[Elecraft] Frequency counters for Alignment

[Ron D'Eau Claire]

Hi, David:

The best way to calibrate a frequency counter is to set its time base
oscillator accurately. WWV is a great reference for doing that.
Unfortunately, the Heath IM-2410 uses a 3.58 MHz time base so a harmonic of
the time base won't hit a WWV frequency exactly (those crystals are cheap
and plentiful for NTSC Color TV sets).  

If one of your counters uses a time base that multiplies to a WWV frequency,
all you need do is tune in WWV using a hunk of wire stuck in your receiver's
antenna socket (10 MHz is usually good daytimes all over the USA, and 5 MHz
is good in most areas at night). You should hear signals coming from the
counter's time base near 10 MHz. Move the wire around and they'll change in
strength. Find a position that gives you a good, strong beat note. 

The divider chain in the counter's time base produces a wide spectrum of
frequencies. You might find one that hits WWV's frequency by placing the
antenna wire near the counter. 

An ordinary AM receiver is ideal for this, but if you're stuck using a
modern CW/SSB receiver (like the K2) carefully adjust it for no beat note to
avoid confusion. That is, put the BFO zero beat with the carrier frequency
just as you'd do or SSB. You should hear the tones and voice announcements
clearly. 

Adjust the trimmer cap on the time base of your counter and you'll hear the
beat frequency between a harmonic of the time base and WWV's carrier change.
Carefully adjust the trimmer for zero beat. As you get close, you'll hear a
slow 'whoosh-whoosh-whoosh" as the two frequencies get within a fee HZ of
each other. When that whoosh slows to a stop, you're zero beat. 

Now your counter will be dead on at any frequency within it's range, no
matter what frequency. The beauty of the counter design is that its just a
digital counter. There's no "range tracking" or other adjustments to make
once the time base is exactly on.

The other approach is to use a signal generator with enough output to drive
your counter. If it's not perfectly calibrated, you can set it to 5 or 10
MHz and zero beat it with WWV, then note the frequency on your counter. If
it's off, adjust the time base oscillator trimmer capacitor (C26 on the
IM-2410) so the display reads exactly 10.000 (to however many digits it has)
MHz. 

Ron AC7AC


 
-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of David Wilburn
Sent: Thursday, March 01, 2007 4:20 PM
To: Elecraft Discussion List
Subject: [Elecraft] Frequency counters for Alignment


I have a couple of frequency counters, and I know they are a little off. 
  When I went through the alignment the first time, they tell you how to 
adjust settings based on zero beating from another transceiver, but I 
wanted to calibrate one of these counters well enough to use one of them.

I have a XG2 that I haven't built yet, and I see that it has a +/- 1khz 
accuracy.  I was thinking of using that to at least get the counter (a 
Heathkit IM-2410) close enough so I don't have to use the other 
transceiver.  The XG2 will work ok for this won't it?
-- 

David Wilburn
dave.wilburn at verizon.net
K4DGW
K2 #5982
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