From: udxf@yahoogroups.com on behalf of Jan Olof Bergstén (sm7etw@gmail.com)
Sent: Tue 8/03/10 3:22 PM
To: UDXF@yahoogroups.com
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HI
These are Ionosonds
Most sweep from 2 MHz to 30 MHz with 100 KHz/s, some with 125 KHz/s and a
few with 500 KHz/s.
They often mute on the emergency channels, and frequencies used at nearby rx
sites.
Some make a sweep every 15 minutes, a few every 5 minutes, and also other
periods.
There are window programs availible to receive them and make your own
Ionograms, or to just identify them.
You can identify them if you note the frequency and time (to the nearest
second) as most start at fixed times.
I have an homebuilt sweep receiver that is locked onto the transmitters and
makes high quality Ionograms.
There is a special list for those interested in receiving this kind of
transmissions (moderator G3PLX).
More information at
http://jcoppens.com/radio/prop/g3plx/index.en.php 73 Jan SM7ETW
On Tue, Aug 3, 2010 at 8:51 PM, vbifyz <3ym3ym@gmail.com> wrote:
> I'm sure everybody here heard these annoying "chirps" many times, like
> somebody quickly turns the dial of the transmitter.
> When looking at them on a 192kHz SDR watefall, I can tell that these are
> really very wide sweeps. They happen once every few minutes on any band
> between 4 and 18 MHz. I think broadcast bands are excluded, I don't remember
> hearing quick short heterodynes when listening to SW broadcast stations. The
> sweep rate is about 200kHz/sec (the whole bandwidth of my SDR is sweeped in
> about 1s, maybe faster). The direction is always up.