Hi,
been playing with antennas on my SOTA activations, in summer linked dipole, in winter a EFHW trapped for 3 bands. Now playing with random wire antennas so started with the 84 foot wire and the 17 foot counterpoise as mentioned in several books. Want to try shorter wires as put forward as useful lenghts i.e 71 foot and then 53 foot. How is the counterpoise size arrived at, is it a percentage of the radiating wire, or is it too truely random ?
Declan
ei6fr
Hi Declan,
I’m a dipole man, but when I looked into trying end fed antennas, it seemed that most sources were staying that a counterpoise need not be very long.
Some reading that might help -
https://www.sotabeams.co.uk/efhw/
VY 73,
Colin
I have had luck with 58/13.
Malen
VE6VID
The 84-foot radiator and counterpoise is in fact the classic W3EDP antenna, invented in the mid 1930’s and still popular today. I built mine following an article by G3BDQ in Practical Wireless. According to him the 17 foot countepoise is correct for 3.5, 7 and 21 MHz. For 10 MHz you need a 23 foot counterpoise, for 14 and 18 MHz you only need 6.5 foot, and for 24 and 28 MHz no counterpoise is necessary. For 1.8 MHz, on the other hand, a 126 foot counterpoise is needed, but for that band I use a shorter counterpoise with a loading coil. For 5 MHz I use the 17 foot counterpoise but I have not experimented to optimise it. As far as I know, W3EDP arrived at the counterpoise lengths by trial and error - by all accounts a LOT of error, he is said to have used more than a thousand feet of wire for his experiments!
I have used a 53 foot radiator and 12 foot counterpoise. How did I arrive there by messing with different lengths in my back yard and it turns out my KX3 seemed happiest tuning it at those lengths. 7m squid pole as support almost inverted L config long end in a tree similar height. On a summit I used it like an inverted V as I did not have any handy trees. Its a compromised antenna compared to an inverted V worked best on 20m, 17m was good to JP1QEC on his summit in JA from my back yard. My best S2S was to Spain from vk5 but that was several years ago not during low point low SFI. Black and red binding post straight into KX3 no coax at all but I have also used a YouKits tuner with short coax lead with ft 817 that works well also 40/30/20m
Regards
Ian vk5cz …
First - This is an antenna/ counterpoise that I’ve only read about, haven’t tried it yet in practice.
About 10-15 years back, I saw an article in a ham magazine (can’t remember which one) that describes an antenna (dipole and vertical wire/counterpoise) made from antenna rotator cable (I think 7 or 8 conductor).
The different wires in the rotator cable were trimmed for different freqs and tuned for the center of the specific freq ranges needed. The wires were not pulled apart from the single rotator cable section, cuts were made at different required lengths. When used as a dipole or vertical/counterpoise, only the two pre-cut sections of rotator cable were needed for multi-band operation.
When used as a vertical/sloper wire with counterpoise, the individual wires in the cable section may have needed retrimming for this configuration; in both the radiator and the counterpoise.
Never got to try it, as usual life intervened. It’s still in the radio plans section of the brain, just needs to be executed. The author did mention that the antenna worked for him with no tuner, but I don’t know about any interaction between the individual conductors; nor the radiation efficiency/pattern.
This MAY work for using a single counterpoise or radiator or both when using a dipole or vertical, but may need a small tuner (ZM-2, SOTA Tuner, SOTABEAMS, etc. ) depending on the current configuration as dictated by available supports. May be useful if the desired radiation direction is in one direction. Or a few rotator cable counterpoise wires could be cut/trimmed to the desired lengths and spread out in different directions.
Again, I haven’t tried this one. Hopefully someone on here may have tried it and can pass more info. It does have the advantage of multiple cut lengths, but is only one physical wire if used as a single wire counterpoise.
Mike, N4VBV
Thanks for the input guys, some reading to be done and some food for thought
Declan
On EFHW I’ve found that 6.5 feet works for me on 20 and 40, and 7 feet on 10 and 15m. You can put knife connectors on 2 lengths of 6.5 feet to swap out. I also have several short lengths of extensions for the radiating wire to fine tune to the CW portion of each band.
Hi,
Note the total lengths mentioned by Brian and Ian. 102 ft and 67 ft. The first is 3/2 half waves on 20 m and the second a half wave on 40 m. Both are off centre fed.
As a basic rule one should use two quarter wave radials in line. This forces the radiator to be less dependent of the single counterpoise for radiating a signal.
A single quarter wave radial should at least force a low impedance at the rig but as it is not balanced by a second radial it is a major part of the radiator.
Many a builder of a short loaded vertical has been puzzled by the difficulty in tuning it up when only one radial is used.
Modern ATUs can resonate and match almost anything, but if the wire l.ength and radial have no engineering optimisation then the results can be disappointing, or sub- optimal.
I have used an 85 ft wire with a 42 ft counterpoise. It is actually an 80 m halfwave with one third lying on the ground. And that’s were 1/3 of the power goes. Plus some more from the main radiator. But it tunes up from 160 to 52 MHz just with the ATU. It is convenient if somewhat inefficient. I have worked ZL easily which is about 2,800 km. Not far for VK but would cover 30 countries if used in Bavaria.
One size does not suit all. Whatever you use, have fun.
73
Ron
VK3AFW