ARLA/CLUSTER: Transmissões misteriosas em 7 e 10 MHz

[João Costa > CT1FBF]

 Rob G3XFD – mystery transmissions on 7 and 10MHz

>From Rob Mannion G3XFD Tuesday March 25th 2014.

I've placed my video on to YouTube in the hope that other Radio
Amateurs/listeners can help me identify the problems that this (very
recent) interference source is causing me here in Dorset.

When I first heard the transmissions - I thought I had a problem with
my Elecraft K3 transceiver. However, transmitting into a dummy load
and other testing – with the help of Phil Ciotti G3XBZ - who assembled
my rig and has one himself – at his QTH, proved there was no problem
from my station. Additionally, he couldn't see or hear anything
similar at his home about three miles away.

When the offending transmissions first appeared (I was using c.w. on
7.020MHz at around the 10W level) the main offending transmission was
about 600Hz below my own transmission) I thought someone might be
causing interference or there were 'round the world echoes' of my
transmissions (a weird but fascinating event that usually occurs on
14, 18, 21MHz, etc., in good propagation conditions). I was able to
use the excellent Elecraft P3 pan adapter to 'see' the problem.
Without the spectrum display unit I would't have 'seen' what was
really happening.

I soon realised that the offending transmitter was automatic and was
left switched on over a 24 hour period – I proved this with several
3am visits to the shack!). The higher the power radiated from my
antenna system, the stronger the transmissions seem to be on my P3 pan
adapter and they also are transmitted for a longer period (30 minutes
plus).

Another friend of mine who lives about five miles away has reported
something similar on the spectrum 'scope screen on his Icom IC-756PRO.

http://www.youtube.com/embed/-bgcuTzfKL0?rel=0

My home in Bournemouth on the south west coast of England is
surrounded on three sides by large houses converted in flats although
(fortunately we are screened from them by tall trees) with many
switched mode power supplies and 'internet over the mains' type units.
My dipole antenna (mounted on a mast with a total height of 35ft. One
leg of the dipole runs above our driveway and there are a large number
of overhead telephone wires.

I've briefly seen the interfering transmitter operating on the 3.5MHz
(80m band) but it's really strong on 7 (from 7 to 7.199MHz) and 10MHz
(again over the whole band) . Incidentally, it doesn't actually
transmit data (or whatever it's transmitting) continually but 'sits
there' (somewhere) waiting to operate.

I would be most interested to hear from other Radio Amateurs who have
identified similar transmissions. However, without a spectrum graphic
display you would just think it was another one of those 'mystery'
signals that appear to annoy us....but this one is different!  I hope
you can help identify the source!

Regards to everyone,

Rob G3XFD