KY1K writes:
 > I need stand alone full transceivers that take audio in and output 
 > audio. They need to use low power so they can run on batteries and 
 > only need to cover 20 to 30 feet indoors (no large metal 
 > obstructions). They do not need to be full duplex, but a full duplex 
 > system is ok.
 > 
 > I want then for a wireless link to my ham radio transceiver, so I can 
 > move about the house some and still be able to talk and listen to the 
 > activity on the transceiver and be able to transmit if I want to.
 > 
 > I can find wireless microphones, and can find wireless 
 > headphones....but I can't find a system that has BOTH.
 > 
 > Any suggestions?

	How about a cordless phone?  The trick here is the legality of
any modification to the phone, invalidating its type acceptance.  You
can use a modified phone under your ham license, but then you have to
move it to a ham band.  49MHz to 6m wouldn't be hard, but 49MHz phones
are getting hard to find, and, unless things have changed since the
last time I looked in Part 97, official "remote control" of a ham
station had to be above 2m.  You could probably stretch things for a
wireless microphone, but T/R control is another thing.  Then, again,
control from within a few seconds' walk may not count as remote
control in the Part 97 sense.

	But you probably want a 2.4GHz or higher phone anyway, since
they are much less susceptible to capture by a neighbor's phone.  You
could use the phone without modification by building a phone line
emulator - rig interface.  This is just some clean DC with appropriate
audio coupling, and a scheme for using the dial to control the rig.
You could feed the phone DC through a transformer winding (or two for
a balanced circuit and better noise suppression) with other windings
for receive and transmit audio.  You might even cannibalize the
transformer from an old phone (or two), in keeping with the general
theme.  There are, of course, non-transformer possibilities.

	Unless you're using a full duplex mode like a satellite cross
band transponder, you can mute receiver audio during transmit, so you
don't need perfect cancellation of receiver audio from the transmit
audio path.  You certainly want some cancellation, however, if using
touch tones to control the rig, since you don't want touch tones heard
from the receiver to affect the controls.

	Another possibility is to use pulse dialing mode to control
things, which has the advantages of being totally insensitive to
receiver audio and never putting tones out through the transmitter.
(A hybrid is also possible, in which you use the switch hook flash to
key and unkey the transmitter, but use touch tones for more general
control, like "lock transmitter off", and tuning, etc.  Such control
would be a great PIC project, though I'd use a touch tone decoder
ship, rather than trying to do DSP decoding on the PIC.  (But then
I've yet to step up from the 14 bit, so called "mid range" PICs.)

	It sounds like a fun project.  Perhaps I'll do one too.
(Or we could collaborate.  QST article, anyone?)

						73 - Bill, KE1G
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