AM / MW tuned loop antenna

[Subbu68]

Those who are tired of only hiss from their radios / tuners ( if you listen to) may try out this.

Rediscovered radio listening a few weeks back thanks to @santaji for his thread on Jetking Radio kits. Added a few more radios to my collection too.

Had been wanting to make a AM tuned loop to receive otherwise hard to get stations in apartments.

Finally managed to rig up one.

I do not have space for large loops that would be ideal. So settled for a 26cm x 26cm IKEA picture frame to make the inductor. 26 turns formed from an old ribbon cable. Had to solder one end of each wire to one of next wire and so on to make a helical coil.

Formula used is UMC-EMC lab formula with an online calculator at https://earmark.net/gesr/loop/

Could have used normal enamelled or insulated 22AWG wire but fixing on the frame would have been a chore. The ribbon cable was fixed using double side adhesive tape.

Used a 2 gang variable capacitor VC1 20-120pf, VC2 20-320pf to tune the loop. VC1 is always connected with VC2 switched for lower end of AM band though calculator says VC1 is enough. Parasitic capacitors and inter turn capacitance of the cable may be affecting.

Still the loop makes a marked difference when listening to distant stations as in the video.

For tuners add one more turn inside the frame of main loop or wind it before sticking the main loop and connect one end to the ground point of the variable cap. Connect the other end of this pickup loop to AM antenna in of the tuner and the ground point to the ground of tuner.

 

[Subbu68]

Circuit and some pictures of AM Tuned Loop

With the pickup loop connected to my Tivoli Model One BT with external AM antenna input, it boost the number of stations received. It can work with Stereo Receivers or Tuners with AM antenna input.

 

[Subbu68]

Though the calcs show VC1 tunes to 535kHz to 1680kHz it does not tune as desired. Parasitic capacitance of the loop plays some part I think.

The circuit shows the normal positions of the switches.

S2 puts VC2 in parallel to VC1 to extend the lower limit of the loop. In higher end, with S2 off, S1 puts VC1 and VC2 in series to lower the capacitance to extend to 1750kHz to cover the band.

Have to rework on it to make it neater.