A Brief Review of the KT-8900D

Over the years we have received a few questions about inexpensive mobile rigs for use with our TNCs.  Mostly what people are after are the cheap Chinese radios that can be had for around $100.  I have never been keen to buy one of these Chinese radios because either they are cheap and incredibly bad or they get decent reviews, cost almost as much as the respected Japanese brands, yet are still lacking important features such as dual receive and a MiniDIN-6 data port.

This review isn’t about one of the more expensive Chinese mobile radios — it is about a $99 radio (the QYT KT-8900Dmobile radio) and my very brief experience with it so far.  And when I say brief, I mean it.  I’ve had it in the shack less than 6 hours as I write this.

I should make it clear why I wanted to review this radio. It has one standout feature that all other radios in this class lack: a 3.5mm jack in the back (link to image) with audio in, audio out, and PTT.  It’s not a standard MiniDIN-6 data port, but it is something we can work with to connect a TNC.

In the 6 hours I have had it, one thing is abundantly clear. The radio is deaf on 2m.  Stay tuned though… we have a bit of a surprise below and we’ll learn a few things along the way.

Setup and Testing

I connected the radio to my Jetstream JTPS35MCMA power supply.  The radio comes with a universal 12V accessory plug connector and the Jetstream has an 12V accessory power port.  I then connected the radio to my DIamond X6000A base station antenna.

I turned on the KT-8900D and tuned the receiver to 144.390.  I could hear a few APRS packets coming through but it wasn’t sounding very good.  I should be hearing a lot more packets, and the packets I could hear should be a lot clearer.  I went through the menu and turned off all the various features that needed to be off and left the radio on with the squelch open to listen.  If you are familiar with the Baofeng menus, you’ll be right at home with this radio.  The similarities between the two are striking.

One item of note is that the user interface on the KT-8900D is challenging.  The radio uses a rotary encoder that doesn’t seem to do a good job of detecting the direction of rotation.  It makes navigating the configuration settings at first a confusing experience, and then a frustrating one.  It randomly jumps backwards instead of stepping forward through the menu items.

With the radio monitoring APRS traffic in the background I made a custom cable by snipping the end off of a 1 meter straight-through 3.5mm TRRS male to male cable and soldering on one of our 3.5mm plugs to match the pinout of the radio with our TNC.

A few minutes later I plugged a prototype TNC I’ve been working on into the radio, went through the config app to get the audio settings adjusted, then let it start decoding while I went off and had lunch.

The 3.5mm jack on the radio is buried pretty deeply in the metal case, with a rather narrow opening.  If the molded connector on the cable I used was any wider, it would not have fit.  The 3.5mm connector I attached to the cable was too wide and would not fit in the hole.

I came back about an hour later and had a total of 3 packets decoded.  I should point out at this point that I can decode anywhere from 4000 to 8000 packets a day depending on the weather and troposphere from my Kenwood TM-V71A or my Yaesu FT-991.  That’s about 170-330 an hour — with 200 an hour about typical.

Some background information…

I’m in Chicago.  There is a lot of out of band RF here.  It is a tough environment in which to evaluate a 2m receiver.

The KT-8900D is another one of those radios from China that covers 136-174Mhz on VHF built primarily for the Chinese domestic commercial market.  And just like the ubiquitous Baofeng HTs and virtually all radios in this price point, it uses an RDA Microelectronics RDA1846S chip for modulation and demodulation. This chip performs horribly in an RF-rich environment.  Unless you have a very narrow filter on the receiver front end, it will desense in an environment like this.  Virtually all Chinese radios of this caliber use this chip and they all suffer to some degree from this same problem.

The RDA1846 was designed as a low-cost solution for cheap bubble-pack FRS and MURS HTs, not for mobile rigs.

This problem does not happen with well designed superheterodyne receivers.  But those cost more money to build.

Well that sucks.  What can we do about it?

I have a notch filter from PAR Electronics in the shack that I purchased a number of years ago to try to help with some out of band interference.  It’s been sitting on a shelf unused for quite a while.  I thought — what the heck, what can it hurt?  So I attached the filter.

I plugged the filter in and immediately started to see packets being decoded. The change was incredible.  I let it go for an hour and the packets kept coming in.

Remember kids, the only difference between screwing around and science is writing it down.

So, I needed to get some real numbers.  I fired up Xastir, which will log all of the packets it receives along with a timestamp.  I configured the TNC port for receive only in Xastir.  And it recorded 117 packets in a one our time span.  I removed the notch filter and recorded for another hour.  Zilch. Nada. 0 packets decoded.  I added the notch filter back in. 97 packets decoded in an hour.

You will notice that this is still at least 30% fewer packets than expected from my normal rigs.  But this is a holiday weekend and the atmosphere can do screwy things to VHF propagation, so I need to do a lot more testing — with the Kenwood, and with the QYT with the notch filter.  There’s really no need to test without the filter. The radio is clearly deaf without it.  2 hours and 3 packets decoded in Chicago. That’s UV-5R bad.

Now here’s the real kick in the pants:  the notch filter costs almost as much as the radio.

So, stay tuned.  We’ll post more as we play around with this.

The KT-8900D is essentially a Baofeng UV-5R with a 20W power amplifier.

First follow-up posted here: KT-8900D Review Follow-up #1

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