Headset with Boom Mic

Headset with Boom Mic

Having tried Pedestrian Mobile operations a few times, I realized that I really needed to have a boom mic to free up my hands. I checked both local Radio Shack stores, but everything they had was at least $20. Checking around in other stores I found an AT&T "Mini Headset," Model 90800 at Staples ("for cordless, cellular, and other telephones") for $13. It works great with the FT-817, and I have received very good reports on the audio from several stations. (I later found this same headset at Target for $10, and have seen similar headsets in other stores, marked with different brand names.)

[Spring 2002 Update] I have found only two problems with this microphone so far: (1) It seems to be very sensitive to ambient noise. When walking near the road, for example, traffic noise will trip the VOX. I have the same problem in the barnyard when the roosters crow. The easy solution to this is to either turn off the VOX function when receiving, or to switch the mode to CW. A better solution would be to go someplace quieter, but you can't always control ambient noise. The best solution might be to add a PTT switch, but I haven't gotten around to this yet. Besides, this would conflict with my goal of "hands-free operation." (2) The microphone is susceptable to wind noise. In order to cure this, I added a foam windscreen as described here.

Here is how I hooked mine to the rig:

I used a Radio Shack Mini Project Enclosure, #270-288 as a terminal box. I cut a small PC board (about 1.2 inches by 1.9 inches) to fit inside, and milled appropriate traces and pads using a Dremel-type tool. After wiring the board, appropriate holes were drilled in the sides of the box for the cables. Mine is configured so that the long side of the box sits parallel with and about two inches or so to the side of the rig, with the cord to the headset coming out the front, or short side, of the box.

Connection to the rig's speaker/headphone jack is via a 1/8 inch mono plug and a short (couple of inches) piece of RG-174. Connection to the mic jack is via an RJ-45 plug cut from the end of an RS Category-5 network cable.

Note that the FT-817's RJ-45 jack has two grounds. One is for audio, the other is for the controls (PTT, UP, DOWN, FAST). More on the pinout later.

Inside the box are the following connections:

Headset earphone connects via the PCB to the speaker/headphone plug. Shield is connected to the audio ground (pin 5 on the rig's RJ-45 jack). +5v (pin 6 on the rig's RJ-45 jack) connects to a 4.7k resistor, which is connected to a 10k resistor, then to audio ground (pin 5). This is a resistive voltage divider, with about 3.5v at the junction of the two resistors. The junction between the two resistors is connected to the mic, and provides the necessary voltage for the electret element. Also connected to the mic is a 1 microfarad tantalum capacitor (at least 16 WVDC), positive lead to the mic. The other side of the capacitor goes to the mic connection on the rig (pin 4). (4.7k, 10k, cap+, and mic are all connected together, then.) Shield goes to audio ground (pin 5). (I don't know if this DC blocking capacitor is really needed, but I included it for safety and peace of mind.)

There is no provision for PTT, but this could easily be added with a small switch. (Use pin 3 for PTT and ground to pin 2). Instead, I use VOX. I can live without the UP and DOWN buttons, but I can't live without the FAST button. Luckily, I found a small normally-open SPST PCB-mount switch on a PC board in my junk box. This is mounted on the PCB in the box, and can be accessed through a hole drilled in the cover of the box. It sits about flush with the top of the cover, so it won't be hit accidentally, but can easily be pushed with a finger tip to engage/disengage FAST tuning.

Here is the RJ-45 pinout, as taken from the schematic:

Pin Function

1 FAST

2 Ground (control)

3 PTT

4 Mic

5 Ground (audio)

6 +5v

7 UP

8 DOWN

Give it a try, I think you'll be pleased. By the way, I have my mic gain set at 50 with the regular Yaesu mic, and I didn't have to change the setting for this new mic.

Here are the pictures:

AT&T headset modified to work with the FT-817.

Inside of the junction box showing the circuit board.

Outside of the junction box showing the FAST switch.

Schematic and pinout. Color coding of wires may not be the same for all Cat-5 cables!