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43' verticals -- what's the theoretical basis?

Oct 11th 2011, 22:00

KE2IV

Joined: Apr 4th 1998, 00:00
Total Topics: 0
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QST is filled with ads from various manufacturers and suppliers offering "all-band" 43-foot verticals. Legitimately, all these ads make it clear that this (and any vertical) will require a good ground plane system of radials for effectiveness.

But why 43-feet? What is the "formula" to explain why this length will effectively radiate on "all bands" (i.e. 160m - 10m) with a decent ground plane system?

I'm interested in puting one up -- but would like to know the "theory" behind such an antenna. Any guidance to the articles or texts to explain would be greatly appreciated.

73,
George
KE2IV
Oct 12th 2011, 12:46

W1VT

Joined: Apr 4th 1998, 00:00
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43 feet is the length you get when you calculate the maximum gain you can get out of a 20M vertical, without resorting to phasing sections. It is the classic 5/8 wavelength vertical. On the higher bands, like 10 and 15 meters, it pattern is actually rather poor, but until recently, band conditions have been so bad that this deficiency hasn't been an issue.
On 30, 40, and 80 meters, it works better than shorter alternatives, as it has a higher radiation resistance. It won't work as well as longer antennas--a 60 ft vertical would work even better, but then a 60 ft vertical wouldn't work as well on 20 meters, a really important DX band.

QRPers, or folks than run very low power, might find a half wavelength on 20 meters more useful--voltage fed antennas can be very efficient--and a half wavelength on 20 meters is an easy to feed resonant antenna on 40 meters. But, most autotuners won't handle high impedance voltage fed antennas, even at moderate power levels--the voltages are too high.

Zack Lau W1VT
ARRL Senior Lab Engineer

Oct 12th 2011, 22:28

W8JI

Joined: Nov 28th 2000, 00:00
Total Topics: 0
Total Posts: 0
Quote by KE2IV
QST is filled with ads from various manufacturers and suppliers offering "all-band" 43-foot verticals. Legitimately, all these ads make it clear that this (and any vertical) will require a good ground plane system of radials for effectiveness.

But why 43-feet? What is the "formula" to explain why this length will effectively radiate on "all bands" (i.e. 160m - 10m) with a decent ground plane system?KE2IV


There is no reason, George. Somehow that number just popped up out of the blue, and then everyone started copying it.

The initial 43 foot vertical had a balun that, through an error in design, drove the coax shield with RF. This error, in some cases, made the SWR very low from 160-10 meters. Hence the "160-10" meter stuff started.

After an eHam thread, the company initially marketing the 43 foot vertical revised the voltage balun to an un-un, and then the SWR was not so good at all but the signal was better.

To radiate 100 watts of actual field power on 160 meters with a 43 foot vertical, the base voltage would be 6500 volts peak at 6.6 amperes!! On 80 meters, it would be 1200 volts peak at 3.2 amperes.

At 500 watts actual radiated power on 160 meters, a 43 foot vertical will blow the insulators apart.

The 43 foot vertical mainly "works" because of power losses in the matching and feed system. They are OK on 60-15 meters, but not especially good anywhere.

If you want a good 80-10 meter vertical, buy a trap vertical. DX Engineering sells Hustler verticals that are OK on 80 (but narrow banded) and great from 40 meters up. HyGain sells a Hytower, that while pricy works excellent from 80-10 and can be loaded to work 160.

When you buy a simple antenna with no band-by-band matching, either through complex tuners, traps, or stubs, matching, you can bet it is throwing power away someplace.

The better SWR it offers in less space with less complexity, the power it throws away. There is no free lunch, George.

Here's a final thought. I know of several very high rated antennas in Internet reviews, one is a 5.0 out of 5 on eHam, that have less than 10% efficiency on many bands.

Anything that makes a QSO and has a low SWR works perfect to some people, even if 95% or more of their power is wasted as heat.

73 Tom
Oct 16th 2011, 17:16

SIZE358

Joined: Apr 19th 2009, 19:30
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Total Posts: 0
the 43 foot vertical is 5/8 wave on 20m and is 1/4 wave on 60m.
Oct 20th 2011, 01:21

W8JI

Joined: Nov 28th 2000, 00:00
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Quote by SIZE358
the 43 foot vertical is 5/8 wave on 20m and is 1/4 wave on 60m.


That doesn't have anything to do with 160, 80, 40, 30, 17, 15, 12, and ten meters. :-)

My guess is someone took the 88 foot doublet and turned it into a Marconi. But that's just a guess.

Whatever it is, a trap vertical like a 6BTV will work a whole lot better.

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