Success story TM-V71A Digirig Lite and APRS with Android

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 :slight_smile: 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.

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Interesting, @Troyboy162, thanks.

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.

yes, 1200baud packet expects emphasized audio.
the 9600baud packet output of a capable radio is much ‘lower’ in volume and has no ‘shaping’.

so aprsdroid would expect a ‘full bodied’ ‘loud’ audio like you would get from the 1200baud packet port.

i’m guessing the AGC option in the other software is ‘making up’ for the lack of audio coming from the flat audio output.

so in short, for working ‘main’ aprs (vhf north american freq), 1200baud packet port in/out.

good luck
kb0wlf

kb0wlf-10 wx3in1 aprs digi-gate still going for more than a decade :slight_smile:

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 :confused:

qsl.

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.

:slight_smile:

(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.

please don’t let me confuse you.
:wink:

kb0wlf

Understood. With the right APRS software you can make the wrong APRS cable work :smiley: 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.

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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.

Hello, just checking to be sure, are you using the 6 pin mini din data jack or the 8 pin mini din on your tmv71a? I just picked one up and I’m using a home brewed 6 pin mini din cable that I made following the digirig schematic with a digirig lite. I’m having no luck with ptt. It seems to receive well using APRS droid. Appreciate any input you have as to what my issues might be. I’m running it with the data band appropriately assigned and set to 1200 baud in the radio. Phone audio is set to music, and is at approximately 75%. Afsk setting in APRSdroid and I can see it triggering the PTT light but I’m not getting any keying of the radio itself.

Thanks, Mat KE8VIK

I am using the 6 pin port. The 8 pin port would be for CAT control I believe on a TM71A and I don’t have any use for that in my setup.

The wire diagram for the cable I’m using is generously given on the store page here. It sounds like that’s what you have followed to build yours so maybe ring it out to be sure?

The schematic for the digirig lite is also given in the store. If the PTT light is on you should be able to measure it at the jack end to be sure

menu 517 to set the data side and see the little “D” icon should be all that’s needed to get it to listen to the PTT input I would think. If the radio was rejecting your data port PTT it will beep at you once to let you know. It does that if you were already TX’ing with the other side of the radio when APRS tries to TX.

do you have another radio to confirm the radio isnt transmitting? If I remember right all it will do is show a full S meter on the TM71A screen while TXing and there no other indications anything is really happening.

Thank you very much for your reply. Indeed it seems that I am doing everything correctly to my knowledge as I believe I have done everything as you said. For some reason I just can’t get it to actually trigger ptt. I think I’m going to double and triple check my pin out on the cable that I built following the schematic and see if I turn up an issue. I suppose there is also a possibility of an issue in my radio as it is a used unit. It’s very clean though so it seems in good condition. I may have to pull the case open to see if theres any obvious damage inside. I also have an Elmer who is very good at this type of thing. I may have to appeal to him for some in person help if I can’t scrap my way through it with a little more troubleshooting.

Edit to add: to answer your other question, yes I have a base station running APRS with a digipeater and igate set up (also using a digirig lite) around the clock as well as a yeasu handheld that does aprs. Pretty confident I’m not getting anything out because I don’t see the s meter display when the PTT light is on the digirig lite and I’m not receiving any traffic on the other stations.

Thanks again! Appreciate your insights!