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Re: The Other Answer Re: ISM interference on 2401 MHz



Joe Mayfield - KA0YOS said:
<snip>
> One commentor lamented that AO-40 is not near as active as AO-13 was
> (this has been my experience as well).  The truth is mode B is easier
> to do which results in more users.  The common mode S downlink
> approach is to build a mode B station and then put a downconverter in
> front of it.  Why not just use the mode B station?

I'm sure that if the VHF downlink were working, there would be far more
people running U/V rather than U/S.  Unfortunately it's not working.  I
would sure love to see it operational however.  Those first few weeks of
the beacon were great!

> The amount of interfering items in the S band is ever increasing.
> The amount of interference on two meters has leveled off and is
> starting to decline.  Mode B allows for much simpler antennas
> where pointing is not as critical.  Mode J is plagued by pirates
> on the uplink, this has not been a problem on mode B.  In band
> amateur use of two meters is on the decline (I believe this is
> true of almost every band) making local congestion less of a
> threat.

I'm sure you are right that the S-band interference will continue to
increase.  As to 2M getting quieter, sure not the case here!  I have had
problems with terrestrial operators using that "quiet" section of 2M - you
know the one between 145.800 and 146.000.  Even have a few that refuse to
move even when told that they are causing interference to satellite
operations.  2M downlinks are very noise to receive.  At least around here,
430 is much less of a problem to receive due to extraneous noise.

> I worked mode B on AO-13 it was a blast!  I have been on mode S
> since AO-40's transponder was turned on.  I have not been
> impressed.

I was not on satellites until after AO-13 re-entered so I can't compare to
that, but mode S works fine IF you have a decent receive station.  The
biggest problem we face is that too many people think that they can't do it
(I don't know anything about microwave).  Right after that is the thinking
that you can take an 18 inch dish, feed it with a poorly designed feed,
then run it into 30 feet of coax before a marginal downconverter and it
will work.  Well, it wont - at least not very well.  Put a little bigger
dish with a proper feed directly into a low noise downconverter and S-band
works fine.  Now all we have to do is convince people out there that this
just isn't all that hard to do.

73
-----------------------
Jim Walls - K6CCC
k6ccc@amsat.org
Mobile Radio Operations
Southern California Edison Co.
Ofc:   626-302-8515   -   PAX   28-515
FAX:   626-302-7501   -   PAX   27-501


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