Newsgroups: sci.electronics
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Boosting output of a little walkie-talkie
Message-ID: <1990Jul28.210610.3544@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <3011@media-lab.MEDIA.MIT.EDU>
Date: Sat, 28 Jul 90 21:06:10 GMT

In article <3011@media-lab.MEDIA.MIT.EDU> adam@media-lab.MEDIA.MIT.EDU (Adam Glass) writes:
>Could I use a high-frequency op-amp as a voltage follower to amplify
>the output of a little walkie talkie?  ...
>Is this possible?  Legal? ...

Possible, probably.  Legal, no.  For one thing, there are severe limits
on the power output of unlicensed radio transmitters.  For another, such
transmitters have to have FCC approval, and *any* private modification
voids that approval.  Only people with proper certification -- notably,
radio amateurs -- can build or modify their own transmitters.  There are
a few specialized exceptions to this, e.g. for operations in the extreme
ends of the spectrum or at very low power, but none that would cover
what you propose, as far as I know.

>Also, can the crystals just be desoldered and replaced with different
>frequencies as long as you get crystals of the same type?  Or are
>other things in the circuit tuned to the crystal's frequency?

In general, such mass-market products will be "single point" designs,
optimized for operation under specific conditions.  Also, changing the
frequency is another illegal modification, and one with potentially
very serious consequences.  If you end up interfering with something
like emergency services or aircraft navigation, you could kill someone.
Even if you don't, the Feds have absolutely no sense of humor about
such interference, and will jump on you with both feet.

This is a possibility even if you don't switch frequencies, given that
a homebrew amplifier may well generate harmonics you didn't really intend
to emit.

If you have the skills to do such a modification properly and safely,
you can easily become a licensed radio amateur so you can do it legally.
-- 
NFS:  all the nice semantics of MSDOS, | Henry Spencer at U of Toronto Zoology
and its performance and security too.  |  henry@zoo.toronto.edu   utzoo!henry