[ARC5] Zero Beat Question

Thu Jul 7 22:27:54 EDT 2016

  Regarding the beat-note:
  With the right speaker (or head-set) you can hear to within 50-60 Hz.
  With care, you can approach the point of zero-beat from "above" and
  "below" and interpolate to the mid-point (true zero-beat).
  If you wish to become "picky" use a CRO or even a center-reading
  analog meter and you'll see the meter (or CRO) move in sympathy with
  the beat-note.

   73 de Les Smith
   vk2bcu at operamail.com

On Fri, Jul 8, 2016, at 10:57, hwhall at compuserve.com wrote:
> >
> If you do you can probably use it to determine the exact zero beat by
> listening to it wax and wane.
> >
>
> I've noticed many radios, when you are very close to zero beat & the
> beatnote is too low to hear as a tone, the volume of the background
> hiss of the radio will be heard to rise & fall in step with the slow
> beatnote, so that you can get quite close to zero by tweaking until
> the rise & fall slows to a stop or nearly so. I think that's what he
> meant by "wax and wane."
>
>  Wayne WB4OGM
>
> -----Original Message----- From: Richard Knoppow
> <1oldlens1 at ix.netcom.com> To: arc5 <arc5 at mailman.qth.net> Sent: Thu,
> Jul 7, 2016 5:57 pm Subject: Re: [ARC5] Zero Beat Question
>
>  I think that either there is an error in the manual or you have
>  misread it.  I found the manual at:
>  http://www.liberatedmanuals.com/TM-11-6625-586-45.pdf It includes
>  some changes, perhaps corrections of errors.  On p.1.2 change 1
>  paragraph l (el) the use of the calibrator is described. I states
>  that when its zero beat the signal frequency is on one of the 1 Mhz
>  calibrator markers.  The zero beat is listened to via a small
>  internal speaker so its probably difficult to tell when its exactly
>  at zero. The paragraph says something about the speaker putting out
>  the beat when its within audible range but, of course, you want to
>  get it to zero. One way is to offset from zero to some convenient
>  frequency in one direction and the move to the other side at the same
>  beat note noting the difference on the dial and setting for the
>  center. However, you can probably get close enough by putting your
>  ear near the speaker.  I think this generator has only FM modulation
>  but you can try it to see if you hear any audio in the calibrator
>  speaker. If you do you can probably use it to determine the exact
>  zero beat by listening to it wax and wane.
>
>  On 7/7/2016 4:14 PM, Robert  Eleazer wrote:
>  > Well, thanks for the explanation.  It makes sense in that context.
>  > Now let me explain what I was really asking.
>  >
>  > I repaired the 1 MHZ oscillator of my URM-103/SG-297 by replacing
>  > it with a 7805 regulator feeding a 1 MHZ TTL oscillator, all built
>  > into a crystal oven case (originally the SG-297 used a crystal
>  > oscillator that employed a 1 MHZ crystal and a couple of 2N706).
>  > That oscillator in turn feeds a harmonic generator to create
>  > calibration signals every 1 MHZ over the total range of the signal
>  > generator, 26 MHZ to 80 MHZ. This unit is pre-digital and there is
>  > no PLL or anything to keep it locked to the reference oscillator;
>  > that is all manual in nature.
>  >
>  > You flip the function switch to "Calibrate" and then tune the
>  > oscillator to the nearest 1 MHZ point.  You get the usual tone over
>  > the speaker when the oscillator and the marker signal beat and then
>  > use a separate control that enables you to move the red frequency
>  > stripe so that it matches what the marker says.  The manual says to
>  > Zero Beat the oscillator with the marker and line up the frequency
>  > calibration that way.  So it may at first show the marker signal is
>  > on 45.050 MHZ and you just move the calibration red stripe to match
>  > the marker, put it right on 45.00 MHZ.
>  >
>  > But if you are Zero Beating the oscillator with the marker, then
>  > there should be no tone, right?  So how can you use the tone to set
>  > the calibration to set the oscillator calibration?  When the tone
>  > disappears you'll be on one side of it, right?
>  >
>  > Thanks,
>  >
>  > Wayne WB5WSV
>  >
>  >
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>  --
>  Richard Knoppow 1oldlens1 at ix.netcom.com WB6KBL
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