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
