Band Reject Coaxial Stubs

[Del Seay]

Tony Brock-Fisher wrote:

> The answer is that the purpose of a stub on the output of the transmitter
> is to reduce unwanted harmonics of the transmit signal, especially
> those which may be generated in the power amplifier. As well as reducing
> interference to another station operating nearby on a higher harmonicly
> related band, the stubs also clean up the transmitter output and may
> therefore eliminate TVI complaints from neighbors.
> 
>

Hi Tony. Not sure I can buy that explaination. Coaxial stubs are not
a very good way of cleaning up spurious (or unwanted) energy.
They are extremely broad, with only 20-25 db of attenuation at an
absolute maximum. A far more efficient approach would be to improve
the signal at the exciter, (Chebychev,etc>) and at the amp output.
(Be nice if push-pull were still the order of the day!)

But - if you put one or more coaxial stubs for say 7. mHz on the
20 meter antenna lead, insertion loss at 14 mHz would be negligable and
a healthy amount of unwanted energy would be eliminated.

But - my knowledge is strictly theoretical, having never spent that
much time de-bugging multi stations.
See ya'  de KL7HF

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