Let's say I build a horizontal dipole, trimmed for minimum SWR @
7.200 mhz. I'll probably use 14-16 gauge insulated house wiring for
this antenna. It'd be a "nominal' quarter wavelength per leg.

This dipole will be fed with 50 ohm coax, and it will be erected
horizontally, 30 feet high over "average" ground.

What SWR reading could I expect to see from this antenna if I tried
to use it at 21.300 mhz........in the same environment as stated
above?

Thanks, folks......

FjLee KA0FPJ

On Apr 6, 5:56*am, " wrote:
What SWR *reading could I expect to see from this antenna if I tried
to use it at 21.300 mhz........in the same environment as stated
above?

EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms.
--
73, Cecil, w5dxp.com

On Wed, 6 Apr 2011 03:56:21 -0700 (PDT), "
wrote:

What SWR reading could I expect to see...?

15:1

73's
Richard Clark, KB7QHC

On Wed, 06 Apr 2011 03:56:21 -0700, wrote:

Let's say I build a horizontal dipole, trimmed for minimum SWR @ 7.200
mhz. I'll probably use 14-16 gauge insulated house wiring for this
antenna. It'd be a "nominal' quarter wavelength per leg.

This dipole will be fed with 50 ohm coax, and it will be erected
horizontally, 30 feet high over "average" ground.

What SWR reading could I expect to see from this antenna if I tried to
use it at 21.300 mhz........in the same environment as stated above?

Thanks, folks......

FjLee KA0FPJ

Google a fan dipole. It sounds like something you may be interested in

On 4/6/2011 6:28 AM, Cecil Moore wrote:
On Apr 6, 5:56 am, wrote:
What SWR reading could I expect to see from this antenna if I tried
to use it at 21.300 mhz........in the same environment as stated
above?

EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms.
--
73, Cecil, w5dxp.com

Hey Cecil -

I got:

Impedance = 85.26 - J 186.3 ohms
SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308

Let's see if we can determine why they don't match.

I adjusted the wire length for no reactance at 7.2 MHz.
I used 99 segments of #14 wire. I did not include insulation effects.

How about yours?

John

On 4/6/2011 2:51 PM, John - KD5YI wrote:
On 4/6/2011 6:28 AM, Cecil Moore wrote:
On Apr 6, 5:56 am, wrote:
What SWR reading could I expect to see from this antenna if I tried
to use it at 21.300 mhz........in the same environment as stated
above?

EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms.
--
73, Cecil, w5dxp.com

Hey Cecil -

I got:

Impedance = 85.26 - J 186.3 ohms
SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308

Let's see if we can determine why they don't match.

I adjusted the wire length for no reactance at 7.2 MHz.
I used 99 segments of #14 wire. I did not include insulation effects.

How about yours?

John

Oops! I just noticed that I had zero wire resistance. Changed it to
copper but only got a slight change:

Impedance = 87.47 - J 184 ohms
SWR (50 ohm system) = 9.960 (75 ohm system) = 7.042

John - KD5YI wrote:
On 4/6/2011 2:51 PM, John - KD5YI wrote:
On 4/6/2011 6:28 AM, Cecil Moore wrote:
On Apr 6, 5:56 am, wrote:
What SWR reading could I expect to see from this antenna if I tried
to use it at 21.300 mhz........in the same environment as stated
above?

EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms.
--
73, Cecil, w5dxp.com

Hey Cecil -

I got:

Impedance = 85.26 - J 186.3 ohms
SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308

Let's see if we can determine why they don't match.

I adjusted the wire length for no reactance at 7.2 MHz.
I used 99 segments of #14 wire. I did not include insulation effects.

How about yours?

John

Oops! I just noticed that I had zero wire resistance. Changed it to
copper but only got a slight change:

Impedance = 87.47 - J 184 ohms
SWR (50 ohm system) = 9.960 (75 ohm system) = 7.042



If you tune it down a bit so you resonate at perhaps 7.15, then the
third harmonic will be closer to 21.3. It's a dipole, so not real high
Q, particularly on the fundamental, so maybe what you do is go for a
compromise tuning.. A bit low on 40 and a bit high on 15.

On 4/6/2011 7:57 PM, Jim Lux wrote:
John - KD5YI wrote:
On 4/6/2011 2:51 PM, John - KD5YI wrote:
On 4/6/2011 6:28 AM, Cecil Moore wrote:
On Apr 6, 5:56 am, wrote:
What SWR reading could I expect to see from this antenna if I tried
to use it at 21.300 mhz........in the same environment as stated
above?

EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms.
--
73, Cecil, w5dxp.com

Hey Cecil -

I got:

Impedance = 85.26 - J 186.3 ohms
SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308

Let's see if we can determine why they don't match.

I adjusted the wire length for no reactance at 7.2 MHz.
I used 99 segments of #14 wire. I did not include insulation effects.

How about yours?

John

Oops! I just noticed that I had zero wire resistance. Changed it to
copper but only got a slight change:

Impedance = 87.47 - J 184 ohms
SWR (50 ohm system) = 9.960 (75 ohm system) = 7.042



If you tune it down a bit so you resonate at perhaps 7.15, then the
third harmonic will be closer to 21.3. It's a dipole, so not real high
Q, particularly on the fundamental, so maybe what you do is go for a
compromise tuning.. A bit low on 40 and a bit high on 15.

Well, yeah, I know. But, I'm trying to simulate based on the OP's info
and Cecil's results.

John

On 4/6/2011 2:51 PM, John - KD5YI wrote:
On 4/6/2011 6:28 AM, Cecil Moore wrote:
On Apr 6, 5:56 am, wrote:
What SWR reading could I expect to see from this antenna if I tried
to use it at 21.300 mhz........in the same environment as stated
above?

EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms.
--
73, Cecil, w5dxp.com

Hey Cecil -

I got:

Impedance = 85.26 - J 186.3 ohms
SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308

Let's see if we can determine why they don't match.

I adjusted the wire length for no reactance at 7.2 MHz.
I used 99 segments of #14 wire. I did not include insulation effects.

How about yours?

John

Are you using 9 segments?

John

On 4/6/2011 8:16 PM, John - KD5YI wrote:
On 4/6/2011 2:51 PM, John - KD5YI wrote:

Hey Cecil -

I got:

Impedance = 85.26 - J 186.3 ohms
SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308

Let's see if we can determine why they don't match.

I adjusted the wire length for no reactance at 7.2 MHz.
I used 99 segments of #14 wire. I did not include insulation effects.

How about yours?

John

Are you using 9 segments?

John

I think may have missed something on how segmentation works. I thought
you needed an even number of segments to split a dipole evenly.

So while 99 is close to centered by my logic, if 9 was used it might
skew things a bit.

If I'm off base please tell me so I can adjust my model of how NEC works.

Thanks.

tom
K0TAR