ARCHIVE: Australian Ham Radio Discussion Forum ( AHRDF )

G'day from a new member. Full disclosure: I'm not a ham, but since a kid I've played around with AM CB (was once the highest base station in the state), was into scanning - mainly airband and police when it was open FM.  These days it's mainly UHF CB.  I thought I'd ask my question here, as I can't find anything on the internet to help me and I don't know where else to turn.

I'm hoping to get a little help making a motorbike helmet headset for a GME Electrophone UHF CB handheld.  I have previously used one of those from Aliexpress (pic attached), which worked well, but is not exactly what I'm after. Firstly, it uses speakers, which I would like to replace with Plugphones, for combined communications and ear protection. Secondly, the connectors used are too robust - I had a little moment that tugged too hard on the connector to the handlebar-mounted PTT button and ripped the cable out of the back of the connector.
The plugphones I can plug straight into the radio, but I would like to construct a flying lead that allows me to connect a helmet-mounted microphone and handlebar-mounted PTT to the MIC input, using standard 2.5mm plug and socket that will simply fail safe via pulling apart in the event I become separated from the motorbike.  I can work everything else out apart from the microphone. The headset I used before had no problem with audio volume, but wiring up my own using an electret microphone from Jaycar, or a lapel-style microphone from eBay has almost no volume.  What microphone can I use to be compatible with what the radio is looking for? Or is there a passive circuit I need to construct to get the electret to work correctly?  The microphone from the Aliexpress unit seems to just be a microphone interrupted by a PTT switch. I thought about reusing this mic, but the wires are tiny, enamelled ones that are so hard and fragile to work with.

Any help would be much appreciated.

Hi and welcome to the forum.  You are not the first non-amateur to post requests for info and probably not the last.

The answer is probably defined by the arrangements within a GME optional speaker/mic, if available. That helps show what type of microphone insert is used and whether there is an integrated preamplifier stage, and whether (and how much) voltage is supplied to the mic insert. By default, electrets are always a very high impedance. Of course it could be that the insert is a dynamic mic and therefore low impedance and thus incompatible.  That would make any recovered audio very low in level.

I doubt that there are schematics available for either the handheld or an optional mic but maybe the radio's specs might tell at least some of the story.  That means you will need to quote the GME model number for any of us to find relevant details.

The image of the headset is not clear enough to see details so a link to it at ALIExpress might prove useful to see it's electronic specs too.

Awaiting more details from you...

Doug VK4ADC

Thanks Doug,

The headset is this one.

The two radios I'm working on are TX667 and TX675.  I haven't been able to find any information on the mics used or the schematics.

Cheers,
James.

James

Well I guess the good news from knowing what model numbers we are working with is that the Aliexpress headset should be wired something like the Baofeng UV-5R since it lists that as suitable for that model.  So the detail at https://pinoutguide.com/HeadsetsHeadphon...nout.shtml then becomes useful.

Looking now at the GME, it lists their HS009 and HS010 as compatible and neither of these have room for an internal mic amp, nor the power supply voltage feed to run one.   That makes it that both use an electret mic insert BUT not all inserts produce the same output voltage level for a given audio/noise level.   The one from Jaycar may produce a lower level regardless.  Back in the old days, the radio specs also included the microphone sensitivity and usually the impedance etc.. Those days are gone and minimal specs are now made available.

One thing that comes to mind is the way an electret mic works... it is essentially a capacitor that has a DC potential applied via an internal resistor and the variations in potential difference through the application of sound waves causes the assembly to produce an 'AC' signal.  What concerns me is that the capacitance of the 'mic lead' may be swamping the mic's inherent capacity thus loading it and reducing that AC voltage. Where a preamp is built into the mic proper then this issue simply doesn't exist.

You mention becoming 'detached' from the cycle so can I suggest that you buy a few in-line-style 3.5 and 2.5mm stereo plugs and sockets from Jaycar (etc) to create a couple of low-tensile short extension leads. If you come adrift, they are the weakest link and meant to break away. You can always re-manufacture these leads in that event. Simply use a thin stranded insulated wire from socket pin to plug pin for each connection..  And always care a spare cable !

In the short term you can use one of these plug-socket leads as an experimental test-bed to try alternate interconnections to get it going, measure any audio or control voltages.

Doug

I had a look at the link you provided, Doug.

The diagram doesn't represent the configuration of the plugs on the Aliexpress headset - My experience with such accessories is not extensive, but I've not come across a case where the mic is on the 3.5 plug and the speaker on the 2.5, so it looks to me that the diagram is wrong.  Either way, the existing headset I have has the mic on 2.5 and the speakers on 3.5.
So too does a 20-year-old speaker mic that I have.  It came with some other plug that I don't remember, but I modified it to a 2-pin 2.5 on the mic and a 2-pin 3.5 on the speaker.  It works fine in the TX667 I have in front of me.
Opening up the case, it looks like the PTT just makes the connection to the electret, but there's what looks to be a diode and perhaps a resistor across the leads of the electret.

James

I have  couple of the headsets to suit the UV-5R (plus the actual UV-5Rs..) and I will do some resistance and 'click' checks on them tomorrow to identify the speaker connections. That will confirm the 2.5 versus 3.5 pinouts for them.  Given the Aliexpress listing shows these headsets as compatible with UV-5R (plus many others), it could explain why things don't work for you with the GME units.

And if it turns out to be that case, you build the in-line plug /socket low-tensile cable sets to go from 3.5mm plug to 2.5mm socket and vice-versa.

Doug

Doug, the aliexpress headset does work fine with my radios (hence why I feel the diagram of the pin out is backwards).  It's the electret microphone from Jaycar that I can't nut out.  Looking inside the speaker mic I have (that also works fine) has those two extra components, which leads me to believe I need something like that in the wiring of the Jaycar one.  The Aliexpress headset has no obvious extra components for the mic, but I haven't cut the mic up to confirm this.

The best case scenario is someone tells me I need electret "X" with no extra components and I can simply wire that up.
Otherwise, if I use electret "Y" I will need component "Z" to match the impedance or whatever needs doing to achieve compatibility. It looks to me like a surface mount diode and resistor in the speaker mic, but I'm not sure of what the components are

Cheers.

While looking into a minor issue with (audio) data between a radio -> DIY Isolation Interface -> sound card I had to reacquaint myself with the specifications of different microphone, line and aux audio levels.

While doing this I came across this article which may (or may not) shed some light on the issue in this thread. TBH an audio oscilloscope is probably needed to measure the values but here it is anyway...

https://www.sweetwater.com/insync/unders...udio-gear/