[BC] FM Exciters (Pic's)

[Harold Hallikainen]

> I gather from all the comments that these are crystal controlled as
> opposed
> to pll?? I assume by the model number and meter scale on the unit that the
> AEL is 20watt output??? and as i recall from an auction i saw on ebay the
> TE-3 was a 10watt unit???
>
> if anyone has any manuals on these units that i can have for cost of
> shipping i'd appreciate it :)
>
> also what is the average value for these on the used market???
>

We need a definition of "crystal controlled." You cannot swing a crystal
far enough to directly FM a crystal oscillator (you can for narrow band
FM, but not for wide band broadcast). The various methods of generating FM
that come to mind are:

1. Serosoid (spelling is bad, I'm sure), which involved phase modulating
the output of a crystal oscillator (not the oscillator itself), then
frequency multiplying like mad to get to the output frequency.

2. Phasitron, similar to above, but with a special Phasitron tube.

3. FM oscillator (either on carrier frequency or a lower frequency that is
hetrodyned up to reduce noise) that is AFC locked to a crystal oscillator.
This is a Frequency Lock instead of a phase lock.

4. FM oscillator that is phase locked to a divided down crystal
oscillator. Both the FMO and the reference oscillator are divided down to
a pretty low frequency (in the kHz, as I recall) so the FMO can be FMd
without losing lock.

5. Direct Digital Synthesis. A crystal oscillator is used as a clock to
advance a "phase accumulator." On each clock, a number is added to the
existing accumulated phase, advancing the phase in a circle. The
accumulated phase goes through a sine lookup table, then a D/A converter.
FM is accomplished by varying the amount of phase that is added on each
clock. A higher number results in a higher frequency.

6. DSP. I'm not sure if there are any special DSP alorightms for
generating FM other than just doing the same as DDS.

Harold



-- 
FCC Rules Updated Daily at http://www.hallikainen.com