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Re: Thoughts on future "FM birds" (was: proposal formaximizing fm le o contacts)



My design thoughts for a new analog SSB satellite for newcomers is:

  10 meters UP with users using 25 watt Radio Shack $139 10m rigs
   2 meters down for minimum doppler and greatest link budget

This then would allow users to only need vertical whip antennas.  No need
for tracking.  THus newcomers would find it trivial to get onto the bird.
It would have only a 30 KHz wide transponder suitable for 10 simultaneous
voice QSO's.  Setting the ground rules that only 25W into an omni is the
required uplink configuration would level the playing field.

The uplink power would be nearly constant.  Although there is a 10 dB
variance due to range between each user and the bird, this is offset by
the pattern of a vertical whip antenna which is 10 dB or more
down in the same area where the satellite is 10 dB closer.

Also, the 2m downlink would have a 9 dB advantage over 70cm, thus
requiring only 11% of the power.  Finally, the bird would have an AGC that
would drop back transmit power when no one was using it to save power for
later when it was over the HAM population (only 10% of the earths
surface).

Anyway, I want to let some students here work up such a design just to
flesh it out...

de WB4APR, Bob

 On Thu, 17 Aug 2000, Tony
Langdon wrote:

> > >> As the FM LEO satellites are used by many to simply say hi to their
> > >> friends and there are many that do not care for collecting 
> > grid squares,
> > 
> > How many times in a day do two people need to say,
> > 
> > "Hi Joe.  How you doing."
> > "Fine Jim.  Just fine.  How's the gout?"
> 
> Good point. :)
> 
> > Seriously, there are some people that say hi to the same 
> > folks nearly every
> > pass.    They should really be asked to rag chew on a different bird.
> > Perhaps we need more than a single channel FM bird if people 
> > really want to
> > limit their satellite contacts to FM.
> 
> Well, ideally, the linear birds are better suited to longer ragchews, as
> they have inherently greater traffic capacity, but perhaps more FM
> transponder space might be a good idea.  Only trouble is that there are only
> so many channels, especially in the 2 metre band), that too many birds
> floating around up there might cause all sorts of traffic conflicts.
> Already, there are occasional conflicts between UO-14 and some of the
> digital birds on the 2m uplinks.  70cm is pretty right, we have 3 MHz of
> space to play with, but the lower bands have narrower satellite segments
> (typically 200 kHz, or 1/15th of the space available on 70cm).
> 
> Perhaps we need to investigate other possibilities.  I'll throw a couple of
> ideas into the ring.
> 
> 1.  23cm uplinks.  - This would make it difficult for portable stations, due
> to the higher Doppler shift, increased free space losses (but 23cm antennas
> can have a heap of gain to compensate), and the low Tx power of most (all?)
> HTs up there (typically 1W).  However, my gut feeling is that this is quite
> feasible, if one takes the time to build a decent Yagi for the band.  
> 
> 2.  Cross-mode satellites.  For example, 70cm FM up, 10m SSB down.  Combines
> the ease of use of FM on the uplink with the spectral efficiency of SSB on
> the downlink.  As these would be single channel birds, sofficient power
> could be achieced to hear the downlinks on handheld 10m gear (like those
> "pirate CBs" that are now on the market).  Actually, I can clearly hear the
> beacon of RS-13 clearly on a Dragon SS-201 10m HT (in USB mode) and a 2 foot
> whip.  A moderately powered (say 5W) SSB signal should be clearly audible on
> the ground with this setup.  Many stations should have capabilities for 70cm
> FM / 10m SSB, so this could be a popular mode.  The Doppler should be pretty
> easy to tune as well, with 70cm being non critical, and the 10m side having
> only around +/- 600 Hz. 
> 
> 2a.  A similar technique could be used with a 2m downlink, and an FT-290R or
> similar utilised on the 2m SSB link, or perhaps "Mode JX" (X for cross
> mode), 2m SSB up, 70cm FM down...
> 
> 3.  Other wierd and wonderful bands, like 13cm downlinks are another
> possibility, but this would require the development of a low cost, easily
> reproducible converter kit to attract a large number of operators.  Let's
> see what Mode L/S on P3D brings. :)
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