[ARC5] Zero Beat Question

[Richard Knoppow]

     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