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Author Topic: Is 2 Verticals Side by Side a bad idea? HF & 2m/70cm on Chimney.  (Read 2441 times)
KJ6GEV
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Posts: 16




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« on: July 16, 2010, 10:39:05 AM »

Hello, I have space restriction i.e., tract home in flat valley, and have been operating on 2m & 70cm with a dualband Diamond X200 mounted on a 10 foot mast attached to my chimney.

My property width is only 60 feet and I'm wanting to take advantage of the HF capabilities of my Icom IC-7000 and am looking at a multiband HF vertical. Since my chimney is the only logical mounting point on the top of my single story home, would it be ok to mount the HF vertical next to the VHF/UHF vertical? If yes should the antennas be at seperate heights? They will not be keyed down at the same time as they will be interfaced to one radio.  Any help would be greatly appreciated as I am on a very small lot, 60 feet wide by 40 feet, no CC&Rs. Thanks much KJ6GEV  
« Last Edit: July 16, 2010, 10:41:50 AM by Johnny Warren » Logged
KG4RUL
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« Reply #1 on: July 16, 2010, 10:57:42 AM »

Use the widest part of the chimney to separate the two antennas and you should be just fine.  Also, to save a run of coax, you could use a diplexer on the chimney to combine the two bands.  Assuming your radio has a combined antenna input you are done or use another diplexer, to separate them out again, if you have separate inputs..
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W3LK
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« Reply #2 on: July 16, 2010, 11:31:15 AM »

Hello, I have space restriction i.e., tract home in flat valley, and have been operating on 2m & 70cm with a dualband Diamond X200 mounted on a 10 foot mast attached to my chimney.


This is a BAD idea. Chimneys are designed to carry smoke and exhaust products away from a furnace or fire place. They are designed to support only their own weight. They are NOT designed to support antennas or withstand the lateral and torsional forces imposed by masts and antennas. Add to that the corrosive effects of flue gasses on aluminum and you will not only weaken your chimney, but destroy your antenna within a couple of years, maybe less, depending upon how active your chimney is.

Yea, I know, there have been TV antennas fastened to chimneys for years, and virtually every one of them has cracked mortar joints and are in a weakened condition. BTW, damage caused by a failed chimney that's been supporting antennas likely will not be covered by your property insurance or your liability insurance in the event the chimney falls on someone. It may, but I wouldn't bet on it.

Mounting a dual-band on a 10' mast is bad enough; putting an HF antenna on a chimney is asking for trouble. There are so many better ways to support antennas.
« Last Edit: July 16, 2010, 11:32:57 AM by Lon Kinley » Logged

A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
KJ6GEV
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« Reply #3 on: July 16, 2010, 12:31:04 PM »

Use the widest part of the chimney to separate the two antennas and you should be just fine.  Also, to save a run of coax, you could use a diplexer on the chimney to combine the two bands.  Assuming your radio has a combined antenna input you are done or use another diplexer, to separate them out again, if you have separate inputs..

Any idea where I can get the 2 diplexers in the USA? Any Links? Thanks

PS:Also the chimey is not used and is filled with concrete.
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WB2WIK
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« Reply #4 on: July 16, 2010, 01:58:44 PM »

Use the widest part of the chimney to separate the two antennas and you should be just fine.  Also, to save a run of coax, you could use a diplexer on the chimney to combine the two bands.  Assuming your radio has a combined antenna input you are done or use another diplexer, to separate them out again, if you have separate inputs..

Any idea where I can get the 2 diplexers in the USA? Any Links? Thanks

PS:Also the chimey is not used and is filled with concrete.


A large chimney filled with concrete should be very strong, especially if it has rebar in it (as it should).  However I'd still worry a bit about it supporting an HF vertical, as those can be very tall and fairly heavy, and many times the load of a dual-band VHF-UHF vertical.

Regarding the diplexers, they are readily available and both HRO and Jun's stock them.  You can look at some here:  http://cometantenna.com/products.php?CatID=1&famID=6&childID=0

Regarding a possible alternative to the chimney mount, especially for a larger HF vertical, you might want to take a look at this:  http://www.eham.net/articles/4148

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STAYVERTICAL
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« Reply #5 on: July 17, 2010, 01:57:57 AM »


Structural considerations aside (although you should really make sure that chimney is not going to fall), in my experience a vertical has very little wind resistance. I use a 17 foot high vertical made of standard wall thickness aluminium, nothing special, which is supported on a broomstick. It has been through many windstorms and just bends until the wind stops. It also only weighs about 4 pounds.
Get a remote atu, mount it at the base of the antenna, put on some radials, and forget it.
That sucker will work from 40 to 6 metres with a reasonable remote tuner.
If you use a remote atu it wont matter about detuning, because you just press the button to retune it anyway.

By antenna I just mean telescope some tubes together to make a radiator, forget about coils traps and all that lossy junk,
you wont need them with a base mounted atu, and your swr will be great, your losses minimal and it will really radiate.
This arrangement is my only antenna and I use it from 60m to 6m with great results.
One caveat though, if you feel tempted to put on a capacity hat, this will GREATLY increase the wind resistance by my experiments.
You don't need one anyway, so if you stick with a pointy thing sticking up you will have only a small wind resistance.
If you are going to be running multiple rigs though, take into consideration if high power close proximity antennas may damage the front
ends of the other rig, so consider this.

Otherwise, have fun, this works greats for me, and punches well above its weight (literally).

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