A cheap and effective solution is to purchase a Van Gordon 130 foot all band
dipole $29.95 with 100 feet of ladder line.

Purchase an additional 100 foot of 450 ohm ladderline $12.00.

find 7 4PDT relays and 2 digitran decimal to binary switches.

use the relays to switch in 1,2,4,8,10,20, and 40 feet of additional ladder
line. cut 10 feet off of the 100 feet that came with the antenna. Now use
the relays to add length as needed to tune. For example to tune your 4.5
would require switching in an additional 78 feet.

E-Mail me and I will send you a chart of frequency Vs what you need to
switch in. I found the relays for a buck a piece and the digital rotary
switches for 3 bucks. feed with your choice of coax with ferrite beads to
act as a balun and your good to go.

Less than $50.00 and I cover nearly DC to Daylight, no tuner and worst SWR
anywhere 1.4:1
"C. J. Clegg" wrote in message
...
On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT"
wrote:

I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5
MHz,
with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but
the
4.5 really messes up the 3.7. Among other things the impedance at 3.7 and
4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average
ground. If the 4.5 is for receive only, I would forget about it, and take
the 10:1 SWR that the 80 meter dipole gives you.

Good evening, Tam.

Thanks for running the simulation for me. Your results don't surprise
me much.

(I'm going to have to get that EZNEC program and play with it for a
while ... thanks to all for mentioning it.)

The 4.5-MHz antenna will be used for transmitting as well as
receiving, and so I need to get the SWR down to something reasonable.

I guess there's no reason why I can't just put up a separate dipole
for 4.5 MHz and the crossed dipoles, fed with a single coax, for 80
and 40.

I could also (and I might...) just put up an 80-meter dipole fed with
ladder line and use a tuner, though I was trying to avoid the tuner.

Thanks (to you and to all) for saving me a bunch of work. :-)

CJ

Fred W4JLE wrote:
Less than $50.00 and I cover nearly DC to Daylight, no tuner and worst SWR
anywhere 1.4:1

Speaking of broad-banding an antenna ... :-)
--
73, Cecil http://www.qsl.net/w5dxp


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On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT"
wrote:
[snip]

CJ,
I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz,
with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but the
4.5 really messes up the 3.7. Among other things the impedance at 3.7 and
4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average
ground. If the 4.5 is for receive only, I would forget about it, and take
the 10:1 SWR that the 80 meter dipole gives you.

I'd be interested to see your Eznec file.

"Wes Stewart" wrote in message
...
On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT"
wrote:
[snip]

CJ,
I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz,
with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but
the
4.5 really messes up the 3.7. Among other things the impedance at 3.7 and
4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average
ground. If the 4.5 is for receive only, I would forget about it, and take
the 10:1 SWR that the 80 meter dipole gives you.

I'd be interested to see your Eznec file.

Gladly, but, how do I get an ASCII file out of it. I thought I had opened
EZNEC files in Notepad, but it is garbage. Also, even from within EZNEC when
I click on View File, I get the same garbage as Notepad. The only
questionable thing I did would be the 0.2 foot stub in the middle that the
other wires are connected to; but that works for other configurations.

Tam/WB2TT

On Sun, 22 May 2005 21:26:49 -0400, "Tam/WB2TT"
wrote:


"Wes Stewart" wrote in message
.. .
On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT"
wrote:
[snip]

CJ,
I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz,
with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but
the
4.5 really messes up the 3.7. Among other things the impedance at 3.7 and
4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average
ground. If the 4.5 is for receive only, I would forget about it, and take
the 10:1 SWR that the 80 meter dipole gives you.

I'd be interested to see your Eznec file.

Gladly, but, how do I get an ASCII file out of it. I thought I had opened
EZNEC files in Notepad, but it is garbage. Also, even from within EZNEC when
I click on View File, I get the same garbage as Notepad. The only
questionable thing I did would be the 0.2 foot stub in the middle that the
other wires are connected to; but that works for other configurations.

Tam/WB2TT

Just send him the *.ez file. Wes can handle that.

Danny

On Sun, 22 May 2005 21:26:49 -0400, "Tam/WB2TT"
wrote:


"Wes Stewart" wrote in message
.. .
On Sun, 22 May 2005 17:41:22 -0400, "Tam/WB2TT"
wrote:
[snip]

CJ,
I ran an EZNEC simulation on a pair of crossed dipoles at 3.7 and 4.5 MHz,
with a 7.2 MHz inverted V below the 3.7. Not good. The 7.2 works OK, but
the
4.5 really messes up the 3.7. Among other things the impedance at 3.7 and
4.5 MHz is about 115 Ohms. I ran the simulation at 50 feet above average
ground. If the 4.5 is for receive only, I would forget about it, and take
the 10:1 SWR that the 80 meter dipole gives you.

