[TowerTalk] Fwd: Adjusting a Gamma Match on a Yagi with an AntennaAnalyzer

[David Robbins]

changing the de length has a very, very, tiny effect on f/b and gain... its only the slight difference in coupling due to the usually small changes in length that would cause changes to f/b and gain and in most cases you will never measure that.  try it in an antenna modeler and see how much you can change the driven element length without affecting the pattern measureably.


Nov 10, 2010 06:28:11 AM, n8de at thepoint.net wrote:

Quoting Bob Alexander 
:

> On 11/9/2010 9:38 PM, n8de at thepoint.net wrote:
>> The gamma match itself is an inductor ... you can only cancel that
>> inductance by putting a series capacitor inline with it. IF you do
>> not, changing the length of the driven element will change the
>> APPARENT impedance, but it will still have an inductive (reactive)
>> component.
>>
>> 73
>> Don
>> N8DE
>>
> 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


> 73, Bob, W5AH
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