[TenTec] Omni VI Plus freq. readout

n4lq@iglou.com n4lq@iglou.com
Mon, 30 Sep 2002 08:13:05 -0400

> Frankly, I don't find the Kenwood's, Yaesu's or Icom's to be any better
> in
> terms of actual frequency vs. displayed frequency. 


-----Original Message-----
From: Robert & Linda McGraw K4TAX <RMcGraw@Blomand.Net>
To: AC5E@aol.com, amishbuggy37@yahoo.com
Date: Sun, 29 Sep 2002 22:09:42 -0500
Subject: Re: [TenTec] Omni VI Plus freq. readout

> Pete has some interesting comments.  Keep in mind that the 7 - 10 ppm
> on 20
> meters is almost 100 Hz and the 10 ppm is 142 Hz error.  Now in this
> writers
> opinion, that's a lot.  As to the 2 - 3 ppm well that still says the
> rig is
> 28 to 42 Hz off.  Eh, so what.   As to those rigs with the "frequency
> counter" being internal, keep in mind that the received frequency is
> the
> compilation of the various oscillators both variable and fixed to
> manage
> from the input frequency through the multiple conversion process. 
> Including
> the LSB or USB oscillator for injection into the product detector.  Any
> of
> these being off a few Hz can make for several Hz error one way or the
> other.
> Most interpolate the frequency and read only one oscillator.  On the
> other
> hand, reading transmit frequency is OK and easy on CW but a challenge
> on SSB
> as the actual carrier is typically suppressed (we hope) some 50 to 60
> dB or
> more below rated output.
> Now, here's a point I pick.  If WWV is 10.0000 MHz and the crystal
> calibrator is say 2 Hz above 10.0000 MHz the two signals produced are
> the
> sum and difference hence 2 Hz and 20.0000 MHz + 2 Hz.  I doubt that
> most
> audio paths in our radios will pass a 2 Hz signal and most assuredly
> the
> human ear can't hear 2 Hz.  In reality, we hear the "beat" which is
> really
> the phase addition and subtraction in terms of time domain.  Hear we
> can
> extract a difference as the rotation of phase cancellation is in the
> order
> of 2 Hz or so.
> For what it's worth, I prefer to measure TX frequency in the CW mode
> using a
> counter of sufficient known accuracy.  Knowing the CW offset ( which
> may not
> be exactly 800 Hz) as it is tweakable via C10 on the TX Audio Board and
> handled by the DSP system based on one's preferred CW offset for
> receive.
> It should be 9.000400 MHz) then I can presume that I know the TX
> frequency.
> In general, I find that my OMNI VI+ is always closer than 10 Hz of
> where
> it's supposed to be.  All is well if the LSB oscillator, adjusted by
> C16,
> is 9.000000 MHz , USB oscillator, adjusted by C12,  is 9.003000 MHz,
> Space oscillator, adjusted by C13, is 9.002295 MHz and FSK Mark
> oscillator,
> is adjusted by C18, is 9.002125 MHz.  Should you want to see where the
> "carrier frequency" is located, just tweak the carrier null pot, R10,
> on the
> L.O. Mixer Board a bit to let a bit of carrier through for the external
> counter to measure.  When finished, don't forget to do a carrier null
> procedure.  Here again I caution,  IF YOU DON'T HAVE THE EQUIPMENT TO
> DO
> In the case of the OMNI VI+, if you examine the L.O. Mixer board you
> will
> see 10 crystals, Y1 - Y10, that are used for the respective bands. 
> There is
> no adjustment to "trim" any of these.  From this, one can expect to see
> some
> band-to-band errors.  Just the nature of a crystal mixer rig.
> Frankly, I don't find the Kenwood's, Yaesu's or Icom's to be any better
> in
> terms of actual frequency vs. displayed frequency.
> Now, lets get back to hammin' and quit twiddling over 5 or 10 Hz.