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Unilab KL Low Idle Power Mods

9 September, 2015 - Reading time: 4 minutes

In this post we describe how to modify the Unilab KL series of repeaters for low idle current for use at solar powered sites, where efficiency is important..

Essentially we remove the receiver and exciter modules from the main board, remove the main board, and then reinstall the modules. Connections to the modules are made by solder joint directly to the underside of the headers.

Since the KL is usually always used as a repeater, we only need one channel.  We lock the channel BCD input to channel 1 by grounding all of the input lines as shown below.  Do the same to both receiver and exciter.

Next we interface the receiver to power and repeater controller audio and logic signals.


Light blue is CTCSS decode logic, green is carrier mute logic, white is receive audio, red +13.8V and black 0V.

Connections to the exciter module are shown next.

Yellow is transmit audio, black is 0V, red +13.8V and blue is PTT.  Connect pins two and three of CN303 together with a solder bridge.  This unbalances the balanced input so that the exciter modulates properly.  Another wire can be seen soldered to the top side of the board far right, this is PTT logic to switch the PA module.

Since we have removed the main board, we no longer have mute and power controls, so we need to fit those.  I remove the trim pots from the front panel.  Receiver mute control can be added to the front of the receive module in the vacant location as pictured below.  This is quite handy, we can adjust mute without having to remove the receive module lid.

Transmitter power control

I remove the 3 pin header from the main board, solder the power control trim pot to it, and then plug it into the 3 wire connector coming from the PA module.  Some might prefer to remove the PA board and install the trimmer back into the original location.

The blue wire from the top of the exciter module gets connected to pin two of the 6 pin connector coming from the PA.  Make these connections, in other words.. This lets the exciter put the PA into TX mode.

Thats all there is to it.. A low idle power KL.  Some repeater controllers have a fan timer logic output.  This can be used to switch a high side FET to control power to unused circuits to further reduce idle current.  A resettable 555 timer could do the same job.