[R-390] Question on COSMOS PTO

[Jim M.]

I see the same effect with my 390a and Cosmos, I think it is basically a 
normal thing.  One thing to be careful of is to be sure the oldham coupler 
is not too tight in pressing against the PTO shaft.  There should be a 1/32 
in. gap.  Any pressure against the PTO shaft can cause changes as you noted.


----- Original Message ----- 
From: "Jon" <jonklinkhamer at comcast.net>
To: <r-390 at mailman.qth.net>
Sent: Friday, March 31, 2006 11:08 PM
Subject: [R-390] Question on COSMOS PTO


> Hello to the Group,
>
> I'm continuing my saga of just zero beating against the calibrator mark 
> and
> have notice the following observations which I think are cause to be
> concerned.
>
> 1. Zero beating against the calibration 100Khz signal at x.000 after using
> the zero adjust knob to be exactly at x.000, I noticed that if I either 
> dial
> up or down from this calibration spot, coming back to this mark, I'm 
> always
> either +/-100Hz off depending on the direction I'm turning. Is this what 
> you
> call backlash or hysterisis?
>
> 2. Doing the same experiment as described above only this time using a
> counter and taking note of the frequency, I observed that starting again 
> at
> 3.455000Mhz with the dial set to x.000 and dialing up or down the 
> frequency
> can be off as much as 80Hz i.e. 3.45508 in returning again to x.000. I 
> also
> noticed that by pressing on the KHz knob with just pressure from my hand I
> can cause the frequency to be off again as much as 80Hz. And since the 
> 390a
> is on its back I can touch the PTO and cause 10s of Hz of be off.
>
> This is my 1st 390a and I don't have any experience in the feel for
> calibration. Am I approaching the design limit being off +/- 100Hz on the
> calibration mark? It seems to me something is either up with the PTO or 
> the
> mechanical linkage to the PTO. The oldham coupler is aligned as best I can
> with a new backlash spring and I'm also keeping to the .032 spacing as 
> best
> I can. The ground strap is present and looks good against the shaft. I'm
> really kinda of frustrated at this point and any help would greatly be
> appreciated.
>
> Thanks in advance,
> Jon,KB1DC
>
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