FINALLY, A WAY TO CONNECT A HEADSET TO
A LATE MODEL YAESU RADIO
Let me start by saying that while I did design
this particular circuit, the concept is not mine. A fellow FT-8800 owner who wanted to use his helmet headset with his 8800
on a motorcycle was the one who came up with the values for the circuit. His article is available on the FT-8800 Yahoo group.
I just combined his adapter circuit with a switching circuit so that I could use either a cell phone headset (not Bluetooth)
or the stock hand mic. I actually use this circuit with an FT-7800, but it should work with any Yaesu Radio that uses the
MH-48 hand mic.
The first circuit diagram above shows a 10uF
polarized capacitor since that is the value Brian used in his. I substituted a 47uF polar cap because that is what I had in
hand. Apparently the higher value works just fine, at least it does for me. If you just want an adapter and don’t want
the switching capability, see the second circuit. You will note that I did change the value of the capacitor in this drawing.
If you wish to use a PC headset instead of a cellular type then use 2 stereo 1/8” jacks and separate the grounds. The
tip and ring connectors on both of the stereo jacks in that case would be tied together, since most PC headsets are only wired
with two wires even though they use stereo plugs. See my article in the July 2007 issue of QST for details on how that type
headset is wired. Personally, I find the audio quality of the cellular headset much superior to the PC version, but as they
say “your mileage may vary”. Also note that pins 1 and 2 are not used in this version since there is nothing for
them to connect to. A word of caution about the PTT circuit is in order. The PTT line on the radios that use the MH-48 mic
demand to see some level of resistance (usually 15K or more) when the PTT switch is depressed. Otherwise the radio will lock
in transmit and will only stop when shut down completely. Therefore do not omit the 27K resistor in the PTT line to pin 6. The
PTT switch can easily be remoted to the steering wheel or handlebars for mobile ops or whatever. The entire circuit including
the PTT could easily be built into a pill bottle or some similar enclosure to lessen the number of cables. Use your imagination
when it comes to an enclosure.
thanks to Brian and the Yahoo FT-8800 group for the adapter design, it really works great and was very easy to build thanks
to Brian’s pin out diagrams for the RJ-12 connector.
I have added circuit diagrams for the FT-817 and FT-8000 to this page in response to requests for them.
2: With help from Bill, W1WAB, we have determined that the Cellular "Earset" Adaptor for the FT-817 also works with no modifications
on the FT-897 and the FT-857 as well. The list of compatible rigs just keeps growing and growing.
3: I have become aware that using a different style cellular headset (or earset, if you prefer) than the one I used for the
adapters I used to sell may cause a deterioration in the audio quality of the transmitted signal. I tried several different
headsets over the development of the adapter and several were fine. Several others however were not so good. If you build
this adapter, be prepared to check different makes and models of the typical wired cellular headset before making a final
selection. The ones pictured in the page on "a cellular headset adapter" elsewhere in this website worked just fine. There
are a few available commercially that do not work so well. The adapter works well in all cases, it is the choice of a cellular
headset that will affect the audio quality of your transmission.
4: Someone on the FT-7800 Yahoo group referred to my web site the other day in reference to the adapter for the FT-7800, 8800,8900
group of radios. Just for fun I followwed the link which was correct except it led to a different page on my site. I also
discovered a typo on this page. The typo has been corrected. The diagram for the "simple" adapter without the switching function was
and is correct. However the values for R1 and R2 in the accompanying text were reversed. The text is now corrected. Sorry
about that, I totally missed it when I originally wrote the page.
UPDATE 5: The circuit below has been slightly modified to include two new .047 uF Capacitors near the 2.5 mm stereo
jack where the cellular headset plugs in. This is to provide increased resistance to RFI which has popped up occasionally.
The actual value is not critical, just the provision of a path to send the noise to ground. This
same modification can be applied to the other circuits on this and other pages on this web site. These aditional capacitors
are not normally needed at all. In various iterations of the design since this page was written, they have been eliminated without
any degradation in audio quality. The RFI mentioned above was, in each case, traced to a malfunction in other equipment around
the radio room, sometimes even outside the house.
Update 6: These circuit diagrams assume the use of a wired cellular headset. These headsets
are becoming truly rare with the advent of Bluetooth. The circuits can easily be modified to use a PC style headset which
has two 3.5 mm plugs. The main change is to run the recieve audio from the external speaker jack on the radio directly to
the jack for the earphone side of the headset. If you are building a mic selector, you will have to run the audio+ from the
external speaker jack on the radio through a switch position on the selector so that you can switch from the headset
to an external speaker and hand or desk mic. If you have any problems figuring out the changes to the circuit just email me
at firstname.lastname@example.org and I will be happy to walk you through it.