[Towertalk] high SWR at receiver inputs

[Paul Christensen]

> In other words, he notices problems at the receive end
of the system with the high SWR problem first. My
justification for this happening is that you can
normally lose a lot of transmitter power and still be
received

When power is applied to the transmission system, oftentimes the root-cause for high VSWR is temporarily lessened during transmit
when RF current is flowing.  What may be a result of high VSWR due to the corrosive properties of say...a connector, disappears when
power is applied.  In other words, system losses are not the same during receive or transmit.  Also note that VSWR at the receiver
input can be vastly different than the VSWR at the antenna: VSWR is a function of the degree of match between the antenna terminals
and the characteristic impedance of the line.  For example, we all know that a 50-ohm line attached to a 50-ohm antenna input
impedance yields a 1:1 VSWR during transmit.  If that same 50-ohm line is connected to the receiver with an input impedance of
100-ohms, VSWR is now present on the transmission line during receive...even though it is not present during transmit.  For the same
reason that VSWR is a function of the line-to-antenna impedance during transmit, the VSWR mechanism manifests as a function of the
line-to-receiver input impedance match during receive.  In the latter case, the antenna, not the transmitter becomes the source
generator.  So, it's quite possible that a 2:1 mismatch during receive is not very noticeable...that is until something else
exacerbates the mismatch which causes additional loss during receive which then becomes noticeable.

-Paul, W9AC