[Hammarlund] SP-600-JX14 and my -JX1

[Kenneth G. Gordon]

On 22 Aug 2020 at 12:56, Richard Knoppow wrote:

>     I am curious which instructions he had. The crystal alignment 
> is very simple. The filter is a patented design by Donald Orem, 
> CE of Hammarlund at the time and first used on the Hammarlund 
> HQ-120-X (the X means it had the filter). Orem's filter, unlike 
> most others, does not detune when the bandwidth is changed. The 
> gain remains fairly constant. There are a couple of silver mica 
> caps in the filter which can go bad or drift which will screw up 
> performance. The crystal frequency is the frequency the 455Khz IF 
> must be adjusted to. The correct aljustment procedure uses an AM 
> signal of about 2Khz with the carrier set at the crystal 
> resonance and the bandwidth at maximum. The loading coil is set 
> for maximum bandwidth (greatest recovered modulation). This does 
> not seem intuitive but makes sense if you understand the theory 
> of the filter. A very similar design is used by Collins in 
> several receivers and in the TMC GPR-90.

First of all, do remember that this incident was over 60 years ago, and I was a relatively new 
Novice at the time, so details are undoubtedly fuzzy.

Even so, as I remember it (dangerous at my age) when he activated the crystal filter after 
having tuned in a signal to its peak, the signal strength meter dropped, precipitously. He told 
me that this was not correct, but that he had followed the instructions in the military manuals 
he had.

He was puzzled by these results

A few days later when I visited him again, he showed me how much better it worked after he 
had done what he intuitively supposed was the correct method. I am not certain that the 
signal meter rose, but I do know that it didn't drop as it had before.

In any case, I remember that the signal he was tuned to sounded louder.

He mentioned how the crystal-filter should cause an increase in the signal-to-noise ratio, 
which makes sense, since the bandwidth is reduced, thereby reducing the total amount of 
noise.

Now I also remember some discussion about aligning the SP-600 and crystal filter some time 
ago on one or more of the discussion groups that the instructions in at least one of the 
miltiary service manuals for aligning the filter was just plain wrong.

I think this was also mentioned in that collection of articles which was compiled by some 
fellow by the name of Barry. The Hollow State Newsletters, as I remember it

I have a collection of reprints from the Hollow State Newsletters. Many of the articles deal 
with the R-390/R-390A though.

Ken W7EKB