Well, one does have to convince someone to pay you to do it..

Browsing the aisles of the local electronics mega-mart... I don't think
I've ever seen "external reference" in the commodity units.  I figure
that the "crystal locked" units have a crystal in the LNB (as opposed to
just running the DRO open loop)..

But, presumably, one could modify the LNB to drive the reference with
something external (and somehow, I doubt it will be 10 MHz.. but anyone
able to modify LNBs will be able to make whatever is needed)

wa1zms@att.net wrote:

BPSK, typically with a lot of residual carrier.  And, at slow rates, the
data is modulated on a (e.g. 16 kHz) subcarrier, which is then phase
modulated on the main carrier with a mod index to create the desired
ratio between power in the data signal and power in the carrier. Typical
mod indices would be 0.2 to 1.3 radian (peak).

For the SDST, which we've been using for the last 10-15 years, threshold
(the signal level at which the carrier can be acquired and tracked) is
<-156 dBm. Tracking loop BW is on the order of 20Hz for small signals.
NF is <2.5dB

You can read more at
nmp-techval-reports.jpl.nasa.gov/DS1/SDST_Integrated_Report.pdf

(actually, googling SDST will turn up a fair amount of data)

The challenge in operating is that you don't necessarily have a-priori
knowledge of where the SDST is listening (temperature and doppler
uncertainty, mostly).. so we sweep the uplink signal over a range that
hopefully covers where it is.  So there's a tradeoff between loop
bandwidth being wide enough to allow a decent sweep rate and narrow
enough to allow working at low signal levels. Because of the long light
time delay, the sweep and acquisition process is open loop (that is, we
assume we swept across the appropriate frequency, that the SDST acquired
and is following, and we can send the data)

Newer radio designs do things like change the bandwidth, or use
parallel detection.

For a given transmitter power, BPSK has a higher average power than OOK.
The problem is that it takes a more sophisticated receiver than a
power detector.  OOK has the virtue of simplicity.

On 11/13/2010 05:32 PM, jimlux wrote:

Once in a while, I end up being paid to do it. :)

But I do not play in Ku-band. Haven't had to... yet.

There is really three types available from my quick search:

1. Open Loop L.O. LNBs

2. Crystal locked L.O. LNBs

3. External referenced locked L.O. LNBs

Searching the web using say Google should get you the part numbers you
would need for your short-hand.

Crystal locked would require modification, but modifying them for a 10
MHz reference would probably be a good choice.

Cheers,
Magnus

Reminds me of a story someone once told me....

This is how it goes:

I decide to water my garden.

As I turn on the hose in the driveway, I look over at my car and decide it
needs washing.

As I head towards the garage, I notice post on the porch table that I picked
up from the postman earlier.

I decide to go through it before I wash the car.

I put my car keys on the table, put the junk mail in the recycling box under
the table, and notice that the recycling box is full.

So, I decide to put the bills back on the table and take out the recycling
first.

But then I think, since I'm going to be near the post-box when I take out
the recycling paper anyway, I may as well pay the bills first.

I take my cheque book off the table and notice that there is only one cheque
left.

My extra cheques are in the desk in my study, so I go into the house to my
desk where I find the cup of coffee I'd been drinking.

I'm going to look for my cheques but first I need to push the coffee aside
so that I don't accidentally knock it over.

The coffee is getting cold, and I decide to make another cup.

As I head toward the kitchen with the cold coffee, a vase of flowers on the
worktop catches my eye - the flowers need water.

I put the coffee on the worktop and discover my reading glasses that I've
been searching for all morning.

I decide I better put them back on my desk, but first I'm going to water the
flowers.

I put the glasses back down on the worktop, fill a container with water and
suddenly spot the TV remote control.  Someone left it on the kitchen table.

I realise that tonight when we go to watch TV, I'll be looking for the
remote, but I won't remember that it's on the kitchen table, so I decide to
put it back where it belongs, but first I'll water the flowers.

I pour some water in the flowers, but quite a bit of it spills on the floor.

So, I put the remote back on the table, get some towels and wipe up the
spill.

Then, I head down the hall trying to remember what I was planning to do.

At the end of the day:
The car isn't washed. The bills aren't paid. There is a cold cup of coffee
sitting on the kitchen work-surface. The flowers don't have enough water.
There is still only one cheque in my cheque book, I can't find the remote, I
can't find my glasses, and I don't remember what I did with the car keys.

