Zero beat

[Dick KF4NS]

Ok guys, I am going to show my ignorance here. I understand the theory 
of which you speak but the "V" thingy is leaving me blank. Exactly 
what is this representation?

73, Dick KF4NS
St Petersburg, FL 33714 USA
Keep The Glow!



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Date:    Wed, 14 Nov 2007 07:56:53 -0800
From:    "Kenneth G. Gordon" <kgordon2006 at VERIZON.NET>
Subject: Re: Zero beat

On 13 Nov 2007 at 23:51, Tom Buchanan wrote:

> I have a Heathkit SB-101 and can't zero beat it with the calibration
> crystal.  The crystal is oscillating.  If I understand it correctly,
> the audible signal should be a "V" with the zero beat at the bottom,
> but it is more like a " / ".

The "V" occurs if the IF filters are either not working
properly, the receiver is simply so broad it essentially has no
filters, or if the BFO is set to the CENTER of the passband
of the filter.

There is a pictorial in your manual which shows where the
BFO frequencies should be in relation to the filter passband.

In a receiver with a properly working crystal or mechanical
filter, AND with the BFO properly offset to one side or the
other of the filter, you will hear only ONE SIDE of the "V", or
the "/", if you like.

In the old days, we used to call this "single-signal
reception".

>  I have a Heathkit HW-100 and it
> definitely has the "V" signal pattern when I use the 100 KHz
> calibration to zero the dial.

If that is the case, that is, if you are hearing BOTH sides of
the 100 Khz calibrator signal at equal volume, then the HW-
100 is the one that is not working properly.

What is most likely wrong with it, is that the BFO crystal(s)
have drifted into the center of the passband of the filter, OR
the filter crystals have drifted high or low so that essentially
the same thing has occurred: i.e., the BFO frequency is no
longer on the edge of the filter, but somewhere closer to
center.

Since there are two BFO crystals in any HW/SB
transceiver, the first question you must answer is does this
"V" occur on both USB/CW and LSB or only on one or the
other?

In any case, the SB-101 is working properly. The HW-100 is
not.

I might add that if the HW-100 is acting as you describe,
your opposite sideband suppression, both for receiving and
transmitting, will be essentially non-existent, which is not a
good thing.

Ken Gordon W7EKB

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