solid aluminum pipe antenna 10-20m
Does anyone have any info on building a one-piece vertical antenna that would be useable on 10-20meters? I currentl have an A-99 which-like many jointed antennas tend to whip around in the wind and weaken at the junctions. I would like to put up a vertical antenna consisting of aluminum pipe 1-2" diameter and wondering if it can be done with a length under 20 feet. (I do have an antenna tuner, but would like to find out if there is an "optimum" length). The antenna would be end fed and no radials, securely clamped at the top of the tower and insulated from same. Is this even possible?
Not really possible.
Without radials, any sort of unipole (end fed vertical) will be pretty poor. You can't get a single length antenna to match coax on both 10m and 20m, as a good match on one will be a terrible match on the other.
There are ways to deal with this, including using multiple lengths; traps; stubs; matching transformers; and so forth, but they are all more complicated than just a length of aluminum tubing.
Here's a design that actually does work on 10-12-15-17-20m and is tubular aluminum. Note it does use resonators and radials, but it's a real antenna that will outperform the A-99 -- a lot, and work on multiple bands: http://www.cushcraftamateur.com/Prod...oductid=MA-5VA
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Originally Posted by WB8IIA
Some of this antenna information is now a century old,
Marconi (1/4-wavelegth vertical) antenna and
Hertz (1/2-wavelength horizontal, or Dipole) antenna.
For vertical antennas, your BASELINE reference is the Marconi (1/4-wave) with appropriate radial field.
Ground losses affect the feed point impedance and antenna efficiency.
A Marconi antenna mounted on a perfectly conducting ground would have an input impedance that is ½ the impedance of a dipole, or approximately 36 ohms.
For 20 meters, a 1/4-wave vertical antenna would be ~5 meters in height (16 feet and 4.85 inches).
Bob at Balun Designs makes appropriate matching unun options for this 1:2 match.
It is common practice to use telescoping aluminum tubing for this vertical element.
Tom at ZeroFive Antennas makes antennas, that you have described.
FOR Multi-Band usage, L-C traps are normally used to provide this Ease of Use.
Commercial 1/4-wave vertical antennas that fit this need (20, 15, 10 meters):
Cushcraft AV-3 (discontinued in late 1990s)
Hy-Gain 12-AVQ (late 1950s to current production)
Hustler 4-BTV (includes 40 meters, late 1950s to current production)
These 3 antennas were designed in late 1950s or 1960s, 20-25 years before WARC bands (1980s),
SO they don't support 30, 17, 12 meters. Parallel vertical wires have been used with these designs to add 12 and 17 meter coverage.
Find a used Cushcraft R5, that is closest commercial antenna that meets your requirements.
The antenna would be end fed and no radials, securely clamped at the top of the tower and insulated from same. Is this even possible?
End Fed Half-Wave (EFHW) Vertical antennas, increased usage with the 1980s introduction of the Cushcraft R-series verticals (R4,R5,R6000,R7,R7000,R8).
All of these models use a matching system (black box) and ~4 foot counter poise wires at the feed point.
The R-series antenna construction was based upon the Ringo design and first prototype -- the R3 (used a motorized matching system).
Steve Yates, AA5TB covers the EFHW antennas
These antennas need a counterpoise and correct matching.
Last edited by W9GB; 05-04-2012 at 06:09 PM.
Nullius in verba
ARRL Antenna hanbook describes GPs & verticals with radials as antennas with capacitive coupling with earth. However, it's unclear, how pure 1/2 wave vertical antenna interferes with ground. I assume, its performance is much much less dependent on ground characteristics. So, pure 1/2 wave vertical should work better than GP ?