[Lowfer] Re: Amplifiers for 136k

[David Willmore]

> My exciter tests last night indicated similar coax matching characteristics 
> as with the loop PA the night before. In testing I have found the following 
> to be true which was not evident before:
> 
> 1) When one drives a coax with a 0 ohm source the load at the other end has 
> to be really close to the Z of the coax or the waveform becomes very 
> distorted. This applies even when the wavelength of the signal is 50 times 
> longer than the length of the coax.

This makes sense as anything reflected from the load back to the source
determined by Zo/(Zo+Zload) will reflect perfectly off of the source impedence
Zo/(Zo+Zsource)=1.  That reflects back to the load, then back to the source,
etc.  With how low loss the coax will be at this freq, the echoes can last
a very long time.  At least at VHF/UHF, they die down after a while due to
simple loss in the coax.

> 2) The sensitivity to load mismatch drops off as you add series resistance 
> to the driven end up the the Z of the coax.

See above, as well.


Cheers,
David