Hi,

I have a 40 meter centre feed dipole cut for 40 and feed direct with 50 Ohm
coax. The house end is connected to the centre of the coax and the pole end
is connected to the braid. Seems to work best this way round.
The antenna is fixed tight to the house and the other end is tight to the
metal pole in a straight-line, diagonal across the garden, both ends are
insulated. The garden is about 64 feet give or take a couple of feet.

I cannot drop the ends down because of the house and metal pole at the end
of the garden being so close. I can only feed the antenna with coax. The
neighbours are OK with coax but not the ribbon feeder hanging down and I
don't want to upset them if I can help it.

My question. What are my options to enable me to operate 80 and 40m on this
same antenna wire?


73 Andy

Andy,

Pretty much any antenna tuning unit (ATU) will work to enable you to use
this antenna on 80 metres. Obviously efficiency will suffer, but you will
get a signal out. The antenna needs extra length or more inductance to bring
it to resonance on 80 metres.

You could experiment with an old metal variable capacitor (around 350 pf)
and a two inch diameter coil with about 12 or 15 turns and a fly lead to
short out the turns. Old mains wiring cable is a good source of wire for
this. Connecting this up in the coax feed in an 'L' configuration will allow
a surprising range of frequencies to be brought to resonance on your
antenna. Check out Google for some ideas on how to wire it up. A metal air
spaced variable should be good for powers up to a hundred watts without
arcing problems.

There will probably be a lot of articles about an unbalanced feed causing
the coax to radiate. Winding the coax into half a dozen 6-inch turns
fastened with cable ties at the feed point of the dipole will help avoid
this problem.

Or, you could add a couple of coils, one each side of the dipole centre to
increase the physical wire length in the air and bridge out the coils to
work at 20 metres, but this would involve raising and lowering the antenna.
You could use a couple of relays to perform the job, but it all starts to
get rather more complex than simply using an ATU.

Regards

Mike G0ULI

"Andy" wrote in message
...
Hi,

I have a 40 meter centre feed dipole cut for 40 and feed direct with 50
Ohm coax. The house end is connected to the centre of the coax and the
pole end is connected to the braid. Seems to work best this way round.
The antenna is fixed tight to the house and the other end is tight to the
metal pole in a straight-line, diagonal across the garden, both ends are
insulated. The garden is about 64 feet give or take a couple of feet.

I cannot drop the ends down because of the house and metal pole at the end
of the garden being so close. I can only feed the antenna with coax. The
neighbours are OK with coax but not the ribbon feeder hanging down and I
don't want to upset them if I can help it.

My question. What are my options to enable me to operate 80 and 40m on
this same antenna wire?


73 Andy

Any,
I think one way is to feed the antenna as a top loaded vertical. What you
do is at the end of the coax (the PL259 connector) you short the center to
the braid. Then you treat it as a single wire, as if it was the bottom end
of a vertical. Use a tuner. You will need a ground on the tuner.
The most optimum arrangement would be for the tuner to be sitting on the
earth, right under the centre of the dipole with the coax coming straight
down to it, and with a series of radials out all over the ground from the
tuner. This will probably not be possible so you start making your
compromises from there.
Rick K2XT

Andy wrote:
My question. What are my options to enable me to operate 80 and 40m on this
same antenna wire?

I would consider a switched loading coil at the feedpoint.
Switch it in for 80m and out for 40m.
--
73, Cecil http://www.w5dxp.com

Andy wrote:

My question. What are my options to enable me to operate 80 and 40m on this
same antenna wire?

You could get trap dipoles for the 80 and 40m band with almost the
dimensions of a 40m dipol, e.g Diamond W-8010


My antenna book shows a short antenna for 80 and 40m which is called
"Morgain antenna". It was originally produced in the USA.

http://i4ewh.altervista.org/ShortWav...in/Morgain.htm

--
73
DJ4PB

Andy wrote:
Hi,

I have a 40 meter centre feed dipole cut for 40 and feed direct with 50 Ohm
coax. The house end is connected to the centre of the coax and the pole end
is connected to the braid. Seems to work best this way round.
The antenna is fixed tight to the house and the other end is tight to the
metal pole in a straight-line, diagonal across the garden, both ends are
insulated. The garden is about 64 feet give or take a couple of feet.

I cannot drop the ends down because of the house and metal pole at the end
of the garden being so close. I can only feed the antenna with coax. The
neighbours are OK with coax but not the ribbon feeder hanging down and I
don't want to upset them if I can help it.

My question. What are my options to enable me to operate 80 and 40m on this
same antenna wire?
===========================================
300 Ohms ribbon twin feeder is hardly more visible than coax feeder .
You don't have to use the 'wide' 450 Ohms ribbon type.
300 Ohms ribbon has an approx velocity factor of 0.8 ,so if you make
half the dipole + the feeder (roughly) an electrical 1/4 -3/4 -etc
wavelength at 80 meters ,you will be home and dry with an appropriate
matching unit or a choke balun in combination with a 'coax-in ,coax-out'
matching box.

Frank GM0CSZ / KN6WH

Thanks for all your suggestions. When this wet weather clears I will try
them all out and see where I end up..

73 Andy


"Highland Ham" wrote in message
...
Andy wrote:
Hi,

I have a 40 meter centre feed dipole cut for 40 and feed direct with 50
Ohm coax. The house end is connected to the centre of the coax and the
pole end is connected to the braid. Seems to work best this way round.
The antenna is fixed tight to the house and the other end is tight to the
metal pole in a straight-line, diagonal across the garden, both ends are
insulated. The garden is about 64 feet give or take a couple of feet.

