Andy,
Quoting Andy Talbot <[email protected]>:
Firstly, bearing in mind there is no scope whatsoever to raise one end
of the capacity hat which is defined by the apex of the house roof,
and the other end would also need some major sugery to raise its heigh
substantially, that only leaves the middle, ie the height of the
actual radiator. It wouldn't be too difficult to raise this to 10m
or even more with a fibreglass pole, but will I be throwing away all
the advantage by having the top-hat drooping down to 7m?
Raising one end of the antenna should increase the radiation
resistance, even if the tophat is drooping.
G4CNN (SK) did extensive calculations on this matter, see
http://www.strobbe.eu/on7yd/136ant/#Umbrella
Secondly, pictures of other peoples antennas aften show a substantial
grounding plate immediately under and around the antenna base. Just
how far out is is worth going with a really substantial base. I
could cut more conductors into the ground; while the ground is still
is still soggy in March may be a good time to do this.
If found out that on 500kHz (ground) losses are much lower than on 136
or even 73kHz. On 136kHz I measured a loss resistance of 130-160 Ohm
(winter - summer), on 500kHz it is 35-60 Ohm. At these values I
reached a point where the loss is the loading coils (abt. 7 Ohm) is no
longer neglectable.
Another thing that might improve teh antenna is placing (a part of)
the loading coil at the top of the vertical part, see
http://www.strobbe.eu/on7yd/136ant/#CombTop
73, Rik ON7YD - OR7T
Any ideas please ...?
Andy G4JNT
www.g4jnt.com
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