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Author Topic: Best indoor 40M QRP antenna?  (Read 9498 times)
W1SFR
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Posts: 21




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« on: March 01, 2012, 04:39:35 AM »

Until the weather breaks, I won't be able to put up anything outside. As you may have seen in my other post about my experience with a mag loop antenna, I'm still looking for something that's more effective. My mag loop will not tune as it stands ( I have to experiment on various changes to it) I'm thinking of a simple hookup wire antenna for now pending more work on the mag loop. What's the simplest, non-permanent antenna I can try that I can put up and take down fairly easily? I'm set up in my kitchen right now. House is a ranch 60' long.  I got a Buddy pole and was going to try that inside, but I would think that the counterpoise would not work running across my floor (about 7' above a dirt basement floor)....would it?

Steve
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OHR 100a QRP XCVR at 5W on 40M
TenTec Argosy 525
40M LNR ParEndFedz Antenna
AA4PB
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Posts: 13032




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« Reply #1 on: March 01, 2012, 05:08:43 AM »

A BuddiPole is a dipole and therefore doesn't require a counterpoise. No small, indoor 40M antenna is going to be very effective, especially when running QRP power levels. Such indoor antennas generally pick up lots of noise from items in the house and very little signal.

It would be much more effective to put the BuddiPole on a 10 or 15-foot mast and set it out in the yard, away from the house, when you want to operate.
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WX7G
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« Reply #2 on: March 01, 2012, 05:12:50 AM »

A full size dipole strung through the house, bent as needed, will be the best of course.

If that is too large you might build a 1/4 wavelength loop tuned with an MFJ-933 loop tuner. If you make the loop with copper tubing rather than #12 wire it will be substantially more efficient. I have one and like it.
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KU3X
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Posts: 145




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« Reply #3 on: March 01, 2012, 09:58:39 AM »

First read this review and then go to Google and search, " LD4030Q"

http://www.eham.net/reviews/review/102189

You need a balanced resonant antenna and the above will fit your needs.

Barry
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K8JD
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Posts: 51




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« Reply #4 on: March 01, 2012, 11:59:20 AM »

A good rule of thumb is; the smallest power needs the largest antenna.
Since your house is 60 ft long , I suggest getting a halfwave dipole into your attic, it needs 66 ft of wire but will fit if you zig-zag it a bit.
I have worked many attic antenna users, some with QRP rigs and you WILL make some contacts ! (at least on CW).
Why no callsign in your signature???
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73...John
SKCC 1395T, FISTS 3853
Official US Taxpayer
AK7V
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Posts: 251




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« Reply #5 on: March 01, 2012, 01:11:54 PM »

Do you have an antenna tuner?

Despite the weather, can you tie a weight to the end of a ~66 foot wire and fling it up into a tree?  Then connect another 30 or so feet to the "shield" part of the antenna tuner connector?  Run that along the baseboards in your house?

I used that antenna, along with a tuner, at QRP levels for years and made plenty of QSOs (CW).  It even worked with the antenna wire pinched in a metal-frame window.
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W4KYR
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Posts: 621




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« Reply #6 on: March 01, 2012, 01:51:19 PM »



 If you don't have landline phone service but have telephone wiring throughout the house. Use one of the telephone wires in the house for an antenna. You are running QRP, it should not cause interference, it is disconnected at the pole or service box by the phone company.
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N6XJP
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Posts: 9




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« Reply #7 on: March 01, 2012, 02:03:51 PM »

I have had huge success with the LnR Endfed antennas at QRP levels.  Maybe tack it to the ceiling.  No counterpoise is required usually ...  But It can be freq specifically tuned which will improve your signal output.  I have worked Japan and Boston from one that is at roof level at 5 watts.  No tuner required, but realize it is  tuned, your bandwidth will be somewhat limited.  On 40, I am good from 7.000.00 to 7.068.00 with no tune.  Dave
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WB6BYU
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« Reply #8 on: March 01, 2012, 07:06:49 PM »

A half-wave dipole on the ceiling, run down the hallway and/or room-to-room.

