[ARC5] Zero Beat Question

[Richard Knoppow]

    I don't know what the current regulation is for medium wave 
broadcast stations, used to be +- 20Hz but I think most transmitters 
these days are very much closer. Since the regulations on quality of 
service now allows much stronger interfering fields its common to hear 
an effect similar to selective fading on many stations at night. The two 
carriers may be within some fraction of a Hz of each other. Very 
annoying.  BTW, the trade news complains that AM is almost dead but 
stations seem never to go off the air. Perhaps AM would be more popular 
if there was anything worth listening to on it (really the same for FM). 
Going to digital won't help if the programming stays the same. Junk in 
hi-fi is still junk.

On 7/11/2016 12:47 PM, Michael Bittner wrote:
> The BCB Dx folks refer to this phenomenon as Sub-Audible Heterodynes.
> Mike, W6MAB
>
>     ----- Original Message -----
>     *From:* D C _Mac_ Macdonald <mailto:k2gkk at hotmail.com>
>     *To:* WB6KBL Knoppow, Richard <mailto:1oldlens1 at ix.netcom.com> ;
>     ARC-5 Mail List <mailto:arc5 at mailman.qth.net>
>     *Sent:* Monday, July 11, 2016 10:45 AM
>     *Subject:* Re: [ARC5] Zero Beat Question
>
>     * *
>     *As others have noted, as two signals get closer and closer *
>     *to equal, you can hear an increasingly slower wah-wah-wah *
>     *sound. The slower that sound gets, the closer you are to *
>     *true zero beat. *
>     * *
>     *You can frequently hear this at night on an AM broadcast *
>     *radio when two fairly weak distant stations are within just *
>     *a very few Hz of **each other. *
>     * *
>     *It's a phenomenon with which we old farts and the primitive *
>     *gear which we used "way back then" are more familiar! *
>     * *
>     ** * * * * * * * * * *
>     * 73 - Mac, K2GKK/5 *
>     * (Since 30 Nov 53) *
>     * Oklahoma City, OK *
>     * USAF, Ret'd 61-81 *
>     ** FAA, Ret'd 94-10 *
>     * * * * * * * * * * *
>
>
>
>      *
>     *> To: arc5 at mailman.qth.net
>     > From: 1oldlens1 at ix.netcom.com
>     > Date: Sun, 10 Jul 2016 20:36:43 -0700
>     > Subject: Re: [ARC5] Zero Beat Question
>     >
>     > I have posted quite a bit on zero beating so this may be too much.
>     > I learned the "three oscillator method" from a General Radio
>     > instruction book for a heterodyne frequency meter which was part of a
>     > frequency standard. The idea was to beat the unknown signal with a
>     > known marker and use a BFO such as that in a communication
>     receiver or a
>     > regenerative detector set to just oscillate to give an audio beat
>     that
>     > would wax and wane as the unknown beat against the signal from the
>     > interpolation oscillator. It is possible to match two frequencies to
>     > within a few Hz per _minute_ if a meter is used to watch the relative
>     > strength of the beat. This can be used to set the calibration
>     oscillator
>     > in a communications receiver to WWV or some other high accuracy
>     > standard. The idea suggested by someone (should look it up) of using
>     > background noise is essentially the same thing, the noise taking the
>     > place of the third oscillator although it may be harder to hear. I
>     just
>     > tried this on a Collins 51J-3 and it works very well.
>     > There are probably other tricks.
>     >
>     > --
>     > Richard Knoppow
>     > 1oldlens1 at ix.netcom.com
>     > WB6KBL
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL