I am trying to find out how far an open stub, dual band, two meter and
seventy centimeter J-pole needs to be from a parallel metal support
mast on which it is side mounted to avoid detuning the antenna. I'm
not concerned about the effect on the radiation pattern as I can mount
the antenna on the side of the mast towards the area I'm trying to
cover. I have to build brackets to accomplish this mounting and I
would like to avoid building multiple sets of them just to test for
clearance. If anyone has the requisite skills and tools I would
appreciate any information that can be readily found by modeling this
antenna in proximity to a metal support mast consisting of four inch
aluminum tube. I have two AB-952 masts on which to mount six
antennas. Three of them will be two meter omnidirectional antennas.
Since we need two limit interaction and interference between the three
two meter stations We will be mounting one of these at the top of one
mast, one a third of the way up the second mast, and the third two
thirds of the way up the first mast. Both masts will be deployed with
extension kits so they will be fifty feet in total height.

In truth I just do not have the skills or the time to develop them to
do this so any help would be greatly appreciated. This is for a
public service event that is now only two weeks away.

--
Tom Horne, W3TDH

On Oct 12, 12:13*pm, Tom Horne wrote:
I am trying to find out how far an open stub, dual band, two meter and
seventy centimeter J-pole needs to be from a parallel metal support
mast on which it is side mounted to avoid detuning the antenna. *I'm
not concerned about the effect on the radiation pattern as I can mount
the antenna on the side of the mast towards the area I'm trying to
cover. *I have to build brackets to accomplish this mounting and I
would like to avoid building multiple sets of them just to test for
clearance. *If anyone has the requisite skills and tools I would
appreciate any information that can be readily found by modeling this
antenna in proximity to a metal support mast consisting of four inch
aluminum tube. *I have two AB-952 masts on which to mount six
antennas. *Three of them will be two meter omnidirectional antennas.
Since we need two limit interaction and interference between the three
two meter stations We will be mounting one of these at the top of one
mast, one a third of the way up the second mast, and the third two
thirds of the way up the first mast. *Both masts will be deployed with
extension kits so they will be fifty feet in total height.

In truth I just do not have the skills or the time to develop them to
do this so any help would be greatly appreciated. *This is for a
public service event that is now only two weeks away.

--
Tom Horne, W3TDH



I'm not a modeler. However, I did investigate this experimentally a
few years ago, although not with 4-inch aluminum mast. I used a 10-
foot section of one-inch galvanized mast. The tested j-pole was a 2m
copper pipe version, hanging vertically in the open, suspended by a
piece of line.

On transmit, I tuned to a simplex channel, keyed up, ID'ed and noted a
small amount of reflected power. I locked the key and slowly moved
the section of mast toward the antenna. I had to get within one and
one-half inches (1.5") before the reflected power increased.

On receive, I tuned to a repeater with a ragchew in progress and
opened the squelch. I inserted a switchable attenuator in line with
the radio and set the attenuator to the crappiest signal I could copy
-- one dB away from unintelligible. Enter the mast section, and once
again, I had to get within an inch and a half to lose the
conversation.

The direction from which I approached the antenna didn't seem to
matter, but I didn't do any real measurements of pattern distortion.

I hope this helps you.

Sal
(KD6VKW)

On Oct 13, 12:29*am, "Sal M. Onella" wrote:
On Oct 12, 12:13*pm, Tom Horne wrote:



I am trying to find out how far an open stub, dual band, two meter and
seventy centimeter J-pole needs to be from a parallel metal support
mast on which it is side mounted to avoid detuning the antenna. *I'm
not concerned about the effect on the radiation pattern as I can mount
the antenna on the side of the mast towards the area I'm trying to
cover. *I have to build brackets to accomplish this mounting and I
would like to avoid building multiple sets of them just to test for
clearance. *If anyone has the requisite skills and tools I would
appreciate any information that can be readily found by modeling this
antenna in proximity to a metal support mast consisting of four inch
aluminum tube. *I have two AB-952 masts on which to mount six
antennas. *Three of them will be two meter omnidirectional antennas.
Since we need two limit interaction and interference between the three
two meter stations We will be mounting one of these at the top of one
mast, one a third of the way up the second mast, and the third two
thirds of the way up the first mast. *Both masts will be deployed with
extension kits so they will be fifty feet in total height.

In truth I just do not have the skills or the time to develop them to
do this so any help would be greatly appreciated. *This is for a
public service event that is now only two weeks away.

