[Hammarlund] Unstable Oscillator adjustments in the HQ-180

[Roy Morgan]

On Feb 1, 2016, at 9:35 PM, djed1--- via Hammarlund <hammarlund at mailman.qth.net> wrote:

> I suspect what you're seeing is normal.  Remember, when you're tuning an IF of 455 KHz, an adjustment of say 1 KHz is 1/455.  If you're adjusting the oscillator to the same tolerance, the ratio is (at 20 MHz) 1/20,000.  So it is a lot harder to adjust the HF oscillator.  I definitely avoid using an output meter to adjust the HF oscillator.  I either use the BFO, aiming for zero beat with the generator, or I couple a frequency counter to the oscillator and set it that way. And any of my Hammarlunds will shift the oscillator frequency a bit when you put a metallic screwdriver on the trimmer.
> Aslong as it is stable when you're done, you probably don't have a problem.

I think Ed is right.

First, When tuning an IF can for peak you are dealing with a low frequency tuned circuit, and moving it’s resonant point around a title bit.  When you do the alignment on the local oscillator coil, you are dealing with a higher frequency oscillator and you are changing it’s frequency.  As it passes the point you want, it peaks the output and zips past it quickly so finding the peak is difficult.  Ed’s suggestion about the zero beat is good… it will be easier to use than a peak in the receiver output.

Second, if you are able to use a NON-metalic tuning device, your life will be easier.  As Ed mentions, the metal end of the timing tool changes the frequency of at the oscillation.  Well made chop sticks (not the split-apart throwaway ones) make fine tuning tools.  Just sharpen with a jack knife, or a file.

Roy