[Hidden-tech] bluetooth headset for "land-line" telephone

j w1eqo at shaysnet.com
Tue Sep 8 22:04:23 EDT 2009

You have a problem.

1. There are many frequenciey bands that are used for wireless products. 
For many applications only one frequency band is used. For other 
applications different manufacturers use different bands. For example cell 
phones are located on two incompatable frequency bands. Another 
protocall, Zigbee, is spread out over two bands.

This is not the case for headsets. They can be on any license free 
band. Even one manufacturer might use different bands as his 
product 'evolves.' (= gets cheaper to make)

2. Some, but not all, wireless headsets use plain old FM or AM modulation. 
Others use something different. These can be called 'protocalls,' but 
actually are modulation schemes. They usually involve reducing the voice 
stream to a data stream, and then a properity protocall.

Bluetooth has it's own scheme. And. to boot, it is a spread-spectrum 
scheme. What that means is the audio modulation has imposed on it another 
modulation that spreads the signal over a wider frequency range.

There are four spread-spectrum schemes, of which two are popular. But 
there even more non-compatable implimemtations of these schemes.

Confusing? YES! Even to someone in the business. At least something like 
Bluetooth has an 'expert group' that publishes standards for compatibility 
between manufacturers.

So, don't even think bluetooth in the same sentance with a plain 
old wireless headset that you might find at Radio Shack.

I have seen a bluetooth headset and associated remote unit that you could 
plug into perhaps a computer. I would look at www.newegg.com  This might
work in your application, but might not. Here's why:

Once you recover the audio unto a wire, the voltage and impedance levels 
may, or may not, be compatable with what you want to interface. Because 
of the way products are so well specified now (I smile at that) you 
have no way of knowing if it will work. So do the engineer's trick. 
Try it, you might get lucky.

All I can suggest is ask about the return policy before you buy.

Jim Ussailis
jim at nationalwireless.com

On Tue, 8 Sep 2009, Stacy Kontrabecki wrote:

>   ** Be sure to fill out the survey/skills inventory in the member's area.
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