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 An antenna in a loft versus an antenna just outside the loft 
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Post An antenna in a loft versus an antenna just outside the loft
I am building a 17m half wave dipole in my loft. It will be at 33ft above the ground. I will be running the legs inside 20mm pvc tubing and using a 4:1 balun.

If i was to mount it outside it would be about 10inches away from where it is to be in the loft. The loft is typical, nothing different - apex wood, roof liner, roof tiles.

What would be the advantage in gain of it being outside 10inches away. Would it be massive, noticeable, or barely noticeable.

Have any of you noticed massive improvements by going outside at the same elevation???

the dipole will radiate NE/SW.

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73

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Thu May 02, 2013 8:37 am
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
I have tired a few methods like your self and the only issue I notice with loft mounting is that the antenna picked up of a little more electrical noise and a very slight drop on receive and transmit on HF, but a marked notice on VHF for your reference. Other than that the compromise is good, sure hope this helps.

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Thu May 02, 2013 8:41 am
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
Thanks for the info John,

So on 17m id expect little difference on if it was out or in at the same elevation?

I will be putting it in at the weekend. Will feed it with RG8 to the balun.

The 4:1 should minimise any noise i get.

73

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Thu May 02, 2013 9:34 am
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
Why a 4:1 balun?

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Thu May 02, 2013 9:35 am
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
G7DIE wrote:
Why a 4:1 balun?


Ye why the balun? And if you put it in the loft you won't need to put it in a tube either.


Thu May 02, 2013 9:51 am
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 An antenna in a loft versus an antenna just outside the loft 
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Post An antenna in a loft versus an antenna just outside the loft
Hi all,

The balun is really just to try to reduce any noise that would be picked up because the antenna is indoors. I have a spare 4:1, im sure a 1:1 would do, but i havent got the parts handy to make a new one.

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Thu May 02, 2013 11:44 am
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
A 4:1 balun is an impedance transformer, it shouldn't be used with a monoband dipole, if you're short of bits and bobs in order to make a torroidal current choke, then check out Steve's chart and simply wind yourself a coax choke specific to the band, nothing more than a few turns of coax on a former, easy ;)

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Thu May 02, 2013 11:51 am
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
Cheers for that. will look at steves chart and throw something together.

73

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Thu May 02, 2013 1:43 pm
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
Greg purely from personal experience, I have always tried to keep loft wire antennas at 90 degrees to the longest continual runs of loft mounted mains wiring.
The longest continual runs in my property seem to be longitudinal, down the length of the building, so I have employed inverted V antennas utilising the A frame of the roof, for some bands from 4 meters, to 20 meters. (That one has loaded ends)
This places them at 90 degrees to the longest runs of cable, and has in my case seemed to minimise mains bourne noise, and RF coupling into the mains wiring.
Other installations may be different of course!
Just a thought.

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Thu May 02, 2013 1:49 pm
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
Thanks for that dave, I will build it as i had planned initially. My house is a quirky shape. It would be possible to mount it perpendicular to my original plan.

I dont have massive experience in antenna building, im not overly 'into' building them as such, but i really enjoy swl'ing and working 17m contacts, so just wanted to build a dipole for it. I will use my 756Pro for 17m, and i may even build a 6m dipole for SWL'ing initially. :)

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Thu May 02, 2013 2:36 pm
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
Don't use the 4:1 balun. Better to use no balun until you have a 1:1. I bought a couple of cheap ones from urbasket.eu, just fine for indoors. As above, a balun should reduce the effect of electrical 'goings-on' in the loft.

I've never noticed any signal loss in the loft on HF. If there is any loss it must be negligible - like fractions of a dB. If a signal has just come down out of the sky from 150 miles up, it isn't going to stop dead when it meets an inch of air-blown concrete crunchie and a layer of bitumen felt. Both of these are lousy stuff to make Faraday cages from :)

Oh, and don't bother with the tube, Just keep the ends a little bit away from anything flammable, but that only really matters if you are running serious QRO.

Good luck.

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Thu May 02, 2013 4:27 pm
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
Thanks for the enzec chris btw.

LOL @ Serious QRO!! What exactly is 'Serious QRO' to a QRP man.

50+ 100+ 200+ ?? :)

I was going to add the pvc because i wanted to run 100w.

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Thu May 02, 2013 4:35 pm
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
MI0HEZ wrote:
Thanks for the enzec chris btw.

LOL @ Serious QRO!! What exactly is 'Serious QRO' to a QRP man.

50+ 100+ 200+ ?? :)

I was going to add the pvc because i wanted to run 100w.


Ur welcome. Of course it was Steve's work, not mine. In fact your antenna will be better than the plot for DX, because the plot was cast for an inverted 'V' in my apex at about 27 feet, and yours is higher, i.e. better.

100W? don't worry. Just use insulated wire and hang the ends a few inches away from the wood. Don't worry about the middle, because of course it's mainly 'current' there and the 'volts' are at the ends.

Have fun this weekend.

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Thu May 02, 2013 4:45 pm
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
G6CSL wrote:
because of course it's mainly 'current' there and the 'volts' are at the ends.




:thumbsup: :D

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Thu May 02, 2013 4:58 pm
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 An antenna in a loft versus an antenna just outside the loft 
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Post Re: An antenna in a loft versus an antenna just outside the
Be aware that some roofing materials that are relatively low loss when dry can cause significant attenuation once they are dowsed in rain water.

For preference I'd always put the antenna outside if it's at all possible.

As others have said you must not use a 4:1 balun; use a 1:1 current balun, aka a choke.

Steve G3TXQ


Thu May 02, 2013 5:06 pm
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