[aprssig] APRS Satelilte in Los Alamitos, CA ... Needs help?

Stephen H. Smith wa8lmf2 at aol.com
Fri Jun 12 11:07:53 EDT 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
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

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