> improved shielding (e.g. buried feedline). * As a last resort, you can
> increase S/N by placing the preamp at the antenna end, before the
> feedline effects are added.
Good advice Gary, but moving the preamp will not affect the system
unless the feedline loss is so high the noise floor is established by
the preamp and not the antenna.
By far the most common problem is common-mode ingress into the
antenna from the feedline, and with that problem moving the preamp
won't change the system. The reason for no change is the common mode
impedance of virtually all preamps are nearly zero ohms, so the
common mode system is affected by the amplifier move.
If we don't change the common mode impedance, we won't change the
effects of the feedline. (This is very similar to the incorrect but
popular notion that moving a balun from the output to the input of a
ground floated tuner somehow improves system balance or relaxes balun
impedance requirements.)
Adding a ground isolated input or output winding on a preamp input or
output transformer might help, but I am not aware of any published
designs like that. In any event, it would be no better than just
adding a passive isolation transformer and keeping the amp in the
house.
73, Tom W8JI
W8JI@contesting.com
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