by loss or thermal noise in the feedline, you can never improve that S/N no matter how low NF and how much gain a preamp has, if installed at the receiver end of the feedline. The preamp has to do its job up at the antenna ahead of the feedline attenuation and possible noise contribution (see Dana’s discussion on feedline noise temperature) . 73 Steve K8DZ > On Jul 1, 2020, at 11:42 PM, Joe via mvus-list <mvus-list@lists.febo.com> wrote: > > Good discussion about the noise figure. > > Steve - So in the case for the Urbana location (very little urban generated noise), where using the low-noise Down East preamp is better than what’s in the Icom 7610, moving the preamp up to the antenna would not improve the situation any more. Is that correct, since you’ve now reached the point where additional noise improvement would not help? > > That leads to the next question. On 144 MHz, how much improvement is gained by moving a preamp from the shack to the antenna, if you use a .3 dB NF preamp for terrestrial (non-EME) use? For 144 MHz terrestrial work, is a preamp in the shack fine unless one had several dB of redline loss? > > For EME, it seems like serious operators go after every tenth of a dB possible from antenna gain. > > Joe - WA8OGS > >> On Jul 1, 2020, at 10:21 AM, Steve Koogler via mvus-list <mvus-list@lists.febo.com> wrote: >> >> Some comments on 6M noise figure. Back in the late 60s, Drake designed and sold 6M converters and the TR6 transceiver. During the design phase, the engineer that designed the front end stages found that data that showed 6 dB NF equivalent was the thermal noise floor or sky temp at the horizon, whatever you want to call it. But does that mean you should be happy if your radio has a 6 dB noise figure (the Icom 7610, Icom 7300, Flex 6600 are all about at that number - 5 to 7 dB) ? There are a couple of other things to be considered - one is coax loss that will add to the rx NF as mentioned in this thread, and don’t forget some insertion loss if your radio is connected through an amplifier whose relays may add a dB. So if you have say 3 dB of feedline and other insertion loss, then you need your rx to have a 3 dB NF to get back to 6 dB NF at the antenna. But your rx might not be 3 dB NF, so you may want to add a preamp. The president of Flex claims that 6 dB NF is good enough for 6M but he is not considering feedline and other losses so I disagree with his statement. >> >> Also, I don’t think people are looking at that 6 dB NF goal exactly right. If your rx system NF is 6 dB at the antenna connector and you are in the middle of nowhere where the sky temp is not increased by human added noise, then you have two equal noises, the rx front end generated noise and the sky received noise. So both are contributing equal noise. If you lower the rx NF to say 2 dB NF you will reduce that component and the sky noise will be dominant. No one seems to ever mention this and I wonder what some of you guys think about that ? Is that a valid conclusion ? >> >> But, regardless of any of the above, at your QTH, compare the noise, when your antenna is connected, to the noise when a 50 Ohm resistor is connected and if the noise comes up maybe 5 dB when the antenna is connected, in your quietest direction, then manmade noise is high enough that you don’t need to try to lower you NF any more. This is the true test and you don’t even need to know any of the theory and you don’t need to know what your NF is. That is my situation at home as my noise will come up 10 to 15 dB on the antenna vs 50 Ohms. But at our contest site in Urbana, using an Icom 7610 or 7300, if the line noise is quiet, I here no increase in noise with the antenna. So I use a 0.5 dB Down East Microwave 24 dB gain preamp in the preamp loop of the 7610. With that much preamp gain, the internal Icom preamp is left off and the radio NF measures about 2 dB at the antenna terminal with preamp this way. There is some loss in the Icom switching. With this improvement, some increase in noise is noted when the antenna is connected vs 50 Ohm resistor. >> >> 73 Steve K8DZ >> >> >> >> >> >>> On Jun 30, 2020, at 7:32 PM, Trevor Clarke via mvus-list <mvus-list@lists.febo.com> wrote: >>> >>> When in doubt, build the preamp and make it remotely switchable so you can >>> compare with real reception. If you don't ever need to use it you'll find >>> another use... Maybe when you install that 250' tower >>> >>> Trevor R.H. Clarke, K8TRC >>> >>> On Tue, Jun 30, 2020, 7:23 PM Dave Sublette via mvus-list < >>> mvus-list@lists.febo.com> wrote: >>> >>>> Well my receiver will be the K3s, which has a built in whiz bang preamp and >>>> attenuator options to manage dynamic range. The Antenna allegedly has 15 >>>> dBd gain and is very quiet due to the loop driver. The feedline loss will >>>> be 2.7 db and I could lower that 0.17 dB by going to 1/2 inch superflex on >>>> the tower. >>>> >>>> So what else do we need to know? BTW I have an Agilent N8973A Noise >>>> Figure Measuring System to measure with. >>>> >>>> 73, >>>> >>>> Dave, K4TO >>>> >>>> On Tue, Jun 30, 2020 at 7:12 PM Dana Whitlow <k8yumdoober@gmail.com> >>>> wrote: >>>> >>>>> Dave, if your receiver system (including feedline loss effects) is not >>>>> perfectly quiet, then you do stand to gain *something* in performance >>>>> by using a quiet LNA at the antenna. But in doing so you will suffer >>>>> some loss in receiver dynamic range. In order to make a wise decision, >>>>> you need hard numbers for the performance of your receiver, and you >>>>> need to find out for sure what noise level comes out of your antenna >>>>> when it's pointed in the quietest direction, which is where the most >>>>> benefit from an LNA will accrue. >>>>> >>>>> Dana K8YUM >>>>> >>>>> >>>>> On Tue, Jun 30, 2020 at 4:59 PM Dave Sublette via mvus-list < >>>>> mvus-list@lists.febo.com> wrote: >>>>> >>>>>> Thanks Trevor, >>>>>> >>>>>> I found that graph, but it stops at 30 MHz. In the meantime, I think I >>>>>> have answered my own question IF the info I found is correct. >>>>>> >>>>>> I found an article by a Dutch amateur that stated "the noise figure on >>>> 50 >>>>>> MHz is >6dB. " If this is true, then the noise figure of my receiver >>>> plus >>>>>> loss in the feedline can be as high as 6 dB and it won't do any good to >>>>>> put >>>>>> a preamp at the antenna. >>>>>> >>>>>> The total loss of 100 feet of LMR400 is .9 dB. The loss of 250 feet of >>>>>> 1/2" superflex is 1.825 dB. The sum of the two in 2.7 dB. My Rx front >>>>>> end >>>>>> is surely less than 3 dB (Elecraft K3s). So I don't think I need a >>>> preamp >>>>>> for my proposed installation. >>>>>> >>>>>> But it all hinges on the statement that the atmospheric terrestrial >>>> noise >>>>>> figure at 50 MHz is 6 dB. Anybody got any better number for this?? >>>>>> >>>>>> 73, >>>>>> >>>>>> Dave, K4TO >>>>>> >>>>>> On Tue, Jun 30, 2020 at 5:29 PM Trevor Clarke <retrev@csh.rit.edu> >>>> wrote: >>>>>> >>>>>>> >>>>>> >>>> https://en.wikipedia.org/wiki/Radio_noise#/media/File:Atmosphericnoise.PNG >>>>>>> >>>>>>> >>>>>>> On Tue, Jun 30, 2020 at 5:19 PM Dave Sublette via mvus-list < >>>>>>> mvus-list@lists.febo.com> wrote: >>>>>>> >>>>>>>> I know that ambient noise drops as frequency increases. That is why >>>> we >>>>>>>> strive for ever lower noise figures in our preamps as we operate >>>> higher >>>>>>>> bands. >>>>>>>> >>>>>>>> What I am looking for is a chart, or graph that shows this noise >>>> level >>>>>>>> from >>>>>>>> about 30 MHz up. >>>>>>>> >>>>>>>> At this moment I am particularly interested in 50 MHz. The reason is >>>>>> I am >>>>>>>> putting a yagi for six meters out on the tower behind the house. I >>>>>>>> will have 100 feet of LMR 400 and 250 feet of 1/2 inch superflex >>>>>> between >>>>>>>> me >>>>>>>> and the antenna. I want to know if I need a preamp. >>>>>>>> >>>>>>>> I went through this exercise when I mounted the yagi at 50 feet right >>>>>> by >>>>>>>> the house and had only 75 feet of 1/2 inch hardline feeding it. It >>>>>> did no >>>>>>>> good to put a preamp at the antenna. >>>>>>>> >>>>>>>> I have been googling and evidently haven't used the proper terms >>>>>> because I >>>>>>>> don't get the results I need. Any