Re: [amsat-bb] Re: Why preference for mode J?

[tlang@xxxxxxxxxxxxxxxxxxxx (Tony Langdon)]

Hello Lee810@aol.com.

31 Jul 00 01:49, you wrote to All:

 L> I listened to this pass and heard absolutely no QRM (at least by U.S
 L> standards).  Are you sure it's the correct recording?  Perhaps someone
 L> should tape a west coast pass in the U.S. and you can hear 10 solid
 L> minutes of Mexican taxi drivers (pirates) QRMing both AO27 and UO14.
 L> Fortunately, we can usually step on these pirates with directional
 L> beams even with low power but they are still a nuisance.

Unfortunately, there was some noise early on that masked some of the QRM, but
you will hear a point where I am unable to get through (with 25 watts), because
of the background QRM.

 L> I prefer Mode J on FM birds because with Mode B, you have to adjust
 L> the uplink frequency for Doppler which is a lot harder to do correctly
 L> and there are about half the stations on the bird who are off
 L> frequency.  It also doesn't lend itself to working very well with the

I find it the other way, in that Mode B is less critical, because the satellite
Rx has AFC and a wider IF.  I just guess when to QSY and get it right every
time. :-)

 L> portable station.   This is because the downlink is so strong on a
 L> 3-element beam that it's hard to figure out which way to point the 440
 L> beam to insure a good uplink signal.

Again, that's a matter of technique.  It is worth noting where the bird should
be at any given time.  I also do a lot of my adjusting in the background _while
transmitting_, to optimise both uplink and downlink.

Tony

.. There is nothing that can't be fixed with a hammer ...
--
|Fidonet:  Tony Langdon 3:633/284.18
|Internet: tlang@freeway.apana.org.au
|
| Standard disclaimer: The views of this user are strictly his own.


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