In message , David Looser
writes
"Ian Bell" wrote in message
...
tony sayer wrote:
In , Brian Gaff
scribeth thus
Its probably being killed by signals from all over europe and it will
get
back to normal when the high pressure puts things back to normal.
Brian
Theres always FM
...
There's no Radio 7 on FM, more's the pity.
If there was a problem with "signals from all over europe" it'd affect FM
far more than it would DAB.
And Radio 7 is on the internet and on Freesat.
There are two 'modes' which are responsible for long-distance
propagation on VHF and UHF.
One is Sporadic-E propagation. The E-layer is the lowest of the
reflecting layers in the ionosphere (about 100 miles up), and is
activated by sunspot activity. Compared with the other layers, it is
very spasmodic and transient, and mainly occurs in daytime in late
spring and early summer. [It's a bit late in the year for significant
Sporadic-E]. It affects essentially only in the range 25 to 150MHz, and
can enable the reception of very strong Band 2 FM radio signals from
distances of up to 1000 miles. It doesn't affect Band 3 (DAB) or UHF TV.
The other mode is tropospheric ducting, which is occurs when the
temperature gradient in the atmosphere becomes inverted. The radio waves
get trapped in a duct, which is typically only 5 or 10 miles up, and get
bent around the curvature of the Earth, landing typically 500 to 1000
miles away. This happens mainly in calm, fine weather, when there is a
large, stable area of high pressure sitting stationary (particularly
over a warm sea). This is what we have at the moment. It can affect Band
3, but it is most prominent at UHF.
--
Ian
DAB signal in North Norfolk
Hybrid Mode