You can drill a small hole at the top of the wall and pass it through if that makes it
easier - you can always spackle the hole later.  It doesn't have to run straight,
but the less it folds back on itself the better.

Push-pins in the ceiling and a short loop of dental floss will support it, or there
are many other options if you get creative.


One antenna we put up in a townhouse was a wire tossed over the second-story
roof that came in through windows front and back.  The ends of the wires met
right over the rig with a 3' feedline.
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W1JKA
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Posts: 1821




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« Reply #9 on: March 02, 2012, 09:30:14 AM »

  Ditto AA4PB reply: You have the Budd stick ,why not use it.? Are your weather conditions so severe that you can't tie wrap it to a broom handle and stick it out a window? My winter backup here in Maine is a hombrew vertical  C clamped onto an 8 ft. step ladder just outside my back door with couple radials thrown down on the snow,it gets me by with somewhat limited performance untill the weather breaks so I can effect main antenna repairs.Improvise and use what you have.
 
« Last Edit: March 02, 2012, 09:40:32 AM by W1JKA » Logged
KB9BVN
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Posts: 116




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« Reply #10 on: March 07, 2012, 11:35:40 AM »

I've been using a 66 foot dipole in my attic for QRP CW QSO's on 40m for about 15 years.  I use an external antenna tuner for it, or I use the internal tuner in my K1.  I've WAS several times and I have 62 DXCC contacts on it.  It's no set of beams, but it gets me on the air.  Try that.  Oh...my house is 58 feet wide in the peak of my attic, so I just bent 4 feet on each end at a 90 degree angle to the dipole. The only complaint I have is my dipole is firing NS and I would like it to be firing EW...but putting a rotor on the house would be too expensive.

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W0RSP
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Posts: 4




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« Reply #11 on: March 07, 2012, 04:56:54 PM »

KB9BVN sums up the situation. A 60-ft roof is not actually "short" for a 66-ft dipole whose ends
drop down vertically -- hardly any radiation occurs from the minimal r.f. current at the ends. The
height is what it is, and the radiation lobe will be straight up. But the ionosphere can do things
even with that angle of radiation.

The Buddipole is what it is -- a highly shortened extremely inefficient tuned antenna. The short
bottom loaded vertical works on an auto because of the large capacitance to ground via the
auto body provides a return current path. Not applicable to a Buddipole.

The problem with your mag loop is puzzling -- what I've had
zeroed out any level of QRM in the plane of the loop. The tuning is touchy, but if you can't
tune yours, something is missing or done wrong.

Good luck and keep trying!  Unfortunately if you propose a low height above ground, you are
fighting odds except for the mag loop which is ground/height independent. It does not need a ground or a counterpoise or anything but its own physical structure and tuning components

72, Ade W0RSP
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N3ZJ
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Posts: 17




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« Reply #12 on: March 13, 2012, 04:07:19 PM »


I agree with N6XJP - the LNR End-fed half-wave wire works quite well!
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W1SFR
Member

Posts: 21




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« Reply #13 on: March 14, 2012, 04:50:08 AM »

I got an LNR 10/20/40 end fed dipole. It's going up into my Maple tree in the next couple of days. Now I have to figure out how to get it into the house and up into the area where I'll have my radio.

Steve
KB1WUD
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OHR 100a QRP XCVR at 5W on 40M
TenTec Argosy 525
40M LNR ParEndFedz Antenna
AA1UY
Member

Posts: 17




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« Reply #14 on: March 19, 2012, 03:14:54 PM »

MFJ 1788 Magnetic Loop antenna.

If you can't get the SWR low enough, first try moving it around (away from other (especially metal) objects).

If still not low enough SWR then open it up and change the shape of the feed loop (small inner loop). Elongate it or make it more round; you'll have to experiment a bit. You should be able to get the SWR to 1:1 pretty easily.
« Last Edit: March 19, 2012, 03:19:25 PM by AA1UY » Logged
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