Thursday, 8 April 2021

Icom IC-9700 - "DX Shop PTT multiplier" solves the multiband PTT issue.

Judging by the large number of people who have read my post of two years ago entitled "Icom IC-9700 PTT switching - something I do not understand", I seem to have identified an issue that resonates with lots of people. There is no need to read it now as the problem seems to be solved.

That posting is one of my most read pages. It deals with my early realisation that the IC-9700 (not then released to the public) does not have a separate PTT line for all three bands it covers, nor even one for two as offered on other Icom radios. I called this a deal breaker, though I ended up with an IC-9700 through other routes than buying one.

Like many amateurs using the wild west of the higher bands, I have a separate linear amplifier for each band, 2m, 70cms, and 23cms, covered by the IC-9700. I did muddle through with a relay linked to my 23cms amplifier PSU, but this is not a brilliant plan. Luckily for me I generally only use the 9700 for two bands, but when for a while I was using it for all three bands it got a bit out of hand.

In reply to a helpful comment by Gavin, GM0WDD, I suggested in that posting that somebody should make a "CIV box" and I described it thus:-

The CIV box I have in mind has a simple CIV decoder (maybe an Arduino) and 3 relays (or solid state switching). It just reads the CIV and switches between the relays to select the PTT. No need to sense the PTT from the CIV as it comes out on a different pin on the same socket as the CIV does. Three LEDS on the box to show which one is selected and for fail safe all three work if the box loses the CIV signal.

Enter now the "DX Shop PTT multiplier", which arrived here today...

DX Shop IC-9700 PTT Multiplier

It is in reality almost what I described in principle - more or less. The detail difference is that it uses a PIC microcontroller rather than an Arduino, and it seems to fail safe to no PTT rather than connecting all three. It gets its CI-V signal via the 3.5mm mono socket on the back of the 9700 and its power and PTT signal via the clunky 8 pin full sized DIN socket which Icom also put on the back of the radio. Both leads are supplied.

This pretty well plugs in and works. There are some settings you need to change in the 9700 menu. They are all on the CI-V tab.

USB Port: Unlink from [REMOTE]

DATA Baud Rate: 9600

DATA Echo Back: OFF.

I did all this and it didn't work. I had WSJT-X running and I had lost rig control. Probably no fault of the device, but for me I had to go back into the CI-V settings and change the USB Baud Rate from 19200 to 9600, and then do the same in WSJT-X. I am not sure why this happened but I remember similar problems with the IC-7300 and the remote control software. Anyway, making the baud rate between WSJT-X and the rig the same as that between the rig and the CI-V box did the trick for me. This is one to watch for because I think that the default setting in Hamlib is for 19200 so this might get reset if I update WSJT-X or change the PC.

Then it only seemed to work on 23cms which was definitely my issue. At some stage I had tinkered about with the "ACC SEND OUTPUT" settings to stop the radio using the 70cms and 2m PTT while I was using 23cms. I needed to go back in and turn all three bands to "ON". I suspect that these are normally ON by default and it was my settings than had changed them.

When the box does not have CI-V communication all three LEDs flash. A quick test suggests nothing happens if you press the PTT in that condition, so no linears would be keyed but the rig still transmits. Whether that is an issue for you depends on your setup. For me I would have preferred all of them to be keyed, which would have triggered my sequencers and turned all the masthead preamps off. I can see also that this might not be possible with the setup inside the box (which I can only imagine because I am not opening it until the warranty has expired). Anyway, I doubt if it will lose the CI-V in normal use. I have RF-VOX protected preamps but not everybody has and even non-amplified RF might be too much for their preamps.

In normal circumstances the box has CI-V working and one LED is lit green. Changing bands moves the LED indication along to 70cms or 23cms as selected on the radio. When you press the PTT the LED changes to red. Perfect. I have buried it inside my shelving - I have no room to put it in front. However I can still see it and the LEDs in the background.

I connected the 2m and 23cms linears up, including the additional SWR cut-out trip I have for my Gemini linear. If it ever trips now only the 2m amp will go off rather than the other ones as well as heretofore. Just to test it I wired up my 70cms sequencer to see if it worked on all bands. It did.

During testing the LEDs displayed perfectly and the box followed the frequency on the rig as you would expect. The DX Shop say that it works in satellite mode which I cannot test. 

The frequency followed in normal operation is the main band, which is correct for the IC-9700 for non-satellite working. If I highlight the sub-band this does not change the PTT connection away from the main band which is also correct for the way the IC-9700 works for non-satellite operation. 

The frequency readout on WSJT-X produces interesting results when using the sub band but the CI-V box always selected the correct antenna for transmitting. I may go further into this later as there is a quirk using the IC-9700 with CAT control when switching to the sub band. This quirk has my head spinning sometimes, but the presence of this box does not change anything.

The result of the test showed that once I had set the PTT multiplier up I could forget about it. The box just changed the PTT line to the right amplifier as required. That is what I have been waiting two years for.

It appears that this issue is resolved, for me anyway. What a pity that Icom had not covered it to start with, just like the frequency stability issue which I had to solve with a GPS frequency source. I had to pay extra for those items which should have been included for no extra cost if somebody had thought about them at the design stage.

So the DX Shop PTT Multiplier costs £59.99 and you can find it here

Thanks to G0DJA for pointing this product out to me.





  1. I'm pleased to hear that the DX Shop unit solved the PTT problem.

  2. Thank you for publishing this post. I recently received my Gemini 23 amplifier from the DX Shop. The PTT multiplier will make PTT keying much easier with the IC-9700. I didn't even realize they carried the multiplier until I discovered your post.

  3. Hello Bill
    You are welcome.
    I think that it might be best for DX Shop to list the PTT multiplier as an accessory for the VHF and UHF amp, given that so many people using them also use the IC-9700.
    It is really an accessory for the IC-9700, and other retailers could usefully stock it too.
    And of course Icom should have dealt with the problem at the design stage.
    73 Jim GM4FVM