In article ,
Ian Jackson wrote:

In message , Dave M
writes
On Thu, 05 Jul 2007 19:00:17 GMT, "Johnny Byrns"
wrote:

TerryJ wrote:

Capable of 100% modulation and has fairly good fidelity.

How do I tell if it uses AM or FM transmission signals? The diagram
shows nothing in reference to a FM or AM transmission bands.


For one thing, the audio input is fed directly to a transformer in the plate
circuit of the oscillator tube. Classic AM.
Next, the oscillator is fixed at 1 MHz by the crystal. No audio gets into
the
oscillator grid or cathode to FM it.

==============

Dave M

Never take a laxative and a sleeping pill at the same time!!

You would find it rather difficult to FM a crystal oscillator. Possible,
but difficult.
Ian.

Some of the early BBC FM transmitters did exactly that, FM a crystal
oscillator.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

You would find it rather difficult to FM a crystal oscillator.
Possible, but difficult.

Not really. It's done all the time in temperature-compensated oscillators,
simply by varying the series or load capacitance.

In message , William
Sommerwerck writes
You would find it rather difficult to FM a crystal oscillator.
Possible, but difficult.

Not really. It's done all the time in temperature-compensated oscillators,
simply by varying the series or load capacitance.


OK then - 'Possible, but much more difficult than with a free-running
L-C circuit'.

When an oscillator is crystal controlled, to get a lot of FM, it usually
takes a bit more than 'slipping a variap' into the circuit. You usually
have to use some form of VXO circuit. Even then, the amount of FM you
get can depend a lot on the characteristics of the crystal. And it may
not be very linear. But it all depends on what you need.

Some early crystal-controlled FM equipment avoids the problems of FMing
the crystal itself. Instead, in a later stage they phase-modulate the
signal (producing a predictable amount of PM) and, of course, multiply
up to the final frequency.

Ian.
--