[TenTec] Shields in Omni VI

[Steve Hunt]

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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