[BC] Frequency Measurements and 1000 Hz tone...

[Glen Kippel]

I don't try to assess a zero-beat using a speaker or headphones -- I hook
the detector output on my Hammarlund SP-600-JX17 to an oscilloscope and
adjust until there is no more "bounce."  A Krohn-Hite tuneable audio filter
allows me to eliminate most of the frequencies in the audio range.  Thus, I
can spot sub-audible heterodynes quite easily.  An old BC-221 serves as a
transfer oscillator and I can measure that with a counter.  I hadn't thought
of using the sidebands of a tone-modulated signal and assuming that the
carrier would be exactly in the middle, but then I don't usually run into
stations running tone modulation anymore.

On 3/21/07, Jim Tonne <tonne at comcast.net> wrote:
>
>
> Glen:
>
> > is the exact frequency of the modulation of no import?
>
> Not important; take the average of the two sidebands.
> 989 for lower sideband and 991 for upper and it
> would be easy to "compute" the carrier frequency.
>
> Also, Richard's comment earlier (coupla days ago or so)
> about using the transfer oscillator is right on.  When
> doing that you can hear the zero beat easily when
> a tone is used to modulate the rig.  More difficult under
> program conditions but doable.
>
> - JimT
>
>
>
> ----- Original Message -----
> From: "Glen Kippel" <glen.kippel at gmail.com>
> To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
> Sent: Wednesday, March 21, 2007 1:50 PM
> Subject: Re: [BC] Frequency Measurements and 1000 Hz tone...
>
>
> >I assume that the 1000-Hz tone does not have to be exactly 1000 Hz due to
> > the fact that a cart may not be running at the correct speed.  Also, if
> a
> > tone generator is being fed directly to air, wouldn't it would be
> > necessary
> > to use a frequency counter ensure that it is indeed running at exactly
> > 1000
> > Hz -- or is the exact frequency of the modulation of no import?
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