[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Interference on AO-51



>I regularly hear those phones also from north africa, 
>both in the satellite sub-band and in cw/ssb part of 
>2m amateur band.  But, what actually can we do?

My preferred approach is to put Ham Satellite Downlinks
in the 2m satellite band:

1) To an omni antenna, 2m has a 9 dB link advantage over UHF
2) 2m downlink requires no doppler tuning for reception
3) Its time we exploit satellites for Mobile Operation
4) Let them put up with our satelliites on their illegal
    phone frequencies rather than the other way around.
5) Everyone has a 2m reeciver.  It should come alive 
    whenever an amateur satellite comes into view...

One of our school's proposed projects is to suggest six 2m 
downlinks on the ISS.  One for FM voice,  one for SSTV, 
one for packet (APRS), one for 30 simultaneous PSK-31 
users and one for 30 KHz wideband transponder (10 SSB
users).  And then to also  encourage other satellites 
supporting those same 6  channels.  As more and more 
satellties got added, soon we would have near continuous 
coverage of these 6 comon modes. 

All easily heard on an HT or mobile with no tracking and
no tuning.  And NO problems from the interlopers and
illegal 2m QRM in some areas.

There is merit in the desire by a lot of satellite designers 
that want to go higher and higher in frequency for more
and more bandwidth.  Yes, that is the frontier.    All of 
which require higher quality hardware, software, tracking, 
gain, and so forth.  And we must go there for the needed 
bandwidth...

But  there is no other band than 2m as a downlink that can be 
heard by everyone, with only a whip antenna and no tuning
while using low power TX on the satellite.   We should not 
be quick to abandon simple applications using this  downlink band.

Although there are good reasons for running mode J (VHF up
and UHF down) as MOST amateur satellites have done, from
an RF link perspective for mobile operations it makes no 
sense at all.

1) UHF needs 9 dB more power on the satellite to be heard
    by the same mobile
2) Mobile has to tune 5 times during the pass for Doppler
    to listen
3) Conversly, on the Uplink, not only is the mobile 9 dB
   better uplink, he usually has 13 dB more power than
   the satellite.

For the above reasons, the link budgets between the mobile
and the satellite are INBALANCED by almost 22 dB!  Making
it too easy to hit with QRM on the uplinks and too hard to
hear on the downlink.

But Mode B (2m downlinks) balances the satellites system for
the mobile operator just fine:

1) 9dB stronger downlink for the mobile receiver for the same TX
2) No tuning needed by the mobile to listen
3) Mobile uses 50W uplink to overcome the 9 dB disadvantage
   on UHF uplink.

This makes the uplink and downlink balanced, and matching 
exxactly what the mobile operator already has in his car...
Lets design the satellite to match the user, not the other
way around (for some of our satellites).

We have Xm and serius Satellite Commercial Mobile Radio.
Why not Amateur Mobile Satelltie Radio?

We have dozens of universities building satellites.  If each
one included a mode B mobile transponder, soon there would
always be something to listen to...

de WB4APR
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home