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Author Topic: AM Radio Reception Improved by Large Coil of Wire - Why?  (Read 3039 times)

Offline ultravista

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AM Radio Reception Improved by Large Coil of Wire - Why?
« on: August 31, 2017, 1409 UTC »
AM radio reception in my office is terrible, despite being near a window.

I accidentally improved reception by placing a large coil of wire on top of the radio. The wire is ~100 feet of two twisted pairs (400 feet of wire).

The AM reception is noise free and very strong with the coil and noisy and weak without it.

Can someone explain what is happening? Is it mutual inductance, the large coil inducing a magnetic field onto the internal antenna? If yes, is it inducing voltage, current, or both.

I would like to understand why this is happening.

Curiosity led me to try other coils, mostly smaller, with little or no improvement in reception - such as a 25 foot coil of CAT 5 cable and various lengths of power cords.


Offline BoomboxDX

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #1 on: August 31, 2017, 1617 UTC »
I can't explain it electronically, but my guess is the large coil of wire is acting like a large, untuned loop, and it is inductively coupling with your radio's internal loopstick. The 400 feet may also be making a difference.

I once set a Realistic TRF down near some railroad tracks, and heard Alaska from here in the PNW. The rail was acting like a beverage antenna.

Large coils of wire may also act similarly -- they are untuned antennas, but the massive coil and long length of wire obviously grabs signals. I have a similar huge coil of wire I should experiment with myself.

I am sure one of the other guys here (several of whom seem to be very well versed in antennas) will be able to explain to you how your coil / radio system works.


PS -- Sony Dream Machines can make good clock DX radios, the weakest link being the small loopstick inside. If you use a tuned external loop, you can probably DX with that radio, making up for the small internal loopstick. Many Sonys have the CXA1019 chip, which was fairly generic in many Sony radios but a hot performer. Their ICF-38 DX portable has one in it.
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

Offline Pigmeat

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #2 on: August 31, 2017, 1849 UTC »
Railroads used to use the rails for LF comms and activating gates at crossings, a wonderful thing to know as boy near a busy crossing. All you had to do was follow the heavy stranded wire cable that went out from the switchbox at the gate to where it ended, place a solid metal bar, pipe, "dead end" sign across the tracks and stand on it. Those gates would go down like magic, or so I was told. A knowledge of where the nearest railroad yard was needed, too, so you could spot them coming in their little rail truck with the flashing yellow light and run away.

Offline Josh

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #3 on: August 31, 2017, 1855 UTC »
The coil might be focusing the available flux into the receiver.
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Offline ChrisSmolinski

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #4 on: August 31, 2017, 1904 UTC »
The coil might be focusing the available flux into the receiver.

Yes, the same principle as the Select-A-Tenna.
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Offline Pigmeat

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #5 on: September 01, 2017, 0121 UTC »
Ol' Doc Fansome and a Select-A-Tenna duct taped to the top of an old Delorean with a 5/8's wave CB antenna coupled via magnet mount to the steel plate in his head as lightening storm rages as he adjusts the capacitor with the car being driven via remote control.  Hmm.... It just might work!


Most compact loops work like that. You've got to learn by trial and error where the sweet spot is in relation to the angle of the loop and the ferrite antenna in the radio if you don't have an antenna jack/connector on the radio. They actually work fairly well, and most are cheap.

Offline ultravista

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #6 on: September 01, 2017, 0404 UTC »
PS -- Sony Dream Machines can make good clock DX radios, the weakest link being the small loopstick inside. If you use a tuned external loop, you can probably DX with that radio, making up for the small internal loopstick. Many Sonys have the CXA1019 chip, which was fairly generic in many Sony radios but a hot performer. Their ICF-38 DX portable has one in it.

DX, do you mean Broadcast AM only?

