And when you fatten the antenna you only need to fatten the ends for
most of the effect. One time I fanned out the ends of an 80 meter dipole
with great effect. Added a second wire about 6' from the ends and spread
the two ends about 6' with a bamboo pole. Moved the resonant frequency
down from 4.05 to 3.7 and now the SWR was under 2:1 over most of the
band. That was an inverted V so getting to the ends was easy. Before the
change the Collins S-line at that MARS station wouldn't tune to that
antenna at 3.6. The Viking 500 didn't mind it though.
73, Jerry, K0CQ
On 2/3/2011 3:41 PM, Steve Hunt wrote:
> Paul,
>
> When you say "bandwidth" I presume you mean "VSWR bandwidth".
>
> The Resistive component of the feedpoint impedance of a dipole varies
> relatively slowly with frequency either side of resonance, but the
> Reactive component varies much more quickly; so it's the rate of change
> of the Reactive component which largely determines the VSWR bandwidth.
> The rate of change of the Reactive component is closely linked to the
> size of the conductor - the "fatter" the conductor, the slower the rate
> of change of Reactance, and the wider the bandwidth.
>
> Hope that helps.
>
> Steve G3TXQ
>
>
>
> On 03/02/2011 21:10, Paul wrote:
>> I have been asked a question about why the diameter of the conductor of
>> antenna effects the band width.
>>
>> This question came up while in a discussion with a guy that had built a
>> 80 meter dipole out of a semi ridged copper tubing 1/2 diameter. One of
>> the newer hams in the discussion was very curious and interested in the
>> subject.
>>
>> I remember learning about this many years ago, but was totally unable to
>> enplane the subject. I know this group is the best repository of
>> knowledge. So your feed back is greatly appreciated. I will forward
>> your replies onto the interested ham.
>>
>> Thanks,
>>
>> Paul K.
>> WA0BAG
>>
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>>
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