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RE: Dedicated APRS LEO bird?



Bob, there is the possibility of overcoming the Doppler effect by means 
of a dedicated satellite and using 23 cm. for the uplink and 13 cm down. 
The orbital parameters could rapidly be calculated through a HT 
microprocessor and the VFO adjusted correspondingly. The yagi antennas 
could be combined in similar fashion to the Arrow and adjustment made in 
polarity according to the sig strength. I recall that the beam width with 
the yagi is fairly wide at 23 cm but I will have to recheck for both 
bands. According to my experience, beam width does not appear critical on 
land for contacts of ~ 20 km. but a LEO is a different animal. You have a 
good point but perhaps one that can be overcome in practice.

The 13 cm. yagi (known as the 'long John') is even more portable than the 
23 cm unit. I have tried to interest Allan Lowe in building a dual band 
prototype since their construction is fairly involved--close tolerances 
and machine shop capability--that the project should be done 
professionally.

Next we need a dual band HT (hopefully SSB) with a TNC for high speed 
packet, perhaps as high as 200K bps. The 23 cm part of it is in hand, 
albeit FM, but the 13 cm half should be doable considering the progress 
in microwave component technology.

At any rate, my thoughts on the future.

Peter de WK9K  




>On Tue, 22 Aug 2000, Peter D. Bayne wrote:
>
>> Bob et al, actually not only are there 23 cm handhelds but the 16 element 
>> yagi's can be easily handheld as well...
>
>Thanks, if the 16 ele yagi has 16 dBd gain then I calculate that 1W
>on 23cm and that antenna will be equivalent to about 4 watts and the 7
>element ARROW antenna on 70 cm.  Assuming equivalent antennas on the bird.
>
>The noticible difference however will be the almost 50 KHz (10 steps) 
>worth of doppler AND the beamwidth will be less than half as wide meaning
>much harder to point.
>
>Hummh...
>
>Bob
>
>


Peter D. Bayne
ARS WK9K
605 Maiden Street
Mineral Point, WI 53565
USA

Grid: EN42vu
AMSAT Member No.: 32904

e-mail: WK9K@AMSAT.org
Voice:  (608) 987-4324
Fax: (503) 210-6618
Packet: WK9K@WD9ESU.wi.us.na



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