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Re: AO-40 Update, 2003-02-10

In a message dated 2/9/03 11:32:58 PM Eastern Standard Time, 
na9d-2@speakeasy.net writes:

<w4sm wrote>
> > When the K-Tx is active PLEASE run minimal uplink power, especially on
>  > CW.  The K-Tx has a hard-limiting AGC, just like the AGC on the old AO-13
>  > S-band transmitter.  Strong CW signals markedly suppress the output and
>  > make comprehension impossible.  It would help greatly if users with 
>  > downlink only, would refrain from using the passband during the K-Tx 
> window.

<to which Jon replied>
>  I guess I am somewhat confused here, Stacey.
>  The time when uplinking is possible with a K-band downlink is MA126 to
>  MA134.  Are you saying that those w/o K-band should not use the satellite
>  during this time?  Are there enough K-band users to justify this?

Let me try and answer a few questions.

I'm currently the only active US K band operator. Jerry, K5OE is working hard 
on a system and hopes to be active this week.

First, we're not asking for people to stop using the satellite during the K 
window. We're asking that those operators who use AO-40 during the K window 
please try and use the lowest power you can if you're within 30 kHz +/- of 
the beacon. This frequency range is the passband for K. Better still, avoid 
this window completely! S has 250 kHz while K has just 50 kHz.

The K-Tx has hard agc limiting. Signal strength of an uplink has a direct 
relation to downlink power and it affects the whole K passband. If you uplink 
an extremely strong signal, you will use a good majority of the power 
available in the K transmitter thereby blocking other users.

Here's an example. I was operating K last Friday. The signals started out 
quite good but rapidly deteriorated to the point they became unusable. The 
cause was a W3 running very high power CW 10 kHz above the beacon. I'm not 
sure whether the uplink was U or L, but the result was all the power in the 
K-Tx was used for the CW downlink. It was so bad that you could easily copy 
his CW by listening to the K beacon pump up and down! This person wasn't 
using K for a downlink, but by running such high power, robbed the K-Tx of 
power for any users.

>  Also, why not just disconnect the S-band downlink during that time then?
>  The beacon could still be on could it not?

Not possible, and thus the request to users.

> Or do those with K-band use S-band to help themselves
>  find the bird first before moving to K?

Some do it this way. I work directly at 24 GHz.

We're asking for a little cooperation in the next few weeks. The increasing 
solar angle will terminate our tests soon. My next windows for use are on 
orbits 1048 and 1049 and not again until orbits 1053 and 1054.

Here's one last thing to think about. How would you test the S band 
receivers? For this to happen, the S transmitter will have to be shut down. 
This leaves only a K downlink to verify receiver operation.......

Thanks for your help.

Mike, N1JEZ
AMSAT #29649
Local Area Coordinator
"A closed mouth gathers no feet."
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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