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

It can actually be much simpler these days using a minicircuits vco (50R output)
and a pll chip, not a lot else to it really.

10mW would give you a fair old range line of sight.

Stick a minicircuits ERA 80mW device (4 legs, 50R in, 50R out) on the output of
the vco if you want a bit more umpf.

Just as easy on 70cms or the unlicensed 458MHz ISM band, same for 23cms and 13cm
or 2.4GHz ISM band. It's SO EASY these days with the building blocks you can
get.

Clive

It can actually be much simpler these days using a minicircuits vco (50R output)
and a pll chip, not a lot else to it really.

10mW would give you a fair old range line of sight.

Stick a minicircuits ERA 80mW device (4 legs, 50R in, 50R out) on the output of
the vco if you want a bit more umpf.

Just as easy on 70cms or the unlicensed 458MHz ISM band, same for 23cms and 13cm
or 2.4GHz ISM band. It's SO EASY these days with the building blocks you can
get.

Clive

R C ) writes:
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.

Look in older books or magazines. Thirty years ago, such FM transmitters
were common in the ham literature. There isn't much sense in using
ICs for such transmitters, and synthesizers hadn't come into play,
so the transmitters were nothing but a crystal oscillator followed
by multipliers. Of course, for compactness you'd want to find something
that started with a relatively high frequency oscillator, say 48MHz,
so you wouldn't need all the multipliers.

There is bound to be something in the ARRL handbooks from that period,
at the very least.

Michael VE2BVW

R C ) writes:
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.

Look in older books or magazines. Thirty years ago, such FM transmitters
were common in the ham literature. There isn't much sense in using
ICs for such transmitters, and synthesizers hadn't come into play,
so the transmitters were nothing but a crystal oscillator followed
by multipliers. Of course, for compactness you'd want to find something
that started with a relatively high frequency oscillator, say 48MHz,
so you wouldn't need all the multipliers.

There is bound to be something in the ARRL handbooks from that period,
at the very least.

Michael VE2BVW