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

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.

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

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

"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

"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 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

"Dan Richardson arrl net" k6mhatdot wrote in message
...
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

Will do. I wanted to post it here.Now that I think about it, it's the SWCAD
files that are ASCII, not the EZNEC

Tam

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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