I'm just about getting around to making my 5 or 6 element marine band yagi,
covering 156 - 162 Mhz RECEIVE ONLY. Do I have to employ a folded dipole or
can I use just a simple hertz dipole as the "driven" element? I'm trying to
get away from using a folded dipole if I can. Any wideband designs out there
that use a simple hertz dipole that I can scale? I'm looking, but if you
have some links aready. TIA.

I'm just about getting around to making my 5 or 6 element marine band yagi,
covering 156 - 162 Mhz RECEIVE ONLY. Do I have to employ a folded dipole or
can I use just a simple hertz dipole as the "driven" element? I'm trying to
get away from using a folded dipole if I can. Any wideband designs out there
that use a simple hertz dipole that I can scale? I'm looking, but if you
have some links aready. TIA.


A folded dipole as the driven element will have the best match over your
frequency range..

What you do have to worry about is the feedpoint resistance. Some Yagi-Uda
designs are expressly designed for (a driven) folded dipole, which in isolation
have a much higher feed resistance than 50 ohms. When you put parasitics in the
near field, in certain gain-optimized Yagi-Uda designs, that feed resistance
falls closer to 50 ohms.

Typically, a non-matched regular dipole as driven has a feedpoint resistance of
much less than 50 ohms in a high gain Yagi-Uda app. Thus you may be seeing 1-2
dB or mismatch from this lower feedpoint resistance. Or you can make a T-match
(for example).

If you have s specific design that uses a folded dipole, I suggest you stick
with it. Unless you want to eat a dB or 2 in possible mismatch, or put a
matching system in on a conventional dipole as a driven.

73,
Chip N1IR

On 31 May 2004 15:28:40 GMT, (Fractenna) wrote:

|I'm just about getting around to making my 5 or 6 element marine band yagi,
|covering 156 - 162 Mhz RECEIVE ONLY. Do I have to employ a folded dipole or
|can I use just a simple hertz dipole as the "driven" element? I'm trying to
|get away from using a folded dipole if I can. Any wideband designs out there
|that use a simple hertz dipole that I can scale? I'm looking, but if you
|have some links aready. TIA.
|
|
|A folded dipole as the driven element will have the best match over your
|frequency range..

Unless of course it doesn't.
|
|What you do have to worry about is the feedpoint resistance. Some Yagi-Uda
|designs are expressly designed for (a driven) folded dipole, which in isolation
|have a much higher feed resistance than 50 ohms. When you put parasitics in the
|near field, in certain gain-optimized Yagi-Uda designs, that feed resistance
|falls closer to 50 ohms.
|
|Typically, a non-matched regular dipole as driven has a feedpoint resistance of
|much less than 50 ohms in a high gain Yagi-Uda app.

Unless it doesn't. For the example I offered earlier:


Freq R X VSWR Gain F/B dB

156 51.50 1.97 1.050 9.95 14.34
157 50.12 2.77 1.057 9.99 16.43
158 49.34 5.22 1.112 10.04 19.20
159 50.38 8.31 1.180 10.08 23.41
160 54.16 9.95 1.230 10.10 30.84
161 59.78 5.68 1.229 10.07 28.01
162 57.99 -8.24 1.237 9.96 21.35

Lucky for those of us when it does, Wes.

Nice model. Seems to meet a certain need. It is possible to get better F/B and
F/S though. Not with your approach, however.

73,
Chip N1IR

On 01 Jun 2004 03:12:14 GMT, (Fractenna) wrote:

|Lucky for those of us when it does, Wes.
|
|Nice model. Seems to meet a certain need. It is possible to get better F/B and
|F/S though. Not with your approach, however.

I'm not taking credit. This is a minor adjustment of a Cebik design.
Seems to fit the OP's rqmts, however: no folded-dopole feed, 50 ohm
matched BW of 156-162 MHz and 5-6 elements.

Regards,

Wes

I'm not taking credit. This is a minor adjustment of a Cebik design.
Seems to fit the OP's rqmts, however: no folded-dopole feed, 50 ohm
matched BW of 156-162 MHz and 5-6 elements.

Regards,

Wes


This looks like a modofied approach to an NBS Yagi-Uda.

Modern Y-U design allows for a higher feedpoint SWR. Matching loss is offset by
higher gain and better consistency of F/B. If no matching, then a shaped,
folded dipole is used. Typically a F/B better than 22 dB (sim) is acheived with
a 10% bandwidth.

The design you discuss sounds more than adequate for this need though, in fact
most needs.

73,
Chip N1IR

On Mon, 31 May 2004 15:59:31 +0100, "Richard"
wrote:

|I'm just about getting around to making my 5 or 6 element marine band yagi,
|covering 156 - 162 Mhz RECEIVE ONLY. Do I have to employ a folded dipole

No.

|or
|can I use just a simple hertz dipole as the "driven" element? I'm trying to
|get away from using a folded dipole if I can. Any wideband designs out there
|that use a simple hertz dipole that I can scale? I'm looking, but if you
|have some links aready. TIA.

All dimensions in inches

X Y Z X Y Z Dia

0.000 -18.553 0.000 0.000 18.553 0.000 0.187
9.275 -18.368 0.000 9.275 18.368 0.000 0.312
12.250 -17.077 0.000 12.250 17.077 0.000 0.187
23.800 -16.672 0.000 23.800 16.672 0.000 0.187
34.213 -16.672 0.000 34.213 16.672 0.000 0.187
47.211 -16.229 0.000 47.211 16.229 0.000 0.187

"Wes Stewart" wrote in message
...
On Mon, 31 May 2004 15:59:31 +0100, "Richard"
wrote:

|I'm just about getting around to making my 5 or 6 element marine band
yagi,
|covering 156 - 162 Mhz RECEIVE ONLY. Do I have to employ a folded dipole

No.

|or
|can I use just a simple hertz dipole as the "driven" element? I'm trying
to
|get away from using a folded dipole if I can. Any wideband designs out
there
|that use a simple hertz dipole that I can scale? I'm looking, but if you
|have some links aready. TIA.

