Bob,
The reference to Dick Weber's article in the last email is the first time I
have heard of shortened radials supposedly being better than full quarter
wave. Seems worth exploring. My vertical is a full quarterwave tall, but
yours won't be too much shorter. Perhaps you can put some top loading on it.
How tall is your tower? Is there a yagi on top? That might be useable as
a folded monopole feed and the radials can still be elevated. Start them
at ground level and bring them up in a Vee to ten or 15 feet high. Then
they would be out of the way for mowing and walking around.
Soil conductivity has a lot to do with performance of radials and how high
they should be. I don't claim to be any sort of an expert. I just try
things, measure them as best I can and hope for the best. Your elevation
and surrounding terrain will affect the performance more than anything else.
73,
Dave, K4TO
On Sat, Aug 29, 2020 at 9:20 PM Robert Harmon <k6uj@pacbell.net> wrote:
> Dave and Grant,
>
> Interesting discussion. I am thinking about stringing up a 160 vertical
> hanging off the side of the tower and am thinking about 4 elevated
> radials. I don't have the real estate to accomodate full length radials so
> they ends will be angled off to the side at about 70 % of their length.
> Will look like a german swastika hihi. I was wondering how to tune the
> radials so hope to pick up some tidbits on how to do it from this
> discussion. Dave, how high is your vertical section ? I can't achieve a
> full 130 feet quarter wave on 160, will have to settle for 115 feet and use
> a loading coil. I am thinking for the radials to be 10 feet high. I read
> that 4 elevated radials are as good as a lot of radials on the ground.
>
> Bob
> K6UJ
>
>
>
> > On Aug 29, 2020, at 5:08 PM, Grant Saviers <grants2@pacbell.net> wrote:
> >
> > Dave,
> >
> > I went thru this with my 160m elevated T, measuring current in each
> radial. With my MFJ RF current meter calibrated on several ranges I found
> the 125ft 10ft up radial currents varied about 5 to 1. None at zero
> though, which would be my first investigation also. The vertical is a #13
> Davis so easy to measure amps and the radial currents summed to very close
> to the vertical current. My radials are 12.5ga Al electric fence wire.
> Your radial currents sum to 46.1 vs the 41 you expected, maybe close enough.
> >
> > I have some R65 still on the ground, prior use AM BCB and the bottom 2x
> 10ft are welded on full coverage steel sheets, and welded together flanges.
> I thought the sheets were there as anti-climb, but perhaps more as
> conductors. I was told welding flanges was common BCB practice, I would
> assume mostly on high current sections.
> >
> > At your low power errors might be significant, IIRC I was using about
> 50w, not much of a concern at 1.8MHz. Your presence might be significant.
> >
> > In my case radial proximity to a steel building, ending near a tower,
> routed thru numerous trees and a couple in the open is why I think the
> currents are different (highest to the tower, then nearest the building).
> Exactly how I would equalize the currents is unknown to me.
> >
> > There is some "expert" wisdom that fairly strongly advises making radial
> currents equal, although I haven't seen analysis to back up those
> assertions. Arguments were, big pattern issues and I^2*R losses. The extra
> I^2*R losses are easy to calculate and were insignificant. If you don't
> believe in my NEC4.2 modeling then anything can be claimed.
> >
> > So I took my T model and inserted a source in each radial equal to the
> measured current and checked the pattern, swr, etc. Maybe 1db skew from
> azimuth symmetry and no significant change elsewhere. My model with my 3
> other towers present shows more skew. So, end of my concern until I'm
> educated more about this issue. My path losses due to fairly dense forest
> is much more of an issue, per the recent QST article, but not there isn't
> much I want to do about that.
> >
> > Grant KZ1W
> >
> >
> >
> > On 8/29/2020 11:23, Dave Sublette wrote:
> >> Having followed the Inverted L discussion and learning lots, I decided
> to
> >> document my 160 elevated ground plane antenna. It has been up for
> thirty
> >> years. I replaced the feedline last year. It is 200 feet from the shack
> >> and I ran a new run of half inch superflex through an underground
> conduit.
> >> I have been very happy with the performance of this antenna. I work the
> >> CQWW160CW contest QRP, an honest five watts output and place in the top
> ten
> >> in North America and top 20 in the world. If I weren't too old to stay
> >> awake a little longer, I might do better. Hi
> >> I hate long detailed emails, but I think you should have an idea of how
> the
> >> thing is made before I ask for your advice. The tower is Rohn 45 with a
> >> length of four inch irrigation pipe at the top to adjust for best SWR.
> SWR
> >> at the moment is 1.6:1. The feed point is a Rohn Broadcast antenna
> section
> >> with the insulators at 27feet. Eight Radials are attached to an
> aluminum
> >> plate which is insulated from ground also. The SO239 connector has
> three
> >> #12 wires, one to each leg. The radials are each tied off with an
> >> insulator and the pigtail fastened to the aluminum plate with threaded,
> #10
> >> screws and terminals. The radials are #13 from Davis RF, insulated.
> >> So I took my KX3 and a battery pack up to the feed point and took data
> in
> >> each wire, while transmitting with 5 watts. I expected to find the RF
> >> current to be divided in thirds in the radiating element and by 8 in
> each
> >> of the radials. I had previously calibrated my RF current meter at five
> >> watts to a dummy load on the bench.
> >> On my RF Current meter, 5W to a dummy load yields 41 micro amps on the
> >> meter.
> >> If the system works as I expected, I should see13.66 microamps in each
> wire
> >> to the tower and 5 microamps + in each radial.
> >> What I measured was unequal currents in the three wires to the tower,
> 13.1,
> >> 9.8, and 15.6 microamps. Close on the total, but not equal.
> >> The Radials measured, 9.8, 6.4, 0,1.8, 26.2, 0, 1.9 and 0 microamps.
> >> My first thought is to go back up and clean up all connections, replace
> >> crimp terminals on the radial ends and re-measure.
> >> Additionally, I should be able to take an antenna analyser up (VA-FA5)
> and
> >> measure the behavior of each radial. I expect to see differences
> because
> >> of variations in droop angle, nearby objects (barn), etc. But I don't
> know
> >> what to think about the radials that measure 0 and less than 2 ua.
> >> Does anyone have any further suggestions for how I should go about
> testing
> >> and troubleshooting this system?
> >> I am totally surprised by this result, since this antenna works (but we
> all
> >> know that this is an inaccurate and unscientific statement).
> >> Thanks for your patience, if you made it this far.
> >> 73,
> >> Dave, K4TO
> >> _______________________________________________
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