80 m Dipole
 

The antenna will work OK. The VSWR may be a little high due to the low
height. Minimum height should be in excess of 65 feet and most hams
can't get that high!

Working on 20 meters will most likely be difficult without a good tuner.

Deacon Dave, W1MCE

whitehat wrote:

I will be building a center fed 80 m dipole, 62.5 feet
each side of center. The ends will be about 23 feet above
ground but the center is not supported to it sags to about
18 feet. I will feed it directly with about 25 feet of
RG-213 50 ohm coax and connect it to an antenna tuner in
the shack that can tune from 50 to 500 ohms.

This should work okay on 80 m, right?

How well will it do on 20 m?

whitehat wrote:
I will be building a center fed 80 m dipole, 62.5 feet
each side of center. The ends will be about 23 feet above
ground but the center is not supported to it sags to about
18 feet. I will feed it directly with about 25 feet of
RG-213 50 ohm coax and connect it to an antenna tuner in
the shack that can tune from 50 to 500 ohms.

This should work okay on 80 m, right?

How well will it do on 20 m?


Any way to get the centre up higher?
With some kind of a pole?
Eskay

For bands other than 80 you would be better off with a balanced feed line
than with the coax.

JD
KA9CAR


"whitehat" wrote in message
...
I will be building a center fed 80 m dipole, 62.5 feet
each side of center. The ends will be about 23 feet above
ground but the center is not supported to it sags to about
18 feet. I will feed it directly with about 25 feet of
RG-213 50 ohm coax and connect it to an antenna tuner in
the shack that can tune from 50 to 500 ohms.

This should work okay on 80 m, right?

How well will it do on 20 m?

whitehat,
Yes, it will work on 80 meters. Don't count on
using it on 20 meters. Depending on the tuner it
may 'tune', but you won't have the 'best' results.
'Doc

I will be building a center fed 80 m dipole, 62.5 feet
each side of center. The ends will be about 23 feet above
ground but the center is not supported to it sags to about
18 feet. I will feed it directly with about 25 feet of
RG-213 50 ohm coax and connect it to an antenna tuner in
the shack that can tune from 50 to 500 ohms.

This should work okay on 80 m, right?

How well will it do on 20 m?


For 80 it will work fine for the heights you have to work with. As most
always the higher the beter. If you want to work 20 meters or other bands
with the same antenna you might want to feed it with open wire or go to an
off center fed or (yuck) maybe the g5rv type.

You will be a much happier camper if you feed it with 450 ohm ladder line.
You will have no trouble using the antenna anywhere from 80 to 10, and if
the ladder feed is more than 70 feet you will be able to load the dipole on
160. If the feed line is not 70 feet long, you still will be able to use
the antenna on 160, just join the two sides of the feedline together and
treat as a longwire.

--
73 es cul

wb3fup
a Salty Bear

"Ralph Mowery" wrote in message
...
I will be building a center fed 80 m dipole, 62.5 feet
each side of center. The ends will be about 23 feet above
ground but the center is not supported to it sags to about
18 feet. I will feed it directly with about 25 feet of
RG-213 50 ohm coax and connect it to an antenna tuner in
the shack that can tune from 50 to 500 ohms.

This should work okay on 80 m, right?

How well will it do on 20 m?


For 80 it will work fine for the heights you have to work with. As most
always the higher the beter. If you want to work 20 meters or other
bands
with the same antenna you might want to feed it with open wire or go to
an
off center fed or (yuck) maybe the g5rv type.

"'Doc" wrote in message ...


whitehat,
Yes, it will work on 80 meters. Don't count on
using it on 20 meters. Depending on the tuner it
may 'tune', but you won't have the 'best' results.
'Doc

Perhaps basic antenna theory needs to be revisited here (?).


A center fed half wave antenna using standard 50 to 70 ohm coax will operate
with a 'reasonable' SWR at the ODD multiples of the fundamental.

Nice and simple.

Dan/W4NTI

Dan,
And compared to a 20 meter dipole, the 80 meter
dipole will stump it's toe on 20 meters.
'Doc

'Doc wrote:
And compared to a 20 meter dipole, the 80 meter
dipole will stump it's toe on 20 meters.

As a matter of interest, I just did an A/B comparison between
my 80m dipole and my 20m rotatable dipole. The guy in CA
couldn't tell any difference in transmitted signal levels
and I couldn't tell any difference in received signal levels.
In other words, in four directions, my 130ft dipole works
just as well on 20m as my resonant 20m rotatable dipole.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil,
Now all you have to do is get everyone to move so
that they are in one of those four directions from you.
'Doc

0 dBd !!!!!!!!!!

Deacon Dave, W1MCE

Reg Edwards wrote:

"'Doc" wrote Cecil,

Now all you have to do is get everyone to move so
that they are in one of those four directions from you.


============================

What is the gain in dB of a rotatable dipole relative to one which is fixed
?
---
Reg, G4FGQ

'Doc wrote:
Now all you have to do is get everyone to move so
that they are in one of those four directions from you.

With a fixed resonant dipole, you only get two directions. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Dave Shrader wrote:
0 dBd !!!!!!!!!!

Not off the ends of the fixed dipole. :-)

Reg Edwards wrote:
What is the gain in dB of a rotatable dipole relative to one which is
fixed?
--
73, Cecil http://www.qsl.net/w5dxp



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I use such an antenna but feed it differently. Mine is 130 ft long and fed
with 300-Ohm xmitting twin lead.

The transmission line connects to the balanced output of a MFJ tuner.

Used it on all bands 80 through 6 till I got a 6-m Yagi and a tribander.

It is still a much used antenna, especially on 80, 40, 18, and 24.

