Loop Antenna Project

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Loop Antenna Project

Postby Jack Crow » 2017-Nov-Sat-19-Nov

Hi all,
Saw mooching through YouTube looking at various Loop Antennas for receiving AM broadcast band and wanted to give them a try.
Got an early start as an AM BCB (Broadcast Band) DXer (one who looks for distant stations.
A whole bunch of years have passed since then.

We have the technology, and we can do it better.

One of the things I observed about the various antennas, was the dimensions were all over the dial.
Not everybody uses the same parts, wire, and tuning cap.

Mine came out to about 15.5 inches on each side.
The highly technical method I used was called a WAG.
Or Wild Assed Guess.
The panels and paddles (need to call them something) that stick out from the center.

At frequencies measured in hundreds of meters, the little bit of metal in the unit is not an issue.

This is the overview.
Since it all hubs at the center, the inner parts I call Paddles.
They are parts that go from the hub and out to the middle.
Beyond a doubt it's a clunky way to do things.
Came up with a better method.
If I make a second one, that will be the way to go.
For now I used the parts already produced and committed.

There is a connection part that lives between the paddles and panels. With holes for hardware.
After I made it started to get the idea that eight screws would be four too many.
Left some empty.

The outer parts are the panels.
These have thirty little scallops one one edge for running the wire over.
To keep the wire from drifting I touched the points with instant glue.
11-25-2017 014.JPG


The whole project works on resonance.
That is a combination of adjustment capacitor and the coil.

Since the shaft and holder of the variable cap are involved in the circuit, they need to be insulated from the operator. (me)
So I made a holder that fit inside the lightening hole in the paddle.
That was a little complicated but it worked.
Then worked out a knob and lock down screws that were recessed from any place the fingers could get at them.
The screws are in hard contact with the cap shaft to keep the knob from rotation on the shaft.

Detail on the knob and holder for the tune cap.
11-25-2017 012.JPG

11-25-2017 013.JPG


The paddles are the inner parts, and panels are the outer part.
11-25-2017 021.JPG


If I make a second one, the parts would be thicker. This unit is a bit flimsy.
Would make a vastly improved center section as a single part.

The panels and paddles would be much stiffer and have a thicker 'foot'.
If you look close they have one thick edge.
That is not braced well enough to hold position properly.

If the question is 'will it work', then the answer is, "It works ok".

Better on the longer frequencies (520 to 1000 khz).
At the high end (and where I wanted to use it) I tend to run out of range of the caps adjustment. (1500 and up)

If I remember the tech, I have too much wire, well at least that is easy to fix.
As time permits, will take one loop off at a time unit I get a good balance between high and lower frequencies.

This is based in a quick test here on the work bench.
A computer and display running inches away from an AM radio is never a good mix.
Always some kind of data noise.
Was able to catch all news stations out of NYC from here in Virginia Beach VA.
Some Canadian and what I suspect was a Mexican station.

That is the news.

Jack Crow
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Loop Antenna Project

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Re: Loop Antenna Project

Postby RetireeJay » 2017-Nov-Sat-22-Nov

Wow, cool! Back in the '60's my brother and I were seriously into AM DXing. A surprisingly good radio for the purpose was our GE clock radio with the "All American Five" set of vacuum tubes and a ferrite rod antenna. But we used others too, including a mashup of a ham radio antenna (and once even a very long wire held by a kite) connected to a plain radio, but sometimes with the 455kHz IF being fed into my Hammarlund HQ-170 ham receiver (through a pin in a vacuum tube socket where I had pulled out the tube). All told, listening from Portland, ME, we logged well over 200 stations in something like 40 states and at least half a dozen countries. I'll never forget the summer vacation afternoon near sundown in Harpswell, ME when the strongest station on the dial was Radio Venezuela! And getting a QSL card from ZBM-1 in Bermuda when I had addressed the request to "NBM-1" because I was unfamiliar with the British Zed. And then there was the time after midnight when the nearby Canadian station on 640kHz was on the air but they had a lot of "dead air" time and I actually heard KFI Los Angeles coming in behind them. Those clear channel stations are really something for distant reception. But the "graveyard" frequencies in the 1300's yielded more total stations due to lots of patience. (My goodness, how many times did I hear the complete weather report for "the airport" and traffic reports for roads I'd never heard of, and then just when the station was giving its ID or city, there'd be a static crash exactly at the crucial instant.)

