Mike is 200% right, just look at the meaning of ERP :
Effective Radiated Power
regarding Mals question : Why do the 'commercials' on LF use giant antennas ?
1. Because they want a certain ERP (let's say 100kW) and in that range of
ERP it is cheaper to have a big antenna (at 50% efficiency) fed with 200kW
than a small antenna (at 1% efficiency) fed with 10MW.
2. Very high power into a small antenna will create additional problems (as
extreme voltage) that can be avoided with big antennas
But we hams live in a different world with our 1 Watt ERP restriction,
apart from legal limitations (building restrictions) a 30 or 40m tower will
be more expensive than a 2kW PA. So it often will be cheaper and easier to
get 1 Watt ERP with a smaller antenna and more power.
73, Rik ON7YD
At 12:35 3/01/01 -0000, G3XDV wrote:
G3KEV wrote:
So you are saying that 1W
erp from a dummy load radiates just as efficiently as 1W from a 200
ft vertical for instance.
and DK8KW retorted:
... no, surely not!
But of course the statement is true. 1W ERP from a dummy load
inside a Faraday screeen inside lead-lined container will also
radiate as well as 1W ERP from a full sized dipole. The key word is
Radiated (the R in ERP). You will need an awful lot of megawatts
(gigawatts?) to get 1W ERP from such a dummy load but once that
watt is radiated there is no difference.
Mike, G3XDV (IO91VT)
http://www.lf.thersgb.net
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