[Elecraft] Question for Wayne about your OCF Dipole

[Don Wilhelm]

Wayne,

Actually, parallel coax runs make a good choice for shielded parallel 
feedline.  The paralleled LMR-400 lines should produce a feedline 
characteristic impedance of 100 ohms.  It is normal to connect the 
shields together at both ends.  At the antenna, the connected shields 
are left floating, but at the rig end, are connected to chassis common 
(your BL2 ground lug) - perhaps "floating" is what you meant by 
"unterminated".  Are the shields connected at the antenna end?

As I recall, the matched impedance loss would be twice the loss of a 
single run of the coax, but at reasonable distances and the low loss of 
LMR-400, it should not be a problem at HF.

The advantages of using parallel coax for a balanced feedline is the 
same as using coax over open-wire or ladderline.  It can be run on or in 
the ground, run next to or thorough conducting metallic surfaces, or 
coiled up with no ill effects.  Open wire and ladderline takes more care 
in its installation and must use gentle turns and be spaced away from 
nearby conducting objects.

73,
Don W3FPR

On 9/18/2017 6:02 PM, Wayne Burdick wrote:

> 
> The experimental feedline, running under the house for half its length, was more deliberate if not justified in the literature. At first I was using 300 ohm mystery twin-lead scavenged from an installation of yore. But given all the RFI sources I decided to try two lengths of LMR-400, taped together every few feet, forming a sortof-balanced-shielded feed. Purists I consulted ahead of time continue to be shocked at how well this works. At the mast, the grounds are left unterminated. In the shack, the two center conductors go to an Elecraft BL2 balun. The shields are soldered together and connected to the BL2’s ground lug.
>