Offline Josh

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #7 on: September 01, 2017, 1459 UTC »
In some dx circuits, the flux capacitor is replaced with a flux inductor.
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Offline BoomboxDX

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #8 on: September 02, 2017, 0555 UTC »
PS -- Sony Dream Machines can make good clock DX radios, the weakest link being the small loopstick inside. If you use a tuned external loop, you can probably DX with that radio, making up for the small internal loopstick. Many Sonys have the CXA1019 chip, which was fairly generic in many Sony radios but a hot performer. Their ICF-38 DX portable has one in it.

DX, do you mean Broadcast AM only?

Yes, I was referring to MW/AM band DXing. The FM antenna in Dream Machines is the power cord (inductively coupled through a separate wire inside the radio). For serious FM DX, you'd need a good whip antenna or a dipole to really pull it in.
An AM radio Boombox DXer.
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The usual Realistic culprits on SW (and a Panasonic).

Offline BoomboxDX

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #9 on: September 02, 2017, 0557 UTC »
I have a large coil of wire (flexible hookup wire in a metal spool) which I set near my Sony ICF-38, and it made no difference whatsoever in MW reception. Does your coil have a plastic spool?
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

Offline Pigmeat

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #10 on: September 03, 2017, 0307 UTC »
I have a large coil of wire (flexible hookup wire in a metal spool) which I set near my Sony ICF-38, and it made no difference whatsoever in MW reception. Does your coil have a plastic spool?

The same here with large spools of the stuff over the years, Boombox. Doesn't do a thing for reception plastic or metal, but they do make a dandy upstairs ground when you twist the conductors together, crimp on a terminal lug, and connect it to whatever radio or audio device you're using. I've got roughly 500 ft. of the stuff on a spool in the shack I use for just that. It works, and has for nearly twenty years.

Online Ray Lalleu

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #11 on: September 03, 2017, 1429 UTC »
How oriented is the ferrite rod in the Sony Dream Machine ?

If the ferrite rod is from front to back (not from left to right), that could explain a good coupling with the spool of wire.

Then, the spool could have some sort of tuning by inter-capacitances.

Try this: get a card/plastic/wooden box about 10 x 16 inches, wind 18 or 19 turns of insulated wire around it (leaving about 1 wire diameter between the turns), connect the ends to a variable capacitor (any standard one for AM tuning, using only the widest gang). That should give you quite a boost !  (Small VC looking like a dice, from a discarded AM-MW radio should do the trick. Don't use bare wire because any contact between the turns will ruin the tuning). You need about (10+16)x2x20 = 1040 inches, about 85 ft, of wire. Think first about how you will affix the VC to the box, and how you will affix the first and last turns to the frame, and leave about 20 inches at both ends to connect the coil to the VC.
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Offline BoomboxDX

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #12 on: September 03, 2017, 1624 UTC »
^^^^^^ also a plastic milk crate, available at Wally's and other big stores, will also work as a home-built MW loop antenna form.

They can work well -- I made one that way.
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

Offline BoomboxDX

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #13 on: September 03, 2017, 1626 UTC »
I have a large coil of wire (flexible hookup wire in a metal spool) which I set near my Sony ICF-38, and it made no difference whatsoever in MW reception. Does your coil have a plastic spool?

The same here with large spools of the stuff over the years, Boombox. Doesn't do a thing for reception plastic or metal, but they do make a dandy upstairs ground when you twist the conductors together, crimp on a terminal lug, and connect it to whatever radio or audio device you're using. I've got roughly 500 ft. of the stuff on a spool in the shack I use for just that. It works, and has for nearly twenty years.

Cool. I'll have to remember that. My spool is pretty big -- same size as the one pictured above, but has green-insulated stranded wire, larger than the usual hookup wire gauges... maybe as large a gauge as a single strand of small speaker wire.
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

Offline Josh

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Re: AM Radio Reception Improved by Large Coil of Wire - Why?
« Reply #14 on: September 03, 2017, 1738 UTC »
The composition and size of the spool may be a factor, with a metal one made of steel being least desirable. Building a proper tunable loop can be a fun project and can be made to look quite lovely if made of wood and finished with varnish or oil, if looks are important ie ladies must be subject to being in the same room as the antenna. Nerds gatta stay seksay.
Conveniently located near Vincennes Indiana.