-=> Tony Frosdick said to Greg Mayman
 -=> about "BAG OF CHIPS" on 01-18-04  22:18.....

 TF> It uses a 'Wadley Loop' to receive up to 30MHz in 1MHz bands.

Ah, yes, I remember that name!

 TF> The first local osc (55.5-84.5MHz) selects the band. It mixes the
 TF> desired RF up to 55MHz.
 TF> A 1MHz crystal oscillator with loads of distortion produces a comb
 TF> of harmonics. The 1st LO is mixed with this comb and a bandpass
 TF> filter picks out the product at 52.5MHz.
 TF> This signal feeds the other input to the 2nd mixer to produce the
 TF> 2nd IF (2-3MHz). Errors in the 1st LO are cancelled.
 TF> The signal is now mixed down to 455kHz with a 3rd LO of between
 TF> 2.455-3.455MHz which is the main tuning dial.

Hmmm... I'm a bit lost in that explanation. I'll have to sit down
and put it on paper. My visulation ain't what it used to be.

But thanks.

I once saw a wonderful receiver -- can't remember any really fine
details, but the main LO was generated by mixing the output of
various dividers from a master oscillator. A most ingenious
setup, and the coarse tuning in 1khz steps was done by five
10-position rotary switches controlling different dividers, to
give adjustments in steps of 1KHz, 10KHz, 100KHz, 1MHz and 10MHz.

These switches also had a mechanical "carry" between adjacent
switches,, rather like a car odometer, so going from -9 to -0 or
the reverse would trip the next switch up or down.

The receiver was triple conversion, but with the 2nd LO and 2nd
IF fixed in frequency.

The 3rd mixer was variable over about a 1KHz range and fed a
crystal filtered 455KHz IF with incredibly sharp cutoff at the
edges of the passband.

The idea of making the 3rd LO variable was so that the signal
could be shifted relative to the passband of the 455khz strip, to
put the sharp cutoff characteristic almost anywhere relative to
the signal. In effect this gave an incremental fine tune with
excellent out-of-band rejection.

From Greg Mayman, in beautiful Adelaide, South Australia
   "Queen City of The South"    34:55 S  138:36 E

... Socialism is the longest road between Capitalism and Capitalism.
___ Blue Wave/386 v2.30

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