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ANTENTOP- 01- 2007, # 009

Long Delay Echoes

 

Because our transmitters were located a couple of miles away, we ran the receivers at full RF gain all of the time.  There was NO muting!  All four receivers were wired to a speaker panel.  That meant any signal heard would be heard throughout the building.  Twice each hour, on the hour and on the half hour, one of us (there were usually only two on duty) would actually sit down at the receivers for "close monitor."  For that, we switched the speakers to a panel down near the desktop, and we would sit for two minutes and monitor.  At all other times, the operator was away from the position and doing other things, so he had to be able to hear the R388s above all the Teletype noise in the building - and we had a LOT of such noise!  Motors for printers and machines, plus air conditioning, fans, and the like.  So the receivers were very loud.

When our transmitters keyed, the AGC action of the receivers served to mute them, as we kept the AGC slow.  The first "beep" of the CW shut down the AGC, which prevented any full breakin.  There was no other muting.  Just pretty much receiver overload!

Now the scene is set.  It is not close monitor time, and I, with my partner, am doing other work in the RTTY section.  We grow accustomed to hearing the receivers go dead as our own transmitters overload them.  Then the background noise returns. 

Suddenly we hear:  VV DE AAA123 AAA123 AAA123 VVV   Then it's gone.  It lasted perhaps five or six seconds.  It did not fade in, it did not fade out.  It "turned on' and then it "turned off."  It was our keying.  At our speed, and automatic.  It was strong, but nowhere near strong enough to kick the AGC and overload the receivers.  It was not strong enough to even "thump" them.  It was simply a fairly strong CW signal. 

For an instant I thought it was someone calling us.  Since that did not happen unless there was a problem, I moved quickly to the console.  I stopped our automatic keying and I listened.  No one on any of the frequencies.  I sent "QRZ DE AAA123 K" with the hand key.  Got no response.  I tried that maybe three times.  No one was out there.  Of course I was keying all four transmitters simultaneously, so no matter what frequency he had called in on, I would hear him. 

Then it dawned on me!  I had heard "DE AAA123!"  He had been identifying as my station!  Not AAA123 DE AAB321, for example.  It was "DE ME!" 

 

By sheer luck, we had been running a slow speed monitor tape on another receiver in a different rack.  That was a rack with two  Collins 51S1 receivers,  that we used to monitor other things, but it had been set up to monitor a couple of frequencies, and I had, earlier in the afternoon, set one of those two receivers on one of our guard frequencies.  The other was on some other frequency. 

What if, I thought, the echo had been on that particular guard channel?  I had no way of knowing which of the console receivers had picked up the signal but it was early evening, and we had been about to close down the 13 mhz guard, as it was no good for us at night, so it wasn't likely it would be there.  I could be on our 4, 6 or 10 mhz frequencies, and there was no way of knowing.  But the 51S1 was on the 6 meg guard frequency.  What if! 

I ran the tape back.  Yes, indeedy, it had been on the 6 mhz guard frequency.  And I had a tape of it.  Not only that, because because the four channel recorder used one of its channels to permanently monitor a highly accurate 1 KHZ oscillator, I could now tell precisely what time the signal had been recorded, using our test gear designed for that purpose. 

All that told me nothing.  Except it was not one of our field stations.  It was not our own transmitter being keyed by our keyer.  It was a received signal, and in ham language would have been RST589.  We gave it a QRK5, QSA5.  The only thing I knew for sure about it now was it had been on our 6 MHZ frequency, not on the four or 10 mhz one. 

I made a copy of that segment of the tape, as it was something we wanted our technical staff to analyze for us.  They did, and learned nothing more.  I kept the tape for a few years but finally erased it. 

Shortly after the actual occurance, (perhaps a few months) which neither my coworker or I understood at the time, I happened across a story on LDEs.  And then we knew what we had heard.  Again I played the tape several times, but garnered no information from it. 

Except one thing.  The "echo" had begun 16 seconds after the end of our transmission.  But it had not begun at the beginning.  It had not echo'ed our entire transmission, only a few seconds of it. 

All this took place outside the USA

 

 

 

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