I'd be interested to see your Eznec file.

Gladly, but, how do I get an ASCII file out of it. I thought I had opened
EZNEC files in Notepad, but it is garbage. Also, even from within EZNEC when
I click on View File, I get the same garbage as Notepad. The only
questionable thing I did would be the 0.2 foot stub in the middle that the
other wires are connected to; but that works for other configurations.

Tam was kind enough to send me his EZNEC file. I asked for this file
since I went through this myself unsuccessfully (so far) and wanted to
see if someone else had a better idea.

My suspicions were confirmed: there are some NEC guideline violations.
I'm don't want this to come off as picking on Tam publicly, but to
keep others from making the same mistakes, (*I* would never make a
mistake [g]) here's what I see.

Tam uses a single wire at the middle of the dipole to contain the
source. This is necessary because NEC doesn't allow a source at a
wire junction. (EZNEC has a split source that works at a wire
junction, but not a multiple wire junction.)

The EZNEC manual recommends that this wire be at least 0.02
wavelengths long and consist of three segments. I believe the three
segment rule is stipulated to force the segments adjacent to the
source wire to be equal to it. If we are careful about this, we can
go to one segment.

Tam's center wire is only 0.2 feet long and has 11 segments. The
segment length of .018 feet is way too short; the wire needs to be
~16' long at 3.5 MHz to meet the guidelines.

Of course with this gross violation comes another one when the
connecting wires are a more appropriate segment length.

Tam, I suggest that you got to Options--Segmentation Check and make
it "Auto".

I'm still looking at this issue and will report back if I see any
progress.

Wes N7WS

It took a lot of going back and forth, but I have an EZNEC simulation of a
75/80 m antenna that has an swr below 2.0 from 3.5 to 4.0. If you do put
up
the 4.5 antenna, you can probably use that to extend the bandwidth of the
80
m antenna on the high side.

Tam/WB2TT


Could you post what the antenna looks like that will do that bandwidth ?

de KU4PT

.... draw a picture of a discone in your mind... yep, that is kinda what it
looks like... only made by Martians... grin

Warmest regards,
John

"Ralph Mowery" wrote in message
ink.net...

It took a lot of going back and forth, but I have an EZNEC simulation of
a
75/80 m antenna that has an swr below 2.0 from 3.5 to 4.0. If you do put
up
the 4.5 antenna, you can probably use that to extend the bandwidth of the
80
m antenna on the high side.

Tam/WB2TT


Could you post what the antenna looks like that will do that bandwidth ?

de KU4PT

"Ralph Mowery" wrote in message
ink.net...

It took a lot of going back and forth, but I have an EZNEC simulation of
a
75/80 m antenna that has an swr below 2.0 from 3.5 to 4.0. If you do put
up
the 4.5 antenna, you can probably use that to extend the bandwidth of the
80
m antenna on the high side.

Tam/WB2TT


Could you post what the antenna looks like that will do that bandwidth ?

de KU4PT


Easy, two dipoles at right angles. One wire is 133 feet long, the other is
119. The height I used was 75 feet over average ground. I double checked
the SWR. It is below 2:1 from 3.5 to 4.0. If you do it at 75 Ohms, the SWR
is below 1.5:1 from 3.55 to 3.975.


Tam/WB2TT

On Sat, 21 May 2005 16:32:14 -0400, C. J. Clegg
wrote:



Questions...

Is the standard 468/F formula likely to be anywhere near accurate, or
will the three antennas interact with one another to throw the
calculations off?


near, yes, but it will be a little short

In particular, is the 4.5-MHz frequency too near the 80-meter band
such that interaction will be greater than otherwise?

If the interactions are sufficient to throw the formula off, will my
antennas end up being longer or shorter than the formula length?

Thanks.... CJ

Wes and I disagree, so you will have to toss a coin on this one. I
have built many of these multiband parallel dipoles over the years. I
still use them. Here is how I do mine.

I space the wires about 6-8 inches apart using the longest wire on top
and they get shorter as they go down. What I generally do is use a
long formula to set up the initial wires such as 495/f = length in
feet. Then I hang all the wires with the spacers. I trim the highest
frequency first and measure it out. I reverse the calculations to get
the X more accurately in the formula, X/f = L in Feet. I trim the
other two and I am done.

I have not tried this with an element so close in frequency as your
80/4.5 MHz elements, but I don't expect a problem. If you have an
antenna analyzer, you can see what the different elements are resonant
on and then calculate the reverse formula trimming only once per band.

The only real difference I see in the multiband parallel dipole is
that the bandwidth on 80 and 40 seem to be broader than on a single
dipole cut to frequency. I have read on some of these forums that
others are getting narrower bandwidth. I can't explain that.

FWIW

--
73 for now
Buck
N4PGW