These days there's so much hash on the AM band from computers, fluorescent and LED lights, etc. etc. that I don't think feats like that will ever be repeated. But I love that antenna you made. Have you read about the ones where people take dozens of ferrite rods and build really strong magnetic field concentrators? I think the best source they mentioned for the rods was on the Russian surplus market.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
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Re: Loop Antenna Project

Postby Jack Crow » 2017-Nov-Sun-09-Nov

RJ
From your text....

Have you read about the ones where people take dozens of ferrite rods and build really strong magnetic field concentrators? I think the best source they mentioned for the rods was on the Russian surplus market.

In a word, no. Never heard of that. Might be worth a look up.

I started out trying to make a "Palomar" antenna. A copy of a desk top unit I had the chance to play with in the early 80's. Couldn't even find one on the web.
This design kept showing up.
It is a classic.
Making the parts on a printer was the only real new twist.

Have the beginnings of another loop on 14mhz for ham service in the living room. Need to finish that.
Have a Bitx40 radio that would make a good match for this. In fact it was my first major project once I got the printer working.
4-2-2017 104.JPG

4-2-2017 103.JPG


Also thinking of a 10 or 11m edition for use in the workshop here.

The local chat crew here on 146.52 have this sick idea of running either 300 baud packet or JT65 on a CB channel between the three or four of us.
Wouldn't that be a scream.

As for static crash, we have the internet now. Links like this should simplify things a bit.
https://en.wikipedia.org/wiki/1320_AM
Same for strange named roads and advertisers.
Technology marches on.

That is the news from here.
Thanks for the kind words and keep it safe
Jack Crow aka Radio Mike in VB
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Re: Loop Antenna Project

Postby RetireeJay » 2017-Nov-Sun-12-Nov

Jack Crow wrote:As for static crash, we have the internet now. Links like this should simplify things a bit.
https://en.wikipedia.org/wiki/1320_AM
Same for strange named roads and advertisers.
Technology marches on.

Back in the day, we had "White's Radio Log", a Bible-sized book with a complete listing of all the AM stations in the country: call sign, location, frequency, power. But we still needed to hear at least some specific identifying information to zero in on which station we were hearing.

By the way, the classic solution for tuning your loop antenna across the whole band is to have taps on the coil with a selector switch or some kind of clip, so you can choose how many turns of wire to use for a given situation.

Here's a link to the article about using multiple ferrite cores: http://www.thomasn.sverige.net/7_Inch_Affordable_FSL.pdf
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
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RetireeJay
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Re: Loop Antenna Project

Postby Jack Crow » 2017-Nov-Sun-16-Nov

RJ
That is an amazing bit of work.
A huge amount of effort and I am chronic short of cash to afford it all.
The one I made was quick and dirty by comparison.
The head is still swimming with all that new stuff.

Was thinking of a more refined edition of this thing.
https://www.universal-radio.com/catalog ... /0445.html

When I was working for Mr Kahn (Am Stereo fame) he had something like this for the shop studio receiver.

It was fairly big, very heavy.
Part of it was a base box, and a top box where I assume was some kind of fairite. Not sure never did see into the thing very much.
On the top box was a slider.
The top box could be aimed in most any rational direction to improve / null the antenna.

That thing was amazing in operation.
Just did a Google search. Examined hundreds of photos and not one of them was that item.

A bud of mine had this problem.
You know that large box gizmo we see in the old movies.
Has a big T handel and is used to set off explosive charges.
Most people call it a plunger. Look that up on Google and you get plumbing tools.

It was called an Explosion Machine. Seems someone else has co opted that name so finding photos is not so easy.

Guess I need to know the proper name for this antenna before I can find them.

Keep it sane.
Jack Crow aka Radio Mike
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Re: Loop Antenna Project

Postby RetireeJay » 2017-Nov-Sun-16-Nov

For your bud, see dynamite detonator

Also see the pictures when you google "directional loop antenna".
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
User avatar
RetireeJay
My next printer is...
 
Posts: 5003
Joined: 2013-Jan-Wed-13-Jan
Location: Greenville, SC
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