Michael Efseaff wrote:
I am proposing putting up a flat top 75 meter dipole at a height of 48'.
I would like to use the antenna primarily on both the 75 and 40 meter bands
but not always. The antenna will have to be located almost 300 feet from
the shack so I intend to use home brew 500 ohm line made with #12 solid
copper conductors. The SWR on such a line will be quite high on both 75 and
40 and be all over the map on other bands. How about 160? My question is,
what kind of transmission line losses will be present with SWR's up to 10 to
1 or even greater? I have my trusty Johnson Viking Kilowatt Matchbox to do
the tuning in the shack.

You might expect matched line loss of around 0.1dB for 300ft of that
type of line in dry conditions. The additional loss due to a VSWR of 10
would be around 0.4dB. The additional loss due to VSWR is probably quite
manageable in this case up to about 25:1 where it would be 1dB. Some
will argue, you could stand an S-point or two... you choose.

There will be losses in the tuner additional to the above, so factor
those into your loss budget.

My present antenna is a 60' flat top dipole over the shack at an average
height of 34'. There is approx. 70' of 450 ohm feed line going to the
tuner. The Match Box loads the antenna on all bands from 75 thru 10 meters
with excellent results and good feed line balance. I had to modify the
Match Box to get it to 75 by utilizing the entire link and adding series
tuning to it. Eznec reports an swr of over 100 to 1 on such an antenna on

You have implied VSWR=100 on the 450 ohm line that you are using, or are
you quoting the VSWR that would occur on a 50 ohm line?

75 but it gets out well. The #18 conductors have got to have hot spots with
my 200 watts of output power! So far I haven't set anything on fire!

Comments Please, Mike K6JSY