W8WWV - Using Cordless Headsets with Radios

Greg Ordy


This page builds upon my Using Cordless Phones with Radios page. The idea behind that page and this page is to figure out a way to let the radio operator walk freely around the station and carry on a voice conversation through a wireless headset which is connected to the radio. This is all about convenience, not much else.

Part of the solution is the coincidence that ICOM radios and computer sound cards both accept electret condenser microphone element signal levels. This means that most all ICOM radios have signals level requirements with are very close to computer sounds cards. This is a wonderful situation since the huge computer market has produced all sorts of audio devices which connect to the computer. In most cases, these devices can be used with ICOM radios. These devices are inexpensive, and widely available. Most other brands of radios use dynamic microphone elements, which have a much lower signal level. The usual problem that this causes is that dynamic element microphones do not have enough signal to properly drive ICOM radios. Conversely, an electret condenser microphone requires a power source, and it's level usually overdrives and distorts microphone inputs designed to accept dynamic microphone elements.

I have written about ICOM microphone elements on another page.

My first solution to this need was the IBM-3330 cordless phone. It had a computer mode, where the cordless headset was redirected to a computer interface as opposed to the telephone line. In some ways, this was an overkill solution for radio use, since the whole telephone interface part of the product is not needed (well, unless you want to make cordless phone calls).

Why did cordless telephone makers add a computer interface?

My guess is that they were anticipating a large adoption of voice communication through the computer and over the Internet connection. While this mode of communication is used, it has not become common. With telephone companies offering inexpensive unlimited domestic long distance calling plans, the incentive to knock down long distance phone bills has decreased. In addition, the quality of these computer-based connections is less than traditional telephone lines, in my opinion.

So, there is some market there, but not a mass market. Perhaps this will change over time. Because the market is of limited size, it can be difficult to find suitable products (cordless phones with computer interfaces).

Users of voice communication over the computer/Internet interact via handheld microphones, speakers, and headsets, all directly wired to the computer. This direct wire connection was long ago severed for the traditional telephone user through the common cordless phone. If you can walk around the house and talk on the telephone, there is no reason why you should not be able to walk around the house and talk to the computer. Since ICOM radios have a similar interface, any product which allows computer users to walk around should also allow ICOM radio users to walk around.

The Logitech Cordless Freedom Headset

I was up at my local Micro Center computer store (September, 2003), and I happened to notice the Logitech Cordless Freedom Headset. This headset was perfect for this application. First, it was very inexpensive, costing $20 (USD). Second, it had a computer interface without the extra telephone interface. The base unit had a cable which terminated in 1/8" (3.5 mm) stereo male plugs which are exactly what is found on wired computer headsets, and I had already built an adapter to match computer headsets to my ICOM 756PRO radio. It was a drop-in solution.

Computer products come and go, often times living no more than a few months. At the time you are reading this page, this particular product might not be available. When I returned home, I searched the Internet, and I found a number of stores selling the headset, some at even a lower cost.

My biggest complaint with the IBM-3330 cordless headset was that its Mute button would cut off the earpiece as well as the microphone. I want my mute button to cut off my microphone, but leave the earpiece on. This is so I can continue to listen to the QSO while making noise that might otherwise trigger the transmitter through the VOX.

By the way, transmission is always controlled via VOX. There is no mechanism to support a push-to-talk switch.

Here is a picture of the headset. Please click for a larger view.

Logitech Cordless Freedom Phone
Logitech Cordless Freedom Headset

The base unit has a typical wall-wart power supply. The remote unit charges while seated on the base. The remote batteries are rechargeable, and NiMH technology. The battery cells are not standard sizes, such as AA or AAA. It is a set of three, 2/3 size AA cells enclosed in a plastic shrink wrap holder. I see this sort of packaging in the typical replacement battery display in stores. I suspect that this pack is easy to replace, but I would personally prefer standard battery sizes.

The Logitech headset is smaller than the IBM cordless phone. It takes up less desk space.

