[amsat-bb] Re: HT supports full duplex satellite operation

Tim - N3TL n3tl at bellsouth.net
Tue Oct 20 10:35:37 PDT 2009

Hi Drew,

My "work-around" (unless someone comes out with a finer-tuning HT between now and then!) is simple. I'm going to use a combination of the 5 kHz and 12.5 kHz tuning steps on my HT to program a set of memories that "Doppller tunes" the uplink in 2.5 kHz steps. That way, I'll be able to stay fairly close to the uplink throughout the pass. I'm confident the "one true rule" will still apply regardless of the receiver design. It has on AO-7 and VO-52 when I've worked passes using AFSK through an HT to send CW on those Mode B satellites. 

I'll use the same downlink in each memory because I've done just the opposite with our Mode J satellites - that is, use the same VHF uplink all the time and only Doppler-tune the downlink.

Please don't mistake my comments as any kind of criticism; they aren't intended that way at all. I'm looking forward to the challenge, and just hope others understand that one true rule and its impact on Mode B operations.

73 to all,

Tim - N3TL

From: Andrew Glasbrenner <glasbrenner at mindspring.com>
To: Tim - N3TL <n3tl at bellsouth.net>
Cc: APBIDDLE at mailaps.org; Michael Chen <michael.bd5rv at gmail.com>; amsat-bb at amsat.org
Sent: Tuesday, October 20, 2009 1:20:17 PM
Subject: Re: [amsat-bb] Re: HT supports full duplex satellite operation

> I am thrilled with the news that AMSAT is moving forward with plans to build and launch a 1U cub sat with a U/V (Mode B) transponder. However, consistently hitting the uplink with HTs that tune no finer than 5 kHz will be a challenge. I learned that last winter when the ISS repeater was active in Mode B. When I used my FT-817 as a transmit radio and could use the main tuning dial to infinitely fine-tune the uplink, I had much better - and more consistent - success hitting the uplink than with my HT, which will only tune in 5 kHz steps.
It's all in the receiver design. The ISS D-700 isn't designed as a satellite receiver, and has a narrow front end.

Think of it this way. With 5 khz steps you are always within 2.5 khz of being "on frequency", right?

We operate the V/U FM satellites all the time without tuning the uplink, and that means we are up to 3 khz off, and everything works fine! So 2.5 khz will be a piece of cake too, plus folks will hear the 2m downlink much easier.

73, Drew KO4MA

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