Yaesu microphone splitter

Not a microphone splitter by Yaesu, but a splitter for Yaesu microphones, purportedly.


I’ve put this in the Off Topic category on here is the link to SOTA is tenuous at best. I will be using my new Yaesu FTM100D mobile rig en route to and from SOTA activations, but moreover, I’d welcome the thoughts and input of the SOTA Reflector community, who I trust more than other AR online groups!

The FTM100D has no possibility to initiate memory scans from the front panel. This can only be done from the UP/DOWN buttons on the supplied MH48 fist microphone. I do not wish to use a fist microphone while driving. Although there is an exemption for this kind of radio use, I do not consider it to be safe or sensible personally (and a traffic officer’s assessment that it was interfering with the quality of driving would be difficult to argue against). Either way, I want to stick with using my hands-free kit.

This is the Watson WM-S - but only the PTT works with the FTM100D. The UP/DOWN buttons send a signal to the rig (indicated on the display), but do nothing. It is reported that the Komunica AV-1KM-Y hands free kit (marketed a compatible with the FTM100D) has the same issue. (From photos, it would appear this is exactly the same product as the Watson WM-S that I have).

So I’ve ordered one of these so that I can have the MH48 on a mic-clip mounted on the dashboard for UP/DOWN buttons, and the hands free kit connected simultaneously for the microphone and PTT switch.

Has anyone any experience of this kind of arrangement? Does it even work? I’ve had one suggestion that the mic pins on one side of the splitter need to be disabled, and the scan pins on the other side. Otherwise the impedance of the two connected mics is affected (though I’m not sure what the effects of this would be).

This diagram was sent to me:

So, trusted SOTA friends with rather more understanding of this sort of thing than me - over to you!

[It is very tempting in the first instance to try it without the mod with both mics connected and see what happens - but is this even advisable?]


Let me be the first to not answer your question.

Bluetooth may make your life easier. I use a Blue Parrot headset with my yaesu radios and you can still use the mic. buttons. The VOX works well.

Just a thought if you have a BT headset lying around.


I though it was the Judean People’s Front who were the splitters. :wink:

I’ll look at the circuit and the FTM100D service manual later Tom. It shouldn’t be too difficult to do what you want.


If you look at the circuit of the microphone you’ll see that it uses 2 voltages on the two signals SW1 and SW2 to encode the various buttons you can press with 9 transistors and a handful of diodes. So your up/down switches need to make the same voltages appear on the SW1/2 as the mic does.


SW1/2 are being received by the FTM100D from the up/down buttons on the hands free control box - as there is a response on the detachable head display panel when they are pressed. But from what you’re saying those signals must have different voltages to those received when the up/down buttons on the MH48 mic are pressed/held? So there’s probably a way (for someone who knows what they’re doing; beyond my skill set I certain!) to add something inline that modifies that voltage…?

I guess this is why - if using the splitter - the specific pins on each side might need to be disabled. This because the change in impedance/resistance will reduce that voltage, possibly taking it further away from what the FTM100D needs to “see” in order for it to respond as desired. And maybe there’s a chance that the PTT switch - which works now - will no longer work if the voltage presented from that is taken out of range.

(Hope I’m understanding this correctly!)

When the splitter arrives, I’ll give it a try - I don’t think we’re in potential “magic smoke” territory! And then take it from there. One might assume that it should all just work straight away - simply because of the existence of the product…

BTW Fraser - I’ve tried Bluetooth headsets before - for phone stuff, or for AR via the TalkSafe Ranger product (a Bluetooth head set with a PTT). I’m not really a fan of having an earpiece in while driving. I did think about getting the BU-2 Bluetooth module to fit to this rig, to then pair it with my car’s Bluetooth to use the car’s built-in microphone and speakers - but that would then require the use of VOX, and I’m not a fan of that either!


I looked this device up and found on Nevada Radio’s website a list of which Yaesu radios it works with and the limitations.

FTM-100DE WM-S-FT Supplied WYL-6M PTT Only on FM Mode

Yes. The numeric pad for example is arranged as a 5x4 matrix. There is an 8V feed from the radio. So when press button 1 (row1 col1) it turns on 2 transistors, 1 for row1 and 1 for col1. The transistor for each row and column have different bias resistors. The result is a voltage on SW1 and a voltage on SW2. If you press button P2 you get row5 and col4 transistors turned on, they have different resistors so you get different voltages on SW1 and SW2. The CPU in the rig knows the output voltage and measures the input voltages and can figure out which key is pressed. It’ll cope with multiple keys because which ever key generates the bigger voltage will win. It’s reasonably foolproof and more importantly doesn’t involve sending digital signals from the radio to the mic to scan the keys. It’s nice and simple and old school.

Your mission Jim, should you decide to accept it, is to measure the voltage on SW1/2 when pressing Up and then Down. Then make a circuit to replicate those voltages and inject that instead of the Watson levels. Or change the Watson to send those voltages. If this is outwith your comfort zone then maybe there is a now-retired ham who lives near you with experience of running a SOTA business who can teach you, probably in exchange for pies and beer :wink:

Seriously, it’s only daunting because you’ve never done this stuff. A suitable Elmer is what you need.