[Hammarlund] HQ-129-X Serial Numbers

[Kenneth G. Gordon]

On 14 Aug 2012 at 15:21, Richard Knoppow wrote:

>      That's what I have.  I checked the LO using a Collins 
> R-388.  I checked _all_ the bands to make sure the LO was on 
> the correct side of the signal.  Just to be clear, its 
> _below_ the signal on the two highest bands and above it on 
> the others.

Excellent. Sounds perfect. :-)

>      Now, about the bandspread.  The bandspread for 80 and 
> 40 turns too far. That is there is a progressive error that 
> reads the frequency low.  That means the bandspread cap must 
> have to turn too far, i.e., must change capacitance more 
> than it should in order to cover the tuning range.  If I 
> arbitrarily set it for a slightly higher frequency than the 
> correct top band edge I can make it read right for 
> _interval_  that is 100 khz points read 100 khz apart.  So, 
> evidently the combined capacitance of the main tuning cap 
> and trimmers is too large meaning the amount the bandspread 
> cap must change to change the frequency by a given amount is 
> too large.  What can cause this?

I don't know for certain, but the manual states that the bandspread cap MUST be set to 200 
on its scale (fully OPEN) when aligning the HFO. If the BS cap is set anywhere else, then the 
main-tuning cap would have to be set at a lower-capacitance setting than it should be to 
compensate, meaning that the BS cap would have to add more to the total capacitance to 
tune where it then should.

Were you careful to set the BS cap fully open, and make certain it stayed there, when you did 
the alignment?

Perhaps that is the problem?

Due to the design of the 9 section BS cap, if it were not set exactly correctly to begin with, it 
MIGHT make a lot less difference on the upper bands than it would on the lower ones, since, 
as I remember it, different sections of the BS cap are used on different bands.

Ken W7EKB