I cannot drop the ends down because of the house and metal pole at the
end of the garden being so close. I can only feed the antenna with coax.
The neighbours are OK with coax but not the ribbon feeder hanging down
and I don't want to upset them if I can help it.

My question. What are my options to enable me to operate 80 and 40m on
this same antenna wire?
===========================================
300 Ohms ribbon twin feeder is hardly more visible than coax feeder .
You don't have to use the 'wide' 450 Ohms ribbon type.
300 Ohms ribbon has an approx velocity factor of 0.8 ,so if you make half
the dipole + the feeder (roughly) an electrical 1/4 -3/4 -etc wavelength
at 80 meters ,you will be home and dry with an appropriate matching unit
or a choke balun in combination with a 'coax-in ,coax-out' matching box.

Frank GM0CSZ / KN6WH

On Jun 17, 4:04 pm, "Andy" wrote:
Thanks for all your suggestions. When this wet weather clears I will try
them all out and see where I end up..

73 Andy

"Highland Ham" wrote in message

...

Andy wrote:
Hi,

I have a 40 meter centre feed dipole cut for 40 and feed direct with 50
Ohm coax. The house end is connected to the centre of the coax and the
pole end is connected to the braid. Seems to work best this way round.
The antenna is fixed tight to the house and the other end is tight to the
metal pole in a straight-line, diagonal across the garden, both ends are
insulated. The garden is about 64 feet give or take a couple of feet.

I cannot drop the ends down because of the house and metal pole at the
end of the garden being so close. I can only feed the antenna with coax.
The neighbours are OK with coax but not the ribbon feeder hanging down
and I don't want to upset them if I can help it.

My question. What are my options to enable me to operate 80 and 40m on
this same antenna wire?
===========================================
300 Ohms ribbon twin feeder is hardly more visible than coax feeder .
You don't have to use the 'wide' 450 Ohms ribbon type.
300 Ohms ribbon has an approx velocity factor of 0.8 ,so if you make half
the dipole + the feeder (roughly) an electrical 1/4 -3/4 -etc wavelength
at 80 meters ,you will be home and dry with an appropriate matching unit
or a choke balun in combination with a 'coax-in ,coax-out' matching box.

Frank GM0CSZ / KN6WH

I just put up a 66' center fed zep, fed with 450 ohm ribbon line.
This line goes to just outside my radio room where it terminates into
a 4:1 Home-made (off the www) balun, coax feeds into the house to a
Nye tuner. Easily tunes 80 to 10 mtrs & works good.
Many good ways, this is just one!
GL.....
Rich WA2RQY/4

Hi all,

I have now tried all sorts of combinations and the best that I have found to
work best in such a small place is a 40m centre fed dipole, fed direct with
40 feet of 50 Ohm RG58 c/u then into a Ugly Balun made of RG58 c/u then into
RG213 back to the ATU. This is just how it all worked out, come the end.
I then made a couple of 40 meter traps for 80m.
The 40 meter section of the dipole barely fits the garden with no room to
spare. The traps and the added lengths of wire are dropped down and tied
back slightly to keep it away from the mounting pole, It is still kept at a
right angle to the main part of the antenna.
I have a 1.1:1 - 1.3:1 on the main frequency that I want to use on 40m and
80m without using the ATU.
It seems to work very well for what it is.
Thanks all for your help.

73 Andy


"wa2rqy" wrote in message
...
On Jun 17, 4:04 pm, "Andy" wrote:
Thanks for all your suggestions. When this wet weather clears I will try
them all out and see where I end up..

73 Andy

"Highland Ham" wrote in message

...

Andy wrote:
Hi,

I have a 40 meter centre feed dipole cut for 40 and feed direct with
50
Ohm coax. The house end is connected to the centre of the coax and the
pole end is connected to the braid. Seems to work best this way round.
The antenna is fixed tight to the house and the other end is tight to
the
metal pole in a straight-line, diagonal across the garden, both ends
are
insulated. The garden is about 64 feet give or take a couple of feet.

I cannot drop the ends down because of the house and metal pole at the
end of the garden being so close. I can only feed the antenna with
coax.
The neighbours are OK with coax but not the ribbon feeder hanging down
and I don't want to upset them if I can help it.

My question. What are my options to enable me to operate 80 and 40m on
this same antenna wire?
===========================================
300 Ohms ribbon twin feeder is hardly more visible than coax feeder .
You don't have to use the 'wide' 450 Ohms ribbon type.
300 Ohms ribbon has an approx velocity factor of 0.8 ,so if you make
half
the dipole + the feeder (roughly) an electrical 1/4 -3/4 -etc
wavelength
at 80 meters ,you will be home and dry with an appropriate matching
unit
or a choke balun in combination with a 'coax-in ,coax-out' matching
box.

Frank GM0CSZ / KN6WH

I just put up a 66' center fed zep, fed with 450 ohm ribbon line.
This line goes to just outside my radio room where it terminates into
a 4:1 Home-made (off the www) balun, coax feeds into the house to a
Nye tuner. Easily tunes 80 to 10 mtrs & works good.
Many good ways, this is just one!
GL.....
Rich WA2RQY/4

Then I would have to say that you have done the best that you can do
with the resources you have available, and that's good! May not be
the 'best' of all possible antennas, but if it works well enough, so
what?
- 'Doc

(Now that you've got yours working... wanna work on mine??)