Review – BTech APRS-K2 Cable (TRRS/APRS)

by John ‘Miklor’

It’s long overdue, but there’s finally a TRRS/APRS cable available for radios using a standard Kenwood style K2 connector.

I’ve been wanting to get involved with APRS for a while now, and this made it extremely easy.

APRS-K2 interface cable
The APRS-K2 cable allows you to interface your handheld transceiver with your existing mobile device, including. iPhone, iPad, and Android.

One end of the cable uses the Kenwood style K2 connector, while the opposite end is aprs-xover-25terminated with a TRRS connector. Also included with the APRS-K2 is a Reverse Adapter to insure compatibility with all devices. This adapter allows cable to connect to earlier 3.5MM TRRS standards, such as Nokia.

App Driven
The APRS-K2 cable uses a virtual TNC found in several apps, such as APRSDroid,, and Pocket Packet. Plug in the cable, turn on the VOX, and you’re pretty much set to go.

Product Description
BTECH APRS-K2 TRRS / APRS Cable A simple way to start using APRS by using devices you already own. The BTECH APRS-K2 Cable will quickly connect your radio to APRS by using virtual TNC (app driven) on your tablet or device. The APRS-K2 cable is built with a custom circuit board that will automatically adjust the audio for clear packet transmissions with minimal adjustment; along with protecting your devices from strong over modulated signals.

Along with allowing APRS functionality the APRS-K2 cable can provide a simple interface gateway to allow several features to your radio!

Easily record radio conversations:
By connecting the APRS-K2 cable between your radio and any recording (line-in) device.

Use the APRS-K2 cable as a Mic In Connector:
Set up VOX on your radio to accept any form of incoming audio – such as a Push-to-talk application on a Phone – or a Line-out application from your computer.

Use the APRS-K2 cable to push transmissions over a speaker system:
Easily play audio over a intercom or speaker system from your handheld.

With a backup radio and your own ingenuity, the APRS-K2 cable can serve as an interface for a variety of applications for any amateur. Compatible with Kenwood K2 Accessory Slot Radios (such as BaoFeng, BTECH, Wouxun, TYT) Compatible with all phones, tablets, and computers with 3.5MM Audio In/Out Ports

APRS-K2 Cable
Reverse Connector Adapter
Quick Start Guide


The cable comes with a simple one page instruction sheet which should have you up and running in about 10 minutes after the appropriate app is loaded.
–  Plug in the cable
–  Set your handhelds volume control
–  Turn on the VOX
–  Set your handheld to 144.390 (US)
–  Activate the app

That’s all it takes. If you’ve been considering building an APRS cable, you might find this an easy Plus and Play alternative.

The APRS-K2 can be ordered from   Amazon, or if outside the US, you can go to their website and contact them directly.   Baofeng Tech

Too many toys, too little time.
John ‘Miklor’   K3NXU

Build your Own Programming Cable

by John ‘Miklor’ K3NXU

CP2102j[1] Frustrated with that generic programming cable?
This $2 solution might just be your ticket to sanity.

Let’s See…

You purchased a radio and programming cable, loaded the software, and that’s as far as you’ve gotten. You’re fighting with error messages:
– Radio did not respond
– Could not open COM port
– Run Time Error
and Windows (TM) 10 keeps changing your drivers.

Now you do what many owners do. Put the radio in the drawer to be worked on later. This is like buying a roll-away treadmill and putting it in the closet until the next time you want to exercise. (NOT going to happen)

But wait, yours has the company name and logo right on the cable.
– It doesn’t matter. Keep reading.

There are a few options available, such as an FTDI cable. It’s truly Plug ‘n Play, and costs about $20.

But here’s a project that just might solve the issue for around $2. All you need is a small flat blade screwdriver, a soldering pencil, and a CP2102 board.


The CP2102 is a USB to TTL UART chip. What?
Long story short… It’s the same thing that’s in your current cable now, except these work.

CP2102 boards can be found on eBay for around $2 and on Amazon.

Here’s How

Let’s start with that original cable.CP2102j[1]

Take a small screw driver and pry the open the case from the back where the cable enters.
It should only be snapped together.CP2102b
Unsolder the 3 wires connected to the board.  GND is Black, TX is Red, RX is White.CP2102c
Solder the 3 wires to the corresponding terminals on the new board.CP2102g

Note 1:
Some boards may have the TxD and RxD reversed. If it doesn’t work the first time, reverse the two wires. No damage has been done.

