Steve,
With all due respect, the problem isn't with the coax, it is with the
antenna which is designed poorly for the frequencies of operation.
Even traps in a decent multiband antenna design, fed with coax, wouldn't
have a 6db loss of the ladder line you're claiming is OK..
73 de Brian/K3KO
list1 wrote:
Hi David and all,
I have done a lot of EZNEC dipole simulations and have come to the
conclusion that the loss in 100 feet of coax off of resonance is about 12 dB
per 100'. Whether you use RG-8x or LMR400 doesn't make too much dfference
concerning losses off of resonance where your SWR with 50 ohm transmission
line can be greater than 200:1.
<http://www.pituch.net/Steve%27s%20Page/Radio/Antenna4/Antenna4.htm>
Because of this if I use 450 Ohm ladder line to a 1:1 baun, I try to keep
the length of coax going into the house less than 15 feet. For your 50 feet
of coax run you should never have a loss greater than about 1 S unit (6 dB).
When I went to 100 percent ladder line including inside the residence, when
I built my balanced tuner, I used two 1/4-20 stainless steel bolts to feed
the signal through the exterior wood wall. I have "U" solder lugs on the two
wires at the end of the 450 Ohm line, and I use two wing nuts to connect the
ladder line to the house connection. When I am finished operating I go
outside at spend 5 seconds loosening the wing nuts and the ladder line is no
longer connected to the residence. If I wanted further protction, I guess I
could drive a ground rod 15 feet away from the residence and wing nut the
end of the ladder line to it when I am not operating.
I don't believe you can keep your antenna connected to your equipment and
ever be completely protected from lightning strikes (and that includes
coax). The air gaps don't work. For coax the gas surge traps may work to a
degree, but I would much rather disconnect the transmission line than depend
on one of these devices.
If you want so-called protection for 450 Ohm line why not use 2 Alpha Delta
coax surge traps - one for each wire of the 450 Ohm line?
The thing about keeping the 450 Ohm line away from metal is overdone a bit.
I find keeping it away from metal about 2 or 3 inches is fine.
Regards,
Steve, W2MY
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