Then, when I try to figure out why nothing got done today, I'm really
baffled because I know I was busy all bloody day and I'm really tired.

:-)

Rob Kimberley

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Mike S
Sent: 13 November 2010 10:57 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] OT loosing things

At 08:15 PM 11/12/2010, Mike Feher wrote...

GFY

time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

It's called a sequential vortex...
Don

Rob Kimberley

--
"Neither the voice of authority nor the weight of reason and argument are
as significant as experiment, for thence comes quiet to the mind."
R. Bacon

Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com

On Sat, Nov 13, 2010 at 07:01:26AM -0800, jimlux wrote:

There are three kinds of LNBs in common use in the VSAT world...


1.  Open loop unlocked DROs, often with around a MHz or two or

more error due to temperature and calibration and drift over time.  More
expensive higher grade ones are tighter spec'd, but rarely much less
than 250-500 KHz over time and temp.  Most all DTH dishes use these,
often with rather loose frequency specs since the DTH carriers are wide,
fast signals.

2.  Closed loop DROs phase locked to a crystal or I believe

about as common, a UHF or higher frequency oscillator phase locked to a
crystal reference with some degree of multiplication to the final LO
frequency (maybe not much these days with fast prescaler/divider chips).
Crystal in this case is - depending on price - just a plain XO or either
a TXCO or in certain cases a OXCO.  More expensive ones have better
stability specs.    Generally these sell for 5-10 times what a cheap DRO
LNB for the mass market might go for.  And can be as good as 1 PPM or
so.

PLL LNBs are mostly used for data or audio transmissions on

narrower, lower  bit rate carriers than TV but also used for many critical
professional TV broadcast and similar applications.

3. External reference LNBs with 10 MHz (pretty universal) going

up the cable that also carries power and brings the L band signal down.
I'm not entirely sure how many of these designs simply bandpass filter
and then limit the 10 MHz and use that directly as a PLL reference and
how many phase lock a VCXO to the 10 MHz coming in.  Otherwise similar
(and often  derived from designs for) the internal reference PLL types
in 2 above.

These ER types are more apt to be used for more exotic

specialized applications where very high frequency accuracy or some
degree of phase coherence  with other equipment or LNBs is useful.

Obviously with the high multiplication factor, one needs a quiet

reference inside the PLL bandwidth (and that is pretty wide to ensure
reliable lock) - one suspects that issues with degradation due to
mechanically induced noise and phase shift in the cables can be a
problem.

--
Dave Emery N1PRE/AE, die@dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."

David I. Emery wrote:

Bummer.. so much for making myself a radio camera with scavenged Ku-band
DBS dishes/feeds (when people around here subscribe, they just junk
the existing, almost identical, assembly)..

I was willing to spend a few tens of dollars/element.. But $100/element
is pushing it out of the "hmm, interesting project for not much money,
can I accumulate some more junk in the garage" category.

And, I'll bet those are fairly pricey.. (after all, it needs another
connector, and that's a price sensitive application..)

Hmm.. I wonder if one could do the pilot tone technique.. I can radiate
a weak Ku band signal, in band, and record what I see from the LNB, then
post process to "close the loop" in software.  Have to think about that
some more.. The Ku band beacon/pilot is easy (a comb), so what I'd need
is a multichannel "softrock" type receiver (which has other uses) that
can deal with the L-band IF from the cheap LNBs.  I wonder if the LO of
the cheap LNBs are within, say, 50kHz of each other.. Then I could use a
common L-band LO.. But based on the discussion above, probably not.

Richard (Rick) Karlquist wrote:

Yes

Bruce

On 11/14/2010 7:24 PM, David I. Emery wrote:

I picked up an LNB a about 10 years back that used this external
reference method.  The LO in the thing was a DRO that locked to a 10 MHz
signal coming up the cable. The LO in this one locked to 10.750 GHz.
Experimenting, I found that the DRO adjustment screw could be turned and
it would lock every 10 MHz. I found it would lock as low as 10.690. I
assume it would tune up about that far too.

I needed an LO in the 10 GHz area, so I hacked mine to use it just as a
LO, not using any of the receive chain. Here's a page where I described
the LNB and what I did with it.

http://www.xertech.net/Projects/sat_lo.html

Maybe the description there will help someone. If nothing else, it show
pictures of what one external ref type LNB looks like.