Hi, I was just reading the user's manual for the MFJ-941E antenna
tuner,
http://www.mfjenterprises.com/produc...rodid=MFJ-941E and on page
5, there is a warning, which reads:

"WARNING: To avoid problems, a dipole antenna should be a full half-
wave on the lowest band.
On 160 meters, an 80 or 40 meter antenna fed the normal way will be
extremely reactive with only
a few Ohms of feedpoint resistance. Trying to load an 80 meter (or
higher frequency) antenna on
160 meters can be a disaster for both your signal and the tuner. The
best way to operate 160 with
an 80 or 40 meter antenna is to load either or both feedline wires (in
parallel) as a longwire. The
antenna will act like a "T" antenna worked against the station
ground."

Half wave for 160 meters is around 264ft. So, it sounds like even with
a tuner (or at least this tuner), I would need at least this much wire
to transmit on 160 meters.

My naive understanding was that I could hang up a 100ft dipole and use
a tuner to transmit on all bands. What bands can I reasonable expect
to transmit on using a 100ft dipole and a tuner?

That last part of the warning about using an 80 meter dipole as a
longwire has me totally confused. Are they saying to snip off the
coax connector and plug the ends into the longwire connector in the
back of the tuner?


Jim

P.s. I finally have the 21st edition of the ARRL Antenna book. I'm
only on chapter 2, so please feel free to point out page numbers or
chapters that would probably answer my questions.

On Mon, 26 Nov 2007 10:47:15 -0800 (PST), James barrett
wrote:

I'm
only on chapter 2, so please feel free to point out page numbers or
chapters that would probably answer my questions.

Hi Jim,

That would be too simple.

However, as to the practicality of the warning from MFJ. It is a
useful point to depart from, and it is more an issue of insurance
against their having to explain why the tuner melt down when you
didn't follow their advice. However, even as a common guideline, it
fails when compared to other points such as don't load into a full
wave antenna. It follows whatever is halfwave in one band must be
fullwave in another (or nearly so, or even twice so).

So, as undoubtedly all the correspondence that will flow from your
simple question will prove: a simple answer does not satisfy your
need.

Just sit back and follow the reactions your question will elicit, and
read other threads as well. Give this a month and you will begin to
discover the borders to the last frontier of design.

Meanwhile, put up as much wire as you can. Try to tune up. There are
no one antenna solutions, so anticipate having more than one.

73's
Richard Clark, KB7QHC

James barrett wrote:
My naive understanding was that I could hang up a 100ft dipole and use
a tuner to transmit on all bands. What bands can I reasonable expect
to transmit on using a 100ft dipole and a tuner?

Make that "all HF bands". 160m is not an HF band.
Also, the dipole must be fed with parallel-line,
ideally open-wire line, for all HF band operation.

W2DU's rule-of-thumb is that a dipole should be
at least 3/8 wavelength on the lowest frequency
of operation.

A 100 ft. dipole can usually be used on 160m,
not as a dipole, but as a Marconi-style fed
system with the transmission line conductors
shorted together and fed against a good radial
ground system.
--
73, Cecil http://www.w5dxp.com

On Nov 26, 2:21 pm, Cecil Moore wrote:
James barrett wrote:
My naive understanding was that I could hang up a 100ft dipole and use
a tuner to transmit on all bands. What bands can I reasonable expect
to transmit on using a 100ft dipole and a tuner?

Make that "all HF bands". 160m is not an HF band.
Also, the dipole must be fed with parallel-line,
ideally open-wire line, for all HF band operation.

W2DU's rule-of-thumb is that a dipole should be
at least 3/8 wavelength on the lowest frequency
of operation.

A 100 ft. dipole can usually be used on 160m,
not as a dipole, but as a Marconi-style fed
system with the transmission line conductors
shorted together and fed against a good radial
ground system.
--
73, Cecil http://www.w5dxp.com

I keep reminding myself about the articles I've read about people
using window screens and rain gutters as antennas. ;-) I'll keep
reading and eventually I will understand Antennas. But (there's always
a but) I have to remind myself that my goal is to be able to make
contacts (CW, and eventually phone when I get my General class
license) and for now that means 10m, 15m, 40m and 80m. With that in
mind should my thinking be to put up a dipole for 80m and tune it down
to 10, 15 and 40, or should I go with some other length? Being that we
are near the bottom of the sun spot cycle, which band has the best
chance for making contacts? Maybe I should put up a dipole for that
and then tune it for the others.

If tuning for 160 meters is different than for the HF bands, then I'll
wait until I actually have my General class license before I start
thinking about that.

Jim

James barrett wrote:

I keep reminding myself about the articles I've read about people
using window screens and rain gutters as antennas. ;-) I'll keep
reading and eventually I will understand Antennas. But (there's always
a but) I have to remind myself that my goal is to be able to make
contacts (CW, and eventually phone when I get my General class
license) and for now that means 10m, 15m, 40m and 80m. With that in
mind should my thinking be to put up a dipole for 80m and tune it down
to 10, 15 and 40, or should I go with some other length? Being that we
are near the bottom of the sun spot cycle, which band has the best
chance for making contacts? Maybe I should put up a dipole for that
and then tune it for the others.

If tuning for 160 meters is different than for the HF bands, then I'll
wait until I actually have my General class license before I start
thinking about that.

Hey Jim,

Using one of those tuners is very simple. (mostly)

Assuming you are using ladder or window line,(not only a good
assumption, but a good idea) put up as much wire as high as you can.

