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7DB mod for 5DJ CTCSS Encode

21 December, 2015 - Reading time: 2 minutes

Borrowing the idea from the NHRC-3.1 CTCSS mod I decided to do the same for the VK5DJ controller.

The same idea applies, but with a slightly different interface.

We take the mute gate logic from the PIC here, which is pin 13 of the 4066 device.  This logic signal goes high when the mute is open, so we use this to drive the base of a NPN transistor to enable the encoder.

The C1000 encoder is modified similarly to the NHRC-3.1 mod.  This time we pull pin 12 low to enable encode rather than driving pin 13 high

The picture isnt very clear, but it shows a NPN transistor connected between pin 12 and ground.  Ground is taken from the bottom of the output level trimmer.  The base has a 10k resistor, this then makes its way out to pin 13 of the 4066.

Thats it, simple.  The CTCSS encoder will now only run when the mute gate on the controller is open, regardless of any other mute activity in the receiver.

7DB mod for CTCSS encode following mute on NHRC-3.1

17 November, 2015 - Reading time: 3 minutes

Today we demonstrate how to mod a C1000 CTCSS encoder to follow the receiver mute on a NHRC-3.1 controlled repeater with noise and CTCSS mute options.

  1. Break the track between pins 13 and 14 on the FX315.
  2. Install a PNP transistor between pins 13 and 14.  I used a BC327 from a KL main board wreck.
  3. Connect a 10k resistor to the base of the transistor, and a fly lead to the other end of the resistor.
  4. Install a 1 pin header socket to the other end of the wire, and plug it onto the left pin of the init jumper on the NHRC-3.1
  5. Jobs done.


The idea is that the controller provides the mute signal to the gate on the controller based on a decision made on the presence of carrier and or CTCSS, this signal is used to switch the encoder.  In the past I have simply taken the logic from the receiver, but this is incorrect, as when CTCSS decode is enabled, and noise opens the carrier mute, the tone encoder runs during tail time causing link receivers to think there is still activity on the channel.  This is undesirable.  So the tone encode follows controller mute gating correctly regardless of the muting options selected on the controller.

Some pictures to make it clear.

NHRC-Squelch into KL RX Module

10 September, 2015 - Reading time: 2 minutes

I'm a great fan of the NHRC-Squelch board, and the additional squelch performance it provides over the standard KL mute.

This is how I install them, they fit nicely into the PLL compartment of the receiver module.

This image shows the connection points in the circuit diagram.

This one shows the points on the board where connections can be made.

Here it is installed.

Follow the instructions for level adjustment and you'll have a nicely performing receiver with the silent mute action that the KL is known for, but with new added ability for it to follow mobile signals into deep fades.

St Valentines Peak - VK7RVP

9 September, 2015 - Reading time: 3 minutes

My favourite site. Soon to get a 6 metre repeater.  I envisage a flowerpot type antenna will get mounted above the UHF 4 stack array on the stand off.  Repeater will be a KL70 conversion with low power mods, and duplexer a Procom DPF 6/6-HX-150.  A spare run of heliax is ready to go, as is the licence.

A few photos.


The Splat! plot gets me a little excited.

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.