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Identify That Noise!
Have you ever tuned over a band and
found one of those noises you just can't figure out what it is or where
it comes from? Well if you are a 4m, 70MHz operator then you most likely
get this more than most amateurs because as the band has traditionally
been UK only with other countries joining late in the 80's onwards, the
band has never enjoyed the 'protection' (I use that expression
cautiously) that other amateur bands receive.
 Now, nearly a decade into the 21st
century EU countries are joining 4m like it was a members' discount
store. I am not complaining, it's more in the log for me. But with this
new found popularity comes the negative issue of EMC. Sheer numbers of
amateurs in the past have ensured a fairly quick response to complaints
of QRM/N on the bands however, 4m has not enjoyed the same attention and
the result is a band which is often filled with birdies and sweepers
like no other amateur band known to mankind. From digital timers to
water treatment devices and just about anything else you can think of
have had their emissions pushed out of 6m and VHF broadcast and found
their way into 4m where they have attained a life of their own, rather
like an unattended pond. . .
Well guys, it's time to change all
that. With 4m finally making it as a footnote to the ECA (European
Frequency Allocation Table) we have some form of recognition for the
band and with it, a small degree of control over the interference we
suffer. I say small, as 4m is for most of the countries which have a
formal allocation, still allocated on a Secondary basis, i.e. on a
non-interference basis. Now that 4m is in the ECA, it is only a matter
of time before the amateur community will begin to see the band become a
Primary, but more work is needed in this area.
So now let's move on to the purpose
of this page, to
identify
that noise! In the
table below will be placed links to recorded interference, along with
(if possible) screenshots of FFT of the relevant bandwidth. Don't worry
if you have not recorded audio from your radio before or taken
screen-grabs, I have provided another page devoted purely to the topics
of grabbing audio and screenshots for the uninitiated.
This part of the site is for YOU!
For US! For EVERYONE who uses 4m. I want to know:-
- What it sounds like; preferably
taken in USB but if better resolution is possible in another mode
then use that.
- What it looks like. Take a
screenshot preferably from Spectran (link) with the bandwidth set to
show the whole signal.
- What frequency it is on. Is it
static (stationary)? Does it sweep? If so approximate DF/DT
- What direction, strength and
propagation mode? Es, Tr, neighbourhood QRM?
- Did you find a cure for it if it
was local?
- Can you identify (with 100%
certainty) what someone else's noise is and whether there's a cure.
I aim to put together a definitive
database of 4m interference in the hope that between us we can help
someone overcome what could seemingly be an insurmountable problem,
thereby giving them back access to the band. I know far too many people
who have quit 4m because they gave up on the band due to the
interference. We have a chance to improve someone's life here so let's
do what we amateurs do best - HELP! ;o) | 
WAB: ST64
