After reading several articles both on and off the WEB regarding a
center fed antenna, only one article mentioned a recommended length for
the feed line.

My shack is located on the second floor of a new home, (24') #8 ground
wire to 8' ground stake with a further connection to the common ground
point for the power and the rebar in the pored walls and flooring of the
basement, telephone and cable. I plan on additional ground rods around
the property and at a new tower. In a new home so progress is on-going.

The 1:1 current balum used to convert the 450 ohm balance line is
external to the tuner, use about two feet of coax from the balum to the
tuner.

Antenna is cut for 80 meters and using about 60-70 ft of line to center
of the antenna. Where the antenna lines leave the shack is about four 4
ft from the location inside of the rig and floor mounted PC.

I use the antenna on all bands until such time I complete a new tower
installation. I want to minimize stray RF around the shack since I rely
on a PC and digital sound card as my primary source for ham enjoyment.
I have already had some problems with a USB keyboard that I think may
have been effected by RF when running over 50 watts on 20 meters only.

One article recommended odd multiples of a wave length is desirable at
the lowest operating frequency while other articles don't address this.

I am having no problem with a match using the tuner on all bands 80-6
meters.

Have used the center fed antenna since 1976 but always had the shack on
the ground level and had a good and effective ground system short runs
with feed lines around the 90 to 100ft in length. never had a RF
problem or surge problem.

Any recommended WEB sites or comments are welcomed.

73 de
Ron W4LDE

Ron Walters wrote:
Any recommended WEB sites or comments are welcomed.

If your ground wire is an appreciable percentage of
a wavelength, it is a radiating element grounded at
one end, i.e. not a ground. An artificial ground
might help to reduce RF in the shack.

If your antenna is balanced, you don't need an RF
ground.
--
73, Cecil http://www.w5dxp.com

"Ron Walters" wrote in message
t.net...
After reading several articles both on and off the WEB regarding a
center fed antenna, only one article mentioned a recommended length for
the feed line.

some antennas, like the g5rv rely on a particular length of feedline because
it becomes part of the antenna and radiates on certain bands. others use it
as an impedance transformer.

One article recommended odd multiples of a wave length is desirable at
the lowest operating frequency while other articles don't address this.

that is a myth that has been around for many years. there is no 'magic
length' that works better than others, except maybe the shortest length that
reaches from the antenna to the transmitter. The only reasons to use longer
lengths is if you need to use it as an impedance transformer because the
antenna isn't matched to the line, or to allow for future rearrangement of
the shack. what can be handy about the 1/2 wavelength line is if the
antenna isn't matched to the line impedance the antenna impedance will be
repeated every 1/2 wavelength along the line. so if you have a 300 ohm
antenna and a 50 ohm coax, every 1/2 wavelength along the line you will see
the 300 ohms again. this of course only works on harmonically related
bands.

Cecil Moore wrote:
Ron Walters wrote:
Any recommended WEB sites or comments are welcomed.

If your ground wire is an appreciable percentage of
a wavelength, it is a radiating element grounded at
one end, i.e. not a ground. An artificial ground
might help to reduce RF in the shack.

If your antenna is balanced, you don't need an RF
ground.

Cecil:

Say I had a situation where I must use a ground wire which IS an
appreciable percentage of a wavelength ... and don't wish it to radiate.

Could I accomplish this by using coax as the ground-wire and choking the
outer braid by sufficient windings on a toroid core, and grounding the
center conductor and the braid to earth though good and deep grounding
spikes or wires?

Regards,
JS

On Jul 2, 8:08 am, John Smith wrote:
Cecil Moore wrote:
Ron Walters wrote:
Any recommended WEB sites or comments are welcomed.

If your ground wire is an appreciable percentage of
a wavelength, it is a radiating element grounded at
one end, i.e. not a ground. An artificial ground
might help to reduce RF in the shack.

If your antenna is balanced, you don't need an RF
ground.

Cecil:

Say I had a situation where I must use a ground wire which IS an
appreciable percentage of a wavelength ... and don't wish it to radiate.

Could I accomplish this by using coax as the ground-wire and choking the
outer braid by sufficient windings on a toroid core, and grounding the
center conductor and the braid to earth though good and deep grounding
spikes or wires?

Regards,
JS

The only way to keep a wire--e.g., piece of coax--from being a
radiator is to keep net current at zero. If there's no net current,
you didn't need the wire anyway (at that frequency, at least). If
it's a protective ground for mains frequency, it will probably still
work for that purpose if you add ferrite for RF choking.

K7ITM wrote:

...
The only way to keep a wire--e.g., piece of coax--from being a
radiator is to keep net current at zero. If there's no net current,
you didn't need the wire anyway (at that frequency, at least). If
it's a protective ground for mains frequency, it will probably still
work for that purpose if you add ferrite for RF choking.


K7ITM:

I was hoping the rf/dc/ac could reach ground via a very low
resistance/impedance to rf on the inner surface of the braid and the
center conductor ...

While it would be virtually impossible to reduce rf on the outer braid
to absolute zero, I was hoping the choke would provide sufficient
impedance to rf to where it became near negligible, at least for
practical purposes.

Regards,
JS

John Smith wrote:
... I was hoping the choke would provide sufficient
impedance to rf to where it became near negligible, at least for
practical purposes.


In the above, change "sufficent" to low ...

Regards,
JS

"Dave" wrote in message news:vNMak.174$P11.105@trndny06...

"Ron Walters" wrote in message
t.net...
After reading several articles both on and off the WEB regarding a
center fed antenna, only one article mentioned a recommended length for
the feed line.

some antennas, like the g5rv rely on a particular length of feedline because
it becomes part of the antenna and radiates on certain bands. others use it
as an impedance transformer.

It is also a myth that the feedline for the g5rv requires a particular length
because it becomes part of the antenna and radiates on certain bands. At the
antenna terminals the feedline becomes a transmission line with opposite
directions of current on each conductor. Thus the fields developed around each
conductor cancel resulting in no radiation from the feedline if it's dressed at
90° from the antenna.

In addition, it's also a myth that the feedline of a shortened antenna radiates.
Some believe that the portion of the feedline that makes up for the missing
length of the shortened antenna radiates--tain't so.

Walt, W2DU

John Smith wrote:
Say I had a situation where I must use a ground wire which IS an
appreciable percentage of a wavelength ... and don't wish it to radiate.
Could I accomplish this by using coax as the ground-wire and choking the
outer braid by sufficient windings on a toroid core, and grounding the
center conductor and the braid to earth though good and deep grounding
spikes or wires?

Offhand, I would say you could accomplish a DC ground
that way but not an RF ground and not much lightning
protection.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

...
Offhand, I would say you could accomplish a DC ground
that way but not an RF ground and not much lightning
protection.

I suspect you to be correct; a "free ride" is just too much to hope for
in these times.

Well, even a dc/60hz ground which does not radiate rf can be useful.

Regards,
JS