Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)
Poul-Henning Kamp schrieb:
In message 4F64F279.4040208@arcor.de, ehydra writes:
Marek Peca schrieb:
This was almost the only reason for ferrite rod -- simplicity and
attenuation of TVs, some LCDs, 50Hz etc.
If you make the antenna about 10x bigger you can omit the whole
ferrite.
I have used two antennas, an unloade air-coil, actually plastic-lid-coil:
http://phk.freebsd.dk/loran-c/Antenna/
Yeah. I remember the red.
The degaussing coil of old TVs can work. Some resonate at 50KHz which is
a little low but it depends on the manufacturer. So try it.
and a vertical monopole based on a Chris Trask design I can highly
recommend:
In my implementation, it covered DC to 200MHz until I low-pass'ed it.
His designs are always a good source but this one is AC-coupled ;-)
A CD4069 is all one needs for first experiments. I was satisfied.
- Henry
--
ehydra.dyndns.info
In message 4F65D971.8070007@arcor.de, ehydra writes:
In my implementation, it covered DC to 200MHz until I low-pass'ed it.
His designs are always a good source but this one is AC-coupled ;-)
Not in my implementation, I have eliminated the input capacitor because
the active element is 3cm from the PCB, and I drive the output with
a centertapped transformer.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
I wonder because ALL of the shown circuits in his pdf are AC-coupled.
It is maybe possible to servo-loop with OpAmps but surely not worth the
effort.
Useful too as a Scope FET-probe.
- Henry
Poul-Henning Kamp schrieb:
In my implementation, it covered DC to 200MHz until I low-pass'ed it.
His designs are always a good source but this one is AC-coupled ;-)
Not in my implementation, I have eliminated the input capacitor because
the active element is 3cm from the PCB, and I drive the output with
a centertapped transformer.
--
ehydra.dyndns.info
On Sun, 18 Mar 2012 13:25:54 +0000
"Poul-Henning Kamp" phk@phk.freebsd.dk wrote:
In message 4F65D971.8070007@arcor.de, ehydra writes:
In my implementation, it covered DC to 200MHz until I low-pass'ed it.
His designs are always a good source but this one is AC-coupled ;-)
Not in my implementation, I have eliminated the input capacitor because
the active element is 3cm from the PCB,
Could you explain how the distance of the antenna to the PCB is related
to a DC block capacitor? And how do you block current flowing from the
input stage of your amplifier into the antenna?
and I drive the output with a centertapped transformer.
Do you really mean a transformer? Or just a center tapped inductor?
And how does that fit into the biasing? Or does your circuit contain
more elements at the output than a transfomer/inductor and the biasing
resistor?
Attila Kinali
--
Why does it take years to find the answers to
the questions one should have asked long ago?
The circuit in question doesn't appear to be in the PDF. You need to use
a lot of caution with Lankford's theories. I don't want to get into a
pissing contest, so I will leave it at that.
Push pull with transformers goes back to the tube days. It is a
convenient scheme to kill 2nd harmonic distortion while at the same time
biasing the single sex amplifier.
Take the center tap and tie it to a positive voltage. Feed the other two
inputs to the transformer with a differential signal. You have blocked
DC from the output, restoring a ground referenced single phase. (as
opposed to differential) output.
These active whips are prone to picking up electrical noise. Fine if you
live in the boonies. Not so good for urban dwellers.
If the antenna is just a wire in the air, I'm not sure what good it does
to capacitively couple the input. Who cares if some DC is floating on a
wire just poking in the air.
While some people think of transformers are bandlimiting devices, note
that all those coupling caps have series inductance. There is no free lunch.
Just meditating out loud, if you were to go push pull with a ferrite
antenna AND you are winding it yourself, you could avoid the biasing
resistors by putting a center tap in the antenna itself, then tie that
center tap to an appropriate bias voltage. I haven't seen this done, so
their may be a gotcha with that scheme, but the science is good.
Generally you will get a lower noise circuit if the input device is an
amplifier rather than a buffer.
Lanksford's input stage is essentially a push pull buffer, but I don't
see that cancelling 2nd harmonics like a push pull amp. But for a whip,
which is a single ended input, I don't see a way to get a differential
input. Not true for a ferrite antenna.
I'd not use a vertical antenna at all. Far too prone to EMI.
My choice would be a center tapped, shielded, air core loop, running into
a low noise instrumentation amp. Center tap of loop to twinax shield,
grounded at preamp.
The instrumentation amp has fixed gain, and very high CMRR and PSRR. It
also does the differential to single ended conversion properly and has a
low output impedance.
YMMV.
-John
================
The circuit in question doesn't appear to be in the PDF. You need to use
a lot of caution with Lankford's theories. I don't want to get into a
pissing contest, so I will leave it at that.
