You will be a much happier camper if you feed it with 450 ohm ladder line.
You will have no trouble using the antenna anywhere from 80 to 10, and if
the ladder feed is more than 70 feet you will be able to load the dipole on
160. If the feed line is not 70 feet long, you still will be able to use
the antenna on 160, just join the two sides of the feedline together and
treat as a longwire.

--
73 es cul

wb3fup
a Salty Bear

"Ralph Mowery" wrote in message
...
I will be building a center fed 80 m dipole, 62.5 feet
each side of center. The ends will be about 23 feet above
ground but the center is not supported to it sags to about
18 feet. I will feed it directly with about 25 feet of
RG-213 50 ohm coax and connect it to an antenna tuner in
the shack that can tune from 50 to 500 ohms.

This should work okay on 80 m, right?

How well will it do on 20 m?


For 80 it will work fine for the heights you have to work with. As most
always the higher the beter. If you want to work 20 meters or other
bands
with the same antenna you might want to feed it with open wire or go to
an
off center fed or (yuck) maybe the g5rv type.

"WB3FUP (Mike Hall)" wrote in message
...
You will be a much happier camper if you feed it with 450 ohm ladder line.
You will have no trouble using the antenna anywhere from 80 to 10, and if
snipped

I need to run the feeder from my dipole (80m) up thro the eaves, thro' the
loft-space to the shack at the other side (1st floor) of the house, approx
50'. No other routes feasible. Because of the route, I thought I'd have
less problems using coax, BUT from the remarks in the above recent post,
will someone kindly comment on viability of 450 ohm twin feeder over such a
route?

Many thanks
Jim M0Jim

Replies to NG pse!!

I need to run the feeder from my dipole (80m) up thro the eaves, thro'
the
loft-space to the shack at the other side (1st floor) of the house, approx
50'. No other routes feasible. Because of the route, I thought I'd have
less problems using coax, BUT from the remarks in the above recent post,
will someone kindly comment on viability of 450 ohm twin feeder over such
a
route?

=====================================

If necessary just squeeze heavy-duty 450-ohm ladder line wires close
together wherever they pass through a small hole. Line holes with a thick
plastic film or a pipe to obtain a higher breakdown voltage. Slowly twist
the cable every 2 feet between holes and keep it at least 1 or 2 inches away
from foreign materials, long metal conductors or otherwise.

If it was possible to do A-B comparisons at HF you would find little
difference - equivalent to a few pF change in a tuner capacitor setting and
1/2-turn change in the roller inductor. To be safe stick to 100 or 200 watts
unless you wish to test to destruction under worst case, but controlled
conditions (eg., very high SWR) just to see what happens. Probably nothing!

At HF a change in impedance Zo over a length of a few inches when passing
through one or two holes in timber or brickwork will have a negligible
effect on performance. The advantage of a balanced line all the way to the
transmitter may be that a tuner can be located in the shack. If an automatic
tuner is used then use easier-to-install coax and locate the tuner at the
antenna end.

Over a length of 50 or more feet, at 28 MHz, the lower loss in 450-ohm line
relative to 50-ohm RG-58 is worth thinking about. At 1.9 MHz forget it.

But it's only a matter of economics, time and labour, and the well-earned
satisfaction of having done a good job which works according to plan.
---
Reg, G4FGQ

Jim,
If you follow the 'normal' rules for using twin-
lead feed line you shouldn't have any more (or any
less) problems than if you used coax. There is always
the possibility that RF will 'eat up' all the electrical
appliances in your house, but maybe not.
Nothing except your pocket says you can't change feed
lines or antenna if you want. So, try it and see what
happens...
'Doc