[TowerTalk] OCFD: Should I be able to do better?

[Jim Brown]

On 5/27/2021 1:46 PM, Haring family wrote:
> What most of the comments you've received probably (or should) mean is that
> you don't have a symmetrical/center-fed antenna, so you're more likely to
> have feed problems and common-mode problems.
> 
> These can be easily dealt with, with a good balun and good common-mode
> choke. However, some people will aim for perfection and may ridicule nearly
> anything else...

No, they can NOT be "cured" with a common mode choke for several 
reasons. First, a choke that could do anything useful to kill common 
mode current will likely fry with the severe imbalance, AND with 
mismatch to the feedline makes that worse.

Second, to kill RX noise, the choke must be at the feedpoint, not 
somewhere down the line.

 > I often find it easier for a temporary installation to use an OCFD
 > than a fan-dipole. Especially in the trees.

Yes, fans are tough if they need to go through tree limbs, even on their 
way up.

 > The one I'm planning to use for FD - well, I am skipping 10 meters 
and > just planning on 15/20/40. 20 needs a tuner (2:1). 40 is high-1's so
 > I'll use a tuner there. 15 has low SWR. That is with the feed at 25%
 > of the length.

That's probably fine -- IF the site is quiet, and ONLY if there's no 
other station on the same band. But if there are others on that band, 
the high common mode and the lack of a choke will cause lots of 
inter-station interference.

73, Jim K9YC