I plan to put up an 80m dipole fed with open wire feeder for multiband
operation. It is down the other end of the house from the shack (50
feet away), so am thinking of mounting a remote tuner under the eaves
near the antenna and coax from there back to the shack.

Anyone tried this combo or similar? Would appreciate
recommendations/hints etc.

Damien VK3RX
Email:
The obvious anti-spam measure; replace mycall_above with my callsign
:-)

wrote:

I plan to put up an 80m dipole fed with open wire feeder for multiband
operation. It is down the other end of the house from the shack (50
feet away), so am thinking of mounting a remote tuner under the eaves
near the antenna and coax from there back to the shack.

Anyone tried this combo or similar? Would appreciate
recommendations/hints etc.

Damien VK3RX
Email:
The obvious anti-spam measure; replace mycall_above with my callsign
:-)

I've used a 102' centre fed wire with 28' home brew 600 ohm ladder to an
SGC 230. 230 is floated by coiled coax (and control lines) 11 turns about
12" diameter plus a couple of clip on ferrites forming a choke balun.
Tunes all bands 160-10. I think you'd be better of with 102' or 135' rather
than a resonant 80 m aerial as these are easier to match on some of the other
bands. An 80 m dipole is not easy to drive on 40 for instance. To get all
bands you obviously have to compromise and those lengths give an easier
match on all bands but don't have a perfect match on any.

My aerial is fairly low 30' - 45' and I don't seem to suffer too badly
from a 'lobey' pattern on the higher bands.

You might take a look at

http://www.camuw.demon.co.uk/web_sit...na/sgc230.html

Which describes a similar setup in more detail.

vy 73

Andy, M1EBV

Andy Cowley wrote:
I think you'd be better of with 102' or 135' rather
than a resonant 80 m aerial as these are easier to match on some of the other
bands.

If he were using 300 ohm or lower Z0 feedline, you might have a
point, but there's nothing to worry about with 600 ohm feedline.

A resonant 80m dipole may have a feedpoint impedance of 60 ohms.
An 80m dipole used on 40m may have a feedpoint impedance of 6000
ohms. In both cases, the SWR on the 600 ohm open-wire line is 10:1.
A 60 ohm antenna fed with 600 ohm feedline and a 6000 ohm antenna
fed with 600 ohm line are equally mismatched. If one doesn't know
the length of the feedline, one can't tell the difference at the
transmitter.
--
73, Cecil http://www.qsl.net/w5dxp



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Andy,

Is there any particular reason why you didn't use a balun on the
_output_ of the SGC rather than on the input?

73,
Bob AD3K

Andy Cowley wrote:

...
http://www.camuw.demon.co.uk/web_sit...na/sgc230.html

Which describes a similar setup in more detail.

vy 73

Andy, M1EBV

--
Robert L. Spooner
Registered Professional Engineer
Associate Research Engineer
Intelligent Control Systems Department

Applied Research Laboratory Phone: (814) 863-4120
The Pennsylvania State University FAX: (814) 863-7841
P. O. Box 30
State College, PA 16804-0030

Cecil Moore wrote:

Andy Cowley wrote:
I think you'd be better of with 102' or 135' rather
than a resonant 80 m aerial as these are easier to match on some of the other
bands.

If he were using 300 ohm or lower Z0 feedline, you might have a
point, but there's nothing to worry about with 600 ohm feedline.

A resonant 80m dipole may have a feedpoint impedance of 60 ohms.
An 80m dipole used on 40m may have a feedpoint impedance of 6000
ohms. In both cases, the SWR on the 600 ohm open-wire line is 10:1.
A 60 ohm antenna fed with 600 ohm feedline and a 6000 ohm antenna
fed with 600 ohm line are equally mismatched. If one doesn't know
the length of the feedline, one can't tell the difference at the
transmitter.


