Another advantage to the capacitor approach is the current maximum is
farther away from the ground/radial system. I think one would see a definate
field strength improvement. I used this approach on my 160 mtr ground plane
and had fantastic results. I know some AM BC stations use the capacitor
approach so it's probably documented somewhere.
----- Original Message -----
From: "K4SAV" <RadioIR@charter.net>
Sent: Thursday, May 15, 2008 11:21 AM
Subject: Re: [TowerTalk] The Vertical and the Balun
> ..."There's more than one way to skin a cat but I think this one gets
> used less frequently than is justified, given how darn cheap and easy it
> Maybe it's because of one of the disadvantages (which you didn't list).
> To change the resonant frequency of the antenna when using the hairpin
> approach, you have to prune the antenna. To change the resonant
> frequency of the antenna when using the long L- series cap approach, you
> just change the value of the cap.
> Jerry, K4SAV
> Dan Zimmerman N3OX wrote:
>>>As to MATCHING the vertical. I'm using, and strongly recommend, the
>>>technique of using top loading to tune the antenna long (that is, to
>>>make it enough longer than a quarter wave that it's impedance is 50 +JX
>>>on the frequency where you want to use it, then add a capacitor of -jX
>>>to tune out the inductance. It isn't practical to use this in some
>>>QTHs, but when you can, it works VERY well.
>>For what it's worth, for matching antennas that are less than 50 ohms,
>>I favor shortening the vertical a tad to show some capacitive
>>reactance and using a *shunt* inductor to step the feed impedance up
>>to 50 ohms.
>>Just to be clear, I'm talking about verticals where adding the extra
>>length doesn't really materially affect the radiating efficiency, so
>>I'm not talking going from 6 ohms radiation resistance to 50 ohms
>>radiation resistance over a 15 ohm ground system, but rather from 25
>>to 50 over a good ground system.
>>Advantages to the hairpin approach:
>>1) No extra length required. In fact, you need to shorten a little.
>>2) Good capacitors are expensive compared to capacitive reactance from
>>a shortened antenna.
>>3) Connected with 2, a shunt inductor for most HF antennas is just a
>>few feet of #10 or #12 solid ( if you want it to be self supporting)
>>wire wound into a small coil. Dirt cheap and you already have the
>>4) Your antenna ends up being DC and low frequency grounded. At
>>frequencies comparable to the operating frequency, the inductor is 50,
>>60 ohms or so, but at low frequencies it's lower. I don't know if
>>there's any real advantage to this, but you can't get static buildup
>>on a hairpin matched vertical and I feel better having my 60 foot pole
>>with a wire on it attached to ground by a #10 wire.
>>The calculations are a little more complicated, but if you've got your
>>Cebik.com login there's a section on Beta matching that tells you how
>>to do it.
>>There's more than one way to skin a cat but I think this one gets used
>>less frequently than is justified, given how darn cheap and easy it
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