[amsat-bb] Re: probably simple

[Alan P. Biddle]

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 at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Bob- W7LRD
Sent: 07 January, 2010 23:59
To: Andrew Glasbrenner
Cc: amsat-bb at 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 at mindspring.com> 
To: "Greg D." <ko6th_greg at hotmail.com> 
Cc: w7lrd at comcast.net, amsat-bb at 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 
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