Bob,
Years ago, Paul Williamson wrote a brief note on the tuning issue. It was prescient in the days of primitive computers, few rigs with easy remote frequency control, and very limited choices of tracking software. Take a look at KB5MU's One True Rule paper:
http://www.amsat.org/amsat/features/one_true_rule.html
If both operators are following it, and SATPC32 (and MacDoppler) does so perfectly, to a large extent it effectively sweeps the Doppler issue "under the rug." You can tune around, and always hear yourself when you key the rig and say "aaaaah." More importantly, if the other station, say 5Y4GB is using the similar technique, when you tune him in, he will hear you on frequency. If WA4SCA then joins the QSO, both of you will hear me on frequency, and I will hear both of you the same. Even more importantly, everybody will remain in sync over the pass. It happens all the time on AO-7, HO-68 in linear mode, etc.
As to your question about 145.950 MHz. If he tunes his RIG to that frequency, and you tune your RIG, you will NOT be on the same frequency initially. However, you will be close. +/- Doppler. This is equivalent to an HF station saying he will be tuning 14.210 MHz +/- 5 KHz. It requires a bit of initial tuning, but it is quick, and completely removes the worry about tuning the uplink radio. The software automagically does it for you. Once you tune him in, just talk. It is well worth the effort to absorb the technique, and as more stations use it, the easier it will be to talk without slowly drifting on top of others. Once you get above the V and U modes, the Doppler shift is so large, and changes so rapidly, that it is truly almost necesary.
With a slight modification to the exiting software, and a paradigm shift in how we think about what frequency we are on, it is possible to specify the "contact frequency" for everybody to use which will eliminate the initial hunting. But that is for another rant. ;)
Alan WA4SCA
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bob- W7LRD Sent: 07 January, 2010 23:59 To: Andrew Glasbrenner Cc: amsat-bb@amsat.org Subject: [amsat-bb] Re: probably simple
Hi Greg, Drew, etc
This conversation is starting to make my head hurt! My example is to connect with some of our European friends. Some of them I share maybe a 60 second window, with PA1TNO it is less than 30 seconds. I have had several false starts in that I heard Paul 2E1EUB, by the time I located my downlink on his, he was gone. I want to predetermine where to set my uplink for a given downlink. There just is no the time be looking around. Like I said this is probably simple I'm just have trouble getting my thinking around the concept. Also if say I am planning on a downlink of 145.950 will Paul be looking at the same frequency? In the past these concepts never concerned me as there was always plenty of time to yak it up with the locals on AO-7.
73 Bob W7LRD
CN87 Seattle, Wa.
----- Original Message ----- From: "Andrew Glasbrenner" glasbrenner@mindspring.com To: "Greg D." ko6th_greg@hotmail.com Cc: w7lrd@comcast.net, amsat-bb@amsat.org Sent: Thursday, January 7, 2010 9:30:44 PM GMT -08:00 US/Canada Pacific Subject: Re: [amsat-bb] Re: probably simple
But any pass where you are really stretching the footprint is going to be a low elevation pass. The more you stretch, the lower the pass. In the limit, I think Bob's ultimate pass has a peak at .001-degrees for both stations. If you're doing that, then you're at TCA, and zero doppler.
That's all I meant to convey,
Greg KO6TH
I understand, but with all due respect your assumption is incorrect that long distance QSOs are always at TCA and zero Doppler, even theoretically . This is only the case when the two stations are at near right angles to the track of the satellite.
Use the following example. If I want to work LU5BOJ/O in FG75 from EL88 on HO-68, my only windows are at either LOS or AOS, depending on whether it is an ascending or descending pass. Neither pass will be a low pass for either station, and neither QSO will occur at TCA or zero Doppler.
In Bob's case, let's look at his next possible window with Paul, 2E1EUB in IO92. Bob is in CN76. At the beginning of the 1 minute window tomorrow at 1251Z, Bob's Doppler shift on 432 is -3.68 khz.
On the next mutual window at 1452Z, the beginning Doppler is -7.93 khz. On the next, at 2020Z, it's -8.3 khz. None of these windows are over 2 degrees elevation, and none are at TCA for either station.
When you have 60s to make the QSO, being right dead on frequency is essential.
Respectfully, Drew KO4MA _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb