There are many ways to skin the cat... As stated the S-Band down on AO-51 is very easy to work with. The other non-interfering easy and cheaper way to do it on AO-13 or AO-40 was to simply tune until you found the beacon and then do everything based your offset from the beacon.
73, Joe kk0sd
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Anthony Monteiro Sent: Saturday, May 17, 2008 2:40 PM To: K & R Yoksh; [email protected] Subject: [amsat-bb] Re: [AMSAT-BB] 145 MHz IF on V/s?
At 09:37 PM 5/16/2008, K & R Yoksh wrote:
Hello Gene (and the list),
Your question reminds me of a question I've been meaning to ask!
My current S-band antenna is a simple integrated antenna/downconverter with 123 MHz IF, but I plan to install a P3E-ready dish and downconverter on my crossboom this summer.
My best downconverter is a K5GNA unit with 145 MHz IF. I wonder how it'll play on mode V/s? Can anyone comment on this?
I also have some more 123 MHz IF units, but their NF is unknown. I'd rather use my AIDC 3731 from K5GNA, even if it means reduced performance on V/s. I plan to optimize for HEO operation, but I'd be happy if I could also work AO-51 in mode V/s.
Hi Kyle,
Just a suggestion...
All downconverters will drift with temperature. The stock AIDC 3731 is spec'd to be within +/- 25 KHz over the temp range. I don't know what the 145 MHz units are spec'd at but I doubt that it is better. Other units I have seen are also around this figure and some are a little worse.
This is not much of a problem on AO-51 becuase there is a nice strong carrier that is easy to find. On a linear passband like P3E, it can be extremely difficult to find your own downlink without QRMing the whole passband.
A better solution and the one that I use, is to put a low noise preamp at the antenna and put your downconverter inside your house where the temp is pretty stable. I have mine in the garage which was fine for AO-40. Leaving the downconverter on all the time is also helpful. On AO-40, my setup was more stable than the LO on AO-40 and I could always hear my own downlink. I used InstantTune (of course!) and loaded the parameters into the config file so it was simple to just turn it on and work the sat. A fine tuning of around +/-1.5 KHz was all that was needed to compensate for AO-40 LO drift.
I used an AIDC 3731 downconverter at 123 MHz which is pretty sensitive but not as good as with the Down East Microwave 13ULNA preamp which is really, really! good. A second advantage of using a preamp at the antenna is that the downconverter sensitivity is then not very important so you can use almost anything, even an old Drake unit.
If you have a really long run of coax, it might be cheaper to add a second less expensive "booster" preamp and then use RG-6 coax from the preamp to the downconverter. I used LMR-600 because I wanted to be able to TX on it but that is overkill for just receiving P3E.
73, Tony AA2TX
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