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Author Topic: 10 meter dipole in apartment  (Read 5593 times)
KB1TXK
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« Reply #15 on: June 08, 2011, 12:06:23 PM »

GODSPEED GOOD SIR! Smiley
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NU9J
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« Reply #16 on: June 08, 2011, 02:05:29 PM »

'Nother question: once I've trimmed the ends to minimize SWR, how can I affix them to the insulators so that I won't detune the antenna? Maybe tape on a piece of nylon cord and use the cord to tie to the insulator?
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~Philip
AE4RV
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« Reply #17 on: June 08, 2011, 06:32:12 PM »

Get the wire on the insulator FIRST.

Then, to trim, just fold the extra wire back. If you're using standard dogbone insulators, just tie the wire around one end and support rope to the other end of the insulator. To shorten the wire, merely mark where the wire enters the insulator with a sharpie, unwrap/untie the wire from the insulator, measure how much you want to "trim", and mark the wire there.

Then, re-wrap/tie the wire with the new mark at the insulator - no cutting necessary.

IE: Once the wire is folded back, it's out of the RF equation.

Worked for me when tuning my fan dipole.
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NU9J
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« Reply #18 on: June 08, 2011, 07:05:09 PM »

Ok, built the dipole with SWR=1.5 but holy NOISE! S9 noise across the band. On a frequency spectrum, looks like multiples of 120 Hz, so is this electrical noise? I have one of those RadioShack switching power supplies, so perhaps that's the cause?
« Last Edit: June 09, 2011, 06:13:10 AM by KI4THS » Logged

~Philip
W0BTU
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« Reply #19 on: June 08, 2011, 11:34:30 PM »

If it were me, and I was experimenting:

LARGE cookie sheet
3/8 x 24 magnet mount
102" radio shack stainless CB whip ...

The 102" whip needs a counterpoise, and a cookie sheet does not qualify because it's NOT big enough (see http://www.w0btu.com/Optimum_number_of_ground_radials_vs_radial_length.html#noground). A "LARGE" cookie sheet might be OK on 2 meters, but no way is it going to work on 10!

Try the dipole. One thing that's going for you is the age of the building (no foil-backed insulation board.) If you're real lucky, you won't have a lot of noise from things inside the building. If you do, run a dipole outdoors, and make it out of thin magnet wire. Nobody will see it.
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N4NYY
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« Reply #20 on: June 09, 2011, 05:03:09 AM »

Quote
Nother question: once I've trimmed the ends to minimize SWR, how can I affix them to the insulators so that I won't detune the antenna? Maybe tape on a piece of nylon cord and use the cord to tie to the insulator?

Usually one of those crimp on lugs, then ty-rap it to an insulator.
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KB1TXK
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« Reply #21 on: June 09, 2011, 06:20:57 AM »

It was a quick and dirty fix for a possibly dirty situation (angry landlord/neighbors).  Maybe a vertical dipole out of two 102" whips (trimmed) would be a better alternative to the cookie sheet thing?

If it were me, and I was experimenting:

LARGE cookie sheet
3/8 x 24 magnet mount
102" radio shack stainless CB whip ...

The 102" whip needs a counterpoise, and a cookie sheet does not qualify because it's NOT big enough (see http://www.w0btu.com/Optimum_number_of_ground_radials_vs_radial_length.html#noground). A "LARGE" cookie sheet might be OK on 2 meters, but no way is it going to work on 10!

Try the dipole. One thing that's going for you is the age of the building (no foil-backed insulation board.) If you're real lucky, you won't have a lot of noise from things inside the building. If you do, run a dipole outdoors, and make it out of thin magnet wire. Nobody will see it.
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KE4JOY
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« Reply #22 on: June 09, 2011, 06:37:29 AM »

Ok, built the dipole with SWR=1.5 but holy NOISE! S9 noise across the band. On a frequency spectrum, looks like multiples of 120 Hz, so is this electrical noise? I have one of those RadioShack switching power supplies, so perhaps that's the cause?

Possibly, 120Hz is almost assuredly some power supply somewhere. Then again it could be a street light or a neighbors fluorescent light.

Only way to know for sure is to figure out how to run on battery and cut everything else off.
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W0BTU
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« Reply #23 on: June 09, 2011, 08:47:09 AM »

Maybe a vertical dipole out of two 102" whips (trimmed) would be a better alternative to the cookie sheet thing?

A much better alternative. :-)

You could just use one whip, and let gravity take care of ~96" of wire hanging down below the feedpoint.

If you could stick it out the window on some kind of long support whenever you wanted to operate,  that would help get it away from hidden wiring in the walls and noise sources.

The feedline should run 90 degrees to the antenna for at least a quarter wavelength.

« Last Edit: June 09, 2011, 08:52:22 AM by W0BTU » Logged

NU9J
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« Reply #24 on: June 09, 2011, 09:30:41 AM »

Couple of pics.

http://farm4.static.flickr.com/3547/5815081081_d992c37b6d.jpg
http://farm4.static.flickr.com/3502/5815081273_e176fcb318.jpg

Also, the noise seems to be down from S9 to S3-S4, so must have been the neighbors or something local.
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~Philip
W5RRP
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« Reply #25 on: June 10, 2011, 06:00:59 PM »

Truth be known, back in the late '70s, as a grad student (with no money) I put a single feed line to 10m, 15m, and 20m dipoles.  Since I was broke, the only wire I could afford, after buying enough coax to feed the antenna, was galvanized cloth line wire.  You have to take into consideration that the sunspots were going crazy back then, but the antenna was in the attic, maybe 12 feet above ground level.  I worked the world -- South Pole, North Pole, Europe, Africa, Asia, Australia -- quite literally the world -- with 150 watts input -- with no problem at all.  Now -- you should probably take into consideration that I was using a tube transciever, and, because of the pi-network, was not really concerned about the swr -- but it worked, and maybe worked as well as anything I have had since.   Ron  W5RRP
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VA7CPC
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« Reply #26 on: June 11, 2011, 09:42:12 AM »

This apartment complex is old: wood slats + plaster walls + red brick. I wish I could stick something out the window, but the management will have issues with that. However, I can try it and leave it outside until someone says something.

If the plaster is laid on metal lath, nothing will get through it.  If it's non-metallic lath, you might be OK.  You might get better results with a ceiling mount, as opposed to a wall mount.

               Charles
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NU9J
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« Reply #27 on: June 11, 2011, 09:53:03 AM »

If the plaster is laid on metal lath, nothing will get through it.  If it's non-metallic lath, you might be OK.  You might get better results with a ceiling mount, as opposed to a wall mount.

               Charles

No metal. I have made one good QSO with BPSK-31 using this choke+dipole setup with someone 900 km away using about 50 W, but he couldn't copy me very well.
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~Philip
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