Re: [Amps] antennas that are 1:1 vswr all over the band

[David Kirkby <david.kirkby@onetel.net>]

HENRY PFIZENMAYER wrote:

> FWIW
>
> RUN OF tentecq.SCH  === SUPERSTAR ===      Fri Dec 24 10:20:18 2004
>
>  Freq       S11                      I11                     A11
> V11
>  MHz      DBANG[]         RECT[]              RECT[]
> .10000 -100.00< .0000  50.00+j.0000   .0200-j.0000   1.000
> .20000 -100.00< .0000  50.00+j.0000   .0200-j.0000   1.000
> .50000 -100.00< .0000  50.00+j.0000   .0200-j.0000   1.000
> 1.0000 -100.00< .0000  50.00+j.0000   .0200-j.0000   1.000
> 2.0000 -100.00< .0000  50.00+j.0000   .0200-j.0000   1.000
> 5.0000 -100.00< .0000  50.00+j.0000   .0200-j.0000   1.000
> 10.000 -100.00< .0000  50.00+j.0000   .0200-j.0000   1.000
> 20.000 -100.00<-.0000  50.00-j.0000   .0200+j.0000   1.000
> 50.000 -100.00<-.0000  50.00-j.0000   .0200+j.0000   1.000
> 100.00 -100.00<-.0000  50.00-j.0000   .0200+j.0000   1.000
> 200.00 -100.00<-.0000  50.00-j.0000   .0200+j.0000   1.000
> 500.00 -100.00<-.0000  50.00-j.0000   .0200+j.0000   1.000
> 1000.0 -100.00<-.0000  50.00-j.0000   .0200+j.0000   1.000
>
> S11 is return loss - here greater than 100 db .
Or to most amateurs, a perfect 1:1 VSWR.

> I11 is rectangular series impedance Rs , jXs
> A11 is rectangular admittance - mhos  - G, jB
> (1/G is Rp , -1/G is Xp)
> V11 is swr referred to R ( here 50 ohms reference)
>
>
> __R_____C_____
> |                            |
> |__R_____L____ |
>  
So there you have it - a parallel LC circuit that has a 1:1 VSWR all 
over the band. I don't know what values you used for L and C, but it 
does not matter - the result remains the same, as long as R=sqrt(L/C).

Now given the equivalent circuit of dipoles are reactances in series 
with resistors, could this be exploited in any way?  Perhaps making one 
arm a dipole resonate above the highest frequency of interest and the 
other arm a dipole resonate below the lowest frequency of interest. As 
the frequency changes, so the reactance of one will become more 
inductive, whereas the other will become more capacitive. Could these be 
arranged to make a system that stays close to resonance? I'm 95% sure 
you could force it to have two resonate frequencies, with some degree of 
compensation in between those frequencies.

Merry Chrismas everyone.

David Kirkby, G8WRB.


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