link to this info would be greatly >>>>>>>> appreciated. >>>>>>>> >>>>>>>> Thanks & 73, >>>>>>>> >>>>>>>> Dave, K4TO >>>>>>>> _______________________________________________ >>>>>>>> mvus-list mailing list >>>>>>>> mvus-list@lists.febo.com >>>>>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>>>>>> >>>>>>> >>>>>>> >>>>>>> -- >>>>>>> Trevor R.H. Clarke >>>>>>> Computer Science House >>>>>>> Rochester Institute of Technology >>>>>>> retrev@csh.rit.edu >>>>>>> http://www.csh.rit.edu/~retrev/ >>>>>>> >>>>>> _______________________________________________ >>>>>> mvus-list mailing list >>>>>> mvus-list@lists.febo.com >>>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>>>> >>>>> >>>> _______________________________________________ >>>> mvus-list mailing list >>>> mvus-list@lists.febo.com >>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>> >>> _______________________________________________ >>> mvus-list mailing list >>> mvus-list@lists.febo.com >>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >> >> _______________________________________________ >> mvus-list mailing list >> mvus-list@lists.febo.com >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com > > > _______________________________________________ > mvus-list mailing list > mvus-list@lists.febo.com > http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com

Thanks Dana and Steve. This has been a good discussion. Now I need to try the 50 ohm load test on my 2 meter 28’ boom yagi pointed in a quiet direction. Take care, Joe - WA8OGS > On Jul 2, 2020, at 10:36 AM, Steve Koogler <k8dzsteve@gmail.com> wrote: > > Joe, yes you are correct as to 6M. 2M is quieter though and we do use a preamp at the top of the tower for 2M even though we have a fairly large hardline going out there. You can do the same test on 2M - compare noise floor with 50 Ohm load on rcvr to noise heard when antenna is connected. If you don’t ‘hear’ the sky when connecting to the antenna, then you likely can improve by moving preamp closer to the antenna. My experience has been that you can always use a better NF, as low as practical, on 2M if you have a quiet location. Remember, once the S/N has degraded by loss or thermal noise in the feedline, you can never improve that S/N no matter how low NF and how much gain a preamp has, if installed at the receiver end of the feedline. The preamp has to do its job up at the antenna ahead of the feedline attenuation and possible noise contribution (see Dana’s discussion on feedline noise temperature) . > > 73 > Steve > K8DZ > >> On Jul 1, 2020, at 11:42 PM, Joe via mvus-list <mvus-list@lists.febo.com <mailto:mvus-list@lists.febo.com>> wrote: >> >> Good discussion about the noise figure. >> >> Steve - So in the case for the Urbana location (very little urban generated noise), where using the low-noise Down East preamp is better than what’s in the Icom 7610, moving the preamp up to the antenna would not improve the situation any more. Is that correct, since you’ve now reached the point where additional noise improvement would not help? >> >> That leads to the next question. On 144 MHz, how much improvement is gained by moving a preamp from the shack to the antenna, if you use a .3 dB NF preamp for terrestrial (non-EME) use? For 144 MHz terrestrial work, is a preamp in the shack fine unless one had several dB of redline loss? >> >> For EME, it seems like serious operators go after every tenth of a dB possible from antenna gain. >> >> Joe - WA8OGS >> >>> On Jul 1, 2020, at 10:21 AM, Steve Koogler via mvus-list <mvus-list@lists.febo.com <mailto:mvus-list@lists.febo.com>> wrote: >>> >>> Some comments on 6M noise figure. Back in the late 60s, Drake designed and sold 6M converters and the TR6 transceiver. During the design phase, the engineer that designed the front end stages found that data that showed 6 dB NF equivalent was the thermal noise floor or sky temp at the horizon, whatever you want to call it. But does that mean you should be happy if your radio has a 6 dB noise figure (the Icom 7610, Icom 7300, Flex 6600 are all about at that number - 5 to 7 