Yaesu MH-48 Microphone with FT-817 TRX

It’s been a while I have written. Meanwhile I am again working my way through started and unfinished electronics projects of mine. One of these unfinished projects was the adaptation of a Yaesu MH-48 Microphone to the 817 QRP transceiver.

A while ago I had bought two used Yaesu radios on ebay. The seller only included one microphone for both and did not respond to me when I asked for the other microphone. So I went back on ebay and bought a random Yaesu microphone with a “modular jack”, assuming it will simply fit.
Boy was I wrong !

So I got a MH-48 DTMF Microphone that does not work with the FT-817 at all. But of course I wanted a working microphone. At best not having to buy a new one.
As I looked back into the accessory list of the FT-817 and saw that the DTMF microphone that specifically works with the 817 is the MH-36E8J.

On the quest to adapt the MH-48 so that it works I found it’s schematics and also looked for the schematics of the MH-36, but could not find any for it directly. From what I found, it seems like the DTMF tones in the MH-36 are generated by an IC for that purpose, whereas the MH-48 is just a bunch of passive switches and some transistors. There is nothing in there that could generate the frequencies for DTMF so I guess they are generated in the specific transceiver itself. This leads to the conclusion that full functionality can only be restored by a major modification. I did not really have the wish to start a bigger thing, I just wanted the basic functions of a microphone so I can use it with the radio.

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Even the basic functions were a little bit more complicated than I thought. Some simple rewiring of the microphone at the jack was not enough. The PTT path in the MH-48 microphone has a 15K resistor and a diode. This prevented the TRX to switch to Transmit mode. So I simply shorted both with a tiny piece of wire. The TX-LED on the microphone still works with this little change.

The electred microphone had all the circuitory it needs to generate audio, I did not touch any of those. At this point I already had what I wanted, the very basic functionality of a handheld PTT-microphone. Then I tried to randomly push the other keys on the microphone. Just to see if anything would happen. I figured that both the top keys for up and down set the frequency one step higher when they were pushed. Since this was somewhat awkward I also wanted the down button to work.

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I looked back into the schematics of the MH-48, I figured I would only need minimal changes for the other one to work. I removed the doulbe diode package that is connected to the down button. Then I got my multimeter and measured random points in the vicinity of that place and found a pad where the down signal is connected to. I shorted those two points with a short wire and I had a working down button. Unfortunately later I also discovered that the first row of the DTMF keys did the same thing, on press they lower the frequency one step. Well, If I ever open the microphone again I might look into that for now it will remain as it is.

Since the backlight of the DTMF keys is directly between supply voltage and ground the lights work when I use the switch. No modification needed for that, but it is pretty useless as long as the keys themself have no function.

As much as I also wanted to have the “fast” button, there were no wires left in the cable. The microphone is designed for a completely different radio.The cable has 6 wires that go directly into a 6 pin modular jack, whereas the FT-817 has a 8-pin port and uses all 8-pins. To figure which one does what I have disassembled the one MH-31 microphone that was delivered with the two radios. There are schematics of that one on the Internet if you need further info.

To conclude, I have now a modified MH-48 DTMF microphone, that I bought falsely because I was to lazy to realize that there are slightly different versions on the market.

With backlight in the dark


I needed a litte bit of distraction. I have been playing around with digital modes for a while, trying to listen on the air and test my own transmissions, of course just as audio recordings without HF. So the time has come to make my first “baby steps” in implementing a digimode.

Today I begun with Hellschreiber. I was inpired by this Project : http://www.swharden.com/blog/2011-08-05-i-before-e-except-after-hellschreiber/ But I did implement Hellschreiber in Java on my PC instead a Microcontroller. Whole implementation till I first saw my message decoded on the screen, took only a couple of minutes since Hellschreiber is really a simple protocol. Here is a picture of the latest Version running in the background and being decoded by MixW.

I have also a audio file that you can play back and decode on your own PC, here: audiofile In fact my code always also produces an acompanying audiofile.

Later I improved the implementation a bit and added more letters and symbols, while I was at it I also added variable width to my output. So the letter I will consume less space as the letter W and wide letters like W, M or O are not squished, they have all the space they need. What is nice about Hellschreiber is that it does define a character set but that is not really fixed. I can add any new symbol or letter, they should even decode propertly on an antique real mechanical Hellschreiber machine. That is a property you won’t find in any other digital mode. Using that, I even added some characters from one of my mother languages, Turkish. They are being decoded properly. Even modern unicode still does not always work as it is supposed to. Here in comparison to the regular letters…

Another funny thing is that you can even do pictograms. Ok, at only 7 pixels height those are very very tiny pictograms but, hey it’s 80 years old technology and extensible as heck !

Also Hellschreiber does not consume any bandwidth or at least it should not. Just like CW, it only switches on and of the transmission power and does not change frequency. Some sources state a “bandwidth” for different Hellschreiber modes, which I don’t quite get why, but I don’t see how a carrier only turned on and of can generate bandwidth…

So much for my Hellschreiber experiments. I would love to test that on a real machine, but I have no idea where to find one.

Other browsers in Windows 8

Just found another quirk, that I want to keep under record in here :

Due to restrictions imposed by Windows 8 however, you will only be able to use one browser at a time in Metro mode. In Windows 8, only one browser will be allowed to run in Metro mode, and that is the browser you set as default. If your default browser is Internet Explorer, you will be able to use only Internet Explorer in Metro mode, all other browsers will open in “classic desktop” mode even if launched from Metro. This is rather annoying limitation since it is quite possible that some people will prefer, say Chrome as the default desktop browser, while Firefox or IE in Metro mode. As such, if you do want to try out this preview, you will need to make Firefox the default browser.

Read the rest at : http://www.devworx.in/features/firefox-metro-version-for-windows-8-now-available-for-preview-128741.html