All dimensions in inches

X Y Z X Y Z Dia

0.000 -18.553 0.000 0.000 18.553 0.000 0.187
9.275 -18.368 0.000 9.275 18.368 0.000 0.312
12.250 -17.077 0.000 12.250 17.077 0.000 0.187
23.800 -16.672 0.000 23.800 16.672 0.000 0.187
34.213 -16.672 0.000 34.213 16.672 0.000 0.187
47.211 -16.229 0.000 47.211 16.229 0.000 0.187


Sorry I'm a bit uncertain of what you wrote.

Obviously an efficient way to provide data for yagi's, but how do you read
it?

Is there a webpage associated with the design, so I can look at the general
construction?

Rich.

On Tue, 1 Jun 2004 10:11:14 +0100, "Richard"
wrote:

|
|"Wes Stewart" wrote in message
.. .
| On Mon, 31 May 2004 15:59:31 +0100, "Richard"
| wrote:
|
| |I'm just about getting around to making my 5 or 6 element marine band
|yagi,
| |covering 156 - 162 Mhz RECEIVE ONLY. Do I have to employ a folded dipole
|
| No.
|
| |or
| |can I use just a simple hertz dipole as the "driven" element? I'm trying
|to
| |get away from using a folded dipole if I can. Any wideband designs out
|there
| |that use a simple hertz dipole that I can scale? I'm looking, but if you
| |have some links aready. TIA.
|
| All dimensions in inches
|
| X Y Z X Y Z Dia
|
| 0.000 -18.553 0.000 0.000 18.553 0.000 0.187
| 9.275 -18.368 0.000 9.275 18.368 0.000 0.312
| 12.250 -17.077 0.000 12.250 17.077 0.000 0.187
| 23.800 -16.672 0.000 23.800 16.672 0.000 0.187
| 34.213 -16.672 0.000 34.213 16.672 0.000 0.187
| 47.211 -16.229 0.000 47.211 16.229 0.000 0.187
|
|
|Sorry I'm a bit uncertain of what you wrote.
|
|Obviously an efficient way to provide data for yagi's, but how do you read
|it?
|
|Is there a webpage associated with the design, so I can look at the general
|construction?
|
|Rich.

This is the format for almost any of the common antenna modeling
programs. See for example:

Free:

http://www.qsl.net/wb6tpu/swindex.html (look for files beginning
4nec2)

Almost free:

http://www.qsl.net/ac6la/multinec.html

Free demo:

www.eznec.com

etc.

With a fixed width font, the columns would line up and each line would
represent one element, starting from the rear (reflector end) of the
boom. The data are the X,Y,Z coordinates of the ends of the elements
and the diameter of that element. Z is this case is zero since the
model assumes free space. It also assumes no effects from the
supporting boom; the usual compensations must be made for this,
depending on the element mounting method. See:

http://www.antennspecialisten.se/en/ham/tech/bc.html

I assumed that you had some experience with Yagi design and
construction and were simply looking for a design that gave both the
required bandwidth and a fifty-ohm feedpoint; something this design
delivers.

"Wes Stewart" wrote in message
...
On Mon, 31 May 2004 15:59:31 +0100, "Richard"
wrote:

|I'm just about getting around to making my 5 or 6 element marine band
yagi,
|covering 156 - 162 Mhz RECEIVE ONLY. Do I have to employ a folded dipole

No.

|or
|can I use just a simple hertz dipole as the "driven" element? I'm trying
to
|get away from using a folded dipole if I can. Any wideband designs out
there
|that use a simple hertz dipole that I can scale? I'm looking, but if you
|have some links aready. TIA.

All dimensions in inches

X Y Z X Y Z Dia

0.000 -18.553 0.000 0.000 18.553 0.000 0.187
9.275 -18.368 0.000 9.275 18.368 0.000 0.312
12.250 -17.077 0.000 12.250 17.077 0.000 0.187
23.800 -16.672 0.000 23.800 16.672 0.000 0.187
34.213 -16.672 0.000 34.213 16.672 0.000 0.187
47.211 -16.229 0.000 47.211 16.229 0.000 0.187

IOW:
X Y Z Dia

REF End 1 0.000 -18.553 0.000 0.187
End2 0.000 18.553 0.000


DE End1 9.275 -18.368 0.000 0.312
End2 9.275 18.368 0.000


DIR1 End1 12.250 -17.077 0.000 0.187
End2 12.250 17.077 0.000


DIR2 End1 23.800 -16.672 0.000 0.187
End2 23.800 16.672 0.000


DIR4 End1 34.213 -16.672 0.000 0.187
End2 34.213 16.672 0.000


DIR5 End1 47.211 -16.229 0.000 0.187
End2 47.211 16.229 0.000

I'll see how I get along with the 4Nec2 program.

What is the DE,just a regular hertz dipole? Is DE specified as to what it is
(hertz, folded) somewhere in 4nec2?

In the Geometry Edit I see "Radius" for wire diameter I suppose. Do I
calculate the radius from the dia given in the table above? TIA.