dB) ? There are a couple of other things to be considered - one is coax loss that will add to the rx NF as mentioned in this thread, and don’t forget some insertion loss if your radio is connected through an amplifier whose relays may add a dB. So if you have say 3 dB of feedline and other insertion loss, then you need your rx to have a 3 dB NF to get back to 6 dB NF at the antenna. But your rx might not be 3 dB NF, so you may want to add a preamp. The president of Flex claims that 6 dB NF is good enough for 6M but he is not considering feedline and other losses so I disagree with his statement. >>> >>> Also, I don’t think people are looking at that 6 dB NF goal exactly right. If your rx system NF is 6 dB at the antenna connector and you are in the middle of nowhere where the sky temp is not increased by human added noise, then you have two equal noises, the rx front end generated noise and the sky received noise. So both are contributing equal noise. If you lower the rx NF to say 2 dB NF you will reduce that component and the sky noise will be dominant. No one seems to ever mention this and I wonder what some of you guys think about that ? Is that a valid conclusion ? >>> >>> But, regardless of any of the above, at your QTH, compare the noise, when your antenna is connected, to the noise when a 50 Ohm resistor is connected and if the noise comes up maybe 5 dB when the antenna is connected, in your quietest direction, then manmade noise is high enough that you don’t need to try to lower you NF any more. This is the true test and you don’t even need to know any of the theory and you don’t need to know what your NF is. That is my situation at home as my noise will come up 10 to 15 dB on the antenna vs 50 Ohms. But at our contest site in Urbana, using an Icom 7610 or 7300, if the line noise is quiet, I here no increase in noise with the antenna. So I use a 0.5 dB Down East Microwave 24 dB gain preamp in the preamp loop of the 7610. With that much preamp gain, the internal Icom preamp is left off and the radio NF measures about 2 dB at the antenna terminal with preamp this way. There is some loss in the Icom switching. With this improvement, some increase in noise is noted when the antenna is connected vs 50 Ohm resistor. >>> >>> 73 Steve K8DZ >>> >>> >>> >>> >>> >>>> On Jun 30, 2020, at 7:32 PM, Trevor Clarke via mvus-list <mvus-list@lists.febo.com <mailto:mvus-list@lists.febo.com>> wrote: >>>> >>>> When in doubt, build the preamp and make it remotely switchable so you can >>>> compare with real reception. If you don't ever need to use it you'll find >>>> another use... Maybe when you install that 250' tower >>>> >>>> Trevor R.H. Clarke, K8TRC >>>> >>>> On Tue, Jun 30, 2020, 7:23 PM Dave Sublette via mvus-list < >>>> mvus-list@lists.febo.com <mailto:mvus-list@lists.febo.com>> wrote: >>>> >>>>> Well my receiver will be the K3s, which has a built in whiz bang preamp and >>>>> attenuator options to manage dynamic range. The Antenna allegedly has 15 >>>>> dBd gain and is very quiet due to the loop driver. The feedline loss will >>>>> be 2.7 db and I could lower that 0.17 dB by going to 1/2 inch superflex on >>>>> the tower. >>>>> >>>>> So what else do we need to know? BTW I have an Agilent N8973A Noise >>>>> Figure Measuring System to measure with. >>>>> >>>>> 73, >>>>> >>>>> Dave, K4TO >>>>> >>>>> On Tue, Jun 30, 2020 at 7:12 PM Dana Whitlow <k8yumdoober@gmail.com <mailto:k8yumdoober@gmail.com>> >>>>> wrote: >>>>> >>>>>> Dave, if your receiver system (including feedline loss effects) is not >>>>>> perfectly quiet, then you do stand to gain *something* in performance >>>>>> by using a quiet LNA at the antenna. But in doing so you will suffer >>>>>> some loss in receiver dynamic range. In order to make a wise decision, >>>>>> you need hard numbers for the performance of your receiver, and you >>>>>> need to find out for sure what noise level comes out of your antenna >>>>>> when it's pointed in the quietest direction, which is where the most >>>>>> benefit from an LNA will accrue. >>>>>> >>>>>> Dana K8YUM >>>>>> >>>>>> >>>>>> On Tue, Jun 30, 2020 at 