Medium Wave AM broadcast band resonant loop antenna.

Medium Wave (MW) AM broadcast band loop antenna. Built using cheap 4 pair (8 wire) telephone 'ribbon' cable,& (optionally) housed in cheap garden 13mm (~half inch) irrigation plastic hose.

The more rigid self supporting version better suits serious use, as it can better null offending local noise or stations and even DF (direction find) when rotated towards remote signals.The weak signal enhancing performance (especially on classic 'deaf' AM radios) of either type has been found ABSOLUTELY OUTSTANDING - signals just leap off the bench!

As they can be built much cheaper (& faster) than traditional tediously wound & mounted loop antenna,this approach suits tight budgets,educational resonance demonstrations,remote weather forecast needs & travellers unable to erect a long wire outdoor antenna.

Step 1

The compact version allows easy storage -suitable portable & traveling needs. 3 metres (~10 feet) of cheap 8 wire cable will resonate nicely over most of the upper 500kHz -1.7MHz MW Broadcast Band with a common 6-160 pF variable capacitor. However use longer lengths for stations at lower MW frequencies, OR add a 2nd capacitor in parallel to the variable.

Comments

[RangerJ]

Ok - this is cool! Anything to do with a radio - especially an AM radio - is right up my alley. Excellent Instructable, very enjoyable.

[FL_Bill]

Thank you for this build. This is something I could 100% use! I will most likely build this one with my 8 year old son. Thank You!

FL Bill

[manuka]

Sorry for answering delay ! MW radios have an internal ferrite rod, so just "link" by placing the radio within the loop. Such linking is magnetic so no extra connections are normally required! If you want however a permanent connection perhaps just run a wire to your MW radio from a tap point at the tuning capacitor. Experiment!

2011 UPDATE: Home wireless technologies have made classic 50' (15m) 4 wire phone cord caddies almost redundant. The 4 wire loop version shown at step 5 may hence have increasing appeal as the cabling will be very cheap/free. It'll be of course easier to connect too, & as the larger loop intercepts more wave front it may even have better performance. Stan ( ZL2APS)

[Johenix]

It seems to me that you could use ONE piece of 4 wire with only five solder joints (two at the capacitor and three to make the 4 wires into one) if you used twice as long a cable and double wound the cable.
A little shrink tubing added before soldering might hold the loop for constant size.
A trimmer capacitor might hold the loop on frequency for a single station.

[manuka]

Johenix: Well said sir! 4 wires may indeed be easier, but the entire loop will be larger. Although this will intercept a larger wave front (& may usefully fit around a door- as shown) it will not suit rigid tube compacting.

[shobley]

One final question - if I wanted to use this as the antenna on a home-made radio how would I hook it up?

Ground and signal on either side of the cap?

Or should I omit ground as I want the signal to resonate in the LC and ground would only leak the signal away.

I've only ever done this before with long wire antennas.

[shobley]

Actually I have to question the comment about twisted wire not working. Traditional loop antennas have been made with Litz wire - multipe individual strands insulated from each other - every spool of Litz wire I've ever looked at has twisted strands in it - so surely CAT-5 has a good chance of working?

I might test this out later today and see what happens...

[shobley]

Actually I was wrong about this, once I read the article I realised that the 8 parallel strands themselved were forming the loop - I was thinking about using CAT-5 and making 8 turns with that.

I built this last night out of 2 lengths of the standard US 4-strand cable.I laid out a 10' piece of masking tape (sticky side up) and carefully placed the cables side by side. I then folded the tape over and sealed it up.

It's quite flexible and will spool up when not in use.

Thanks for finally explaining what all the trimmers do on a radio cap!

[gnomedriver]

Great instructions. Ive got a small SW radio when I travel and normally use a long length of wire as an antenna. Ive experimented with making my own loops and wrapped the wire around a cardboard carton. It is all a little messy. But using computer cable is a great idea. It is cheap and easy to find. Feed it through a hula hoop or garden hose for some rigidity and away you go. I like the idea of direction tuning using the door too.

[rimar2000]

Very good idea, very good work. The steps 2, 3 and 10 are BRILLIANT for its simplicity and effectiveness.

[manuka]

Thanks- following the addition of extra material to support an article in the Jan. 2009 "Silicon Chip" ,these steps are now renumbered 4,7 & 14.

[manuka]

The cable really has to be flat-surely such 8 wire (4 pair) cable is available in the US? It's just ~(US$) ~50 cents a yard here in NZ via Jaycar (WB-1625)! Perhaps 2 x 4 wire cables could be used if held neatly side by side - maybe hot melt glued? Sorry,but twisted pair style cat5 isn't suitable, as the twist deliberately reduces pickup!

[BigCommieNat]

this is a great idea! A question though... the 8 connector wire you have, it looks flat. here in the US the only 8 wire cable I can think of is twisted - cat5. would unshielded cat5 work for this? or would the twisting ruin it?