[Space] aprs

nils at shkoo.com nils at shkoo.com
Tue Feb 23 05:08:49 UTC 2010

I did not yet attempt to get the vox mode working on the pg777.  It works 
on my vx8r fine.

It'd be nice to detect existing transmissions, but I'm not sure how 
effective it'd be.  They're pretty short, so the 0.5 second minimum vox 
delay that I have on the vx8r means that there's a big window for the race 
condition.  I don't know if the vox delay is less on the pg777.

I guess the other way to do it would be to have an external signal 
detector that activates the PTT; I think you should just need a diode, a 
resistor, a capacitor, and a transistor.  (The values of which would have 
to be worked out)

See attached for a screenshot of me driving over the bay bridge hitting my 
transmit button every couple minutes. :)  (or 
http://aprs.fi/?call=KF7FWZ-3 if you get to it before it expires)

I would really prefer to figure out some way to activate the PTT without 
having to wait for the VOX to kick in, and having to transmit a period of 
dead-air afterwards.


On Mon, 22 Feb 2010, Mikolaj Habryn wrote:

> 2-way communication does open some possibilities, but nothing that I
> think we'll be ready to use for the next launch. Getting a solid
> downlink is going to be much more useful in the short term - and you
> should let the list know about this, too; I suspect people will be
> interested.
> Oh, and I take it vox mode (?) on the radio works as advertised?
> (another stray thought - rather than doing full decode of incoming,
> you could maybe just FFT a few milliseconds of audio to look for 1200
> baud tones to detect in-progress transmissions?)
> m.
> On Mon, Feb 22, 2010 at 10:03 AM,  <nils at shkoo.com> wrote:
>> Yes.  Here's the aprs specification if you're interested:
>> http://www.aprs.org/doc/APRS101.PDF
>> The '@' format that I got working is the easy-to-encode one. :)
>> I'm now working on encoding using the "mic-e" format now which is
>> significantly shorter.  It's a real pain to encode, but it increases the
>> chances of successful transmission if the communications channel is iffy.
>> The hardware is probably capable of receiving packets too.  Let me know if
>> you can think of any really good uses for that and maybe I'll work on
>> implementating that half too.
>> -nils
>> On Mon, 22 Feb 2010, Mikolaj Habryn wrote:
>>> That's seriously fantastic :) Congratulations! I take it you can send
>>> arbitrary packet types?
>>> m.
>>> On Sun, Feb 21, 2010 at 11:40 PM,  <nils at shkoo.com> wrote:
>>>> Rock on:
>>>> http://aprs.fi/?c=raw&limit=&call=KF7FWZ-3
>>>> I apparently wasn't sending enough gard data after the packet and it
>>>> wasn't
>>>> all making it out or something.  I'll fine tune it later I guess
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