[IRCA] Perseus captures from 1991

[Mark Connelly <markwa1ion@xxxxxxx>]

I finally got around to going through a box of VHS videotapes from the 
late '80s / early '90s spectrum capture experiments, as originally 
developed by Craig Healy (NG1U), and mentioned in this article:
http://chowdanet.com/markc/webpage/WA1ION/vcrdx.pdf

There were about 6 tapes in the box.  Two of these, when played into a 
receiver, had reasonable performance.

One of these was the tape Craig had originally supplied me.  This was 
made at his QTH near Providence, RI.  The whole AM band is captured.  
Sensitivity on the lower half was quite low so it's primarily the local 
stations such as 630, 790, and 920.  Some skip signals can be heard on 
the upper half of the dial.  I still have to review the tape to 
determine the exact date and times of recording.  Items on a news / 
sports station, possibly with some Google follow-up, will nail down the 
date.  At some point in the recording there should be a time check on 
one station or another.  I looked into the lower shortwave spectrum but 
noted little in the way of "real" (non-birdie) signals, so no CHU or 
WWV assistance on the time.

The second tape was one I made at Billerica, MA in April 1991 during 
the "wee hours" of the morning: 0643-1043 UTC.  Because 50 kW WRKO on 
680 is only 2.8 miles / 4.5 km from the receiving site, a notch filter 
for 680 was inserted ahead of the VCR input.  Usable sensitivity for 
the capture came in starting around 800 kHz and up.

One thing that must be kept in mind is that this primitive version of 
spectrum capture had a rather small dynamic range: only about 30 to 40 
dB from a hashy noise floor up to the level of a strong local on the 
verge of causing distortion and spurs.  The tapes, obviously, are not 
going to produce much in the way of weaker signal DX.

Before the tapes have a chance to deteriorate, I'm porting at least 
some of the contents over to Perseus files.  This also gives a ready 
method for sharing the experiment results with others.  I reset the 
computer date/time so that the Perseus time-stamping is relatively 
close to the occurrence of the original recordings.

After I get all this stuff digitized, I'll go over it for any 
interesting audio clips.

Though the "VCR DX" method became known to the MW DX world about a 
quarter century ago, it is widely believed that, as far back as the JFK 
administration, "spook" agencies such as the NSA were able to store 
substantial RF bandwidths for later review.  Broadcast studio grade 
videotape, or something similar but custom-designed, was used.  
Converters allowed any chunk of spectrum to be heterodyned to the 
baseband range (0-3 MHz?) the tapes could accommodate.  The late Gordon 
Nelson (WA1UXQ) seemed aware of it.  Maybe some tapes will show up at a 
Fort Meade, MD fleamarket / yard sale so we can tune around and hear 
stuff like Belize 834 and Bermuda 1235 once again, as well as 
Murray-the-K on WINS proclaiming his status as the Fifth Beatle.

Mark Connelly, WA1ION
South Yarmouth, MA

 

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