[Hammarlund] Hammarlund Reflector Activity

[Richard Knoppow]

    I am pretty sure the HQ-140-X uses the same arrangement as in the 
HQ-120-X and HQ-129-X with one overcoupled IF. That is to broaden out 
the pass band without losing skirt selectivity. I am not sure which If 
is overcoupled but think in the earlier ones it is the stage that is 
link coupled. In any case, if you just peak all the cans the passband 
will be too narrow. A sweeper is the best method. A spectrum analyzer 
with a tracking generator works very well.
    The whole If must be peaked at the crystal center frequency. While 
it is nominally 455Khz the crystals vary a bit.
    I use an alignment procedure for the crystal that is somewhat 
different from the handbook. The driving transformer is peaked at the 
center frequency and the loading coil is then set for the widest 
passband with the crystal in its wide position. I use a signal generator 
with an audio signal of about 2Khz and just adjust for maximum output. 
That is the only adjustment in the Hammarlund patented crystal filter. 
make sure the phasing control is at _minimum_ bandwidth when centered. 
There is a trimmer in all of the crystal filters but its not the same in 
all. In the SP-110 and later, there is a compression trimmer in the can, 
in the HQ-129-X there is a bend wire acting as a capacitor but both do 
the same thing. One advantage of the Hammarlund filter is that its 
center frequency does not change with bandwidth so there are no other 
adjustments. It is the best of this kind of filter and much easier to 
adjust than the earlier form used in the SP-10-X, HRO and Hallicrafers 
receivers. This filter was introduced in the HQ-120-X (the X indicates 
it has the filter) and adopted to the Super-Pro later.
    The Super-Pro, including the SP-600-JX has the transformers 
critically coupled at narrower bandwidths so can be aligned by just 
peaking although the note about the crystal filter still holds: peak at 
the crystal frequency.

On 11/22/2023 2:25 PM, Dan Martin wrote:
> Bill, on the 140X are you planning to do a sweep alignment of the 455 kHz IF (amplitude, symmetry, and coincidence!) or simply peak all the IF cans on a fixed 455?


-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998