The "mostly" part is that you don't want the wires to be 1/4 wavelength
total on any of the bands you are going to operate. I think the MFJ
manuals point out some lengths you don't want to use.

All this is to say that if you can put say 96 feet of wire in the air,
that is what you put up. Such an antenna will work a treat on 40 and up,
decently on 80 meters, and almost so-so on 160.

You are ready. Get a couple buds, your slingshot or favorite method of
launching fishing line into the air, and put up that dipole. Run the
window line to the house, avoiding running it too near to metal objects,
say keep it around 4 inches away. Connect it to the balanced line input
on the tuner, go coax to the rig, and there you have it. Make sure you
do the grounding thing correctly, but that's another subject.

- 73 de Mike N3LI -

Using one of those tuners is very simple. (mostly)

Assuming you are using ladder or window line,(not only a good
assumption, but a good idea) put up as much wire as high as you can.

The "mostly" part is that you don't want the wires to be 1/4 wavelength
total on any of the bands you are going to operate. I think the MFJ
manuals point out some lengths you don't want to use.

All this is to say that if you can put say 96 feet of wire in the air,
that is what you put up. Such an antenna will work a treat on 40 and up,
decently on 80 meters, and almost so-so on 160.

You are ready. Get a couple buds, your slingshot or favorite method of
launching fishing line into the air, and put up that dipole. Run the
window line to the house, avoiding running it too near to metal objects,
say keep it around 4 inches away. Connect it to the balanced line input
on the tuner, go coax to the rig, and there you have it. Make sure you
do the grounding thing correctly, but that's another subject.
======================
Whatever the length of the dipole ,ensure the the length of 1 half of
the dipole + the length of the 'window feeder' is approx 1 quarter
wavelength of 160m . This will result is a reasonably low impedance at
the matching unit (tuner) , which that unit will happily accept.

Frank GM0CSZ / KN6WH

"James barrett" wrote in message
...

I keep reminding myself about the articles I've read about people
using window screens and rain gutters as antennas. ;-) I'll keep
reading and eventually I will understand Antennas.

Take comfort from the knowledge that sub-optimal antennas, including rain
gutters, are still OK. Until I get a tower up, I am contenting myself with
sub-optimal. Heck, I loaded up an aluminum extension ladder and had a QSO
with Hawaii from San Diego.

This NG had a recent thread on multiband fan dipoles. I made one and it
works fine. I started with a 10m copper pipe dipole a few feet over my
garage roof, coax-fed through a balun. It is parallel to the peak of the
roof.

I added two 20m elements of #16 insulated stranded wire (lamp cord,
actually) and ran them downslope toward opposite corners of the garage roof.
They make about a 45-degree angle with the 10m antenna. Construction
articles encourage separating elements of different bands. The first
measured 20m elements were too long and the SWR dipped at 12-something MHz.
I trimmed them to 14.1 MHz, SWR = 1.1:1 at the radio. The only change to
the 10m performance was a very slight increase in SWR (1.5:1 vs. 1.7:1 per
MFJ-269).

I output only 100 watts and have logged 20m QSO's to Canada, Alaska, Hawaii
and the US East Coast on those hunks of lamp cord laying on my garage roof.
I plan to add some 40m elements and see what happens. ("Let's see what
happens if ... " is one of the very best things about ham radio.)

"Sal"
(KD6VKW)

On Nov 26, 7:22 pm, "Sal M. Onella"
wrote:

I added two 20m elements of #16 insulated stranded wire (lamp cord,
actually) and ran them downslope toward opposite corners of the garage roof.
They make about a 45-degree angle with the 10m antenna. Construction
articles encourage separating elements of different bands. The first
measured 20m elements were too long and the SWR dipped at 12-something MHz.
I trimmed them to 14.1 MHz, SWR = 1.1:1 at the radio. The only change to
the 10m performance was a very slight increase in SWR (1.5:1 vs. 1.7:1 per
MFJ-269).



Hi, I don't understand how you can add elements to an existing antenna
and have it still work on the band it was originally made for. Do you
still need a tuner? Or do you remove the 20m elements to transmit on
10m?

Jim

On Tue, 27 Nov 2007 07:35:07 -0800 (PST), James barrett
wrote:

Hi, I don't understand how you can add elements to an existing antenna
and have it still work on the band it was originally made for. Do you
still need a tuner? Or do you remove the 20m elements to transmit on
10m?

Hi Jim,

Adding a new band's element will likely disturb the performance of an
existing one. However, it will be slight, and if you anticipate this,
you can construct a two band antenna and tune both. Similarly, you
can construct three, four, five.... band antennas using similar
principles. There is, of course, the compounding of difficulty as you
increase this count, but that doesn't preclude it being done
successfully.

73's
Richard Clark, KB7QHC

James barrett wrote:
Hi, I don't understand how you can add elements to an existing antenna
and have it still work on the band it was originally made for. Do you
still need a tuner? Or do you remove the 20m elements to transmit on
10m?

The RF source energy will follow the path of least
impedance. If we have dipole elements for 40m, 30m,
and 20m on the same antenna, when we are on 30m, for
instance, the 30m dipole has a low impedance while
the 40m and 20m dipoles both have high impedances
to the 10.125 MHz source signal. This configuration
can function without a tuner.
--
73, Cecil http://www.w5dxp.com