[R-390] R-390/URR Antenna Trimmer Position

[Don Heywood]

Barry, I'm home from the hospital now and I've got it straight. On the tech manual page that shows the alignment for the RF deck it says set the antenna trim to zero. I have penciled in zero equals red dot up.
That 3 o'clock position makes it easy to see the dot when the RF deck is out.
So, red dot up at zero on the dial, and the alignments are done in this position
Sorry for the confusion, must've been the anesthesia
Don WC4G
Sent from my iPhone

> On Sep 22, 2024, at 15:14, Barry Scott <72volkswagon at gmail.com> wrote:
> 
> Another list member, Don Heywood, let me know that, like the R-390A, the
> shaft on the R-390 also has a red dot which is used to align the
> capacitor.  It's also mentioned in the Pearls document.
> 
> With the dot pointing to the 3:00 position, the knob should point to the
> 12:00 position.  I just looked and, indeed, that dot is on mine (and
> somehow, I had the knob pointing to almost exactly where it should be
> pointing).
> 
> I still don't know where that's described in the manual but apparently it's
> there somewhere.
> 
> Thanks,
> Barry - N4BUQ
> 
> 
>> On Sun, Sep 22, 2024 at 9:50 AM Jacques Fortin <jacques.f at videotron.ca>
>> wrote:
>> 
>> Hi Barry,
>> 
>> Well... the problem will arise when you will try to align the Antenna
>> circuit RF transformers...
>> During that operation, the ANT TRIM position is specified to be a "0" (ANT.
>> TRIM caps meshed halfway).
>> I vaguely remember that -4 position relates to fully meshed ANT. TRIM caps
>> and that I had "marked" the related shaft position when I worked on mine.
>> But trying to determine the caps position when the whole RF deck is in
>> place
>> is... well.. not that easy.
>> 
>> I have an idea, but it will require the use of a handheld capacitance
>> meter,
>> plus the removal of T201...
>> The logic behind is that both sections of the ANT. TRIM cap are connected
>> to
>> T201 pin 5 when the MC control is at 00.
>> With the T201 out of the way, a capacitance meter can be connected to the
>> T201 socket between pins 4 and 5 and the measured capacitance value looked
>> at when the shaft is rotated.
>> There should be a maximum and a minimum capacitance value measured.
>> When the value is maximum, the caps are fully meshed and that is the "-4"
>> position of the control.
>> 
>> I never tried to do it that way.
>> So I do not know if that make sense overall... or not !
>> 
>> 73, Jacques, VE2JFE in Montreal
>> 
>> 
>> While I had the RF Deck out to work on the gear train, I rotated the
>> Antenna
>> Trimmer and left it at some unknown rotational position when I installed
>> the
>> RF Deck back into the cabinet.
>> I'm now trying to determine the rotational position of the Antenna
>> Trimmer's
>> shaft and where that position should be located with respect to the
>> markings
>> on the front panel.
>> I realize the trimmer can just be rotated to where the signal is best and
>> the numbers may not really have much meaning but I'd think that some
>> position (say, 12:00) should correspond to a given mesh value of the cap's
>> plates (e.g. when the knob is at -4, the plates should be fully meshed,
>> etc.).
>> The only reference to that that I've found are the paragraphs that deal
>> with
>> the removal and installation of the front panel.  The manual states to
>> position the knob at the -4 position before removing the front panel and
>> then, when replacing the front panel, replace the knob (presumably at the
>> -4 position).  That's fine but if the Antenna Trimmer is rotated while the
>> front panel is removed, then it isn't clear to me how to replace the knob
>> properly w.r.t. to the capacitor's plates.
>> Anyone know?
>> Thanks,
>> Barry - N4BUQ
>> 
>> 
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