Re: Balloon Mail successful WB8ELK balloon recovered by W7QO

Bill Brown

On my homebrew APRS transmitters I put a very short beep before or after sending the APRS transmission when I'm flying it on a regular flight. That and knowing when it is timeslotted really helps to identify it. But in my latest code I have it so that it alternates frequency. It transmits every 30 seconds...once on 144.39 and then the next on 144.36 and so on. The end result is a once per minute transmission on 144.39 and also 144.36.

- Bill WB8ELK

-----Original Message-----
From: James Ewen ve6srv@... [GPSL] <GPSL-noreply@...>
To: Leo Bodnar Cc: GPSL List
Sent: Mon, Oct 6, 2014 9:03 pm
Subject: Re: [GPSL] Balloon Mail successful WB8ELK balloon recovered by W7QO

There are a few things I can add to your "must-have" list. 

Because of the wonderful flexibility of these payloads, and having immediate access to the guy writing the code, think about these features. 

Send a series of tones on frequency immediately before sending your position report for DFing. The tones will be distinctive, allowing one to identify the payload transmission audibly, and if necessary, get a beam pointed at the payload before needing to decode the APRS data.  The OpenTracker line has a function called SQUAWK, which can be used to make the payload send alternating tones in a bee-doo bee-doo pattern. Very difficult to mistake for an APRS packet. 

Switch to an alternate frequency, and do the above. 

One of the hardest things to do when searching for a downed payload is to be able to differentiate your "braaaaaap" from other "braaaaps" out there.  The times slot helps, but there's always someone clobbering, or a far off digipeater making noise out there right when your payload should be up. Getting off the national channel and to a quiet frequency really helps. Oh yeah, get your search teams to turn off beaconing if they switch their APRS radios to the non-standard frequency. 

Of course, you would probably only enable these features once the payload has determined it is on the ground.  Look for altitude below a preset value, and/or look for 0 groundspeed. A combo of both, with some leeway on the speed due to GPS wandering is probably best. Kicking in the DF tones before landing might be an idea so even teams without beams can add in "heard reports" as the payload drops below their local horizon. If the teams are surrounding the payload, these heard reports might be enough to help figure out who's closer and who's further from the payload.  

Of course, Leo's probably not interested in any of this, since all of this is concerning recovering balloons after flight termination, and someone seems to have missed the memo about flights terminating, and just leaves them circling the Earth endlessly!

On Monday, October 6, 2014, Leo Bodnar leo@... [GPSL] <GPSL-noreply@...> wrote:


That's what all B-flights do as well.  There is no compressed timestamp available in APRS specification so i just dreamt up my own.

There are encoded time and datestamps in each realtime and backlog message sent from B-**.  Without them there is no way to untangle APRS timing mess.  

There are stations sending packets with 30-60 minutes delays and dutifully lists them under delayed times.  
The worst I had was 18 hours delayed packets from some unlisted igate in Russia.

For example, last B-64 packet was:

2014-10-06 07:10:43 UTC: M0XER-4>APRS64,LD9TK,WIDE2*,qAR,LA9UI-2:!/)IQ1Q_7)O W{h)/A=040836|+fI7&W=r!,|

...note "W{h)" in front of /A=040836 - this is an encoded GPS date/time stamp.  It decodes to "10th of October, 07:10:41" 


On 6 Oct 2014, at 22:51, Mark Conner mconner1@... [GPSL] wrote:

Another item to consider is using the hhmmss format for the time spec.  This helps reconstruct logs afterwards, especially data collected from others.  It's really handy to have a good time stamp right in the packet instead of relying on others' clocks.  I can't remember if that's part of the APRS compressed format or not.  We generally run more towards the "plain" format, which is harder on the TX/battery budget but has more flexibility.


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