Hi Terry,
What is there about 80 meters that means it doesn't need a carefully done
radial field? If anything, the low bands need "careful" worse...
Your elevated radials will be hard coupled, like transformer windings, to
the buried radials. If a radial and its connections are high R, you will be
coupling that R with the raised radials.
The dip in your SWR telegraphs that the lengths of the HyTower are probably
OK. The R=83 tells us that you have 50 ohms, give or take, of junk
resistance somewhere. Everything all chipper, and you should be seeing
thirty-ish. That could conceivably be a really bad joint connection in the
HyTower, but unlikely as all three joints at the point would have to be
bad. Also the resistance at a point trouble has more effect closer to the
feedpoint.
It also implies you are losing 4.3 dB, something like 2/3 of your power
wasted in ground/radial/connection loss. 940 watts of your 1.5 kW converted
to heat by your antenna system.
With that many radials, a single, or even ten radial problem will not move
the R much. But if ALL the radials are a problem, or the connection point
is bad that could happen.
The first problem you have is that electric fence wire does not worry about
skin effect, or about low resistance for current. It's a high voltage
application. The designed for "signal" is high voltage DC, and low R just
simply does not matter for the intended use.
The second problem is that electric fence wire is NOT designed to be left
laying on the ground or buried. Aluminum can be dissolved by many common
"dirt" compositions when wet. The wire is supposed to be in the open,
supported by insulators, and can dry off after every rainstorm.
On the other hand, for 80 meters, which DOES have skin effect, and in a 1/4
wave vertical which REQUIRES essentially zero R conductors, any kind of
corrosion or typical higher wire resistance, or aluminum connections going
bad, and a long list of problems using fence wire at RF, all can raise your
R. If I had to bet 100 bux on either the HyTower or something related to
the radial wire, it's immediately on something related to the wire. You
probably would have cleaned up corrosion on the joints as you erected the
HyTower.
The absolutely most important part of your HyTower, with nothing in second
place, is the state of the radials underneath and the connections to them.
If any antenna on low bands needs a counterpoise, solve the counterpoise at
maximum efficiency, and insure permanence of that efficiency, before
anything else.
You may hear from here and there that junk wire for radials worked "OK".
Use junk *copper* wire if you want, and solder and corrosion proof all the
connections. What you are looking for is ZERO effective series resistance
at RF from your radial field at the lowest frequency in use, and
construction practices and treatment that insure that it STAYS zero.
In my first house up in New York state, it had aluminum power wiring to the
outlets. The stuff had to be tightened down every couple of years and was a
never-ending source of electrical problems. That was at 60 Hz and no skin
effect. So there's a part of me permanently against aluminum wire unless
you're talking about aluminum tubing, properly treated and fastened at all
the joints.
Good luck, and let us know what you actually find. Theorizing and
speculating on the reflector is one thing, and finding an actual problem
and fixing it is another. :>))
73, Guy K2AV
On Mon, Jan 29, 2018 at 6:48 PM, terry burge <ki7m@comcast.net> wrote:
> Hi guys,
>
>
> Even though my main focus is on 80 and 40 mtrs right now I thought I'd
> throw this out to see what other thought. My hy-gain Hy-tower is using 14
> gauge electric fence wire for radials. Most of them are 65 foot or maybe a
> bit longer. About 63 or 64 of them by now. Since it was mainly 80 meters I
> wanted the antenna for I figured the electric fence wire would work just
> fine. Lately I've even added 4 elevated 12 gauge insulated multi-strand
> copper radials raise about 3-4 feet off the ground. Also one of those 1116d
> RF chokes near the feed point on the LMR-400.
>
>
> I also use the radial system on my 160 meter inv-L over a tree near the
> hy-tower. The 110 feet or so of lengths just goes up and across the top of
> the Oak tree. You can see the pictures of all this on myhttp://
> www.qrz.com/KI7M page FWIW. One of the things that always bothered me
> about this brand new hy-tower is that on 80 mtrs it's lowest SWR point is
> 1.6:1 around 3.785Mhz with an R= 83 ohms and X= 11/13 ohms. I've even added
> the elevated radials and now am up to three 8 foot galvanized ground rods
> trying to get it to dip in more like a 1/4 wavelength antenna of 36 ohms.
> No such luck, that is where it want to sit. I use an old HF6V coil and tap
> it to adjust the resonant point on the 80 mtr stinger. Other bands are
> similar strange SWR dips for the most part....40 mtrs 7.130 Mhz R= 49.2
> ohms X= 0.0 ohms SWR 1.16/1.13:1; 20 Mts 13.950 Mhz R= 44.1 ohms X= 0.0
> or so, SWR 1.22:1; 15 Mtrs 21.300 Mhz R= 34.3 ohms X= -14.3 ohms SWR
> 1.9/1.7:1 (lowest point); no 10 mtrs added. Woul
> d you believe it even works on 12 mtrs being resonant around 24.470 Mhz
> R- 50.6 ohm X= -1.0. At 24.930 Mhz it has an SWR of 1.4:1.
>
>
> By now I've pretty much figured out that the Hy-Tower uses the 80 mtrs
> stinger for a 3/4 WL 20 mtr antenna so you are stuck with where ever the
> compromise point is there. I've also added the MK-17 17 mtrs stinger (stub,
> whatever) and it dips in pretty good. Way, way down from my Steppir 3
> element beam at 118 foot of course.
>
>
> I've had two or three different hy-towers in my time and I don't recall
> any of them having this high of SWR on 80/75 mtrs at resonant. Maybe it is
> the galvanized radials from the local farm store (Wilco)?
>
>
> Terry
>
> KI7M
>
>
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|