I have a (home built) 40 m ground plane with the base elevated about 8
feet and with 7 elevated sloping radials. The 50 Ohm feedline drops
straight down the 8 feet and then runs on the surface of the ground.

Would a choke balun at the feed point be advisable?

W0BF

On Feb 23, 11:13*pm, TOF wrote:
I have a (home built) 40 m ground plane with the base elevated about 8
feet and with 7 elevated sloping radials. *The 50 Ohm feedline drops
straight down the 8 feet and then runs on the surface of the ground.

Would *a choke balun at the feed point be advisable?

W0BF

it wouldn't hurt, but unless you have problems with rf on the feedline
getting back into the shack i wouldn't bother.

On Feb 24, 12:51*am, Dave wrote:
On Feb 23, 11:13*pm, TOF wrote:

I have a (home built) 40 m ground plane with the base elevated about 8
feet and with 7 elevated sloping radials. *The 50 Ohm feedline drops
straight down the 8 feet and then runs on the surface of the ground.

Would *a choke balun at the feed point be advisable?

W0BF

it wouldn't hurt, but unless you have problems with rf on the feedline
getting back into the shack i wouldn't bother.

p.s. it might also help if you are picking up local noise that is
being conducted on the shield.

On Tue, 23 Feb 2010 16:52:03 -0800 (PST), Dave wrote:

On Feb 24, 12:51*am, Dave wrote:
On Feb 23, 11:13*pm, TOF wrote:

I have a (home built) 40 m ground plane with the base elevated about 8
feet and with 7 elevated sloping radials. *The 50 Ohm feedline drops
straight down the 8 feet and then runs on the surface of the ground.

Would *a choke balun at the feed point be advisable?

W0BF

it wouldn't hurt, but unless you have problems with rf on the feedline
getting back into the shack i wouldn't bother.

p.s. it might also help if you are picking up local noise that is
being conducted on the shield.

The location is in the boonies of northern MN and is generally very
quiet. I am more concerned about disturbance to the radiation
pattern.

On 2/23/2010 3:13 PM, TOF wrote:
I have a (home built) 40 m ground plane with the base elevated about 8
feet and with 7 elevated sloping radials. The 50 Ohm feedline drops
straight down the 8 feet and then runs on the surface of the ground.

Would a choke balun at the feed point be advisable?

W0BF


If rf is on the feedline, to a noticible degree, there is an easy
indication I have found and think worthwhile to look at. That is, a
field strength meter placed at a strategic point to make it more
"susceptible" to the rf on the feedline. Now move the feedline. If the
feedline is carrying enough rf to worry about, you will see it, at
least, that has been my experience.

The only problem with the above are those "weird" antennas where the
feedline actually plays a role in the antennas performance ... so, use
with caution.

I don't believe rf on the feedline is what you want with your groundplane.

Regards,
JS

On 24 feb, 00:13, TOF wrote:
I have a (home built) 40 m ground plane with the base elevated about 8
feet and with 7 elevated sloping radials. *The 50 Ohm feedline drops
straight down the 8 feet and then runs on the surface of the ground.

Would *a choke balun at the feed point be advisable?

W0BF

Hello,

When that 7 radials don't touch ground and are about 1/4 lambda in
size, you have a very good floating ground. It will depend on the
length of the radiator whether you get significant voltage between
your floating ground and Earth.

When using a 1/4 lambda radiator (or longer with a series capacitor
and transformer) in my opinion you don't need it. During JOTA we use
a 0.4 lambda radiator over 6 elevated quarter wave radials (7..8 ft).
Last year we only used three of them. Moving high impedance cores
(for 7 MHz) along the coaxial feeder did not change VSWR. Also a good
diode probe with whip didn't show common mode issues with the coaxial
feeder.

Best regards,


Wim
PA3DJS
www.tetech.nl
without abc you have a functioning email address.