antenna question
 

Taking a break from computers, I had an actual practical question about
an antenna. Sort of hypothetical, but maybe some practical use.

Situation:

Yard with a maximum antenna possibility of 100 feet. Height around 60
-70 feet.

All band is desired

in line with that, a decision to run ladder line (not window line)


Obviously, a tuner will tune the antenna.

But an antenna cut for somewhere in the 75 or 80 meter band is often
touted as a good length, around 130 feet for this antenna.

Is there an advantage to loading the antenna to place it in the band,
and tune the rest, or just to string up in the available space?

Perhaps something to allow it to une easily on 160?

Or, is there anything that would contraindicate using this approach?

- 73 de Mike N3LI -

antenna question
 

On Mon, 10 Oct 2011 22:58:03 -0400, Michael Coslo wrote:

Taking a break from computers, I had an actual practical question about
an antenna. Sort of hypothetical, but maybe some practical use.

Situation:

Yard with a maximum antenna possibility of 100 feet. Height around 60
-70 feet.

All band is desired

in line with that, a decision to run ladder line (not window line)


Obviously, a tuner will tune the antenna.

But an antenna cut for somewhere in the 75 or 80 meter band is often
touted as a good length, around 130 feet for this antenna.

Is there an advantage to loading the antenna to place it in the band,
and tune the rest, or just to string up in the available space?

Perhaps something to allow it to une easily on 160?

Or, is there anything that would contraindicate using this approach?

- 73 de Mike N3LI -

I'd try an inverted V cut for 80

antenna question
 

Mike,
Would it work? I think it will certainly work. That doesn't say how -
well- it would work, naturally, but you could put some kind of signal
on almost any band.
One option with that 100 feet and an 80 meter 'length' is to just drop
about 15 feet straight down (or tilted?) on each end of that 100 foot
span. That might even work for an 160 meter 'length' but not real
well, sort of, who knows?
One option on making something link that 'tunable' is by varying the
feed line length. Or, have a really 'capable' tuner. I doubt if it
would be the "best" radiator in the world, but it can certainly be
made to work.
- 'Doc

(Wish I had that 60 - 70 foot height capability!)

antenna question
 

On Mon, 10 Oct 2011 22:58:03 -0400, Michael Coslo
wrote:

All band is desired

Fan Dipole.

But an antenna cut for somewhere in the 75 or 80 meter band is often
touted as a good length, around 130 feet for this antenna.

As offered, dropping ends.

Perhaps something to allow it to une easily on 160?

The 80M length with tuner shouldn't be a problem.

73's
Richard Clark, KB7QHC

antenna question
 

Michael Coslo wrote in news:j70bc2$g87m$1
@tr22n12.aset.psu.edu:

....
But an antenna cut for somewhere in the 75 or 80 meter band is often
touted as a good length, around 130 feet for this antenna.

Indeed it is stated as the minimum length andtenna (being a half wave on
the lowest operating frequency), fed with open wire feed of any type, and
touted as a no-brainer, you can't go wrong.

As with most simplistic advice, it is flawed.

You gave lots of info on the system, well done, but ommitted the preferred
feed line length.

It may well be that your preferred feedline length should dictate the
dipole length.

Owen

antenna question
 

On 10/10/2011 9:58 PM, Michael Coslo wrote:
Taking a break from computers, I had an actual practical question about
an antenna. Sort of hypothetical, but maybe some practical use.

Situation:

Yard with a maximum antenna possibility of 100 feet. Height around 60
-70 feet.

All band is desired

in line with that, a decision to run ladder line (not window line)


Obviously, a tuner will tune the antenna.

But an antenna cut for somewhere in the 75 or 80 meter band is often
touted as a good length, around 130 feet for this antenna.

Is there an advantage to loading the antenna to place it in the band,
and tune the rest, or just to string up in the available space?

Perhaps something to allow it to une easily on 160?

Or, is there anything that would contraindicate using this approach?

- 73 de Mike N3LI -

In theory, for 80m use, I don't see much benefit to cutting it exactly
for 80m. The difference in matching loss should be fairly unnoticeable
as long as you are in the general ball park.
Ladder line should be pretty low loss, even with a high SWR.
So if there were to be excess loss, it would likely be the tuner.
And in this case, I don't think the difference would really be
noticeable on the air.
But... If it were me, I'd probably cut it to length anyway. But only
for the reason that I might decide to use coax at some later
date, and could still use the same wire. Or.. at least make it
too long, not too short.. That way it could be re-used with any
kind of line. But, maybe I'm just overly cheap and hate to see
a perfectly good stretch of wire go to waste.. :/

For 160 use, I'd feed it as a single conductor. Either short the
feed line, or feed just one leg. I'd generally prefer to short the
feed line to add more top loading. Makes it act like a T vertical.
If you fed one leg, it would be like an inv L. Either way should
be easier to match with a lower loss than trying to feed it as a
1/2 size dipole. The tuner loss will get you in most cases trying to
do that.

antenna question
 

On 10/11/2011 9:51 AM, 'Doc wrote:

(Wish I had that 60 - 70 foot height capability!)

Here in Park Forest ( i kid you not) we have some really amazing oak
trees. I could get 100 feet if I didn't mind the droop in the middle for
all the movement.

- 73 de Mike N3LI -

antenna question
 

On 10/11/2011 5:59 PM, Owen Duffy wrote:

You gave lots of info on the system, well done, but ommitted the preferred
feed line length.

It may well be that your preferred feedline length should dictate the
dipole length.

Lessee, I have standoffs holding the present window line, and can back
of the envelope this. five feet to the roofline, then 25 feet to
transition to where it heads verticaly. Then allowing for some droop,
I'd say another 40 feet given the 20 foot roof height.

So we're looking at around 90 feet total, not counting the foot or so in
the house.

- 73 de Mike N3LI -

antenna question
 

Michael Coslo wrote in
:

So we're looking at around 90 feet total, not counting the foot or so
in the house.

One of the risks of using a centre fed dipole with arbitrary open wire
feed is that you may find the impedance at the tx end of the line to be
extreme on some bands, driving problems with volage baluns, and ATUs.

In the case of a 80m half wave, feedline lengths near 60' and 180' are
likely to be troublesome. Same dipole on 40m and feedline lengths near
60' and 120' are likely to be troublesome.

Some folk would advise feeding at a current maximum, but of course, for
this dipole, a current maximum for 80m at the tx end of the feedline is
a voltage maximum for 40m.

Your 90' option might well be effective in avoiding some of the
impedance extremes on the lower bands that damage componets, cause
excessive loss, or are just difficult to match.

Owen

antenna question
 

On Oct 10, 9:58*pm, Michael Coslo wrote:
Yard with a maximum antenna possibility of 100 feet.

Make it 102' and you could hang a G5RV for 75m, 40m, 20m & 12m.

Or, is there anything that would contraindicate using this approach?

The SWR on the ladder-line will be very high (~30:1) on 75m and too
high on 160m. When a dipole is less than 1/2WL on the lowest frequency
of operation, the feedpoint resistance goes down and the feedpoint
reactance goes up as the frequency is decreased. As the antenna-length/
wavelength ratio goes down, the SWR goes up. Here is some information
on a 130' all-HF band ladder-line fed dipole.

http://www.w5dxp.com/notuner.htm

One could short the ladder-line wires together and feed the antenna
against ground for 160m operation.
--
73, Cecil, w5dxp.com