RadioBanter - View Single Post

January 22nd 06, 03:14 PM posted to rec.radio.amateur.antenna

On 21 Jan 2006 13:52:57 -0800, wrote:

ml wrote:
In article , ml
wrote:

i see this month arrl magazine qst reviews a new hf comet verticle
that dosn't use radials

i am just wondering how does this work?

it specifies that its not a stelar performer has low swr but dosn't
explain the technology"" it uses to 'work' w/o radials

anybody know?

thanks

i reamain eager for an answer to my question

Just a guess, but I'll bet that thingey down at the bottom of the
antenna is a resistor. Although it says it doesn't need radials, they
would help, although they might mess up the broadbanded appeal of the
antenna.
Gary N4AST

Is a resistor used in matching a bad thing? My intuition is that it
is, but I have no math to back up the position.

One of my current projects is to understand the matching problem for
an electrically short vertical.

Using EZNEC+, when I run the SWR function with the radiator (simulated
real ground) I get an indication of Z = R + j. If I add an inductive
load at the bottom of the radiator equal to the j value it brings the
match into a reasonable range. At this point I have not grasped the
relationship of the "R" in the equation. If I use the figure for R
equal to 10% of the XL, the match gets even better, but not 1:1. 10%
comes from the suggested estimate in the help file.

Question 1: What is this "R" thing? I started out thinking it was
series DC resistance and lower is better. My interpretation of the
EZNEC results contradict this position. More "R" seems better.

Question 2: Is this an effective method of matching a 50 ohm line to
the vertical radiator?

I do understand this is a math model and it ignores radiation from the
inductor.

Question 3: Looking ahead, I think the next matching technique should
be an inductor in series with the ground end of the radiator and the
ground. The 50 ohm line would feed a tap on the coil 50 ohms up from
ground.
Do I compute XL from the bottom to equal 50 or is this strictly a cut
& try thing?

I have yet to physically model anything with these tests but I am
getting close to it.

I know there are better matching methods than what I am attempting,
this is an academic exercise for me!

John Ferrell W8CCW