I would shoot for 60 1/4 wl on the ground (like W3LPL says). This will
be "very close to" optimum and the losses in the near field will be well
below 1 dB. Anything less is going to be "dB down".
Measuring SWR or Z or bandwidth is not a way at all to measure how
efficient the antenna is. The only way to find out is to measure the
radiated field strength.
Good reading is what N6LF writes, http://www.antennasbyn6lf.com/
Also what K2AV writes on this reflector is good reading.
I can tell you a true story, this is no science and no measurements
was done to confirm anything. When I first got on 160 back in the
1980´ties I did put up a 110ft top loaded radiator. Then I started
to put out radials....I put out 10...went inside and made QSO´s and
got 559 569 reports most of the time....went outside and put out
some more...in to the shack and made QSO´s...etc etc etc. It was
not until I came up to 70-80 radials I started to get 599 reports
and started to "get a feel" that the antenna was kicking. At that
point I was only using 100W but power level is not important in
Now after this I went all silly and crazy and nuts, I did put out
even more radials and didn´t stop until I had 250 radials, then I
was very tired. This was over 20 years ago and during this time
I have had a number of different vertical radiators above this ground
screen and everything seems to radiate very well. Now I´m old and
even more tired and do not have the same interest so I would not
do it again (I think!), but you never know when you go nuts.
On 2010-11-04 16:22, Brendan Minish wrote:
> Under my 1/4 wave Inverted L (~18M vertical section) I have a mix of
> buried radials and radials lying on the grass (for the winter months
> In total there are around 20 radials with lengths of between 1/8 and 1/4
> wavelength long.
> the ground here is very good, in the winter the field is saturated
> nearly all the time and the system seems to play well.
> The far field ground is the same type of soil and the Irish weather
> keeps it well saturated all winter..
> With all the radials out the feed point impedance at resonance is around
> 25 Ohms but it's hard to say how much of this is due to the proximity to
> the tower and other antennas.
> I have the opportunity to roll out a couple of rolls of chicken wire on
> top of the radials, however there is significant work involved and I'll
> have to get it back up again in the string. Am I likely to be able to
> improve things further or would my efforts be better spent getting more
> radials out ?
> Any suggestions on how to make some quantifiable measurements as I
> change things?
UR RST IS ... ... ..9 QSB QSB - hw? BK