"N4aeq" wrote in message
ps.com...
Im trying to match 50 ohm coax (lmr400) with a log peroidic which
should have a 75 ohm feedpoint
the SWR is flat across the 6 m band but high. Im thinking i need a
better match but not sure
where to start.

I can't remember the numbers, but there is a procedure in either the ARRL
Handbook, or antenna book for doing this. Basically, you have a short piece
of 50 Ohm coax, a short piece of 75 Ohm coax, and then an arbitrary length
of 50 Ohm transmission line.

If the antenna is 75 Ohms, your SWR on the 50 Ohm line should be no more
than 1.5:1. Are you sure you don't need a 4:1 balun? If your SWR is around 3
or 4, I would try the balun; easy neough to make out of a 1/2 wave piece of
coax.

Tam/WB2TT

Tam/WB2TT wrote:

I can't remember the numbers, but there is a procedure in either the ARRL
Handbook, or antenna book for doing this. Basically, you have a short piece
of 50 Ohm coax, a short piece of 75 Ohm coax, and then an arbitrary length
of 50 Ohm transmission line.

You are thinking of a nonsynchronous balun described he

http://www.k1ttt.net/technote/matching.html#k1xx

HOWEVER, this only works for one band (i.e. a monobander...not a
log-periodic covering multiple bands). If the antenna is 75 ohms, why
not simply use 75 ohm coax to the shack and then a tuner to convert to
50 ohms? Seems much simpler and you can normally get free 75 ohm
hardline for the asking at your local cable company (i.e. reel ends).

73, Bill W4ZV

wrote in message
oups.com...
Tam/WB2TT wrote:

I can't remember the numbers, but there is a procedure in either the ARRL
Handbook, or antenna book for doing this. Basically, you have a short
piece
of 50 Ohm coax, a short piece of 75 Ohm coax, and then an arbitrary
length
of 50 Ohm transmission line.

You are thinking of a nonsynchronous balun described he

http://www.k1ttt.net/technote/matching.html#k1xx

HOWEVER, this only works for one band (i.e. a monobander...not a
log-periodic covering multiple bands). If the antenna is 75 ohms, why
not simply use 75 ohm coax to the shack and then a tuner to convert to
50 ohms? Seems much simpler and you can normally get free 75 ohm
hardline for the asking at your local cable company (i.e. reel ends).

73, Bill W4ZV

He was talking about 6 meters.

Tam

Tam/WB2TT wrote:
I can't remember the numbers, but there is a procedure in either the ARRL
Handbook, or antenna book for doing this. Basically, you have a short piece
of 50 Ohm coax, a short piece of 75 Ohm coax, and then an arbitrary length
of 50 Ohm transmission line.

1/4WL of RG62 followed by 1/4WL of RG59 will give a good
match from 75 ohms to 50 ohms.
--
73, Cecil http://www.w5dxp.com