Fw: Re: [Antennas] More Ladder Lines and Beams

2002年1月27日 09:51:11 -0600

Again, helpful info, Don. I had no idea that toroid balun losses were 
as low as 2%. Re your note........
>I still wonder why you would rather deal with all the problems of:
>1. interaction with surrounding objects
>2. impedance bumps/changes with variations in line and 'wind sway'
>3. matching to the antenna
>4. loss of antenna discrimination by having the feedline 'part of the
>antenna'.

.......long run (250ft) to the antenna, can't afford or dig the trench
for
hardline, it's a little less power loss when running QRP, it's different
from the coax most people use, readily lays the groundwork for more
experimentation, more of a challenge, and I don't want to use a linear.
Like my Radio Homepage says: "If I just wanted to talk, I'd use a cell 
phone".
>You COULD use a T-Match or Delta-Match, both of which would require you
>to eliminate the open feed point at the boom, grounding the driven
>element there. The Delta-Match would pair up with your open-wire line
>better than the T-Match. Read the info in any antenna handbook about
>those two matches. [I use T-Matches, adjusted for about 200 ohms, and
>matched to 50-ohm coax]

.......Worth looking into.
>That 'choke' is a BALUN [of sorts].

....yep
>Depends on how you're feeding the driven element! IF the connection is
>directly to the driven element .. NO .. if through a balun, then the
.GROUND [common] of the Balun is connected to the boom of the antenna
>VERY close to the feedpoint. [some people do NOT do this, but simply run
>the coax down to the shack - you'll have to ask them why!]

....I agree with that.
>In my experience, the loss in the baluns I have built [some from Press -
>the Wireman's - kits] runs in the neighborhood of 2% or LESS.

......good information. I've never seen any real measured data, thanks.
>Why three cores? The impedance transformation is NOT dependant 
>on the number of cores, but on the number[s] of TURNS in the BALUN!

....yes, I realize normal impedance transformation is a result of turns
and 
the number of cores has nothing to do with it. In fact, an UNbalanced 
to UNbalanced impedance transformer is easy on one core. However, 
draw up a 9:1 unbalanced to balanced bifilar/trifilar/whatever balun on 
one core. Required three cores to work for me 
>Any GOOD core material that will NOT saturate under use will do.

.....that's the key, never saturate the core.
73s Kees K5BCQ