Hi Ken,
Thanks for the suggestion.
I don't believe it is a stage self-oscillating because the frequency is so
stable once the rig has warmed up.
I did a few measurements this morning. I was surprised to find that it took
only a 50 Hz shift in the 15.3 MHz oscillator to move the spurious by 1KHz. Can
it really involve the 20th Harmonic? The other thing I noted was that pitch of
the spurious is 0 Hz when the PBT oscillator is on 15,300,000Hz. Also for a
given shift on the PBT oscillator the pitch moves in opposite directions
depending whether I have selected USB or LSB.
I've put an Email in to TT to see if they've come across the problem/feature!
73,
Steve G3TXQ
----- Original Message -----
From: Ken Brown
To: Discussion of Ten-Tec Equipment
Sent: Monday, November 27, 2006 5:28 PM
Subject: Re: [TenTec] Shields in Omni VI
Hi Steve,
That the pitch changes suggests that the loading of the different
filters is changing the frequency of a spurious oscillation, somewhere.
If it is a harmonic of the 15.3 MHz PBT oscillator, it would only have
to be a small shift of 15.3 MHz to produce a few hundred Hz shift of say
the 15 harmonic. Changing the 9 MHz filter being used should not change
the loading on that oscillator though. Maybe one of the 9MHz IF amp
stages is oscillating.
Ken N6KB
Steve Hunt wrote:
> Ken,
>
> Gary, W7TEA, kindly sent me a photo of the underside of his early Omni VI+
which has the screening in place. There are no holes in my "inner panel" which
would allow screens to be attached, so this must have been a mod on later Omni
VIs / Omni VI+s.
>
> I have put temporary screens in place but they made no difference!
>
> One final symptom on the "birdies" which totally mystifies me: If I adjust
the PBT control until I hear a birdie, then press the NAR button, the pitch of
the birdie changes by a few hundred Hz; pressing the NAR button again returns
it to its original pitch. I can't see anything on the schematics that would
suggest that the NAR button affects any of the oscillators!
>
> I think I'm just going to have to live with it.
>
> 73,
> Steve
> ----- Original Message -----
> From: Ken Brown
> To: Discussion of Ten-Tec Equipment
> Sent: Monday, November 27, 2006 2:01 AM
> Subject: [TenTec] Shields in Omni VI
>
>
> Hi Steve,
>
> The photos in the manual for my Omni VI do not show any of the shielding
> in place. I was wondering if I was confused and that the cover plates I
> remembered are in my Paragon and not in the Omni VI. When I read the
> manual for the Omni VI in the section describing how to install the
> optional filters, it clearly states that you need to "Remove the panel
> covering the PBT board" or "Remove the panel covering the 9 MHz filter
> board." So, even without opening up my Omni VI, I think I can say with a
> fair degree of certainty, "Yes there should be cover plates over the 9
> MHz and 6.3 MHz optional filter access holes." I will be interested to
> hear whether adding shielding plates over those holes makes the birdie
> go away.
>
> Ken N6KB
>
> Steve Hunt wrote:
> Ken,
>
> I only just spotted your question about shield covers over the optional
> filter slots.
>
> There aren't any - just holes! Should there be? I don't recall seeing
> any obvious fixing holes for covers or I might have been suspicious.
>
> 73,
> Steve G3TXQ
>
>
>
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