Just documenting this for the next guy since most android APRS how- to’s are for HT
equipment used TM-V71A Digirig Lite Digirig MiniDin6 9600-baud Audio/PTT cable Pixel 8 pro OS:Android 15 (needs a USB hub to see the digirig)
Kenwood TM-V71A
Demod improvements with APRSdroid seemed be had by using side A (menu 517) and setting data to 1200 baud (menu 518). Yes the 9600 baud cable works with the radio set to 1200. That was not intuitive for me Also unexpectedly to me the side you set for data operates independently and you do not need to give that side the PTT focus for it to TX via the data port input. You can still switch PTT focus over and talk on the APRS side if want of course and that wont interrupt anything automated coming in the data port. squelch and radio volume settings make no difference.
APRSdroid relevant settings:
-Connection protocol Audio (AFSK)
-high quality demodulation checked didnt seem to do much
-frame sync prefix 200 (seems to work well thanks to the digirig lite and gives you a nice short APRS transmit)
-audio out Music (several other worked but music does not have some of the unwanted mic/speaker tricks applied to it like voice call. music volume set to ~80%)
Android notes:
Demodulation success is very app dependent with APRSDroid being the worst I tried unfortunately. IGATE2 is almost 100% effective when “IF AGC” is checked. Demod doesn’t matter if you are just looking to have your track up on APRS.fi but if you want to receive text messages it will factor in heavily since they are not sent more than once. Seeing other APRS users will work ok since you will demod at least 1 of their packets and see them.
The 1200/9600 radio menu setting is for the transmit audio. The 9600 setting does not apply the normal high frequency emphasis that FM transceivers typically apply (so “flat” audio is transmitted, which is what you want for high speed data such as VARA FM), whereas the 1200 setting does apply the emphasis (as it does for normal mic TX audio) and is suitable for low speed data, such as APRS over packet.
The RX audio depends on which pin in the MiniDIN-6 connector on the radio you use (i.e. which Digirig cable you buy). The 9600 pin (pin 4 as I recall) taps the receive audio in the radio prior to high frequency de-emphasis, resulting in the “flat” audio you need for high speed data modes (although it works fine for low speed modes too). The 1200 pin (pin 5 as I recall) taps the RX audio after de-emphasis is applied. These 1200 and 9600 RX audio taps are hard wired to the minDIN-6 connector and have nothing to do with the radio’s 1200/9600 menu setting.
Thank you! That’s a wonderful explanation of what’s happening. I found the baud stuff very confusing and made lots of incorrect assumptions.
Do you think apps like APRSdroid might cater to de-emphasised audio better for AFSK connection? I’ve tried everything I can to improve the success rate demodulating incoming packets. IGATE2 doesn’t have any documentation on its “IF AGC” setting but that allows almost a 100% success rate for any clear packet coming in. APRSdroid is about 1 in 5 or so.
The adapter cable from mobilinkd is cheap enough I might try it as a experiment.
ok that checks out thank you! darn…I should have not bought the 9600 baud cable. To my defense I got some bad advise on that lol.
Mobilinkd got my money on the adapter cable. I’ll update the original post. Ok I cant edit it…so I guess I’ll trash it after a test. Dont want to leave bad advise on here
the flat audio is a ‘must’ for vara-fm WIDE (the ‘fastest’ mode) rather than vara-fm NARROW (pretty fast but not super fast)
the flat audio is a ‘must’ for 9600 packet found on many uhf packet networks.
so, the cable/advise isn’t the worst thing ever but it is wrong for aprs using a smartphone running aprsdroid.
(other aprs appliances have menus to select if you’re feeding it emphasized or flat audio)
i’m pretty sure the mobilnkd cables are not pin compatible with digirig audio/ptt cables.
there is an adapter cable sold in the digirig store to convert either direction.
i own a mobilinkd, maybe version 2? and the cables i got with it are not pin compatible.
or is it a cable that routes the 6pin din port pins between 1200 and 9.6k?
that would make sense.
Understood. With the right APRS software you can make the wrong APRS cable work That’s really only a android specific problem I think. The best android program is APRSdroid and its been on life support for years.
That’s the cable I bought. It just flip flops the pin 4 to pin 5 with everything else wired straight through. Its reasonably priced to boot. In hind sight I should have just made something out my old PS/2 mouse stuff, but I wanted to hit the easy button. Now I should have the right cables to do a proper APRS supported adventure this weekend. It will be some long shots to repeaters so I greatly appreciate the help getting this working as best as possible.
Very interesting results over the weekend. I have the 1200 baud conversion cable from Mobilink now. Right off the bat that didnt seem to work as well with APRSdroid. The other oddity was the incredibly poor initial results using a nice Samsung tablet. I’m beginning to think the cable or rather what pin you grab audio from (at least on my TM-V71A) is just one variable among several others that may be more influential. I’ll update again if I figure out some solid data points to share, but the 9600 cable from digirig appears to be the best (and good advise) for my particular soup of APRS items
I feel that something like this program below I am using may end up being the largest factor on demodulation in android for myself and others. My Samsung tablet will not work hardly at all without it.
Also, I focus on RX but the setup is TX’ing like a champ. I’m getting my packets out much better than the small sample size of people I’ve looked at operating in the same remote area. Who knows what they are using, but TX is solidly exceeding my expectations.
Also unexpectedly to me the side you set for data operates independently and you do not need to give that side the PTT focus for it to TX via the data port input. You can still switch PTT focus over and talk on the APRS side if want of course and that wont interrupt anything automated coming in the data port. squelch and radio volume settings make no difference.
That’s really only a android specific problem I think. The best android program is APRSdroid and its been on life support for years.