Note 2: Some boards have pins on the back requiring small connectors. You can either remove the pins, solder to them, or use the connectors. (Whatever floats your boat.)


When you insert the new board into the USB port, give Windows a chance to find and load the new driver. Should take about 30 seconds. When it says Driver Found, you’re done.

If the driver is labeled CH340 instead of CP210x in Device Manager, that’s not a problem. Both chips are designed to do the same thing.

But I don’t have a Cable

If you don’t have a generic cable, you can use 2.5 and 3.5mm stereo jacks. Here are the pin outs, and what Jim’s (KC9HI) cable looks like.
CP2102jim CP2102o



If you are adventurous, try retrofitting the new board inside the original plastic housing. This will require a Dremel tool, X-Acto knife, Glue, and some patience, but it can be done.

If the board only has 5 terminals instead of 6, it’s not an issue. You only need GND, TX and RX.

Some come protected with a piece of clear heat shrink over the board so you can see the cool blinking lights.

Note 3: If you are trying to retrofit the board inside an existing shell, the red board below is a bit shorter and easier to fit.          Amazon       eBay
For about a dollar or so more, you can find the same boards in a metal case.

What’s the Advantage

– First and Foremost, it works. Take the radio out of the drawer, program it and have some fun.

– Next, it only cost around $2 to save the generic cable from the trash.

– Very Important – Bragging Rights. Now, when you go to a club meeting and someone says they can’t get their cable to work, tell them they can build their own, just as you did.

I hope you had fun with this project. It’s super simple and very rewarding. I’ve made several and never had a failure. Say goodbye to driver issues.

My thanks to Jim KC9HI for his input on this project

More Information:

Sainsonic GT-3, GT-3 Mark II additional notes

Thanks to a reader in Denmark I ran into a new, undocumented feature present in modern UV-5R varieties which have both a Band and an A/B button. The feature has been confirmed in the GT-3, GT-3 Mark II and the to-be-reviewed GT-3TP, but might be true for recent UV-5Rs also.

1750 Hz and 2100 Hz burst tones
In most parts of the world burst tones were once used to open up repeaters but abandoned in favor of CTCSS.  It’s one of the reasons why I don’t look into that feature too closely anymore; it became sort of irrelevant. Some European repeaters will still open up when a 1750 Hz tone is transmitted in order to stay compatible with older ham equipment.

Without notifying anyone (what’s new) Baofeng added the 2100 Hz burst tone to its bag of tricks. The problem is that this tone is not documented anywhere in the manual, and that they use the Band key to generate 2100 Hz instead of 1750 Hz. So, if you follow the manual, you’ll send 2100 Hz instead of 1750 Hz.

This is what you should do:

  • Ignore the manual
  • press PTT + A/B to generate 1750 Hz
  • press PTT + Band to generate 2100 Hz.

I mailed this to John ( so it can be included in the documentation.

Burst Tones

GT-3 antennas
The SMA thread on GT-3 antennas isn’t very precisely made. You might feel some resistance once every 180 degrees when screwing it on. It’s no biggie an will resolve itself after some use, but worth knowing.

UV-5R ‘reverse’ function oddity
When you have a repeater programmed in one of the memories and assuming you only programmed a CTCSS tone for TX, not RX, you would expect CTCSS to be irrelevant when listening reverse. That’s not the case; your Baofeng will ‘invent’ R-CTCSS on the fly. According to some hams this behavior can also be found on certain Kenwood models.

Baofeng GT-3 Additional Notes

I borrowed a second sample, in the hope that the poor harmonic suppression was a fluke. Nothing changed, my initial review of the Baofeng GT-3 still stands. Note: the initial results were cross-checked on two different analyzers at two different locations, just to make sure we didn’t make a mistake.

I did some more tests with after market antennas. It didn’t make much of a difference which one I picked: the $3.79 antenna, the Nagoya NA-701 or the antenna that comes with the UV-82 and the UV-B5. I really like the UV-82 / UV-B5 antennas because they perform above average, are sturdy and fit perfectly (no gap between the base of the antenna and the radio).

With the GT-3 stock antenna hearing and/or opening up some distant VHF repeaters proved to be hard or impossible. With the other three it was no problem.

Some owners complained that they can’t charge the radio while the belt clip is attached. Mine doesn’t have that problem. Either there are two different chargers delivered, or different (longer) belt clips.

I had to pay the full amount, $70. Listings now show that the price went down to just under $50. That’s more realistic for what you get, and on par with the average price of the Baofeng UV-82.