Alex ) writes:
Can anyone provide some part #'s for these one chip FM TX & RX IC's? I'm
interested too.

Those Motorola FM transmitter ICs aren't particularly useful. By the
time you add the needed external components, you aren't really saving much.
And, for most amateur applications, you'll need some sort of multiplier
to get up to frequency, and most will want an amplifier. You might as
well start with discrete components, because you can get them easily,
you will get the design you want, and you would be saving very little
space with the IC.

The transmitter ICs are designed for 49MHz operation, yet the cordless phones
I've taken apart don't use them, and the 49MHz FM walkie talkies that I've
looked at don't use them. Instead, they use discrete components.

Doug DeMaw did write about the MC2831 in the March 1990 issue of QST,
though it was more an idea article. Looking in old Motorola databooks
will also turn up information about the ICs.

The receiver ICs are more useful, because they fit in more. Motorola
had a few generations of such ICs, starting with one that took 10.7MHz
and converted down to 455KHz and you'd get the audio out the other end.
There were various part numbers, again look in old Motorola databooks.
You do see these quite frquently in older cordless phones. Buying
such phones at garage sales has the advantage that you get the 10.7MHz
and 455KHz filters and the crystal to convert from the first IF to the
second. (Note, some of those phones use these ICs in a single conversion
configuration, going from 49MHz down to 455KHz directly.) If you're careful,
you could just extract the whole circuit from the phone (and indeed, you
get two such circuits, one in the base and one in the remote).

I found similar ICs in Radio Shack 49MHz superhet walkie talkies. I've
yet to check baby monitors to see if they use the ICs (or indeed
if they are even superhet receivers). These are pretty useful because
the boards are small, and either a bit of conversion of the front
end will put it on a useful frequency, or strip off the front end
and add your own.

Older cellphones, the bulky kind, will offer up lot so useful parts
including some sort of IF strip. I don't think I've found a recognizable
IF strip IC number yet. And they too will include the filters and conversion
oscillator.

Of course, at this point I've pulled in a number of FM two-way receiver
boards that have such things, or could even be used without conversion.
I've found these at the local hamfest, and they were going for a couple
of dollars each.

Motorola came out with a second generation of FM receiver ICs, that
were double conversion receivers in a package. So you wouldn't need
an external front end in front of the IC. I haven't seen these in
consumer equipment, and I'm not sure how available they were as
parts.

They even came out with a third generation of receiver ICs, not really
adding much in ways of features or integration, but did have higher frequency
performance. There were an article or two in the old COmmunications Quarterly
magazine.

Michael VE2BVW


Marcus Sleightholm wrote:
Motorola did a number of one chip FM TX ICs, - they are cheap and widely
available and produce about 50mW output which can be use to drive something
like a 2N3866 output stage (I only give that device number as I have one in
the junk box!)

73 Marcus M3ChB

"R C" wrote in message
m...

Hi, I'm looking for a small, 2m FM fixed frequency TX design for a
backup telemetry link on a model craft. I've seen designs based on
discontinued Motorolla baby-monitor ICs, but simple varactor/tripler
designs seem less common. Weight/size are important, and I'd like
output around 1-2W. Duty cycle will be fairly low. There is 4.8V or
12V available already; 4.8V is likely to be noisier, as it drives the
servos. 12V is prefered.

What I was thinking was ~48 Mhz crystal oscillator with varactor, fed
into a tripler, then a bandpass, then into an amplifier (RF
transistor?)?

I've seen a number oscillator designs floating around (handbook and
otherwise), but I don't know how to find out what's most appropriate.
Any suggestions, designs I've missed, books to read, etc? Something
like the Ramsey FM6 (preraid)?

Plan B is to find another HTX-200 or similar, pull out the guts, and
use that. But I'd rather have something I can lay out myself.

Thanks,
R C
KG4MVB