[Hallicrafters] Calibrating that old BA receiver

[Philip Atchley]

Hello all
Well, today I dug out my homebrewed "Boatanchor Calibration Aide" and
mounted it back under the shelf over my listening table (over the
Hallicrafters SX-71).  It's been stored on the parts shelf  for a year or
more.  This is a handly little crystal controlled marker generator that
generates known marker frequencies every 10, 5, 2 and 1 MHz and 200, 100, 50
& 25kHz (switch selectable marker frequency).  The timebase is a cheap TTL
computer clock running 20MHz.  Not precise but within 200Hz at 15MHz, close
enough for the task at hand.

This is connected to one of the antenna positions on my antenna switch and
has an adjustable attenuator.  This allows me to do very accurate frequency
tuning on nearly any BA receiver.  25kHz steps and I can usually easily
interpolate 10kHz (and sometimes 5 depending on the receiver bandspread)
even at 21.5 MHz.  Try that on your "average" BA receiver with no
calibrator!

I then made up logging scale (0 to 100) calibrations of the bandspread dial
of the SX-71 for the 41, 31, 25, 19 and 16 meter bands.  I'll catch the
other bands later.  This way I can set the bandspread tuning for a known
even frequency at either 0 or 100 on the bandspread dial and then easily
tune to any frequency in that band.  Example:  For the 31M band, I calibrate
for 10MHz (WWV) at a bandspread setting of 100.  If I want HCJB on 9745kHz
it is just a hair below 66.5 on the bandspread dial (which is 9750).  In
this case it's actually 66 even on the dial.     If I'm looking for RNZI on
17675, using the BA Calibrator I calibrate for 18.0MHz at 100 on the logging
scale then tune to 52.2 on the same scale.  Voila! There's RNZI.  Almost as
easy and accurate as your modern Whiz bang digital rigs, AND a whole LOT
more class.

If you use BA's a lot you might consider building one.  It only takes a
cheap ttl clock and some cheap divider chips and some way to switch them.  I
went the elegant way and use 4066 analog fet switches controlled by a cheap
10 position Radio Shack switch.  This was all stuffed in a salvaged "two
compartment" shielded box with the attenuator (potentiometer) and switch in
a compartment separate from the digital stuff.  This kept bleedthrough of
unwanted markers to a minimum.

Something like the above is almost a necessity if you intend to do any
serious DXing with the average BA.

73 de Phil  KO6BB
Loving home provided for wayward Boatanchor Receivers
k06bb at elite.net
Merced, Central California
37.18N  120.29W  CM97sh



---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.351 / Virus Database: 197 - Release Date: 4/19/02