[amsat-bb] Ao 73 problems

[David G0MRF]

Hi Bob.
 
AO-73 is difficult to track using a PC as there is a fixed offset on the receive crystal oscillator together with a variation in frequency which is temperature dependent.
Consequently, the ideal midband frequency when the satellite is at TCA will be different for a pass in eclipse or a pass during the illuminated part of the orbit.

As you know, it takes a bit of getting use to, but once you get the feel for it, manual tuning can get good results.
I agree the published frequencies should probably include the fixed offset so people can get a little closer to the 'correct' frequencies for success.

73

David


 
 
-----Original Message-----
From: Bob <WB4SON at gmail.com>
To: George Henry <ka3hsw at att.net>
CC: mm0kjg <mm0kjg at googlemail.com>; AMSAT-BB <amsat-bb at amsat.org>
Sent: Mon, 26 Oct 2015 13:52
Subject: Re: [amsat-bb] Ao 73 problems


Hi George,

You are one of many who have said manual tuning is best, and after
so many
similar comments, I should probably give that a whirl.

Of course
this will vary for rig and doppler, but I'd be curious to know
what you find
your tx frequency to be at mid pass?

The reason for asking is the published
spec is

Uplink 435.150 - 435.130 MHz LSB (Inverting)
Downlink 145.950 -
145.970 MHz USB

Implying that a RX of 145.960 (mid band) would have a TX of
435.140.  From
my tests it appears that I would actually have to transmit on
435.156 to
hear myself at mid-pass.  That, of course, appears to be outside of
the
published passband, and those published specs probably prevent anyone
new
to the bird from ever finding themselves.

I appreciate and data or
feedback.

73, Bob, WB4SON




On Mon, Oct 26, 2015 at 12:21 AM, George
Henry <ka3hsw at att.net> wrote:

> I have found that computer tuning for AO-73
simply doesn't work...  the
> satellite frequency drifts enough that your up-
and downlinks won't stay in
> sync for long.  I leave my downlink frequency
alone as much as possible
> (unless needed to chase the other guy), and
manually adjust the uplink, and
> that has worked well for me.
>
> George,
KA3HSW
>
>
> ----- Original Message ----- From: "mm0kjg via AMSAT-BB" <
>
amsat-bb at amsat.org>
> To: <amsat-bb at amsat.org>
> Sent: Sunday, October 25,
2015 6:24 AM
> Subject: [amsat-bb] Ao 73 problems
>
>
> Hello all.
>> I
seem to have a wee problem with working Ao-73. The problem I cant work
>> it at
all. I am hearing people talking but when I attempt to find my
>> downlink
nothing heard. I have tried sending cw up and tuning downlink and
>> also
tuning uplink and nothing.  I have set up tuning for 145.950 down and
>>
435.150 up. Am missing something here?
>> I spoke to my good friend and very
good Sat operator Derrick Gm0fmw and
>> he also cant access it with a fairly
good antenna set-up. We are both in
>> Edinburgh Scotland Is this the
problem?
>> Please all help will be appreciated .
>>
>> Thanks Kev MM0KJG
>>
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