4:59 PM Dave Sublette via mvus-list < >>>>>> mvus-list@lists.febo.com <mailto:mvus-list@lists.febo.com>> wrote: >>>>>> >>>>>>> Thanks Trevor, >>>>>>> >>>>>>> I found that graph, but it stops at 30 MHz. In the meantime, I think I >>>>>>> have answered my own question IF the info I found is correct. >>>>>>> >>>>>>> I found an article by a Dutch amateur that stated "the noise figure on >>>>> 50 >>>>>>> MHz is >6dB. " If this is true, then the noise figure of my receiver >>>>> plus >>>>>>> loss in the feedline can be as high as 6 dB and it won't do any good to >>>>>>> put >>>>>>> a preamp at the antenna. >>>>>>> >>>>>>> The total loss of 100 feet of LMR400 is .9 dB. The loss of 250 feet of >>>>>>> 1/2" superflex is 1.825 dB. The sum of the two in 2.7 dB. My Rx front >>>>>>> end >>>>>>> is surely less than 3 dB (Elecraft K3s). So I don't think I need a >>>>> preamp >>>>>>> for my proposed installation. >>>>>>> >>>>>>> But it all hinges on the statement that the atmospheric terrestrial >>>>> noise >>>>>>> figure at 50 MHz is 6 dB. Anybody got any better number for this?? >>>>>>> >>>>>>> 73, >>>>>>> >>>>>>> Dave, K4TO >>>>>>> >>>>>>> On Tue, Jun 30, 2020 at 5:29 PM Trevor Clarke <retrev@csh.rit.edu <mailto:retrev@csh.rit.edu>> >>>>> wrote: >>>>>>> >>>>>>>> >>>>>>> >>>>> https://en.wikipedia.org/wiki/Radio_noise#/media/File:Atmosphericnoise.PNG <https://en.wikipedia.org/wiki/Radio_noise#/media/File:Atmosphericnoise.PNG> >>>>>>>> >>>>>>>> >>>>>>>> On Tue, Jun 30, 2020 at 5:19 PM Dave Sublette via mvus-list < >>>>>>>> mvus-list@lists.febo.com> wrote: >>>>>>>> >>>>>>>>> I know that ambient noise drops as frequency increases. That is why >>>>> we >>>>>>>>> strive for ever lower noise figures in our preamps as we operate >>>>> higher >>>>>>>>> bands. >>>>>>>>> >>>>>>>>> What I am looking for is a chart, or graph that shows this noise >>>>> level >>>>>>>>> from >>>>>>>>> about 30 MHz up. >>>>>>>>> >>>>>>>>> At this moment I am particularly interested in 50 MHz. The reason is >>>>>>> I am >>>>>>>>> putting a yagi for six meters out on the tower behind the house. I >>>>>>>>> will have 100 feet of LMR 400 and 250 feet of 1/2 inch superflex >>>>>>> between >>>>>>>>> me >>>>>>>>> and the antenna. I want to know if I need a preamp. >>>>>>>>> >>>>>>>>> I went through this exercise when I mounted the yagi at 50 feet right >>>>>>> by >>>>>>>>> the house and had only 75 feet of 1/2 inch hardline feeding it. It >>>>>>> did no >>>>>>>>> good to put a preamp at the antenna. >>>>>>>>> >>>>>>>>> I have been googling and evidently haven't used the proper terms >>>>>>> because I >>>>>>>>> don't get the results I need. Any link to this info would be greatly >>>>>>>>> appreciated. >>>>>>>>> >>>>>>>>> Thanks & 73, >>>>>>>>> >>>>>>>>> Dave, K4TO >>>>>>>>> _______________________________________________ >>>>>>>>> mvus-list mailing list >>>>>>>>> mvus-list@lists.febo.com >>>>>>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> -- >>>>>>>> Trevor R.H. Clarke >>>>>>>> Computer Science House >>>>>>>> Rochester Institute of Technology >>>>>>>> retrev@csh.rit.edu >>>>>>>> http://www.csh.rit.edu/~retrev/ >>>>>>>> >>>>>>> _______________________________________________ >>>>>>> mvus-list mailing list >>>>>>> mvus-list@lists.febo.com >>>>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>>>>> >>>>>> >>>>> _______________________________________________ >>>>> mvus-list mailing list >>>>> mvus-list@lists.febo.com >>>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>>>> >>>> _______________________________________________ >>>> mvus-list mailing list >>>> mvus-list@lists.febo.com <mailto:mvus-list@lists.febo.com> >>>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >>> >>> _______________________________________________ >>> mvus-list mailing list >>> mvus-list@lists.febo.com <mailto:mvus-list@lists.febo.com> >>> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >> >> >> _______________________________________________ >> mvus-list mailing list >> mvus-list@lists.febo.com <mailto:mvus-list@lists.febo.com> >> http://lists.febo.com/mailman/listinfo/mvus-list_lists.febo.com >