Quoting Bob Alexander <realex@flash.net>:
>
>>> I have a couple of homebrew 4 el on 3/4 wavelength boom yagis with
>>> gamma matches. The antennas were designed to have a -j component at the
>>> feedpoint. Using a gamma match without a capacitor resulted in a
>>> slightly inductive feedpoint impedance. After shortening each end of
>>> the DE a 25 dB return loss was measured at the design frequency. No
>>> inductive component.
>> And what happened to the resonant frequency and f/b and gain? Any
>> change to the DE length will affect all three of those!
>> 73
>> Don
>> N8DE
>>
>>
>>
> The gamma match inductance has the same effect as adding a loading coil
> to the element thus making it electrically longer.
NO ... the gamma match inductance has little/no effect on the
electrical length of the driven element.
The Gamma match is simply ONE SIDE of the original DELTA match which
has a balanced feedline tapped onto the driven element the same
distance on either side of center, providing an impedance match.
The T-match is the same idea, but utilizing line parallel to the
driven element, rather than simply taps on the driven element from the
two sides of the balanced feedline.
The Gamma match is one-half of a T-match ... but, due to its
configuration, parallel to the driven element, it has an inductive
component.
The T-match does NOT require capacitive reactance to cancel inductive
reactance due to the 180-degree phasing of the feedpoints. (See ARRL
Antenna Handbook for further info).
The matching network, be it Delta, T-match, or Gamma match, does NOT
change the resonant frequency of the driven element .. as they are
only impedance matching devices.
73
Don
N8DE
> Reducing the
> physical length of the element moves the electrical length back to the
> design frequency.
> It is the electrical length not the physical length that matters.
> There is no change in antenna performance.
> 73, Bob, W5AH
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