--
Tom Horne, W3TDH

I'm not a modeler. * However, I did investigate this experimentally a
few years ago, although not with 4-inch aluminum mast. *I used a 10-
foot section of one-inch galvanized mast. *The tested j-pole was a 2m
copper pipe version, hanging vertically in the open, suspended by a
piece of line.

On transmit, I tuned to a simplex channel, keyed up, ID'ed and noted a
small amount of reflected power. * I locked the key and slowly moved
the section of mast toward the antenna. *I had to get within one and
one-half inches (1.5") before the reflected power increased.

On receive, I tuned to a repeater with a ragchew in progress and
opened the squelch. *I inserted a switchable attenuator in line with
the radio and set the attenuator to the crappiest signal I could copy
-- one dB away from unintelligible. *Enter the mast section, and once
again, I had to get within an inch and a half to lose the
conversation.

The direction from which I approached the antenna didn't seem to
matter, but I didn't do any real measurements of pattern distortion.

I hope this helps you.

Sal
(KD6VKW)

I never tried it as close as Sal but It did mount one that stood off
about 2 ft from the tower with no discernible problems. I was also in
on making a J antenna where the tower was part of the antenna.

Jimmie

Jimmie

You'll have better isolation between systems if you mount all three 2M
antennas on the same mast, directly above/below each other. I'll recommend
19" spacing off the pole. Mounting one quarter-wave away from the reflector
is one of the easiest pattern changes to model; it gives a nice cardioid
pattern on 2M. The UHF side of the J-pole antenna will therefore be 3/4
wavelength from the reflector and the pattern on 440 will have three lobes,
much like a clover leaf.

I suggest using 1/2" CPVC Schedule 40 water pipe for both the vertical
support and the arms at top and bottom. That stuff is cheap, easy to cut,
and glues together very quickly - don't make any assembly mistakes! Put a
"T" fitting at the bottom to let both the coaxes and residual water vapor
drop out of the radome assembly.
--
Karl Beckman, WA8NVW


"Tom Horne" wrote in message
...
I am trying to find out how far an open stub, dual band, two meter and
seventy centimeter J-pole needs to be from a parallel metal support
mast on which it is side mounted to avoid detuning the antenna. I'm
not concerned about the effect on the radiation pattern as I can mount
the antenna on the side of the mast towards the area I'm trying to
cover. I have to build brackets to accomplish this mounting and I
would like to avoid building multiple sets of them just to test for
clearance. If anyone has the requisite skills and tools I would
appreciate any information that can be readily found by modeling this
antenna in proximity to a metal support mast consisting of four inch
aluminum tube. I have two AB-952 masts on which to mount six
antennas. Three of them will be two meter omnidirectional antennas.
Since we need two limit interaction and interference between the three
two meter stations We will be mounting one of these at the top of one
mast, one a third of the way up the second mast, and the third two
thirds of the way up the first mast. Both masts will be deployed with
extension kits so they will be fifty feet in total height.

In truth I just do not have the skills or the time to develop them to
do this so any help would be greatly appreciated. This is for a
public service event that is now only two weeks away.

--
Tom Horne, W3TDH

Hi Jimmie,

Inquiring minds want to know dept: You mentioned an LOM antenna.

Did that have something to do with aviation markers; loran or position
locators?

Rick
W9ZD

On Oct 16, 3:38*pm, wrote:
Hi Jimmie,

Inquiring minds want to know dept: You mentioned an LOM antenna.

Did that have something to do with aviation markers; loran or position
locators?

Rick
W9ZD

Aviation, one of the first grunt jobs I had after working with the FAA
was the decommissioning of an LOM site. The took out the equipment and
the building but the antenna was there for several years. I didnt have
a place I could put up a decent antenna so I would grab my 100 watt
Icom and MFJ tuner and ride out to the site. I do mostly radar work
now.

Jimmie

"JIMMIE" wrote in message
...
On Oct 16, 3:38 pm, wrote:
Hi Jimmie,

Inquiring minds want to know dept: You mentioned an LOM antenna.

Did that have something to do with aviation markers; loran or position
locators?

Rick
W9ZD

Aviation, one of the first grunt jobs I had after working with the FAA
was the decommissioning of an LOM site. The took out the equipment and
the building but the antenna was there for several years. I didnt have
a place I could put up a decent antenna so I would grab my 100 watt
Icom and MFJ tuner and ride out to the site. I do mostly radar work
now.

