I read recently, maybe on this forum, that 32 ft radials were "long enough" if
thats all you could get.....I thought they needed to be longer as well, mine
for my inv L are 132 ft long, but "bent" to keep them in my lot size.....when
we were talking about the feedpoint impedance of my L, thats when someone
suggested that more radials 32 ft long, would be better than fewer radials that
were longer....
Mike, get rid of the 15' cable, try to measure the impedance with as short a
piece of coax as possible, as close to the feedpoint as possible.....thats what
got me recently...ideal impedance will be mid to upper 30 ohms....I think
theoretical is 32 ohms or so, add a few ohms for the ground.....the more
radials you add, the lower it will get....
----- Original Message -----
From: "Mike Smith VE9AA" <ve9aa@nbnet.nb.ca>
To: topband@contesting.com
Sent: Wednesday, January 16, 2019 7:32:09 PM
Subject: Re: Topband: Inverted L improvements - Part 3
Hi Todd and thanks for answering so quickly.
I am no expert. (I'm an Electronics Engineering Technologist and a ham for
40+ yrs,fwiw)
I won't debate the exact numbers on that table by K3LC referenced by K9YC,
(they are experts) but I will tell
you that it makes me go "hmmm" (as in a mild doubting tone)
A 42' radial on 160m is only something like 1/12th of a wavelength long.
(pretty short)
AM Broadcasters talk about the point of diminishing returns for on-ground
radials being
around 120 (or is it 240?) for full sized 1/4wl radials. That would be the
equivalent of ~15,240feet on 160m.
You've laid out aprox 1260feet of wire (give or take).so aprox 1/12th or
.08% of optimum.
It's just not a lot of wire for a 160m antenna. I have 2x 160m antennas
here. One with about 7500' of wire on/in the ground and another with 2
raised radials (tuned, raised, 1/4wl each) and I can tell you the one with
7500' of wire under it always works better in true A/B comparisons. Not by a
lot, but it's noticeable.
I can't imagine you're anywhere' s near optimum.
I know "tone" doesn't come across in emails and postings, so I am not saying
this all in a sarcastic or snarky tone. Just as a "matter of fact" type
tone.
With what you've described, it's probably as good as you'll get if you have
a typical small city lot and average soil. You could play around with
chicken wire, tying your pool and well casing, fence, metal garden shed and
neighbours dog-run ,in to give you just as much conductive material under
the antenna as humanly possible or you can accept the limitations of a small
lot.
Personally, I don't give up easy..if it were me, I'd buy another couple
thousand feet of wire and put it down.
Something is just not right.
I'll let the *REAL* experts chime in, but my experience (such as it is),
tells me you're warming the ground or there's something else going on we
aren't yet aware of. (ginormous metal bldg. next door, hi).
GL with it Todd. I hope there is an epiphany~!
truly.
Mike VE9AA
Hi Mike,
Yes, it is a space issue. The presentation I was referring to is
http://audiosystemsgroup.com/160MPacificon.pdf where it has a table the
references a paper by K3LC that has "Optimum Use of Wire On/In Ground Over
Average Soil" and it lists 12 radials at 42' each to essentially use a 500'
spool of wire. I had more wire than that but not much more room. I could
run out a few wires in few directions to about 100' if that might help. I
did use the antenna for a couple of evenings with only 12 radials and
yesterday I tacked on the additional 18.
That is why that decision was made.
I didn't think that SWR curve was good at all. But another guy just emailed
me and said that the BCB filter is probably messing up those readings and
they aren't accurate. I can take SWR readings from my radio (in the shack)
with the filter not in line. Maybe that will show different values but it
will be attached to a 150' long piece of coax after the choke.
73,
Todd - NR7RR
Mike, Coreen & Corey
Keswick Ridge, NB
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