On 40 it is a fullwave doublet and has about 1.5 dB gain over a dipole.

I have used it in 160 by shorting the two wires of the twinlead together and
feeding it as a Marconi antenna.

I agree with other posters who wud like to see the center a little higher, but
a man's gotta do what a man's gotta do!

Have fun, Jack K9CUN

That's simply untrue. But I guess that's what the smiley face means?

Roy Lewallen, W7EL

W5DXP wrote:

With a fixed resonant dipole, you only get two directions. :-)

The gain of a dipole is the gain of a dipole.

Now, Directivity is another matter :-)

W1MCE

W5DXP wrote:

Dave Shrader wrote:

0 dBd !!!!!!!!!!


Not off the ends of the fixed dipole. :-)

Reg Edwards wrote:

What is the gain in dB of a rotatable dipole relative to one which is
fixed?

"WB3FUP (Mike Hall)" wrote in message
...
You will be a much happier camper if you feed it with 450 ohm ladder line.
You will have no trouble using the antenna anywhere from 80 to 10, and if
snipped

I need to run the feeder from my dipole (80m) up thro the eaves, thro' the
loft-space to the shack at the other side (1st floor) of the house, approx
50'. No other routes feasible. Because of the route, I thought I'd have
less problems using coax, BUT from the remarks in the above recent post,
will someone kindly comment on viability of 450 ohm twin feeder over such a
route?

Many thanks
Jim M0Jim

Replies to NG pse!!

Roy Lewallen wrote:
That's simply untrue. But I guess that's what the smiley face means?

Yep, *two* major lobes with a fixed resonant dipole. With a 130 ft.
dipole on 20m, I get two times or three times as many lobes. :-)

W5DXP wrote:
With a fixed resonant dipole, you only get two directions. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Dave Shrader wrote:
The gain of a dipole is the gain of a dipole.

Yes, and a fixed dipole doesn't have much gain off the ends compared
to a broadsided rotatable dipole. EZNEC says the maximum gain of my
dipole off the ends is "MAX GAIN = 0.88 dBi". I am extremely pleased
with my rotatable dipole. So much so that another element is just
not worth that extra half an S-unit.
--
73, Cecil http://www.qsl.net/w5dxp



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I need to run the feeder from my dipole (80m) up thro the eaves, thro'
the
loft-space to the shack at the other side (1st floor) of the house, approx
50'. No other routes feasible. Because of the route, I thought I'd have
less problems using coax, BUT from the remarks in the above recent post,
will someone kindly comment on viability of 450 ohm twin feeder over such
a
route?

=====================================

If necessary just squeeze heavy-duty 450-ohm ladder line wires close
together wherever they pass through a small hole. Line holes with a thick
plastic film or a pipe to obtain a higher breakdown voltage. Slowly twist
the cable every 2 feet between holes and keep it at least 1 or 2 inches away
from foreign materials, long metal conductors or otherwise.

If it was possible to do A-B comparisons at HF you would find little
difference - equivalent to a few pF change in a tuner capacitor setting and
1/2-turn change in the roller inductor. To be safe stick to 100 or 200 watts
unless you wish to test to destruction under worst case, but controlled
conditions (eg., very high SWR) just to see what happens. Probably nothing!

At HF a change in impedance Zo over a length of a few inches when passing
through one or two holes in timber or brickwork will have a negligible
effect on performance. The advantage of a balanced line all the way to the
transmitter may be that a tuner can be located in the shack. If an automatic
tuner is used then use easier-to-install coax and locate the tuner at the
antenna end.

Over a length of 50 or more feet, at 28 MHz, the lower loss in 450-ohm line
relative to 50-ohm RG-58 is worth thinking about. At 1.9 MHz forget it.

But it's only a matter of economics, time and labour, and the well-earned
satisfaction of having done a good job which works according to plan.
---
Reg, G4FGQ

But, it has the same gain as the dipole when both are configured the
same for Az and El.

BTW, the gain off the end of a rotatable dipole is the same as the gain
off the end of a fixed dipole.

When modeled in EZNEC, I don't see an input for rotatable dipole!!! If
the X,Y,Z coordinates are the same then the gain is the same. Rotate
both 90 degrees and the gain is still the same.

Trolling tonight is very poor. The Red Sox are playing. I don't know
whether to be happy or sad.

Deacon Dave, W1MCE

W5DXP wrote:

Dave Shrader wrote:

The gain of a dipole is the gain of a dipole.


Yes, and a fixed dipole doesn't have much gain off the ends compared
to a broadsided rotatable dipole. EZNEC says the maximum gain of my
dipole off the ends is "MAX GAIN = 0.88 dBi". I am extremely pleased
with my rotatable dipole. So much so that another element is just
not worth that extra half an S-unit.

Roy Lewallen wrote:
Having two lobes is way different than radiating only in two directions.

Depends on the defined courseness of the directions. With my rotatable
dipole running North-South, it only radiates well in two directions,
East and West, which is approximately half of the two out of four possible
course directions.
--
73, Cecil http://www.qsl.net/w5dxp



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Dave Shrader wrote:
BTW, the gain off the end of a rotatable dipole is the same as the gain
off the end of a fixed dipole.

Thus the advantage in being able to rotate it.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil,
Since mine isn't at the 'optimum' height, I hear
stuff from all around me.
'Doc

Jim,
If you follow the 'normal' rules for using twin-
lead feed line you shouldn't have any more (or any
less) problems than if you used coax. There is always
the possibility that RF will 'eat up' all the electrical
appliances in your house, but maybe not.
Nothing except your pocket says you can't change feed
lines or antenna if you want. So, try it and see what
happens...
'Doc