On 05/12/2015 03:40, wrote:
In rec.radio.amateur.antenna Spike wrote:
On 03/12/2015 12:45, Brian Howie wrote:

By coincidence my morning training run took me near the EDN NDB

http://www.b-howie.demon.co.uk/lfbcon.htm

It's a top loaded vertical, but looking over the fence, I could see a
lot green earth wire radials on the surface. It's possible there are
buried ones too , but there are only about 6 and they can't be more than
15ft long,

For the beacon to be of maximum use, they'll need a good sky-wave
signal; it sounds like the visible radials are there to provide a DC
path to earth probably in association with a ground spike, rather than
for getting the main lobe lowered.

Sky wave propagation doesn't happen at those frequencies for all practical
purposes.

That's amazing. So all those aircraft at 35000 feet in its service area
can't hear the beacon? If it didn't have sky wave, it would merely be a
ground-wave beacon, not much use as there aren't that many airports
within 35 miles of Edinburgh, and the aircraft captains would know where
they were anyway.

Sky wave propagation was discovered when amateurs started using frequencies
greater than 200 meters.

What's interesting here is now much of the radiated power goes
sky-wards, and how much goes into surface wave. But apparently no-one's
ever thought to determine this, so it'll remain a mystery.


--
Spike

"Crime butchers innocence to secure a throne, and innocence struggles
with all its might against the attempts of crime"

- Maximilien Robespierre