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 Post subject: Rebuilt outdoor loop antenna
PostPosted: Nov Sun 11, 2012 12:06 am 
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Joined: Jan Mon 18, 2010 2:13 am
Posts: 21285
Location: Dayton Ohio
After 3 years of being in the weather, my loop antenna I built for receiving AM740 CFZM Zoomer Radio out of Toronto, Ontario Canada was damaged in a windstorm.

Today, I spent most of it rebuilding it and getting it ready to go back in the air.
Unfortunately, I have run out of steam and it won't go up today. I also still need to put a weather tight connector on the control cable. Probably a military grade connector as I have easy access to those at work :wink:

This stands over 8 feet tall and is 81 inches corner to corner of the loop. It is 7 turns of 16 AWG stranded extension cord wire.
Yes, I bought a 100 ft extension cord at Lowes and cut it up to make my loop. Hey, it was the least expensive way to go!
The link winding is a single turn in the center of the loop. That goes down an RG-11 coax to any radio with ANT and GND connections.

The tuning control box has survived quite nicely in the weather-proof box I built it in. I'm quite happy with how it held up.

The variable cap is driven by an old stepper motor taken from a junk Seagate 40 MB hard drive. It is driven by a little circuit I built with two MOS-FET H bridges and a rotary encoder. The pot attached drives a meter to indicate where the variable cap is positioned.

I certainly hope it is good for at least another 3 years! :D

-Steve


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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Nov Sun 11, 2012 12:31 am 
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Joined: Nov Sat 22, 2008 3:04 pm
Posts: 2402
Location: Gormley, Ont., Canada
Very nice work there, Steve. Well thought out and engineered. It really does look like you just built the tuning control box...amazing!

Stupid question. Does the loop antenna pull in 740 during the day or is it only useful for night time reception?

BTW. i was listening to WLW this morning on the R-7000-2 until reception faded at 6 am.

Bruce Webster

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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Nov Sun 11, 2012 12:42 am 
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Joined: Mar Fri 11, 2011 4:21 pm
Posts: 793
Location: Hunter NY
That is really nice. How does the relay on the left work? I can't tell if the brown and black wires are going to the motor or the antenna connection.


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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Nov Sun 11, 2012 1:04 am 
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Joined: Jan Mon 18, 2010 2:13 am
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Location: Dayton Ohio
Thank you both!

Yeah, unfortunately, I can only receive AM740 here at night. :( If only WLW was like AM740...

The relay switches a tap of the last turn to extend the range slightly. I incorporated that relay "Just in case".
I have not made use of it as of yet. :wink:

-Steve

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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Nov Sun 11, 2012 10:40 am 
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Joined: Jun Sun 03, 2012 8:21 pm
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Location: APO AP
Nice job! One question though, does the tuning cap have to be phyically near the loop or is it possible to put it in a box in the house near the radio? Thanks.

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Interests: 1920's sets: Federal, Clapp-Eastham, Kennedy, De Forest, Airway, R. Mitchell, Paragon


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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Nov Sun 11, 2012 1:04 pm 
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Joined: Jan Mon 18, 2010 2:13 am
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Location: Dayton Ohio
Thanks!

Well, I suppose it would partially work, but the added capacitance of the wires going down to the variable capacitor as well as the added inductance would severely limit the tuning range as well as the "Q" of the tuned circuit. It wouldn't tune sharply and give the best gain.

Tuned circuits work best when the losses are brought to a minimum. :D

It is not without problems. The motor does add RF noise as it is tuning the antenna which is annoying. I need to solve that issue.

-Steve

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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Nov Mon 12, 2012 5:25 am 
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Joined: Jun Sun 21, 2009 5:05 am
Posts: 141
Location: Cincinnati,OH
Bruce,

I had lunch right next to the WLW transmitting tower yesterday. The tower is original built in 1933,
wish I could get 740 but there is a station across the river from me that has a stronger signal. My friend who lives several miles away in s.e Indiana picks it up great at night.

Phil


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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Dec Wed 12, 2012 10:23 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 6217
Location: Cleona, PA
Fantasy trip: get WLW to go off the air and allow you to connect a DX crystal set to the base of their antenna!

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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Feb Wed 05, 2014 2:56 am 
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Joined: Nov Fri 04, 2011 3:12 am
Posts: 1045
Location: Parksley, VA.
For those who wish to build an outdoor or remotely tunable loop--

http://www.goldmine-elec-products.com/p ... ber=G19745

This motor has a nice approximately 2 inch round cupped disk. It is not a toothed gear, but has a smooth plastic cup 3/8ths deep which will easily drive a variable cap. Drill it, and you can easily use dial cord or a belt to drive a gear on a cap. This cup is screwed on, so I am sure you can substitute some other method such as a rotating arm or whatever floats your boat.

It runs from as little as 3 volts. Reverse polarity, it reverses direction. So you can use a center off switch to jog it back and forth.

You can't get simpler than this!

John S.


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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Feb Wed 05, 2014 4:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 6236
Location: Portland Oregon
If the link winding is the green one on the inside isn't it more that a single turn?
Ed


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 Post subject: Re: Rebuilt outdoor loop antenna
PostPosted: Feb Sun 09, 2014 2:37 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 11020
Location: Omak,wa,usa
Hello Steve,
I listen to that station sometimes 740


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