Jimmie


http://en.mimi.hu/aviation/lom.html

Chris

Dear Group:

Still not as clear as it could be. "Jimmie" is not talking about the 75 MHz
yagi pointing straight up that provides a reference cone. The context seems
to indicate a non-directional beacon that operated in the 200 kHz region
using AM and a T antenna often supported by wooden poles. See:
http://en.wikipedia.org/wiki/Locator_Outer_Marker


I recall, in an earlier life, 160 meters on a daytime-only AM broadcast
antenna at night.

73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"christofire" wrote in message
...

"JIMMIE" wrote in message
...
On Oct 16, 3:38 pm, wrote:
Hi Jimmie,

Inquiring minds want to know dept: You mentioned an LOM antenna.

Did that have something to do with aviation markers; loran or position
locators?

Rick
W9ZD

Aviation, one of the first grunt jobs I had after working with the FAA
was the decommissioning of an LOM site. The took out the equipment and
the building but the antenna was there for several years. I didnt have
a place I could put up a decent antenna so I would grab my 100 watt
Icom and MFJ tuner and ride out to the site. I do mostly radar work
now.

Jimmie


http://en.mimi.hu/aviation/lom.html

Chris

On Oct 17, 10:35*am, "J. Mc Laughlin" wrote:
Dear Group:

Still not as clear as it could be. *"Jimmie" is not talking about the 75 MHz
yagi pointing straight up that provides a reference cone. *The context seems
to indicate a non-directional beacon that operated in the 200 kHz region
using AM and a T antenna often supported by wooden poles. *See:http://en.wikipedia.org/wiki/Locator_Outer_Marker

I recall, in an earlier life, 160 meters on a daytime-only AM broadcast
antenna at night.

73, * Mac * N8TT

--
J. McLaughlin; *Michigan, USA
Home: "christofire" wrote in message

...





"JIMMIE" wrote in message
....
On Oct 16, 3:38 pm, wrote:
Hi Jimmie,

Inquiring minds want to know dept: You mentioned an LOM antenna.

Did that have something to do with aviation markers; loran or position
locators?

Rick
W9ZD

Aviation, one of the first grunt jobs I had after working with the FAA
was the decommissioning of an LOM site. The took out the equipment and
the building but the antenna was there for several years. I didnt have
a place I could put up a decent antenna so I would grab my 100 watt
Icom and MFJ tuner and ride out to the site. I do mostly radar work
now.

Jimmie

http://en.mimi.hu/aviation/lom.html

Chris- Hide quoted text -

- Show quoted text -

Yes an NDB, sorry I was a newbie back then with a hand that fit a
shovel. I went into radar and automation instead of Navaids. Sorry for
confusion. I think the site was called LOM/NDB. Sometime I confuse the
heck out of all those acronyms. I never learned what most of them
mean, just what they are. Stuff I work on like FDIO,SCIP,SRAP, I know
what they are but cant tell you what the acronyms mean. Nav-aids stuff
has really gotten foriegn to me over the years.

NDB is non directional beacon I forget what LOM stands for. It may
have something to do with "outer marker". I believe that was part of
the equipment and it was on centerline.

JImmie

On Oct 17, 10:35*am, "J. Mc Laughlin" wrote:
Dear Group:

Still not as clear as it could be. *"Jimmie" is not talking about the 75 MHz
yagi pointing straight up that provides a reference cone. *The context seems
to indicate a non-directional beacon that operated in the 200 kHz region
using AM and a T antenna often supported by wooden poles. *See:http://en.wikipedia.org/wiki/Locator_Outer_Marker

I recall, in an earlier life, 160 meters on a daytime-only AM broadcast
antenna at night.

73, * Mac * N8TT

--
J. McLaughlin; *Michigan, USA
Home: "christofire" wrote in message

...





"JIMMIE" wrote in message
....
On Oct 16, 3:38 pm, wrote:
Hi Jimmie,

Inquiring minds want to know dept: You mentioned an LOM antenna.

Did that have something to do with aviation markers; loran or position
locators?

Rick
W9ZD

Aviation, one of the first grunt jobs I had after working with the FAA
was the decommissioning of an LOM site. The took out the equipment and
the building but the antenna was there for several years. I didnt have
a place I could put up a decent antenna so I would grab my 100 watt
Icom and MFJ tuner and ride out to the site. I do mostly radar work
now.

Jimmie

http://en.mimi.hu/aviation/lom.html

Chris- Hide quoted text -

- Show quoted text -

Yeah, the device in the pictue is usually just called a OM, MM, IM
dependening on its position and has evolved from a wire antenna from
when I got into the FAA to the double Yagi to the single Yagi . I
havent been out there in a long time but I think there is a single
yagi OM there now and all the wooded area is now turned in to condos.


Jimmie