Added a few turns.....
 

I was running my dipole with a 6 turn, 2-5/8" dia rg8x coax choke
at the feed point. I got the following "dips" on my SWR meters:

2.330 mhz, 1:1
8.000 mhz 1.8:1
23.615 mhz 1.2:1

A message I got specified that at 6 turns (2.342 uH), I might want
to consider adding a few turns. I added 3, for a new inductance of
4.798 uH. Now I get the following "dips" in my SWR meters:

2.330 mhz, 1:1
8.040 mhz, 1.8:1
13.630 mhz, 1:1 new!
23.615 mhz, 1.2:1

I didn't add any coax to make the turns - I simply used the slack
in the line I had to wind the turns. I can't wind any more without
adding coax at this point..... I have 8-1/2' of rg8x between the
coil and my Z11 autotuner.

Anyone know what's going on here? FYI the antenna is a 153'2"
dipole wrapped closely around a brick building. The feedpoint
is on the third floor window, the ends are 1) chest height and
2) 10' high. Everything is very well grounded (covered here
before)......

72's de Ken KG0WX

On Tue, 26 Aug 2003 09:28:53 -0600, "Ken Bessler"
wrote:


2.330 mhz, 1:1
8.040 mhz, 1.8:1
13.630 mhz, 1:1 new!
23.615 mhz, 1.2:1

I didn't add any coax to make the turns - I simply used the slack
in the line I had to wind the turns. I can't wind any more without
adding coax at this point..... I have 8-1/2' of rg8x between the
coil and my Z11 autotuner.

Anyone know what's going on here? FYI the antenna is a 153'2"
dipole wrapped closely around a brick building. The feedpoint
is on the third floor window, the ends are 1) chest height and
2) 10' high. Everything is very well grounded (covered here
before)......

Hi Ken,

One of several things going on, barring more data.
I have 8-1/2' of rg8x between the
coil and my Z11 autotuner.
How much distance between the choke and the feedpoint? How much
distance between the auto tuner and your station?

If considerably less then that means you and your domicile are
immersed in the very near fields of the antenna. This complicates
matters and certainly offers the prospects of Common Mode issues
galore (simply through imbalances offered by life in the 'burbs).

How near is too near? For 160M you cannot escape being part of the
radiator by living in the conventional house in a conventional tract.
Higher frequencies only reduce this prospect by degrees. For 20M the
near field, by various assessments, extends as little as 20M away from
the antenna to more conservative expectations of 100M to 200M.

How much does it matter? You seemed to have reduced what Common Mode
issues you could perceive enough. This doesn't mean you completely
removed them, just reduced them below your thresh hold of detection.
So, in that sense, mattering is an issue of detection and if your
neighbors do not detect your activity, nor do you burn yourself on
equipment ground, then there is no "problem."

If you want to increase your thresh hold of detection, break a ferrite
bead in half (to get a C shaped, half torus) and wrap the leads of a
high output LED around it once (same thing as shorting the leads and
inserting the half torus through them). Red LEDs rated at 1 Candela
or better are very suitable and can be found at Radio Shack. Hold the
half torus near conductors and check for a glow. This should offer 10
to 100µA sensitivity and something new to worry about. ;-)

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
Hi Ken,

One of several things going on, barring more data.
I have 8-1/2' of rg8x between the
coil and my Z11 autotuner.
How much distance between the choke and the feedpoint? How much
distance between the auto tuner and your station?

Between the choke and the feedpoint is 3 3/4".
Between the Z11 and the station about 6"....


If considerably less then that means you and your domicile are
immersed in the very near fields of the antenna. This complicates
matters and certainly offers the prospects of Common Mode issues
galore (simply through imbalances offered by life in the 'burbs).

How near is too near? For 160M you cannot escape being part of the
radiator by living in the conventional house in a conventional tract.
Higher frequencies only reduce this prospect by degrees. For 20M the
near field, by various assessments, extends as little as 20M away from
the antenna to more conservative expectations of 100M to 200M.

How much does it matter? You seemed to have reduced what Common Mode
issues you could perceive enough. This doesn't mean you completely
removed them, just reduced them below your thresh hold of detection.
So, in that sense, mattering is an issue of detection and if your
neighbors do not detect your activity, nor do you burn yourself on
equipment ground, then there is no "problem."

I rember reading a thread awhile back that suggested one could get
an RF burn even at 5 watts, so I tested for that. I transmitted on all
freqs while touching various points (case screws, Pl-259 cases, etc.)
while I ramped up the freq from 1.8-30 mhz continuos sp. I felt no RF
and saw no change in SWR or power draw when tapping these points.


73's
Richard Clark, KB7QHC

Thanks for the good info, Richard - I hadn't though of near field issues...

72's de Ken KG0WX