I should have been more specific. The line loss, in a 500 ohm open wire
tuned feeder system, IF MATCHED, can be assumed to be negligible. The
presence of the additional losses caused by the amplitudes of the
reflected components at a VSWR of 10:1 will be about 3 dB.

Is 3 dB negligible? It's approximately 1/2 S unit. Whether or not 3 dB
is negligible depends on the individual station. I get one judgment if I
consider QRP and a different judgment if I consider QRO. For me, 3 dB on
75/40 is acceptable due to a single antenna limitation and 1 KW output.

Roy, thanks for challenging my 'loose language'.

DD

Roy Lewallen wrote:

Hm.

All in the same sentence, that "line losses are negligible" and "line
losses will be about -3 dB"? I assume, of course that you mean 3 dB, not
-3 dB. But does this mean that you consider 3 dB to be negligible? And
how did you calculate that as the line loss?

Roy Lewallen, W7EL

Dave Shrader wrote:

Assuming a VSWR of 10 to 1, reasonable for 80 meters, and assuming
line losses are negligible for open wire tuned feeders, also
reasonable for a first approximation, your line losses will be about
-3 dB.

EZNEC indicates that you will also have a VSWR of about 10:1 on 40
meters.

Conclusion: you will experience about -3 dB loss [1/2 S unit] on both
75 and 40 when fed with 500 ohm line.

Deacon Dave, W1MCE