Free Counter


From: Mike Czuhajewski (
Date: Sun Jun 26 1994 - 17:08:52 EDT

I offered this on a semi-local distribution list on packet with no
takers--either no one wanted it or they didn't want to drive to
Severn to pick it up, so here's your chance--
Free (for shipping charges) to good home: Relatively old, sort of
heavy, rather clunky frequency counter with somewhat limited
resolution. (Not a pocket sized, 2 ounce LCD readout model with 17
digits.) Watkins-Johnson model DRO-309A--the DRO probably stands for
Digital Read Out, and is obviously a plug-in part of some larger
electronic system although it functions as a stand-alone counter as
well. (No charge since it was given to me free by someone when he
retired from the Coast Guard and went back to Alaska.)
Size is 8" wide, 3 1/4" high and about 16" long including knobs. Has
no cabinet--designed to slide into an open spot in the main unit,
whatever that was. It's heavy, solid and well built. Runs off
110/220 (selectable on rear). Has 4 ranges: 0.1 to 50 MHz, 30-300
MHz, 235-500 MHz, 490-1000 MHz. Inputs are through 3 BNC connectors
on the rear: DIRECT/0.1-50 MHZ, "VHF LOW (VHF/UHF)", and UHF LO.
Display is red LED dot matrix (6 digits); legend over the display
says "MEGAHERTZ". On the low range the decimal point is after the
first 2 digits, giving readout to 1/10 KHz. On the other 3 ranges
the decimal point is after the 3rd digit, giving readout to 1 KHz.
No good for matching crystals for a homebrew filter but could be used
as frequency display for a VFO, signal generator, etc.
No clues to date of manufacture, probably in the '70s. No idea what
sensitivity or maximum input level is. I tried it on some HF
frequencies on a signal generator and got stable readings with about
3000 microvolts output (0.003 volts RMS). On the other 3 ranges I
got stable readings with 10,000 uV, or 0.01 V RMS. I checked it up
to about 400 MHz, the limit of my generator and seemed to work OK.
(See "Quirks" section below.)
Other features--switch and output BNC for DAFC, whatever that is; has
a non-functioning tuning meter (indicator for main system?); round
connector for BCD output (no data on pinouts available); has
capability of display frequency preset--off, internal presets, or
external input; internal/external range control (lets you override
the front panel range switch with external control). I have no
documentation of any sort; W-J is still in business and may or may
not be willing to dig into their archives (perhaps at a large cost),
but basic frequency counter use is pretty straight forward. (I
haven't played with the feature, but if it still works you could use
the preset input to accommodate odd VFO frequencies.)
Quirks--sometimes displays random frequencies on one or more ranges
when there is nothing connected to the input, or even with a 50 ohm
termination, but connect the signal generator and it functions OK.
Also requires use of appropriate BNC input connector for the range
selected, or you can get other odd effects (and bogus readings) if
you don't have the "correct" one for the range.
If interested, reply by e-mail. First request gets it unless there
are several messages waiting for me when I log on, in which case the
person with the best "story" wins. (Estimated shipping charges well
under $10.)
        73 and Queue Our Pea DE WA8MCQ

Mike Czuhajewski, user of the UniBoard System @
The WB3FFV Amateur Radio BBS - Located in Baltimore, Maryland USA
Supporting the Amateur Radio Hobby, and TCP/IP InterNetworking

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