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Amateur Radio Antennas - For discussion of all amateur band designed antennas and related accoutrements. This includes base, handheld, mobile and repeater usage. For commercial antennas on the amateur bands please use Commercial Radio Antennas below.

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Old 12-17-2017, 12:28 PM
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Default Need help choosing in-line switch for dipole

I have a 40m dipole antenna, 14 ga stranded THHN. I would like to cut the elements at 8 (ish) feet, separate them with a dogbone type insulator, then have a switch to connect/disconnect the two sections so I can toggle the antenna for use with either 40m or 10m.

1. What type of a switch would be good for this? It would exposed to rain/snow/sunlight.

2. How long does the insulator need to be? (how much distance between the two sections)

3. Should I expect this to degrade the performance of the antenna when it's being used for 40m/80m?
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Old 12-17-2017, 12:36 PM
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Research Fan Dipoles. It'll do what you want without the switch.
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Old 12-17-2017, 12:57 PM
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Thanks for the quick reply!

I'm pretty sure I don't have the room to set up a fan dipole properly. My antenna is about 12' off the ground, strung through pine trees between my yard and my neigbor's yard.

If if would work with the 10m element being about 6 inches below the 40m element, then I might be able to manage it, but I'm thinking the elements would be too close. It would also require running another 120' feet of wire, which would not be desirable.

I thought of the switch Idea because it would keep everything 12 feet off the ground and low profile /stealthy, which is a requirement. If it can give me good performance, it would definitely be better than adding more elements to my antenna.

Mouser has about 20 different categories of switches, and about 100,000 different items, so I have no idea where to even start looking.
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Old 12-17-2017, 1:07 PM
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Traps would work too. They effectively separate the antennas by bands.

Switches would work, but how they'll handle RF would be a question. Also, how well they'll stand up to being exposed to the environment for a long time would be a question.

Other option, if you've got the space, is to put them in an "X" pattern, your 40 meter dipole going off in it's direction, and the other at 90║/180║ to it.
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Old 12-17-2017, 2:01 PM
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How are you going to switch these? At 12 feet above ground, it will be a reach. Maybe a pair of 10M series traps is what you need?

Otherwise any properly rated hermetically sealed switch with some means to toggle it with a pole should work.
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Old 12-17-2017, 5:00 PM
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Quote:
Originally Posted by RFI-EMI-GUY View Post
How are you going to switch these? At 12 feet above ground, it will be a reach.
My feedline is on a 2-piece mast -- It is easily taken down, so my main concerns with the switch are:

1. What would be appropriate type of switch to look for? I am not knowledgeable about switches, and there are way too many types to browse, so I was hoping to get the name of a type of switch that would work for something like this.

2. would need to be somewhat weather-resistant

3. would not degrade the performance of the antenna.

I am going to look into traps -- I had not considered that option. I also might be able to hang a support line for a 10m element from the 40m element and go the fan dipole route as McKenna suggested. These options might be more practical than using a switch.
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Old 12-17-2017, 8:06 PM
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I really think your best options are:
Fan dipole.
Traps,
Or just add a dedicated 10 meter antenna.

As was said, activating a switch 12 feet in the air without climbing up and down a ladder each time is going to be difficult. It'll need to be something large enough you can hit reliably with a stick, by pulling a cord, etc. It'll need to be waterproof, which makes it harder. Also, running RF through a cheap switch may not be your best choice. Arcing shouldn't be an issue unless you are running a lot of power.

What I've seen people do is use a short jumper with an alligator clip, but that requires being able to reach it. Unless you were in the NBA, that's likely not going to be something you can do.

Other option is to look into a remote coaxial switch or relay. Use that on the mast to switch the coax feed from one antenna to the other. Or, just run a second run of cable and use a coax switch near the radio.

Personally, I think the fan dipole is going to be a whole lot easier.
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Old 12-17-2017, 8:07 PM
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Quote:
Originally Posted by Rastaman147 View Post
My feedline is on a 2-piece mast -- It is easily taken down, so my main concerns with the switch are:

1. What would be appropriate type of switch to look for? I am not knowledgeable about switches, and there are way too many types to browse, so I was hoping to get the name of a type of switch that would work for something like this.

2. would need to be somewhat weather-resistant

3. would not degrade the performance of the antenna.

I am going to look into traps -- I had not considered that option. I also might be able to hang a support line for a 10m element from the 40m element and go the fan dipole route as McKenna suggested. These options might be more practical than using a switch.

You could use some hermetically sealed magnetic reed switches and find some way to place a magnet next to them when you want it closed. Get some heavy duty reed switches like used for burglar alarms. But frankly a 10M series trap sounds like less worry.
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Old 12-17-2017, 10:00 PM
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A 10 metre/40 metre combination dipole is a rather odd duck, Rasta Man.
.
..... I agree, you can use traps- but unless you are particularly patience and adept at winding them, tuning them. etc. -- why mess up your working 40 metre antenna? Inserting anything into it will change its tuning characteristics... you are setting yourself up for a lot of avoidable pains, when it is so easy to assemble a separate 10 metre antenna..... a 10 metre dipole, or a vertical is easy...
.
Or even- have you looked at how that 40 metre dipole loads on 10?... I know; it shouldn't- but strange things happen with antennas-- if the SWR is 2:1 or so, use it--- when 10 is open, a wet string for an antenna will work the world.
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Old 12-20-2017, 10:28 AM
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Rather than a fan dipole, you can just 'hang' a 10 meter dipole 'under' the 40 meter one (say about 2 inches) and use spacers to keep them separated. If you feed them in parallel, the SWR of the 'wrong' dipole will keep most of the RF going to the 'right' antenna. One issue wiht this may be more noise pickup on receive.

73
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Old 12-26-2017, 10:10 PM
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What you envision is a 10 meter dipole with extensions on both end and that can be attached to resonate on 40 meters. Attaching is done manually when the 12 foot high antenna is lowered. Perfectly workable but a head scratcher for the group as evidenced by the alternative suggestions.

With this background, let me speculate on what the group may be thinking.

First, we hear almost nothing on 10 meters and we still have years before the sun spot cycle begins to recover. 12 or 15 meter bands at least have some activity. Why 10 meters?

Second, the manual up and down switching will get very old very quickly. Electric switching of two switches will require a lot of wire, a lot of weight to support, coupling problems. and a lot of messing around to get everything to resonate again. Remote control is a consideration not withstanding weight and battery life.

Third, we know that a trap dipole or fan dipole or (slightly more complex) an Off-Center-Fed or End-Fed half-wave dipole are multi-band... and instantly available. Why do any switching? And (thinking outside the box) ideas like wyShackĺs linear loading of a second, even a third radiator become interesting for a multi-band antenna.

Finally, just consider the thoughts the group presented but pursue your own ideas on antenna development. I encourage you try things then figure out what could be better. Research what others have tried. Maybe look into antenna modeling to save time and effort. Antennas are one of the most interesting aspects of the amateur radio hobby.
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Old 12-27-2017, 9:27 AM
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There is no practical switch for what the OP wants except maybe a small knife switch. I've made lots of dipoles in the past where I put jumpers across insulators to enable other bands.

Simply make a 10m dipole with insulators on each end and leave about a 2" wire pigtail to bridge the insulator. Then add another section of wire to the other side of the insulator leaving a 2" pigtail there and make that resonate on 40m or whatever when the insulator is shorted.

I use automotive "butt connectors" on the pigtails to make a solid connection that can easily be broken. This should satisfy the OPs original idea, although I prefer using traps or making a fan dipole so you don't have to go out in the cold to change your antenna.
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