Part of a low-pass filter.

https://www.winlab.rutgers.edu/~crose/322_html/envelope_detector.html

 

How well do you think that a ferrite rod antenna would work fr transmitting?? Aside from being much smaller for a given frequency?? Would core saturation be a problem??

 

The 200 pf filters our the RF carrier, so the only thing that is presented to the headphones is the peaks, which correlates with the baseband (voice or music) signal.

https://en.wikipedia.org/wiki/Crystal_radio#:~:text=Modern crystal sets use modern,is connected to the detector.

 

How well do you think that a ferrite rod antenna would work fr transmitting?? Aside from being much smaller for a given frequency?? Would core saturation be a problem??

Will a magnetic microphone work as a loudspeaker? Yes but not very well because of the impedance mismatch with the coupling media. It's the same for ferrite rod transmit antennas. The conductor resistance is a significant fraction of the radiation resistance.

The low radiation resistance makes efficient radiation power coupling and matching difficult. At MW it's a physically small cross section of the wavelength and is electrically short. It's like how a good RF match can tune a door-knob (so the story goes) for low reflected power but it's a poor antenna.

 

Mine just doesn't seem to work. I am using pretty small ferrite rods (8mm x 45mm). Im going to try bigger ones. Everything else matches the schematics I've been looking at online and what's been posted here. Because of the small size of the rods, I have had to compensate for low inductance (168 - 173 micro henries) by changing capacitor values accordingly (my variable cap ranges from 20pf to 400 pf) (calculations for 830 kHz call for 218.86 pf, but im using a variable cap so I just test it by turning the knob all the way and listening for a signal). My theory is that there's just not enough inductance, although I cant really conceptualize why it would matter given the right capacitor values...


(sorry I got my units wrong when I first submitted this post. they're all fixed now.)

 

ferrite antennas are very directional. If you are not getting anything, try rotating it by 90 degrees.

 

Mine just doesn't seem to work. I am using pretty small ferrite rods (8mm x 45mm). Im going to try bigger ones. Everything else matches the schematics I've been looking at online and what's been posted here. Because of the small size of the rods, I have had to compensate for low inductance (168 - 173 micro henries) by changing capacitor values accordingly (my variable cap ranges from 20pf to 400 pf) (calculations for 830 kHz call for 218.86 pf, but im using a variable cap so I just test it by turning the knob all the way and listening for a signal). My theory is that there's just not enough inductance, although I cant really conceptualize why it would matter given the right capacitor values...


(sorry I got my units wrong when I first submitted this post. they're all fixed now.)

The inductance/capacity ratio also matters. That affects the tuned circuit "Q". AND the 830 KHz station may not be in the direction your directional loop-stick is sensing. In addition, wire size does mater a bit.

 

I have been rotating it in a circle as well as rotating it upside down and back up again, playing with the variable cap at each angle

still not getting anything...

 

Once you achieve the correct resonant frequency changing the angle should not require adjusting the capacitor. So I suggest first, using a long wire antenna to verify that a signal is even present, and then adjusting the cap for strongest reception, and then try it with just the coil and cap. It might also be that you need a lot of amplification. It may be that you have the signal present but at a level way to low for hearing. Also, try 870 KHZ (WWL), and 890 KHZ (WLS)

 

Thanks guys, I just wanted to report that the radio receiver finally seems to be working. I fixed a couple things, and im getting a faint signal.

Now I just need to find a more powerful amplifier. I used an op amp in line with a simple transistor (bc547) amplifier circuit...any suggestions for more gain? (I can barely hear the signal i'm getting even with the speaker up to my ear)

 

Thanks guys, I just wanted to report that the radio receiver finally seems to be working. I fixed a couple things, and im getting a faint signal.

Now I just need to find a more powerful amplifier. I used an op amp in line with a simple transistor (bc547) amplifier circuit...any suggestions for more gain? (I can barely hear the signal i'm getting even with the speaker up to my ear)

Post a schematic if you want help with it. We are not mind readers.

 

just wanted to report that the radio receiver finally seems to be working

Get a cable and connect its speaker to the AUX input of your home stereo.

 

The most common circuit to amplify a detector type receiver is an LM386 IC amplifier. It can provide both useful gain and an adequate output in a very simple package. OR you can try using a crystal earphone. Those are very sensitive.

 

The youtube maker named "Offset Volt" shows peaking the loop stick.
He is mostly following the Elenco directions and he does nicely. Over all the video is valuable to someone who really wants to
know the math on the elenco from beginning to end, much can be learned from this video, The oscillator/mixer is also explained nicely.
For this thread, the peaking of the ferrite loop stick antenna L4 to the aligned radio, jumping forwarding in the video to about 39 minets. For a test signal he has a loop of wire under the circuit from the signal generator.