Ed wrote:
My QUESTION(s): How effective would a balanced fed dipole of
about
100 feet length be on 75M ?

Make it 102 ft. and you will have the G5RV length about which
virtually everything in the world is known. It works so well
on 75m that you should not be able to notice the difference.
How easy/hard it is to match will depend upon the feedline
length.


Thank you, Cecil. Very few here responded to my questions the way I
had hoped, although there was some very good info in those responces.

I had wondered what the effect of inductance in the dipole legs would
have on a balanced fed antenna. It now appears that to get decent
results on 75M I don't need to do that, anyway.

I had not thought much about adding dropping wires to the ends of my
dipole legs, as one fellow suggested, because the trees are so conical
shaped that their lower branches would likely be in the way of the
vertical wires coming down off the ends.

I guess I need to research the G5RV antenna. Someone else here
posted a nice URL to a site on it and I will be perusing it more.

Cecil, I definitely can make my dipole 102 feet accross the top. I
am guesstimating that I will need approximately 35 or 40 feet of feedline
from the shack to the feedpoint. Do you see any issues with that?

Ed K7AAT

Ed wrote:
Cecil, I definitely can make my dipole 102 feet accross the top. I
am guesstimating that I will need approximately 35 or 40 feet of feedline
from the shack to the feedpoint. Do you see any issues with that?

That's a very good length for 40m, 17m, & 10m. You can analyze the
antenna yourself by downloading the free demo version of EZNEC
from www.eznec.com. If you want, I'll send you a model of your
antenna so all you have to do is click the mouse.
--
73, Cecil http://www.qsl.net/w5dxp

That's a very good length for 40m, 17m, & 10m. You can analyze the
antenna yourself by downloading the free demo version of EZNEC
from www.eznec.com. If you want, I'll send you a model of your
antenna so all you have to do is click the mouse.


Thanks for the offer, Cecil, but at this time I will decline. I plan
on just putting up as much wire as I can effectively mount between the
two trees, about 100 feet, and just feed it at the center with ladder
line. A new balanced tuner will tune the whole thing. I expect this to
give me a bit more flexibility than the G5RV would.


Ed K7AAT

Ed wrote:
Thanks for the offer, Cecil, but at this time I will decline. I plan
on just putting up as much wire as I can effectively mount between the
two trees, about 100 feet, and just feed it at the center with ladder
line.

That's the antenna I was offering to model for you. You will,
no doubt, run into some pitfalls, for instance an impedance
of 8 ohms or 4000 ohms that your tuner may not be able to handle.
EZNEC can predict such problems before they bite you.

As a data point, the MFJ-974 gives you a matching range of 12-2000
Ohms.

EZNEC can also predict your radiation patterns which are important
on the high bands if you want to hit certain areas of the world.
Rotating my dipole in AZ by 15 degrees made a lot of difference.
--
73, Cecil http://www.qsl.net/w5dxp

On Tue, 18 Oct 2005 03:18:39 GMT, Cecil Moore wrote:

Ed wrote:
Thanks for the offer, Cecil, but at this time I will decline. I plan
on just putting up as much wire as I can effectively mount between the
two trees, about 100 feet, and just feed it at the center with ladder
line.

That's the antenna I was offering to model for you. You will,
no doubt, run into some pitfalls, for instance an impedance
of 8 ohms or 4000 ohms that your tuner may not be able to handle.
EZNEC can predict such problems before they bite you.

As a data point, the MFJ-974 gives you a matching range of 12-2000
Ohms.

EZNEC can also predict your radiation patterns which are important
on the high bands if you want to hit certain areas of the world.
Rotating my dipole in AZ by 15 degrees made a lot of difference.

For any given frequency, would that 8 ohms or 4000 ohms be decided by
the length of the dipole or the length of the ladderline, or both?

bob
k5qwg

Bob Miller wrote:
For any given frequency, would that 8 ohms or 4000 ohms be decided by
the length of the dipole or the length of the ladderline, or both?

Both. For instance the resonant impedance of a G5RV on the lower
part of 80m is usually about 8 ohms. If the feedline for a one
wavelength dipole is 1/2WL, the impedance will be about 4000 ohms.
The feedline impedance seen by your tuner is somewhat unpredictable
and EZNEC can tell you what ballpark impedance to expect. EZNEC
has saved me an enormous amount of time - 10 minutes of simulation
Vs 10 hours of antenna erection time.
--
73, Cecil http://www.qsl.net/w5dxp

The loss in a switched transmission line tuner is somewhat greater
than in a conventional tuner which can be adjusted for an exact,
low-loss, impedance match.
---
Reg.

That's the antenna I was offering to model for you. You will,
no doubt, run into some pitfalls, for instance an impedance
of 8 ohms or 4000 ohms that your tuner may not be able to handle.
EZNEC can predict such problems before they bite you.

OK. I'll take you up on the offer, afterall. Figure 100' of #14
copperweld, centerfed with 450ohm ladderline or with 600 ohm open wire
line (2"). Height should be about 45' at ends and 35 feet center.
Length of feedline is projected at about 45 feet.

I'll go with the 600 ohm wireline feed if I can find it, otherwise,
the cheap 450 ohm plastic stuff for now and build wireline next summer.



EZNEC can also predict your radiation patterns which are important
on the high bands if you want to hit certain areas of the world.
Rotating my dipole in AZ by 15 degrees made a lot of difference.

Not real concerned with the patterns of anything above 40M. I'm
mainly interested in 80/75/60/40M use. I'll take what I get and see
how it goes..... might be nice to see 20M and 10M patterns, though.
Thanks.


Ed

600 ohm open wire line is available from W7FG [800-807-6146].

50 feet $23
100 feet $40.

I've used it for years at the KW level. No problems.

I'm just a satisfied customer and have no financial interest in their
business.



Ed wrote:

That's the antenna I was offering to model for you. You will,
no doubt, run into some pitfalls, for instance an impedance
of 8 ohms or 4000 ohms that your tuner may not be able to handle.
EZNEC can predict such problems before they bite you.


OK. I'll take you up on the offer, afterall. Figure 100' of #14
copperweld, centerfed with 450ohm ladderline or with 600 ohm open wire
line (2"). Height should be about 45' at ends and 35 feet center.
Length of feedline is projected at about 45 feet.

I'll go with the 600 ohm wireline feed if I can find it, otherwise,
the cheap 450 ohm plastic stuff for now and build wireline next summer.



EZNEC can also predict your radiation patterns which are important
on the high bands if you want to hit certain areas of the world.
Rotating my dipole in AZ by 15 degrees made a lot of difference.


Not real concerned with the patterns of anything above 40M. I'm
mainly interested in 80/75/60/40M use. I'll take what I get and see
how it goes..... might be nice to see 20M and 10M patterns, though.
Thanks.


Ed

600 ohm open wire line is available from W7FG [800-807-6146].

50 feet $23
100 feet $40.


Thanks. I've noted the number (what an interesting set up numbers!),
and will call in a few weeks when I'm ready to order.


Ed