APRS spotting on the (very) cheap

While my quest for a cheap APRS tracking/messaging device lives on, I found a cheap backup solution for when there is no phone coverage on SOTA summits (yes I know about RBNHole but I don’t do CW yet).

It turns out that the classic Baofeng Audio-In pinout (Kenwood plug?) corresponds to the standard mobile phone Audio-Out (=headphones)… and they’re both 3.5mm jacks.

So to spot via APRS:

  1. I connect my iPhone to my Baofeng UV-5R with a 3.5mm jack male to male cable (I need also an adapter as my iPhone only has a lighnting port). In other words, there is no need for a non-standard cable.
  2. I prepare my spotting message in the PocketPacket app (iOS app - other apps may work but I tested the set-up with this on). I set the volume to the maximum.
  3. On my Baofeng set to the APRS frequency, I press the PTT button, send the message via iPhone, release the PTT button after 2 seconds.
  4. Yes, I won’t receive packets with this setup, but do I have to? I have to call CQ one way or another anyway :slight_smile: To increase my chances I send the message 2-3 times at 30 seconds intervals. If I hear a packet a couple of seconds after sending my message, it is likely my message was digipeated.


What a great idea!
For those with Android smartphones rather than Apple, I guess APRSDroid or APRS Messenger may work in a similar fashion. I’ll have to try it.

73 Ed DD5LP


Romain, I am working on the same thing with Android. Could you give me an example of what your message format looks like in the app?

Yes - I actually have a small note in an app on my phone for easy reference:

<Association/Reference> <Frequency> <Mode> [callsign] [comment]

Example: SP/SP-001 7.090 ssb SP6SUD/P qrv now

Remember that you have to register for the APRS2SOTA service first.

More details here: APRS2SOTA User Guide


Hi Paul - this is the website you need:


And as Romain says you need to register your call sign to have access to the gateway. Send a note to its creator Stewart Wilkinson G0LGS stewart.g0lgs(@)gmail.com

I have run a test from my Android phone (via the Internet) and it worked. I found unfirtunately that the battery in my UV-3R HT ius flat and wont charge and so I have ordered a new one. I have also ordered the required components to creat an interface cable to go between my Android smartphone and the HT.

Parts and battery are expected to arrive here early next week, so I should (hopefully) have APRS reporting via 2m RF from the summits later next week.

This APRS is quite interesting looking at the messages. Several clubs here use APRS to advertise their On-Air Nets and On-Line meetings!

73 Ed.


Cheaper again - There are some apps that dont even require the cable,

Type message in app, hold to radio, press PTT, send audio, release PTT.


Hi Wade,
I know of android-apps for other modes like SSTV and PSK but which one works well without a cable for APRS. I tried exactly that with APRSDroid and couldn’t get it to work.

I’m currently at the stage of building the 3.5" 4-pole to 4-pole TRRS connector cable to go between my Mk1 UV-3R and my smartphone and while I can send packets, I can’t receive as the smartphone isn’t switching to the mic input from the Baofeng, rather it’s staying on the internal microphone. It’s a known problem, I just have to play around with capacitor and resistor values in the cable to get the right load on the smartphone’s headset socket for it to recognise it has to use the microphone from there instead of the internal one.

An interesting little project to use the little UV-3R that’s been literally laying around doing nothing for a few years!

73 Ed.

there must be a resistor (DC path) to ground on the MIC input.
See my KX3 to tablet interface:

I used a 10k resistor

Hi Luc,
I had done that - I’m still having issues! I have the smartphone acknowledging that there is a headset attached (icon appears) but it continues to use the internal microphone, not the line-in through the 3.5mm socket!

Different phones apparently can look for different resistances anywhere from 2-12k - I am now on 5.6k - still the same problem. I also have a capacitor in the circuit to protect the audio line - basically, your 2nd circuit but without the isolation transformer as all the circuits I can find on the web do not use a transformer, rather just resistor and capacitor (as you have, prior to the transformer).

I’m not dealing with data here, purely audio. I will run VOX on the UV-3R so PTT isn’t needed. This “should” be simple!

I’ll get there - it’s just a matter of finding what my Lenovo S5 is happy with.

73 Ed.

Did you test with a TRRS headset (or earbuds with mic)?
If that works, measure the resistance (to GND) on the MIC pin of that headset.

Not all phones or tablets have a MIC IN (my good old Nexus 7 didn’t have it !). Check the manual if it is mentioned.

And check if you used the correct pinout (I’m sure you did all that :wink:
For once … Apple is RIGHT , Android is LEFT … in the picture I mean, haha.


And just asking ; you didn’t put the capacitor at the phone side , did you ?

PS : good news, I’ll be doing a few summits next week, finally !


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I used 2k2.

Thanks Luc, Thanks Simon,

Luc - the connections to my Smartphone are the usual SmartPhone connections CTIA as you have it labelled. The design where the one nearest the chassis on the socket is NOT earth/screen. A strange standard as most would assume the outer connector to be earth. In any case I am happy the connections are as described. The UV-3R that I am using is a little different to most Chinese HTs, that it just has one 4-pole 3.5mm socket for the external speaker mike/programming, not the usual “kenwood style” 3.5 plus 2.5mm jacks.
One Youtube video shows what is described as a “straight through” cable being plugged in between a UV-3R and smartphone and everything working straight away. Either that phone is wired in an odd way or it wasn’t a 4-pole to 4-pole lead and then who knows what is being shorted out!

As Simon says there are many different circuits on the web for the interface (by the way the link " [This page] specifies the connection standard for Android." in your article gives a 404 page not found error.

So far I have used a 0.1ufd to isolate the DC bias voltage on the smartphones mic. line but as so many designs don’t use this tomorrow, I will use a very simple design with just two 500 ohm resistors and see if that shows any more life?

If not I’ll be trying a different smartphone.

73 Ed.

UPDATE 20/6/20: I have found that my Lenovo S5 smartphone is designed so that it can use either CTIA or OMTP wired headsets! Hence any headset will work with the phone. To do this they must be working with a floating earth probably simply going into a transformer off the first two contacts on the 4-pin plug. Great idea, but NOT when one is trying to interface to a HT and you need an earth contact …
I re-tried my cable (Scriibled diagram below) with a cheapo “Doogee” Android phone and guess what - it’s working - at least on transmit. I have been able to send some test spots to SOTAWatch today and to page out my position to the APRS network and see it on aprs.fi - both of these functions are working over RF via the Baofeng not over the Internet.

… Now to find why recieved packets are not being decoded

I did this 4 or 5 years ago and then got a FT2 which workes a lot better. Much better reception and higher chance of getting out. APRS Kabel für Baofeng und APRSdroid selbst gebaut

Recently built up a few of these: AFSK DRA818 APRS Tracker – Projets radio - they could easily be adapted to send ‘on summit’ spots (automatically, potentially) and built in to a tough case

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Although I have been able to submit a test spot to SotaWatch3 over RF using my set-up shown above, because I am sending the FR to a local iGate, not a digipeater, I do not know if this configuration works on receive also. I have left the configuration monitoring the APRS frequency for sometime but so far have not caught any passing cars running APRS or any further away digipeater.

I have no reason to think that receive would not also work, but I guess I’ll have to wait until I am up on a summit increasing the receive range, before I can confirm that everything is working to receive APRS packets as well as sending them.

73 Ed.

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