Three antennas on one mast

[ka1njl]

I would like to mount two discones and one 2M/440 dual band antenna on a single mast and I need some advice. The mast will be installed on a one story building and it will extend about 10 feet above the eaves. I anticipate mounting the dual band antenna on the mast itself and installing a cross member on the mast for the two receive antennas, in a configuration that will look like a "t". The mast will be comprised of two 10' pieces of galvanized fence rail (1 3/8", 17 gauge) but I don't know how to mount, or what material to use for, the cross member. Has anyone done this or does anyone have any ideas about how I can achieve my goal?

Thanks and 73,

Gary

 

[Thunderknight]

Assuming you will be transmitting on the dual band antenna, you need to be thinking about coupled power back into the discones and the receivers they are connected to. You don't want too much RF power when you transmit to make it back down to your receiver on the discone.
Vertical separation is one way to mitigate this...mount the cross arm with the discones below the dual band antenna, so the discones are below the radiation lobes of the dual band antenna.
Also having the discones on the same level as the dual band may affect the antenna patterns of all of the antennas (probably most noticeable on the dual band)
The bracket you need to make the "T" is a cross-over bracket (or cross-over plate).

If you have the roof space, you might want to consider mounting the dual band at one of the structure and the discones at the end, to provide more horizontal seperation.

 

[prcguy]

I would recommend Nu Rail or Speed Rail fittings. These come in T, cross, 90 deg elbow and lots of shapes and are used to make hand rails and other structural stuff. They also make a really clean looking antenna installation. I believe the size made for 1" id schedule 40 pipe is what you need for 1 3/8" od tubing.

Here is a cross bar I made to mount a Discone, 700-900MHz vertical and a Big Stick CB antenna on the same mast. The mast will go up through the center cross fitting about a foot to hold the Big Stick then the Discone and 700-900MHz antenna will mount on the outer sides. I'm using 1" sched 40 aluminum pipe on this project but have used these fittings with galvanized fence rail in the past. I typically use 90 deg elbows for the end masts but in this case I had some T's laying around so I used those.

You can go to the Nu Rail or Speed Rail website to find the part # you need then go on eBay and buy the stuff cheap used like I did. I believe Home Depot sells somethign similar but eBay prices will be lower.

 

[MUTNAV]

I would recommend Nu Rail or Speed Rail fittings. These come in T, cross, 90 deg elbow and lots of shapes and are used to make hand rails and other structural stuff. They also make a really clean looking antenna installation. I believe the size made for 1" id schedule 40 pipe is what you need for 1 3/8" od tubing.

Here is a cross bar I made to mount a Discone, 700-900MHz vertical and a Big Stick CB antenna on the same mast. The mast will go up through the center cross fitting about a foot to hold the Big Stick then the Discone and 700-900MHz antenna will mount on the outer sides. I'm using 1" sched 40 aluminum pipe on this project but have used these fittings with galvanized fence rail in the past. I typically use 90 deg elbows for the end masts but in this case I had some T's laying around so I used those.

You can go to the Nu Rail or Speed Rail website to find the part # you need then go on eBay and buy the stuff cheap used like I did. I believe Home Depot sells somethign similar but eBay prices will be lower.

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View attachment 144302

I got stuff like that from Grainger.

Thanks
Joel

 

[ka1njl]

Assuming you will be transmitting on the dual band antenna, you need to be thinking about coupled power back into the discones and the receivers they are connected to. You don't want too much RF power when you transmit to make it back down to your receiver on the discone.
Vertical separation is one way to mitigate this...mount the cross arm with the discones below the dual band antenna, so the discones are below the radiation lobes of the dual band antenna.
Also having the discones on the same level as the dual band may affect the antenna patterns of all of the antennas (probably most noticeable on the dual band)
The bracket you need to make the "T" is a cross-over bracket (or cross-over plate).

If you have the roof space, you might want to consider mounting the dual band at one of the structure and the discones at the end, to provide more horizontal seperation.

Thanks Thunderknight. I think the cross-over bracket may be the way to go. I'll need three (at around $19 each from Amazon) to complete the project but they will do exactly what I need.

Since there will be only one operator it will be easy to control who is transmitting when the receive antennas are being used.

Gary

 

[ka1njl]

I would recommend Nu Rail or Speed Rail fittings. These come in T, cross, 90 deg elbow and lots of shapes and are used to make hand rails and other structural stuff. They also make a really clean looking antenna installation. I believe the size made for 1" id schedule 40 pipe is what you need for 1 3/8" od tubing.

Here is a cross bar I made to mount a Discone, 700-900MHz vertical and a Big Stick CB antenna on the same mast. The mast will go up through the center cross fitting about a foot to hold the Big Stick then the Discone and 700-900MHz antenna will mount on the outer sides. I'm using 1" sched 40 aluminum pipe on this project but have used these fittings with galvanized fence rail in the past. I typically use 90 deg elbows for the end masts but in this case I had some T's laying around so I used those.

You can go to the Nu Rail or Speed Rail website to find the part # you need then go on eBay and buy the stuff cheap used like I did. I believe Home Depot sells somethign similar but eBay prices will be lower.

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View attachment 144302

This too is a great idea. The components are available from Amazon as Hollaender fittings and they're a bit pricey but they will do what I need. Armed with this new informatoin I'm going to spend some time thinking about which approach is best. Thank you for the great suggestion.

 

[iMONITOR]

That's going to be a fair amount of wind resistance. Make sure the mast is strong and mounted securely.