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

[Jacques Fortin]

Don, If I am following everything right, it means that the ANT. TRIM knob line have to be inline with the red dot.
I agree: that’s how my own R-390/URR is settled.

Take care,

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de Don Heywood
Envoyé : 22 septembre 2024 17:16
À : Barry Scott <72volkswagon at gmail.com>
Cc : Jacques Fortin <jacques.f at videotron.ca>; R-390 Mailing List <r-390 at mailman.qth.net>
Objet : Re: [R-390] R-390/URR Antenna Trimmer Position

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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