multiband vertical
 

On Thu, 19 Apr 2007 12:24:52 -0400, "Jimmie D"
wrote:

Cecil, I was thinking of trying your no= tune antenna and the 16 ft piece
may not be doable at my QTH, I have to keep it all hidden behind the bushes.
Could this piece be replaced with a circuit using lumped LC values.

Hi Jimmie,

I've been doing it with a binary switched coax matcher for 15 years.
It occupies about half a cubic foot and tunes in increments of 1, 2,
4, 8, and 16 feet.

73's
Richard Clark, KB7QHC

multiband vertical
 

Jimmie D wrote:
Cecil, I was thinking of trying your no= tune antenna and the 16 ft piece
may not be doable at my QTH, I have to keep it all hidden behind the bushes.
Could this piece be replaced with a circuit using lumped LC values.

That would work at one frequency but not others. What I do with
the 16 foot length is coil it into a spiral of 4 turns. The
diameter of the spiral is about 16 inches and the overall
length of the spiral is about 24 inches. That should fit
"behind the bushes". I use a piece of fiberglass rod to
which to tiewrap the coils.

There's nothing magic about the 16 foot length. It is only
necessary if you need to vary your length from 0 to 31 feet.
In actual practice with my 130 foot dipole, I only needed
to vary the length from 0 to 23 feet so I made the "16 ft"
section just another 8 foot section. The 16 foot section
was required from 3.5-3.6 MHz and I never use those frequencies.
That's why I could get away with replacing the 16 ft section
with another 8 ft section.
--
73, Cecil, w5dxp.com

multiband vertical
 

Richard Clark wrote:
I've been doing it with a binary switched coax matcher for 15 years.
It occupies about half a cubic foot and tunes in increments of 1, 2,
4, 8, and 16 feet.

Are you using 50 ohm coax to try to match to 50 ohms
or just using it to vary the virtual impedance?
--
73, Cecil, w5dxp.com

multiband vertical
 

On 18 Apr, 15:11, "Andre & Sharon Walker"
wrote:
Wow..looks like I opened a can of worms here!
Thanks to all for the many links and advice..much food for thought. I think
ill have to re assess I was considering end fed longwire also, but an
inverted V might be a better option. Anyway, should be on the air within 4
weeks...the licence is the easy bit, diverting funds for the radio from the
XYL is the tricky part!!! But ive been offered a FT101z , inc Yaseu Desk mix
+ spare set of finals ( is too early to rember the number of the tubes off
hand...just finished night shift), so ill have wind the wick WAY back to
start with. I don't care what they say at the club...I like boat anchors!!
( I'd love to replace the Murphy B40 I sold 10 years ago :-( )

Cheers

Andre"Owen Duffy" wrote in message

...



Cecil Moore wrote in
t:

Andre & Sharon Walker wrote:
I was hoping to get away from traps, but i dont think its possible
:-(. I only have a smallish yard, with just 30m from the chimmny
(brick ) to the back of the yard, so i think a decent wire antenna is
out...but i am open to suggestions. I guess the other considerstion
is to keep "she inside" happy .

A 1/2WL dipole is 20m on 40m and can be made to work on
all HF bands 40m-10m. That's probably what I would do
and then do something romantic to keep the XYL happy.

Cecil, Andre will not have access to most HF bands, just 80, 40, 15, and
10m.

It takes about 6 hours to train and assess a Foundation Licencee, so your
tunerless concept is perhaps more complex than Andre's current knowledge
base.

For example, I worked a FL chap a couple of days ago on 40m with a 80m
half wave dipole fed with a long run of coax, and he was confident that
his antenna worked real well, despite my expectation that it was likely
that well less than 10% of his permitted 10W PEP was radiated. It was
impossible to tell this chap that if he cut the dipole to half the length
it would work better on 40m.

It is no good telling people that an antenna isn't likely to work real
good, they will cite all the contacts that they have had with it, and as
we know, anything "works", doesn't it. However, most people listen to the
positive suggestion that with change, and antenna will work better (and
in the above case, more than 10 times the EIRP).

Andre, keep it simple. A coax fed half wave dipole is easy to get going
will limited knowledge and experience, and you should have a high
confidence that you will be able to deliver a suitable load to your
transmitter (ie it will deliver its rated power), and the antenna will be
quite efficient (ie that most of your 10W PEP transmitter power is
radiated). It will also work well on receive.

If you hear strong FL signals around, they have good antennas, and / or
are flaunting the power limit. It is easy to do the latter, but if you
get the antenna right, you still have the room for improvement when you
upgrade to the higher power limit.

Owen- Hide quoted text -

- Show quoted text -

Andre you did indeed open a can of worms!, A vertical antenna is the
most complicated thing in the world that even a newsgroup full of
antenna experts are having difficulty in solving.
It is quite possible that this thread will top a hundred replies
before you arrive at the right question that they can answer.
Cheers and beers
Art

multiband vertical
 

On Apr 19, 12:40 pm, Cecil Moore wrote:
Jimmie D wrote:
Cecil, I was thinking of trying your no= tune antenna and the 16 ft piece
may not be doable at my QTH, I have to keep it all hidden behind the bushes.
Could this piece be replaced with a circuit using lumped LC values.

That would work at one frequency but not others. What I do with
the 16 foot length is coil it into a spiral of 4 turns. The
diameter of the spiral is about 16 inches and the overall
length of the spiral is about 24 inches. That should fit
"behind the bushes". I use a piece of fiberglass rod to
which to tiewrap the coils.

There's nothing magic about the 16 foot length. It is only
necessary if you need to vary your length from 0 to 31 feet.
In actual practice with my 130 foot dipole, I only needed
to vary the length from 0 to 23 feet so I made the "16 ft"
section just another 8 foot section. The 16 foot section
was required from 3.5-3.6 MHz and I never use those frequencies.
That's why I could get away with replacing the 16 ft section
with another 8 ft section.
--
73, Cecil, w5dxp.com

Thanks Cecil, I have been wanting to put up an antenna like yours for
quite a while now. Today I was doing a liittle clean up in the attic
and found a box of DPDT open frame relays that should work well for
remote switches. I should be able to run coax out to my garden shed
and and ladder line from there to the antenna locating the switches at
the shed. I can hang the dipole at about 40ft and was wondering what
the pattern would be. I was thinking this low to the ground it would
be almost an omni- directional antenna. If I could ever get all my
crap organized I could probably put together one hell of a station.

Jimmie