A little story about false decodes

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OZ7IT
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Joined: 2010/05/27 - 13:38
A little story about false decodes

When I see a 4 letter grid, a strange call or an odd power decoded, I normally check qrz.com for the call.
Next I check if the grid is on land somewhere and not in some ocean.
Then I check if I was the only one who decoded.
False decodes are normally seen on the map with only 1 line to me = I was the only one decoding.

No rule without an exception!

Once in a while I check my good swedish friend SM6WZI, to see how he is wspr'ing.
February 24/25 I saw a strange call from the South Atlantic Ocean. But but but - the map showed spotting by SM6WZI and me, i.e. 2 lines on the map. That I found very strange.
Here is the 24/2:
database:
02-24 23:24 1K4XST 1.838183 -26 0 ID94 5 OZ7IT JO65df 12374 8
02-24 23:24 1K4XST 1.838181 -25 0 ID94 5 SM6WZI JO67mp 12647 8
my main text window:
2324 3 -1.0 1.838071 0 G3ZJG IO92 37 *
2324 -9 -1.1 1.838108 0 ON7KO JO21 37 *
2324 -10 -2.1 1.838137 0 G4BOO IO91 37
2324 -5 -1.0 1.838146 0 DD5KD JO31 37
2324 -26 -1.0 1.838183 0 1K4XST ID94 37

OK - that was strange, maybe a real call ? hmmmm !

A little later another call decoded from same grid and same power!!!:
database:
02-25 00:04 1I8TTO 1.838058 -19 0 ID94 5 OZ7IT JO65df 12374 8
02-25 00:04 1I8TTO 1.838156 -22 0 ID94 5 SM6WZI JO67mp 12647 8
my main text window:
0004 -8 -0.8 1.838021 0 DF2JP JO31 37
0004 -25 -1.0 1.838037 0 <...> ZBZ3VP 63
0004 -19 -1.0 1.838058 0 1I8TTO ID94 37
0004 0 -0.9 1.838071 0 G3ZJG IO92 37 *
0004 -6 -1.1 1.838109 0 ON7KO JO21 37 *
0004 -19 -0.9 1.838124 0 <...> TPL2WC 63
0004 -24 -0.9 1.838159 0 1I8TTO ID94 37

Spooked ? I think it was intermodulation from the 2 relatively strong stations G3ZJG and ON7KO that produced the false decodes. They both transmitted in the 2 timeslots shown.
Maybe more signals are involved. The decoded calls are different, but the grid and the power are the same. The difference could also be a result of a tiny time difference between G3ZJG and ON7KO from 23:24 to 00:04.
Interesting I find, that we were 2 stations 270 km apart with different type of stations (FT-817 and Tentec OMNI VII),that got the same decodes. I am quite sure, that the signals are produced in the receivers mixer (first or second).

Vy 73 de OZ7IT, Jorgen