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Author Topic: Stranded Uninsulated Copper Wire Suitable for Attic Loop?  (Read 4305 times)
KD4ALY
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Posts: 9




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« on: December 13, 2012, 08:21:03 PM »

I have approximately 200 feet of 14 gauge stranded copper wire and a bunch of "screw into wood" standoffs.  I would like to run this wire around my attic to form a somewhat asymmetrical loop, using the standoffs to hold the wire into place and to keep the wire a few inches from the trusses.  I won't quite need all 200 feet to make a complete loop and will trim off any excess.  This wire is not insulated - should that be of any concern if I run a max of 100 watts?  I want to make sure I don't catch anything on fire using uninsulated wire (I plan on nothing touching the wire except for the hard plastic centers of the standoffs, and the SGC 230 tuner it will be connected to). 

I do realize there are other hazards to running an indoor antenna.  I may not be able to run 100 watts on a given band since there is alarm wiring in the attic that might receive RF and trigger the alarm (or perhaps the garage door may start opening/closing as I transmit.)

Thanks for reading and offering any advice. 

Tommy
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K7KBN
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Posts: 2782




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« Reply #1 on: December 13, 2012, 10:00:55 PM »

The RF doesn't notice the difference between solid/stranded and insulated/bare wire (for all practical purposes).  Build it.  Put it up.  Test it.  Avoid pipes and other metallic things.

Experiment.  Take lots of notes.  Have fun.
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73
Pat K7KBN
CWO4 USNR Ret.
GW3OQK
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Posts: 136




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« Reply #2 on: December 14, 2012, 01:07:03 AM »

A 1:1 balun at the tuner output, and to use ladderline to feed it, would be more experiments to do in the dry.
73
A
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WB6BYU
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Posts: 13120




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« Reply #3 on: December 14, 2012, 08:34:16 AM »

The wire will work just fine.

The only issue would be arcing, and as long as you are keeping it a few inches away
from anything that won't be a problem.  The location of the high voltage points will
change from one band to the next, so you'll need to test it on all bands at full power
to make sure.  If you tune the antenna for low SWR at low power and the SWR
starts jumping at high power, that's a big clue that it may be arcing.  If you run
into problems and need more insulation in specific spots, check the electric fence
section of your local ranch supply store for insulation you can slip over the wire.
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W5WSS
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Posts: 1683




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« Reply #4 on: December 14, 2012, 09:15:47 AM »

Are the standoffs the kind that have a body of insulator inside the circle that the wire passes?

I have built all sizes of loops for indoors and have used insulated wire.

Once used motor winding Aluminium wire though an insulating material was on the wire some kind of enameled stuff probably beyond any breakdown tolerances of 100 watts into a large transmitting loop.anywhere around the perimeter.

I always used low power though.
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KD4ALY
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Posts: 9




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« Reply #5 on: December 14, 2012, 07:37:08 PM »

Thanks for the replies and the suggestions.  I'm going to give it a shot.  I'll make sure it is not close to other things in the attic, especially anything metallic.  I'll definitely run low power to check SWR through the bands, and gradually increase power to see what happens. 

The standoffs do have a body of insulator inside the ring.  They are 3 1/2" standoffs, and are like the standoffs I used years ago to run 300 ohm twinlead from my TV antennas. 

This is definitely an experiment.  I have a 40 meter resonant dipole outside, mounted rather low.  I've been curious what the attic loop might do, not only on 40 and 15 but other bands as well.  I'm not expecting miracles but really interested to see what happens (as long as "what happens" is safe).

Thanks again. 
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KC4MOP
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Posts: 731




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« Reply #6 on: December 15, 2012, 06:12:21 AM »

Are you in a townhouse or a single family unit?
Full legal limit will always have some fire danger to it from arcing.
A condo or Townhouse will be massive RFI to your neighbors.
Single family home, you will deal with  your own RFI issues as RF is transferred to your electrical system.
I was ok with a Spider antenna and 100 watts whilst living in a townhouse; then a single family house later and what a difference with antennas breathing fresh air about 65 feet up!!!

Fred
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K1CJS
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Posts: 5981




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« Reply #7 on: December 15, 2012, 06:21:41 AM »

One old house I used to live in had a loop of wire in the attic made out of just that.  It was a receiving antenna for an older AM radio, owned by someone who owned the house before us.  His relatives said he was a ham also, but not at all an active one.
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KD4ALY
Member

Posts: 9




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« Reply #8 on: December 15, 2012, 07:43:16 AM »

Fred,

I'm in a single family unit.  I definitely won't run full limit - due to RFI concerns, I just don't see running more than 100 watts.  The attic is rather large and the alarm wiring runs along the "floor", so although I'll be probably no closer than 5-6 feet at any one location to that wiring, I still figure I might trigger the alarm.

Tommy
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KC4MOP
Member

Posts: 731




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« Reply #9 on: December 15, 2012, 11:02:00 AM »

Fred,

I'm in a single family unit.  I definitely won't run full limit - due to RFI concerns, I just don't see running more than 100 watts.  The attic is rather large and the alarm wiring runs along the "floor", so although I'll be probably no closer than 5-6 feet at any one location to that wiring, I still figure I might trigger the alarm.

Tommy
Tommy, see what barefoot power does to your alarm system. You might need to have shielded alarm cable run to keep from falsing the alarm unit.
I had low dipoles right over the house, single story house,  and ran QRO (AM mode) and my ADT system with shielded cables never had a problem.
Fred
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W5WSS
Member

Posts: 1683




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« Reply #10 on: December 16, 2012, 02:45:01 AM »

Fb good luck on the fun project as long as you do it during the cooler months man it gets hot up there.

The mutual coupling of the other conductors about the antenna will be a participant relative to pattern development and ultimately field strengths will be attenuated by the structure materials etc.

I have enjoyed many indoor antennas and low power.

I am currently working with a multiband vertical dipole and top hat Assembly.

The antenna is still being analysed and preliminary results are promising for long range dx service.

 The horizontal family of indoor antennas are never very high and their long range dx utility is somewhat limited being predicated to higher HF bands,Their shortrange skywave utility for the group is very good.

For indoor transmitting antennas The horizontal loops or multiband dipole for shorter skywave propensities low band such as 30m to 75m and perhaps the vertical dipole for 17m-10m. longer dx would be a good combination offering service for both longer and shorter skywave tasks.
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WB6BYU
Member

Posts: 13120




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« Reply #11 on: December 16, 2012, 07:43:27 AM »

If you have problems with the alarm system then there are a number of possible solutions,
including replacing the wire with shielded cable and adding ferrite chokes at both ends
(and along the wire if needed to break up resonances.  A quick solution might be to
wrap it in aluminum foil.

And don't be afraid to crank the power down to 5 or 10 watts if you need to.
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KD4ALY
Member

Posts: 9




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« Reply #12 on: December 16, 2012, 04:09:27 PM »

Thanks for the additional responses and suggestions, especially regarding the alarm wiring.  I'll have to test thoroughly before having any serious QSOs since it would be somewhat embarrassing (and frustrating) should I activate the alarm while carrying on a conversation. 

The antenna is now installed.  Next I'll acquire the SGC tuner and bias tee - definitely before the weather warms up. 

Tommy
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N4NYY
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Posts: 4745




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« Reply #13 on: December 16, 2012, 04:19:42 PM »

Just try and keep it away from any electrical wires.
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KD4ALY
Member

Posts: 9




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« Reply #14 on: December 16, 2012, 07:35:43 PM »

Started thinking (which is dangerous for me) - is there a benefit to using a balun since the SGC is a remote tuner?

Thanks again for all of the responses. 
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