All true for the two bands. But - I did know the length of the feedline.
I did do the EZNEC simulations for the impedance seen looking into the
feedline for all bands and the lengths chosen do result in the 'easiest'
tuning solutions. The SGC is a good bit of kit but it won't tune just
any old thing, there are limits to the amount of L and C it can supply.
AFAIK it uses a simple 'L' solution always. If you get the wrong feedline
length and aerial length combination you can quickly get solutions which,
even when in range, produce excessive voltages at 100W. The SWR on open
wire line is not the significant factor here, losses are very low even at
very high SWRs, but the impedance transformation required in the tuner. The
SGC has fairly low voltage limits so I think 'tis best to treat it as
gently as possible.

I hope you don't think I'm recommending a G5RV here. The only good G5RV
is one without the coax, in which case I believe the design with those
lengths is due to Arthur Collins, (W9CXX?) in a prewar QST.

Thanks for the input anyway, Cecil.

vy 73

Andy, M1EBV

Damien,
It's a fairly common practice, if you have a remote
tuner handy. How well it will work depends a lot on the
tuner, if it can handle the impedances presented to it.
Not having a remote tuner, I do about the same thing except
the coax run is very short and the parallel feed line is
very long (lol). Are there any 'problems' with doing it
this way (or your way)? Sure, the same ones you see in
almost any antenna installation. There are frequencies
where the RFI is more objectionable than others. What
those frequencies are is going to be different for every
installation / situation, so you'll just have to try it
and see. Good luck...
'Doc

Andy Cowley wrote:
If you get the wrong feedline
length and aerial length combination you can quickly get solutions which,
even when in range, produce excessive voltages at 100W.

My point was that the wrong feedline length yields the same results for
a 60 ohm antenna as it does for a 6000 ohm antenna. If you feed that
60 ohm antenna with an odd multiple of 1/4WL of feedline, the impedance
seen at the tuner will be 6000 ohms. If you feed the 6000 ohm antenna
with a multiple of 1/2WL, the impedance seen at the tuner will be 6000
ohms. The impedance of the antenna doesn't really matter as long as it
is 1/2WL on the lowest frequency of interest. What matters is the SWR
on the feedline and the length of the feedline. The feedpoint should be
in the ballpark location of the current maximum point, not the voltage
maximum point.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Andy Cowley wrote:

If you get the wrong feedline length and aerial length combination you
can quickly get solutions which, even when in range, produce excessive
voltages at 100W.

My point was that the wrong feedline length yields the same results for
a 60 ohm antenna as it does for a 6000 ohm antenna. If you feed that
60 ohm antenna with an odd multiple of 1/4WL of feedline, the impedance
seen at the tuner will be 6000 ohms. If you feed the 6000 ohm antenna
with a multiple of 1/2WL, the impedance seen at the tuner will be 6000
ohms. The impedance of the antenna doesn't really matter as long as it
is 1/2WL on the lowest frequency of interest. What matters is the SWR
on the feedline and the length of the feedline. The feedpoint should be
in the ballpark location of the current maximum point, not the voltage
maximum point.

My statement is assuming 600 ohm open-wire feedline as specified earlier.
--
73, Cecil http://www.qsl.net/w5dxp



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Thanks for all the good info. gents.

Actually 80m is not critical for me. I was really looking for
something that will work nicely on 40 - 10m (including WARC would be
nice), and have been looking over the 44' design on the W4RNL page
http://www.cebik.com/aledz.html

The plan was to mount an SGC tuner or similar under the eaves near the
antenna and run coax back through the roof, because running open wire
feeder just isn't practical in the physical situation.

I run 250w PEP SSB, but it would also be nice if the system could
handle 120w of AM because I'm into that as well. Unfortunately that
means one of the high power tuners.

I have tried a Carolina Windom (40m "Beam" version") here, but while
it works well on 40m it gets progressively deaf above that.

H'm.... all food for thought.

Damien VK3RX

Open wire feedline is an excellent alternative and is much lower loss than
coax, especially at high SWRs. This way you can use a tuner in the shack.

73s,

Evan