The ICOM Connection

The ICOM radio headphone connector is typically a 1/4" jack. I connected a common 1/8" to 1/4" adapter to the black plug coming from the base unit, and plugged it into the radio. This provided audio from the radio to the base unit, and then to the headset. The headphone jack signal level is controlled by the volume knob. I found the level adjustment to be relatively noncritical. Something around 9:00 o'clock provided an undistorted level.

The standard convention is that the microphone signal is on a red plug. I plugged this into the adapter which I've been using, which is described on another page. This lash up immediately worked, and I could operate voice modes via VOX while walking around the house and yard (see comments below on range).

I somehow always manage to wire up a cable, even when they are not needed. In this case, with the separate headphone and microphone connectors, I wanted to make it easier to swap between my wired headset and the wireless headset. I decided to build a cable that would have the ICOM 8-pin microphone connector on one end, and two, 1/8" female jacks on the other. This meant that there would be only one cable to swap, although it has a screw-on retaining nut. The ICOM microphone connector includes an audio out pin which is similar to the headphone jack in that the level is controlled by the volume knob. The other reason that I wanted another cable was that the cable provided with the Logitech base unit was not long enough to reach the radio from the anticipated location of the base unit.

Building ICOM microphone cables is easy, since the male plug is a standard Radio Shack part, making it easy to obtain. The only hard part is soldering to the pins, which requires a small soldering iron, a steady hand, and whatever magnifying aids your eyes require. The junk box produced two shielded stereo extension cables which I could cannibalize by  cutting off their male ends. Ouch. One cable is audio in, and the other is audio out. I made then into a single unit with heat shrink sections spaced every few inches. Here is a schematic of the cable.

Generic Interface Cable Schematic

Note that there are no resistors or capacitors involved, just wire and pins. The cables are stereo cables, and both signal wires are joined together at the microphone plug.

The microphone signal, on the red connector, has both the ring and tip wires connected to pin 1 on the ICOM connector. The shield from the microphone cable goes to pin 7, the microphone ground. The receiver audio signal begins at pin 8 of the connector and is connected to the ring and tip wires going to the 1/8" female jack. The ground shield from the receiver audio cable goes to microphone connector pin 6, which is the normal radio ground (as opposed to the microphone ground).

NOTE: while this cable was constructed for the Logitech cordless headset, it is very generic in function, and can be used, for example, to allow any two-plug computer headset to connect to an ICOM radio. The microphone element must be electret condenser, and both plugs must be stereo plugs. The only function  which is not handled in this schematic is PTT (push to talk) or keying the transmitter. I use VOX. You could bring out the PTT signal (pin 5) to a switch. You could use a footswitch or a hand operated switch. On most ICOM radios it is possible to put the radio into transmit with signals on rear accessory jacks. The solution depends upon your needs.

Here is a picture of my cable. Please click on the picture for a larger view.

Logitech Interface Cable
Logitech Interface Cable

I wrapped a piece of red electrical tape around the microphone jack to match the red plug on the base unit.

I decided to substitute the Logitech for the IBM cordless phone on my desk. I ran the cable around the back of the desk, and the microphone connector sits off to the left of the radio. If I want to go wireless, I unscrew the wired headset microphone, screw in the Logitech cable, and make sure that the volume knob is at 9:00 o'clock. Also make sure that the VOX is enabled, if you wish to transmit. The other setting which I found useful was to turn off the monitor function. Monitor is used to let you hear your voice in the headphones, which I find desirable. Not because I like my voice, but the otherwise dead headphones seem strange without either receiver audio, or, my audio. I found that with the lightweight Logitech headset, with a flat earpiece, enough audio could escape the earpiece, hit the microphone, and generate feedback.  Since it's a single ear headset, the lack of monitor audio is less important because I can hear my voice the old fashioned way, from mouth to ear via the atmosphere.

Issues and Nits

In experimenting with the phone and the radios, several issues and nits have emerged.


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Last update: Saturday, September 27, 2003 11:28:18 AM
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