FM square loop antenna connection

[eejournal]

Hi all,

I have made a full wavelength square loop antenna for my FM radio (3m in length). My radio has a telescopic antenna which has just one connection to the PCB. I don't see any coupling capacitor on the line from antenna. I have found a 1N4148 here though. My problem is I don't know how to connect my external antenna to the PCB. I am thinking about connecting one end of the antenna to the PCB GND and then using a capacitor (picoFarad range - read this somewhere) between the other end of the antenna and my PCB antenna connection. Will this work. Any help is greatly appreciated.

 

[kspalla]

Hi,
is the problem with 3mm loop antenna or telescopic antenna integration?
Check the loop antenna without telescopic antenna is working sine and have good sensitivity. loop antenna variants use shunt capacitor across loop-end.
adding telescopic antenna may change /degrade loop antenna, this case you need to tune the capacitor.
I see a series cap in your picture. probably you can connect at this cap.

I believe a series and shunt cap should meet the requirement. all needed is to have a variable capacitor in shunt and a fixed Cap ( may need some experimentation to fix the value) in series.

Hope this helps you.

 

[WimRFP]

Why you want to use a full wave loop instead of a folded dipole with 1:4 balun, or just a half wave dipole with a 1:1 balun (ferrite bead/tubes around coaxial cable)?

No matter the balanced antenna, I would consider a balun.

You can connect the center of the coaxial cable at the connection of the telescopic antenna. Use your series capacitor to avoid any DC path.

The braid of the coaxial cable goes to the nearest ground connection with respect to the telescopic antenna connection. Keep the distance between the coaxial cable and the braid connection at the PCB as short as possible. First connect the braid and then the center conductor to avoid ESD (electro static discharge). Disconnect the telescopic antenna to avoid noise pick-up from man-made noise sources (power supplies, PC's, etc)