Quote:
Originally Posted by John KC0G
Hello Jez and Sirius
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Hello 2U2 John KC0G (and now also Paula) !
It's now the morning. I had a quick look at this thread before I went to bed last night to see the comment from John about the 7.8125 Hz tuning steps -- W H A A A T ! This was news to me. I'd always taken the minimum tuning step size to be a nice, round 8Hz (I knew that the rate increased depending on mode and spin rate etc).
I went to bed, but not before taking a look at the HF-150 user manual and, in particular, the Circuit Description on page 27 which has a paragraph stating:-
"Receiver tuning is achieved by varying the frequency of both the local oscillator and the IF conversion (heterodyne) oscillator. The local oscillator covers 45.030MHz to 74.999MHz in 1kHz steps, and fine tuning is provided by the heterodyne oscillator covering 44.544MHz to 44.545MHz in 128 steps...."
Bingo! Light bulb moment
(44.545MHz - 44.544MHz) / 128 = 7.8125 Hz
I see it now !
This also explains the six versus eight bit burst strategy. If the user enters a frequency in full kHz, this will be applied to the local oscillator (and the hetrodyne osc just zeroed presumably?) But, if a fractional frequency is entered, the integer part (6 burst) will be applied to the local osc, and the fractional part (burst 8) will be applied to the hetrodyne osc.
Since realising that, I noticed John's and Paula's later comments - great stuff - we're all thinking on the same lines. Last night I was thinking maybe they just used a lookup table or something to resolve the fractional part but, now, probably not.
John, I'll try the 0.039 and 0.961 FRQ commands later this morning. Going to have some breakfast and get the shopping in first !
Cheers,
Jez