Loopsticks, AM radio, which topology might be best?

Thread Starter

Hamlet

Joined Jun 10, 2015
495
Anyone have any experience with loopsticks? I have a surplus available,
and thought I might try something different. I haven't seen a radio
with more than one loopstick, except perhaps for a nulling loopstick added to
sharpen tuning.

1640580473130.png
 

MisterBill2

Joined Jan 23, 2018
11,602
Mostly, a single rod is used because it is cheapest and adequate for most. Also, with a reasonable number of turns the inductance will be correct to resonate at the desired frequency. So that is how the loop-stick for a common consumer broadcast radio is selected. Other applications may require alternate arrangements. The size and amount of core will affect the inductance per turn, and that will often affect the performance of the radio.
 

ronsimpson

Joined Oct 7, 2019
2,007
AM radios sound awful. Most high audio frequencies are missing like on an old phone.
At one time that sounded wonderful. Music over the air. Wow.

From an audio engineer, now dead 40 years. "We did not know there was audio information at high frequencies." Our microphones said there was very little high frequency information, and the speakers could not make high frequencies. "When we made better microphones, we were surprised."
 

MisterBill2

Joined Jan 23, 2018
11,602
Given the ten KHz channel spacing and the resultant 5 Kc max signal frequency, it is not so very awful for a lot of the stuff. Certainly actual AM broadcast audio is, and was, a bit better than that. So one person's music is another person's noise. And on FM, Andre Castilanitz and his 101 strings sound just as awful on the best system in the store as they do played on a PA system through a 5 inch paging trumpet.
So while the technical numbers are much better, the "awful" aspect is in the ears of the listener.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
11,602
Note for youngsters: kc = kHz
Sorry about the slip. Kilocycles remained long after electronics stopped using condensers. And I never could figure out why condensers were used in electronics, when they were providing capacitance. But that would be a completely different discussion.
 

DickCappels

Joined Aug 21, 2008
8,686
No problem, it took me a very long time to stop thinking kc and to start thinking kHz. Kind of like going from Gauss to Teslas but less stressful.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
495
Mostly, a single rod is used because it is cheapest and adequate for most. Also, with a reasonable number of turns the inductance will be correct to resonate at the desired frequency. So that is how the loop-stick for a common consumer broadcast radio is selected. Other applications may require alternate arrangements. The size and amount of core will affect the inductance per turn, and that will often affect the performance of the radio.
I was thinking a larger ferrite rod loopstick might increase signal, because the rod acts as the antenna.

In a web search, folks that repair radios report that gluing broken loopsticks back together results in little degradation of signal. I suppose this means I can bundle rods together to create any size I want. (however, this doesn't work very well for SMPS, as I discovered, you loose half of your inductance fidding with a broken toroid.)
 

MisterBill2

Joined Jan 23, 2018
11,602
Certainly a larger loop-stick should collect more signal, but if the application uses a TUNED RESONANT loop-stick then if the inductance has changed there may be a loss. But I have not experimented to see how much loss.
 

DickCappels

Joined Aug 21, 2008
8,686
A ferrite rod antenna is a lot like a loop antenna with a core. Yes, you can glue rods together to improve sensitivity.

I think it is now gone from the web but I remember an web page about Lowfer Radio from about 15 years ago in which the author had stacked and bound together several long strips of magnetic material to a huge rod antenna, maybe 3 meters long, upon which he wound a coil and added a resonating capacitor and preamp to pick up distant Lowfer radio signal.
 

MisterBill2

Joined Jan 23, 2018
11,602
I did read some articles about some sorts of resonant LowFer receivers and antenna sections. The challenge always being the conflict between wire size and coil "Q", with the coils needing higher Q also needing many turns to be resonant. And the many turns wanting thinner wire to reduce size and weight.
 

Thread Starter

Hamlet

Joined Jun 10, 2015
495
I swapped in one of my new 300mm ferrites loops, and I've got 3x the DX that the previous 75mm ferrite loopstick was showing. I don't know if the effect is linear (problably not) but I'll try gluing two of them together and see what I get. Thanks everyone for the input.
 
Top