Creating a programming cable for a QYT KT-8900 with some soldering / 2016-11-24

2016-11-24 Creating a programming cable for a QYT KT-8900 with some soldering7 months ago
QYT KT-8900 radio with homebrewed interface cable, CC-BY-SA
QYT KT-8900 radio with homebrewed interface cable, CC-BY-SA
I bought a cheap 2m/70cm mobile/base radio, a QYT KT-8900 which has the special feature of being very small but still able of putting out 25 Watt on the 2 meter VHF band and 20 Watt on the 70 centimeter UHF band.

The display looks a lot like my Wouxun KG-UVD1P, complete with battery status indicator which is not much use when the radio has a constant 13.8V feed. The menus are quite similar, so this is probably not a coincidence.

I bought it via aliexpress and it got shipped at a reasonable speed to my house. In the original listing was mention of a programming cable, but it showed up without one. I asked the seller about this and directly a baofeng programming cable was shipped to me.

But, the QYT KT-8900 has a different programming interface, just a 3.5 millimeter plug with ground, rx and tx data. So I found a very good resource for chinese radios which has the answers: 3 PIN Programming Cable for a BTech, QYT, etc Mobile which has the right pinout. I just cut the Baofeng cable to get at the gnd, rx and tx wires.

Next I had to wait for a cable with the right 3.5mm connector to show up. The connector in the back is sunk into the case and the 3.5mm connectors I had in the junkbox did not fit. But a broken PC speaker set wanted to donate a cable with 3.5mm connectors that were slim enough. Next trying the result with chirp radio programming software under Linux. And suddenly I could copy a list of channels I had and upload it to the radio in 5 minutes, which is a lot faster than manual programming where getting more than one channel programmed in correctly under 5 minutes is hard, see for example Programming Repeaters into the QYT KT8900 Mini Dual Band Mobile Radio Review - AF5DN - Youtube.

At the moment the cable looks very experimental. Now it has been tested I will use tiewraps and heatshrink tube to make it sturdier and make it look a lot better.

As a radio it's ok, but not ideal. I was testing with meetnetwerk baretta - hobbyscoop and the antenna on the roof for 2 meter and 70 centimeter and noticed I had pulsing audio of the output frequency of PI2NOS on the Baretta frequency. Pulsing audio is a known problem in this radio, see KT8900 FAQ at miklor.com but I have no channels with receive CTCSS.

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