[Space] aprs

nils at shkoo.com nils at shkoo.com
Mon Feb 22 21:49:55 PST 2010


I'm not *that* worried about it, but I don't really want to use up excess 
airtime.  With a quarter-second of actual data it seems really wasteful to 
use multiples of that in overhead.  If 144.390 was less busy I probably 
wouldn't care...

Also, the AX25 specification section 3.11 kind of sounds like the 
interframe flag pattern should really be used instead of a dead carrier.

-nils

On Mon, 22 Feb 2010 grog at piratelabs.com wrote:

> Nils... you're worried about a dead carrier after the packet is transmitted?  Why?
>
> -g-
>
> Gregory Stramback
> grog at pirate.org
>
>
>
>
> On Feb 22, 2010, at 9:08 PM, nils at shkoo.com wrote:
>
>> 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.
>>
>> -nils
>>
>> 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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