Topband: Fwd: [TowerTalk] Loss in CCS conductors at low freqs (was Voltage Breakdown For Enameled Wire)
ki7m at comcast.net
Mon Jan 29 18:48:47 EST 2018
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. Would 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)?
-------- Original Message ----------
From: Dan Maguire
Date: January 29, 2018 at 2:36 PM
Subject: [TowerTalk] Loss in CCS conductors at low freqs (was Voltage Breakdown For Enameled Wire)
Jim Brown wrote:
>>> ,,, but the steel causes losses to increase at lower frequencies as compared to copper or silver coated copper.
It just so happens that I've been working with a fellow who has been
measuring loss in Wireman 551 (aka JSC 1318) window line. The
conductors are solid #18 CCS. Using a DG8SAQ VNWA in 1-port mode, he
made sweeps from 0.25 to 30 MHz with the DUT terminated first with an
Open and then with a Short. There was a CMC choke (with
characteristics unknown to me) on the test fixture cable and OSL
calibration was done at the end of that cable using 400 ohms as the
load, not the usual 50 ohm OSL load.
The OC/SC data was then manipulated using a variation on Chipman
equations 7.28 and 7.29 with the following results:
The way I am interpreting the rise in loss at lower frequencies is due
to current flowing in the steel rather than the copper. I would very
much appreciate hearing comments on the shape of that curve from folks
more knowledgeable than me. (Of which there are many!)
BTW, here's a good N6LF article on the subject:
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