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Author Topic: 40 and 80 meter wire dipoles... How far apart?  (Read 3710 times)

KE7TRP

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40 and 80 meter wire dipoles... How far apart?
« on: July 06, 2013, 04:05:04 PM »

I am thinking of trying a few different options for 40 and 80. 

I was thinking of trying out the 80 meter Double bazooka.  Mainly because it will cover a wide bandwidth. This antenna will be mounted from a fiberglass arm off the top of the 55 ft crank up tower and set up as an inverted V.

For 40,  I was thinking of making a standard dipole or another bazooka but then hanging this antenna off a side arm from the middle section of the crank up tower. 

Two dipoles, on the same tower.  One at the top and one at the top of the middle section. 

The distance apart would be 6ft when tower is cranked down for summer and 15 to 20 ft apart when the tower is up all the way. 

I have never ran two dipoles this close.  Will this work out ok since the two are on different bands.

Is there any real reason, I cant put both separate antennas on the top of the tower?   The 40 wires would run out and be tied off away from the 80 wires.  Kind of like a fan dipole but with two Bazookas and two coax lines.

Thanks for any thoughts on the subject!

C

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W5LZ

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Re: 40 and 80 meter wire dipoles... How far apart?
« Reply #1 on: July 06, 2013, 09:47:16 PM »

I don't see any reason it wouldn't work.  If you could mount them 90 degrees from each other (an 'X') it would minimize any interaction.  There will be some, but it shouldn't be all that objectionable.
 - Paul
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KE7TRP

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Re: 40 and 80 meter wire dipoles... How far apart?
« Reply #2 on: July 09, 2013, 02:11:47 PM »

That would be hard to do here because of the house being in the way.  I am going to try it and see what happens.

C
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WD5JOY

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Re: 40 and 80 meter wire dipoles... How far apart?
« Reply #3 on: July 12, 2013, 08:20:33 AM »

You didn't note or I do not see what you plan on using as feedline. EITHER METHOD YOU CHOOSE WHY NOT USE ONLY ONE FEEDLINE FOR BOTH ANTENNAS?  Attach at the apex of each and run the legs as far opposing each other as you can.  Saves the cost of another run of coax and the antennas take care of which length to use as you change bands; tune each individually as you would if there was only one antenna. I would tune the 40M then the 80M - but either should work since the close proximity to the earth will come into play.

If you use coax - you best use or at least consider using a 1:1 CURRENT balun at the apex. Then simply connect the 'legs; of each dipole to each side of the BALUN and RUN THE COAX straight down the tower to a point where it can "turn" and go to your shack. 

If using OPEN WIRE / LADDER LINE AS FEEDLINE (instead of coax) --- be sure to use "standoffs" to keep it away from the tower and other metal objects by one to two feet if possible.  As with the coax - run the feedline straight down the tower - turn at the appropriate place and run to the shack. NO BALUN at the FEEDPOINT - but rather use one just prior to ENTRY INTO THE SHACK where you would make the transition from LADDER LINE FEEDLINE to A SHORT RUN OF COAX TO THE RIG.

If you are 'gutsy' and have a tuner with a balun installed you could run the LADDER LINE through the wall, into the shack and put the CURRENT BALUN just before the first connection point at the tuner.  KEEP STRAY RF from wandering around the rig and accessories and biting the heck out if your lips and other tender parts. I'd keep the balun OUTSIDE the shack and run the shortest coax jumper as possible to the rig.

Do at least consider using ONLY ONE FEEDLINE --- no need for the second if the connection at the apex is the same. I run a 80M / 160M combo this way - using coax and it works great in spite of the 160 being WAY to close to the ground.  Your 80 will likely be a NVIS for the most part - but it will serve you well.

73 Don / WD5JOY
Old Senile Don - Today is a "good day"!
« Last Edit: July 12, 2013, 08:37:58 AM by WD5JOY »
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KE7TRP

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Re: 40 and 80 meter wire dipoles... How far apart?
« Reply #4 on: July 12, 2013, 09:44:08 AM »

I am familiar with Fan dipoles.  Around here they are called Maypole antennas.  That's a great option and one I might test some day. Two wires for 40 and two for 80.   I am not sure you can make a bazooka style antenna in this fashion.  I really need to test this out.   

Currently,  I have 600 ohm open wire line from either a KW matchbox or a HB tuner in the shack.  The 600 ohm line runs out of the shack and then through two large inductors to ground for static discharge.  Then, the open wire line runs up the tower to a fiberglass stand off that is 3 feet off tower.  The open line splits off to 130 ft of wire in an inverted V.

C
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