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.
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.
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 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.
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.
In experimenting with the phone and the radios, several issues and nits have emerged.
The headset is separate from the receiver/transmitter unit, connected with a short cable. This means that you have to put the headset on your head, and find a place on your body for the unit. Perhaps a shirt or pants pocket, or clip it onto your belt. This is not quite as convenient as the IBM headset, where all of the electronics are in the headset.
On the other hand, having a separate headset means that you can substitute the Logitech part. This is a very flexible configuration. I tried all of the alternatives I have over here, all worked. For example, you could get a headset with a two earpieces. Or, you could use one of the tiny headsets used with cellphones, the type where the earpiece fits in the ear canal, and the microphone might clip on your shirt.
The microphone on the supplied headset is very sensitive. Too many normal noises seem to trigger the VOX back on the radio. The most frustrating situation is that the audio from the earpiece can leak out to the side of your head and trigger the VOX. This results is a feedback loop, where you keep triggering the VOX once or twice a second. My only solution was to reduce the earpiece volume to the lowest level. I suspect that the solution for both problem, the VOX sensitivity and earpiece leakage is a better headset, with a more directive microphone, and an earpiece which seals and isolates the ear to keep audio from leaking out.
The Logitech unit uses the 900 MHz band. I found it's range to be less than other 900 MHz and 2.4 GHz cordless phones I have around the house. Even within the house, I would sometimes hear a little burst of static as I walked around. I could always remove the static by reorienting the remote unit. Once I got outside the house, the tendency for noise bursts increased. I don't think you could work in the garden and ragchew, but you can certainly visit the kitchen for a sandwich, or do many other activities in the house while keeping up with the QSO.
The receiver on the remote unit has an up/down volume control with 8 steps. The receiver also uses a noise gate to mute the reception when there is no signal from the radio/base unit. The turning on and turning off of the gate can be heard, and it follows the speakers voice. You can set the ICOM radio volume and the headset volume as a set to minimize this background noise. The procedure appears to be to make the radio volume as high as you can without distortion, then you can lower the headset volume so that the signal to background noise ratio is as high as possible. Still, the hiss is present around signals.
You may need to adjust the input gain when swapping microphones if your existing microphone level is not the same as the headset level.
I found that the VOX was very sensitive, and that I would trigger the transmitter without transmitting any signal. These may be little noise pops that can trigger the VOX. For ragchewing and casual conversation, this doesn't much matter. Perhaps the VOX could be adjusted a little better. Since the unit has a mute button, it's probably desirable to mute the transmitter white actively walking around, or doing any activity that can generate noise.
Back to my Experimentation Page
Back to my Amateur Radio Page