Jag laddade ner Bjarne Meldes 2-minuters wav-file som nu finns tillgänglig via en länk på "Perseus-groupen". Det var fantastiska signaler från Västra USA, Kanada och Alaska. Men det som jag mest blev intresserad av, är den hemska störningen som ligger över hela mellanvågen. Vad är det som låter så?
På samma gång är det intressant att få ta del av kommentarer från DX-are i USA som tydligen inte noterar detta, utan jublar över den extremt låga störningsnivån.
Visst är det märkligt?
Jag använder en ALA 100 placerad mitt i ett litet samhälle vid kusten utanför Stockholm. Den lösningen är helt fri från elstörningar. I mitt tycke extremt low-noise.
PS
Svaret på min fråga kom snabbt direkt från Bjarne och finns på Perseus-chatten, och jag tar mig friheten att kopiera in det direkt här eftersom det är utförligt och intressant:
"This post to sum up comments and questions regarding my recent upload to
box.net.
Anders queried about the background noise. I assume you're referring to the
"ticking" noise which is my local powerhouse, the Loran C. It is 250 kW, 14 km
away as the crow flies, and in the same direction as North America. The
frequency is 100 kHz. This is an extremely challenging adversary, if you excuse
the expression. In order to avoid overload to broadband receivers like the
Perseus (and many others), a 100 kHz notch filter is crucially important. Stefan
Wikander made one for me many years ago, and I've copied that design (and a
modified design by Dallas Lankford) for all my antenna feedlines.
To avoid excessive noise bleed, maintaining the rest of the equipment at a 100%
quality level is equally important and takes a lot of time. The recent
discussions about preamps and noise are examples of how important this issue is.
For me, one poor connection is detrimental.
Setup: The beverage was fed with RG-316 coax to a self-made antenna connector
made up of a cannibalised SE-6 switch box (an accessory to the Sherwood SE-3
sync detector). From the antenna selector to a Wellbrook 10 dB preamp w/ bypass,
then to a 1:8 Wellbrook splitter/13 dB preamp w/ bypass. Bypass is important.
During nights, often no preamps are engaged. During the lightest part of the
day, often both preamps are engaged. I don't remember the preamp settings at the
time of the recording, but at least one preamp was on to compensate for the loss
in the 1:8 splitter. Probably both.
Some of the Russian stations are quite strong, such as 657, 1134, 1449 and 1521.
These are "local" stations, located on the Kola peninsula. Other Russian
stations of potential interest are the VOA station on 810 (Kurkino) and one on
846 ID'ing as Radio Moscow Oblast. Location Electrostal?
Bjarne"
