[aprssig] APRS Satelilte in Los Alamitos, CA ... Needs help?
Stephen H. Smith
wa8lmf2 at aol.com
Fri Jun 12 10:07:53 CDT 2015
On 6/11/2015 2:53 PM, Robert Bruninga via aprssig wrote:
> All we need is someone to configure a radio to RX on 144.39 on a good outside
> antenna, and another radio to TX the audio on 145.825 (low power into a dummy
> load) near the spacecraft.
> This will provide some “traffic” on the 144.825 channel (low power) to make
> sure the spacecraft does not do anything weird when it begins to see user packets.
> It will take two 2m radios and GOOD audio response so that packet do not
> degrade as they are retransmitted on 145.825.
> The trick will be giving it a high enough receive antenna so that it can hear
> source packets, and then to have the other TX on low power and into a dummy
> load placed near the spacecraft so that the 145.825 repeated packets don’t QRM
> the satellite channel.
The Los Angeles area is so super-saturated with non-stop APRS RF you DON'T NEED
a "high-enough" antenna !!!
Any hand-held with a rubber duck at ground-level will hear nearly non-stop
traffic from the multiple digis at 2,000-5,000 feet in the mountains
surrounding the greater L.A. area.
You can create a far more repeatable test, and avoid the
de-emphasis/pre-emphasis uncertainties of a random pair of radios connected
back-to-back, by using my APRS test CD. It contains a track of worst-case Los
Angeles rush-hour non-stop total overload APRS traffic recorded off the air.
It was recorded "flat" (non-de-emphasized), directly from the discriminator of
a radio. Because it is a recording, you can play back the identical half-hour
of audio over and over as needed.
Use a CD player (earphone jack of an old CD/DVD-ROM drive) connected to the
external modulation input of an RF signal generator or service monitor set to
145.825. You can then vary the generator's attenuator to determine the minimum
signal level that works. You may even discover a noise floor from other
hardware that limits weak-signal receive.
Details here: <http://WA8LMF.net/TNCtest/index.htm>
Stephen H. Smith wa8lmf (at) aol.com
EchoLink: Node # 14400 [Think bottom of the 2-meter band]
Home Page: http://wa8lmf.net
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