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QYT KT800 & KT8900D and variants X-band repeater system interface

QYT KT8900 and QYT KT8900D Repeater system

QTY KT8900 and QYT KT8900D chinese radios and variants have a built in repeater function that works out of the box without additional modification on the radio. You just need to enable the repeater function (cross band repeater VHF/UHF or UHF/VHF) via the menu system. Connect the two radios via the mic port using the cable shown here and enable the repeater function on the radio. The radios will work in the repeater mode cross band and will re-transmit your audio either on the VHF or UHF and vice versa.

QYT-X-Band-repeater-interface

Download the PDF Document here

The repeater interface will work on the variants of these radios in either combination of at least 2 KT8900 RX/TX,
2 KT8900D RX/TX or 1 KT8900 and 1 KT900D and of course Baofeng Tech radios. The configuration is done on individual radios by setting the REP-M (Repeater transponder function on both radio). Once a matched Carrier, CTCSS/DCS, TONE or DTMF is received in either of the radios it will re-transmit the audio on the other radio and vice versa.

The repeater interface will work on the variants of these radios in either combination of at least 2 KT8900 RX/TX,
2 KT8900D RX/TX or 1 KT8900 and 1 KT900D and of course Baofeng Tech radios. The configuration is done on individual radios by setting the REP-M (Repeater transponder function on both radio). Once a matched Carrier, CTCSS/DCS, TONE or DTMF is received in either of the radios it will re-transmit the audio on the other radio and vice versa.

QYT KT8900 and KT8900D Repeater System

Build the cable

Do it yourself using RJ45 modular connector and a piece of LAN UTP cable

DIY X-Band Repeater Cable for KT8900 and 8900D and variants

Finished Cross Band X-Band repeater interface

Let’s see how it works

Testing video of working repeater system

Features

1. Easy deployment for field work to extend portable radio range with acceptable results
2. Will fit easily in a go box
3. Inexpensive but it works

Caveats

1. Recommended for light usage as QYT Radios tend to heat up easily
2. Use the upgraded version of QYT the KT8900D for more stability
3. Suitable only for Cross Band configuration
3. KT 8900 heats up like a barbecue grill if it didn’t burn your finals at least bring a hotdog to grill …

25 replies on “QYT KT800 & KT8900D and variants X-band repeater system interface”

Cool, the audio shoukd still be adjusted or you have all.mpbile backgrounds repeated, there shoukd also be an audio speech filter to remove the hiss and flutter which will also be transmitted.

friend, I have a doubt, pin 1 and pin 7 do not connect?, because I am having problems, after a while of use, both radios change frequency, unlock and it is as if someone was manipulating the microphone, then I came to the conclusion that I connect pin 1 and pin 7, so I must cut them?

I don’t see any reason why it shouldn’t work on same band configuration with a duplexer, the only reason why it is configured to work as cross band is due to isolation between transmitter and receiver to prevent degradation of receiver sensitivity.

Yes of course spaced vertically apart will provide a good isolation between your antennas just like in repeater setup. However if you will use this radio on the same band transmit I’m not sure if it will provide sufficient isolation between rx and tx as the manufacturer of this radio also specify that it should only be used on a cross band repeat mode. I haven’t tried it yet on the same band tx/rx.

Out of the China made radios, the KT8900 has fairly decent selectivity. It’s nice that the engineers took some time in this area. I purchased two of these radios, made the control cable and installed high volume computer fans for cooling. Even though I was via Tx/Rx Vhf/Uhf, I still built two band pass filters. The crossband was configured to go in one direction (Vhf Tx) (Uhf Rx) because there is no need unless one in going to set up a link to another repeater etc. After all, one can configure any uv5r blowfang radio because of it’s endless offset. I built a simple vertical dc coupled dipole for the (Uhf RX) and on top of that a D.I.Y. co-linear 2 pole array for (Vhf Tx) A Repeater will pretty much hear one on the ground. NOT the same in the other direction. I wired in a cheap compressor/limiter to keep the audio stable. Behaves quite nice. It works damn near as good as some of the commercial junk I have built . Oh and the fella that was going to go in band without a $1600.00 duplexer. It will not behave. Take care and 73′ de, Dave.

It’s not designed to be use on same band repeater because it lacks filtering, also GMRS service is for short distance communication only so no need for a repeater depending on your country if you set up a repeater you maybe violating a provision for the use of GMRS service check your laws.

I’m allowed to operate a repeater up to 50 watts here in Ohio. I’ve seen other hook up two radios similar to this set up though. Thought since I have two of these I would see about setting them up, looks like I’m buying two more radios.

To clarify, I want to change channel but not using the included microphone. I will be using a DIY build to do this.

Hi DV1YGQ, you need to check the state (status) of up/down function when it triggers using your ptt see if the signal that triggers it is either active high or active low (voltage levels) that way you can control the direction of the channel going up or down you need to be in memory mode and the channels save on your radio to easily move between your saved frequencies it can be done using push buttons switches or via DTMF function (you need a DTMF encoder/decoder for that to work using DTMF).

It will only work with push button combination if it has a dedicated up/down line to trigger the channel up/down direction, most probably it passes thru a DTMF encoder/decoder IC on your microphone so you need to check the correct DTMF frequencies assigned to up down button and pass the same signal through the RJ45 pin check the encoder/decoder datasheet for this.

I had the same experience as John in Ohio. My gmrs high (467.600) comes from the antenna thru the duplexer to radio 1. I set REP-M to tone 123. That does trigger the radio to respond. It should then via the interface cable retransmit to radio 2, which is set to 462.600 to retransmit. It’s REP-M is set to carrier. There is no tone set for the outgoing radio. It doesn’t work. It also causes the radio 1 to go into alarm mode and start to program a new frequency all by itself. The cable pinout is correct. Set squelch high on receiving radio. Don’t know what the mechanics of what is going on.

Hi @Heffe, it’s probably because the interface was not intended for same band repeater, due to the design of QYT which doesn’t have enough frontend filtering so even though the signal passes through the duplexer it is not enough to give good isolation since it is directly connected to the RJ45 of both radios which causes undesired operation. I don’t have a duplexer so I haven’t tested it on the same band, but when playing with it using QYT and another baofeng radio as a receiver passing through an arduino repeater controller I have observed the same behavior, the radio is performing erratically when I’m using it as same band repeater especially if, I’m transmitting my portable radio very close to it. The repeater interface for QYT was not intended to be used as same band repeater it is explicitly mentioned in their documentation it’s from Baofeng Tech here: >>> https://baofengtech.com/cross-band-repeater-with-2-btech-mobiles/

Thank you Ephraim! I did get it to work by simply setting radio 1 (rx) to carrier also. Oddly, my friend can transmit to it only .5miles away and it repeats loud and clear to me 4 miles away. I cannot do the same from here. Almost like squelch is set too high. But it’s on setting 1. We can both get it to kick back to us 15 miles away, but no audio. Must be related to your comments. Thank you again

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