Push pull with transformers goes back to the tube days. It is a
convenient scheme to kill 2nd harmonic distortion while at the same time
biasing the single sex amplifier.
Take the center tap and tie it to a positive voltage. Feed the other two
inputs to the transformer with a differential signal. You have blocked
DC from the output, restoring a ground referenced single phase. (as
opposed to differential) output.
These active whips are prone to picking up electrical noise. Fine if you
live in the boonies. Not so good for urban dwellers.
If the antenna is just a wire in the air, I'm not sure what good it does
to capacitively couple the input. Who cares if some DC is floating on a
wire just poking in the air.
While some people think of transformers are bandlimiting devices, note
that all those coupling caps have series inductance. There is no free
lunch.
Just meditating out loud, if you were to go push pull with a ferrite
antenna AND you are winding it yourself, you could avoid the biasing
resistors by putting a center tap in the antenna itself, then tie that
center tap to an appropriate bias voltage. I haven't seen this done, so
their may be a gotcha with that scheme, but the science is good.
Generally you will get a lower noise circuit if the input device is an
amplifier rather than a buffer.
Lanksford's input stage is essentially a push pull buffer, but I don't
see that cancelling 2nd harmonics like a push pull amp. But for a whip,
which is a single ended input, I don't see a way to get a differential
input. Not true for a ferrite antenna.
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My choice would be a center tapped, shielded, air core loop, running into
a low noise instrumentation amp. Center tap of loop to twinax shield,
grounded at preamp.
The instrumentation amp has fixed gain, and very high CMRR and PSRR. It
also does the differential to single ended conversion properly and has a
low output impedance.
I have used an instrumentation amp in my breadboard, however, without
center tapping and shielding. But it seemed to me to be a very good
component for such low frequencies.
Marek
ehydra wrote:
I wonder because ALL of the shown circuits in his pdf are AC-coupled.
It is maybe possible to servo-loop with OpAmps but surely not worth
the effort.
Useful too as a Scope FET-probe.
Not really the gain inaccuracy is somewhat excessive.
One can do much better with the right circuit.
The AC coupling between input and output stages isnt actually necessary
if the output stage is biased appropriately.
A higher supply voltage also helps.
- Henry
Bruce
In message 20120318182440.7cb729c2b018b0b2ca5f957b@kinali.ch, Attila Kinali w
rites:
On Sun, 18 Mar 2012 13:25:54 +0000
Not in my implementation, I have eliminated the input capacitor because
the active element is 3cm from the PCB,
Could you explain how the distance of the antenna to the PCB is related
to a DC block capacitor? And how do you block current flowing from the
input stage of your amplifier into the antenna?
The input to the amplifier is just a piece of metal, there is no need
for a capacitor in series with it.
The output from the amplifier goes to a transformer which drives a piece
of "twin-ax" cable back to my lab.
The reason for the transformer is that to go really deep in frequency
the usual choke to separate the DC supply from RF signal doesn't work.
I the 'cable-side' of the transformer, in both ends, is centertapped
and that's how I provide power to the antenna.
I have successfully received the Russian "Omega-like" system at
9-15 kHz and I have detected but not demodulated the 86Hz submarine
transmission.
That's DC enough for me :-)
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
DC in a transformer raises the low frequency corner a bit. Obviously not
a problem in your case.
I should point out that every active device Lankford puts in the signal
chain adds noise since the amp is really just a buffer, not an
amplifier. You really want front end gain so that devices after the gain
stage do not add as much to the noise floor. It is input referred noise
that is significant, and Lankford's design is terrible in this respect.
Oops, I almost started that pissing contest. ;-)
On 3/18/2012 11:44 AM, Poul-Henning Kamp wrote:
In message20120318182440.7cb729c2b018b0b2ca5f957b@kinali.ch, Attila Kinali w
rites:
On Sun, 18 Mar 2012 13:25:54 +0000
Not in my implementation, I have eliminated the input capacitor because
the active element is 3cm from the PCB,
Could you explain how the distance of the antenna to the PCB is related
to a DC block capacitor? And how do you block current flowing from the
input stage of your amplifier into the antenna?
The input to the amplifier is just a piece of metal, there is no need
for a capacitor in series with it.
The output from the amplifier goes to a transformer which drives a piece
of "twin-ax" cable back to my lab.
The reason for the transformer is that to go really deep in frequency
the usual choke to separate the DC supply from RF signal doesn't work.
I the 'cable-side' of the transformer, in both ends, is centertapped
and that's how I provide power to the antenna.
I have successfully received the Russian "Omega-like" system at
9-15 kHz and I have detected but not demodulated the 86Hz submarine
transmission.
That's DC enough for me :-)