[AMRadio] Collins 618S-1 tuning experiments


Patrick Jankowiak recycler at swbell.net
Sun Jul 25 02:01:12 EDT 2004


I have been playing with a Colling 618S-1 AM/CW HF tranceiver.

It has many crystals, so I wrote a prgram to print out the
possible frequencies in a list. (BASIC - runs with the screen or
a DOS-type dot matrix printer, er. sorry, I am no programmer)

1. to calculate what frequency the radio will be on depending on
the crystal and which of four bands was selected.

2. calculate the required crystal frequency for a given radio
tuning frequency.

208.190.133.201/Collins_618S1_calculators.zip

well anyway:

I used a PTO from the subsequent channelized model, to inject a
signal instead of a crystal, and noted the movements of the slug
racks in all bands across the frequency range.

The racks are servo'd to the crystal frequency, which is 1.75 to
3.5 MC (MHz is inappropriate for this vintage), and 250KC is
added to the crystal frequency to obtain the operating frequency
on band 1 (2-3.75 MC), and all the slugs are tied together.

It is explained in the manual that for each band, the
relationship between crystal (PTO) frequency and operating
frequency is:

Band 1: Fc + 0.25 MC + 0 = Fo (2-3.75 MC)
band 2: Fc + 0.25 MC + Fc = Fo (3.75-7.25 MC)
band 3: Fc + 0.25 MC + 3Fc = Fo (7.25-14.25 MC)
band 4: Fc + 0.25 MC + 7Fc = Fo (14.25-25.0 MC)

oops.. if band 4 is subjected to the full range of the PTO, then
the output should rise to 28.5 MC. The manual says the radio
only tunes to 25 MC, but it is observed that the slug racks move
properly in band 4 (as they do move more or less identically in
all bands) as if the set is tuning to 28.5 MC.

I have not powered the final amplifier (have not keyed the unit /
spun the dynamotor), and since its servo is a separate system, it
leaves a question as to whether it will tune to 28.5 MC.

Has anyone experimented with this unit?

Patrick




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