HQ-140X Calibration Question

[nq5t]

The IF calibration using a sweeper worked easy peasy, and looks good.  Just finished the RF cal process, and rechecked it at the band edges.  After setting everything per the book, it turns out that the calibration at intermediate markers tends to be pretty poor.  Even the resulting band spread calibration is not very good across the  ham bands (well, at least on 20 and 40 where I've checked -- kind of takes resetting to a marker every 50 or even 25 Khz to be relatively close

Wonder if this is typical, or if there's something else I should be looking into.

Grant NQ5T

Added:  I did go back and check the main dial ranges throughout, and in between the edge frequencies used for calibration, the frequency accuracy is acceptable although it's off at obvious spots, like 15 Mhz -- probably about as good as can be expected.  Still, the ham bands on the band spread dial aren't terribly good.  Set to the center of the band with a marker, they're off 10-20Khz or more on the band edges.

[W7TFO]

You prolly already know, but Hammy sez set tuning to top of allocation, BS dial to max and work same down for tuning.

73DG

[nq5t]

You prolly already know, but Hammy sez set tuning to top of allocation, BS dial to max and work same down for tuning.

73DG

Yeh, I prolly do

If I do it that way, the ham bands are typically way out at the bottom end.  It's a little closer overall if I set band spread to a mid-band frequency, e.g. 7200 or 14200 etc., and then use a marker to adjust the main dial. I was just hoping for better.  My GPR-90 isn't perfect either, but it's a whole lot closer than this HQ-140 is.  I seem to recall that the HQ-170A/180A radios I owned at one time had similar dial errors, no matter how finely (or often) one went through the calibration procedure.  Sometimes fiddling with the low frequency and high frequency ends of the range used for calibration has some effect, but I've generally found that all that does is move the errors around.

I can only guess that during design, the dials were printed to match some "standard" prototype radio, and then through a combination of component variability, differences in stray capacitance, aging, whatever, the production radios didn't all match the dials precisely even new out of the box.  These were never meant to be frequency meters in any case ..

Still, it's a nice receiver with just the right look, and plays really well ...

[N8ETQ]

  Hey Grant,


      it could just be some bent plates on
the Main tunning cap. Inspect the Oscillator
section. You will see "ussually", 1 plate
at the end of each section of the cap.
 It will be sectioned into three or four parts.
 Thats where they "Tweak It".

       Set up a modern rig and listen to the LO.
Should be loud and clear at "Freq your tuned to"
- IF (455?). You can make a "Plot" of it's
Non-Linerity and Either keep it handy , or,
attempt adjustment.

       It makes for a "Fun Day". Prolly "Easier"
to pull it and use a "C" meter. Then you could
Verify that the Converter section and the RF
Amp section Track linearly with the Oscillator.

       Even an R-390/A your supposed to CAL
every time. If it's off more than 50KC or so
it's probably bent.

GL

/Dan

[nq5t]

Thanks ... I'll pull the cover and take another look at the caps.  I checked them, because I've seen bent plates before in another radio -- once what looked to be a hambone attempt at re-knifing them.  I tried it once, too, in a junker where it wouldn't matter how it came out.  It was ... naturally ...  a disaster ... 

[KA2DZT]

The outer plates on the tuning caps sometimes have slots cut in them.  Those slotted sections of the plates were meant to be bent slightly to improve tracking.  If no slots, you can still bend the plates a bit if that helps.  Don't look to get it exact, not going to happen.  Most of those receivers have a moveable cursor to improve the dial readings along sections of the whole dial.  They made that feature because they knew that it's unlikely the dial readings were going to track perfectly, even when the set was new.

Fred

[nq5t]

Typical of general coverage 2-dial radios, the 140 doesn't have adjustable fudicials.  I'm going to take a look at the band spread cap, and may ..maybe, possibly, haven't decided yet .. see if very slight adjustment of the slotted plates might bring it a bit closer.  Don't plan to touch the main tuning cap -- it's actually close enough, and for the most part in the 1% error range worse case, which is the receiver's spec.

All of the ham bands on the band spread dial are off in the same way.  If I set them at the high frequency end, the low frequency ends all read LOW in frequency, e.g. with the band spread dial set against a 100 Khz marker at 14.3 Mhz, 14.2 reads around 14.195 on the dial, 14.1 reads 14.085, and it get progressively worse going lower.

[KA2DZT]

From what you described, it seems you need a bit more capacitance from the band spread cap.  You're having to increase the capacitance by lowering the dial reading yielding more capacitance to hit the marker.  Seems the plates need to be a little closer.  So, if the outer plate is bent away the stator plate, bend it closer.

Fred

[nq5t]

A closer look at the band spread tuning cap indicates that nothing is apparently bent out of whack, and the capacitor plates aren't amenable to adjustment.  There are no slotted sections, and too much could go wrong trying to warp a solid end plate.  I've decided to button it up for now.  It is what it is, and it will do ...



Grant NQ5T