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Re: RE: S band for 6 bucks

----- Original Message ----- 
From: "Woody" <kj4so@nc.rr.com>
Subject: Re: [amsat-bb] RE: S band for 6 bucks

> This is NOT a beginner's project.  The mod is very straight forward, *
> IF * you have very good soldering skills and are comfortable working on
> surface-mount PCBs.


Hi Woody,

Great information!

> The LO was originally 2380 MHz., divided by 256 and locked to a 9.29687
> MHz. crystal.
> With a new downconverter input freq. of 2.4 GHz. and an IF output of 144
> MHz., the LO needs to be changed to 2.256 MHz.  I have not found any
> published specs for this downconverter, so I do not know what the
> crystal specs are.

One of the things that has always bothered me about these converters is
their instability. I understand why it happens. The crystal doesn't even
have the most basic of heaters that we typically use in Uwave.

Here's a project I was going to try someday when we got a good Mode S SSB
bird back in the air...

Disconnect the LO on one of these units and feed it from a GPS locked
source. This sounds hard, but there are fairly easy ways to do it...

I've been developing a simple GPS Stabilized 10 MHz source based on the
original design by James, G3RUH. We have a bunch of them working in New
England. See: http://mysite.verizon.net/n1jez/index.html near the bottom of
the page

With these simple units, we're seeing accuracies on the order of  < 2 Hz per
GHz "woggle". So if this was used as a reference, you could expect to see <
5 Hz woggle at 2.4 GHz.

Now, how to use this to generate 2256 MHz for the LO? As part of the 10 MHz
project we're using "Qualcomm" boards to generate very accurate signal
markers for Microwave use. I used the system this past weekend during the
VHF Contest for a long distance contact on 24 GHz. Both stations lined up
their IF's with our GPS based markers and when we transmitted, we instantly
heard each other with no retuning! That's at 24 GHz. Should be a piece of
cake at 2.4 GHz.. (it's DC <grin>)

The Qualcomm boards can be seen at the SBMS website. See:

Scroll down to the "3036/3216 Rectangular" and "Texas" boards. These are
programmable PLL VCXO's that use a 10 MHz reference. This sounds scary, but
if you look at the conversion info, it's pretty straight forward. I have
several in use here as signal markers for all bands 2304 MHz through 47 GHz.
There is a spreadsheet that allows you to set the programming for 2256 MHz.
The key to the board is that it uses a 10 MHz reference. That's where the
simple GPS 10 MHz oscillator comes in. You simply inject the reference and
you have an LO that is easily within 5 Hz on Mode S. If you're looking at
doing computer controlled doppler correction, imagine a Mode S downconverter
that was rock stable....

> Now, all that is left to do is to retune the combline input filter.
> Looking at Roger's photos at:
> http://www.themidwives.org/CalAmp/ (thanks kc8zfn).
> I retuned the filter by observing the IF output of the downconverter on
> a spectrum analyzer.  However, if you have a good clean and stable, but
> low level 2.4 GHz. test signal AND you keep the downconverter's input to
> your receiver from overloading it, you can retune the combline filter
> without a spectrum analyzer.

Here again the "Qualcomm" board and 10 MHz ref can help. The board can be
programmed for 2400 MHz. It will generate a _very_ strong accurate marker
there. But there's even an easier way. We've found that the 10 MHz VC-TCXO's
that we use in the GPS Osc will actually generate harmonics every 10 MHz
through 2.5 GHz.....

Also for a simple receive indicator, if you have an FT-817, the S meters in
these things are non-linear on the low end, but in a good way for our use.
The typical FT-817 has been found to exhibit about 1 dB per S unit on the
low end of the meter.... So it gives a decent indication of small changes.
I'm told the sensitivity can be adjusted in the hidden "alignment menu" on
the unit, but I haven't played with it.

Those of you thinking about trying 10, 24 and even 47 GHz on P3E will really
appreciate having accurate signal markers on these bands. Right now we're
seeing accuracy of about 15 Hz at 10 GHz, 35 Hz at 24 GHz and 75 Hz at 47
GHz. These are measured with complete systems that take into account all the
variables in a Uwave system. Certainly good enough for our purposes as a

One final thing for those thinking about P3E 10/24/47 GHz, check out
VE1ALQ's new updated Reflock 1 board. See:
http://www.ve1alq.com/clpd_pll/clpd_pll.htm  Darrell has solved the problems
that plagued the original CT1DMK design. I have built up 2 and they work
superbly! One is being used at 47 GHz. Interestingly one problem we're
running into is something call "Mode Hoping" or "Mode Jumping" of the
crystal. You can hear examples of this at:
http://www.ve1alq.com/clpd_pll/47_ghz_warble.htm There are several files
from VE4MA and myself of a couple of our crystals....

Just some quick thoughts....

Mike, N1JEZ
AMSAT #29649
"A closed mouth gathers no feet."
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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