Circuits for Learning LRL

[Esteban]

Hi,
yes right... but he wrote also that this "RF sniffer" works in FM : and I read this both frequency modulation and FM-band ...if he doesn't modify the radio he will tune e.g. from 88-108MHz and so ?

What's relationship between a 50KHz signal not modulated in frequency (do you know any detector that made this modulation of signal ???) and a frequency modulation receiver that maybe runs at 88Mhz (if he doesn't modify radio) ???

This thing seems have no sense. But maybe he will explain us what kind of relationship will be between the two things!

Kind regards,
Max

Maybe no relation between these both frequencies, but put a loop around a radio an generate a tone... you'll hear clearly in audio section... See here a loop that creates the tone.

Isn't in books!

[Esteban]

Esteban has said the workable frequencies are between 45 KHz and 160 KHz.

Best wishes,
J_P

Yes, more low frequencies mean minus hertz variation. "Excess" of Khz (300) you have here detected very well paper plated of box cigarettes...

[Max]

Maybe no relation between these both frequencies, but put a loop around a radio an generate a tone... you'll hear clearly in audio section... See here a loop that creates the tone.

Isn't in books!

Hi,
some FM radios (almost all old stuff as far as I know) can detect small amplitude modulation (narrow) when they are in frequency demodulation mode. This happens cause of some transistor there that works as rectifier and then some detection happens by amplitude too not just frequency modulation.

My guess is that, if you put the coil with tone signal (amplitude modulation) near radio in FM mode... it will pick up that tone by amplitude demodulation that happens there.

Very easy to test... nedd just one e.g. remote control and an FM radio... put it into FM and near the remote on the back side... the inductive coupling between radio coils and remote tracks with currents flowing in... will give you hear the sound of on-off modulation at IR led(s)... so to sense the currents and relative EM fields.

But if you switch in AM mode you will hear much more loud... cause it's dedicated demodulator there... with e.g. germanium diodes (old stuff radio like you posted).

My question is: why use FM if you look for amplitude modulation ?

When you talk about BFO you mean there's some frequency mixing somewhere and this will be detected by FM radio as frequency (variant) modulation ... and thus amplitude modulation residual information is just a part of what you are looking for?

Kind regards,
Max

[Esteban]

Hi,
some FM radios (almost all old stuff as far as I know) can detect small amplitude modulation (narrow) when they are in frequency demodulation mode. This happens cause of some transistor there that works as rectifier and then some detection happens by amplitude too not just frequency modulation.

My guess is that, if you put the coil with tone signal (amplitude modulation) near radio in FM mode... it will pick up that tone by amplitude demodulation that happens there.

Very easy to test... nedd just one e.g. remote control and an FM radio... put it into FM and near the remote on the back side... the inductive coupling between radio coils and remote tracks with currents flowing in... will give you hear the sound of on-off modulation at IR led(s)... so to sense the currents and relative EM fields.

But if you switch in AM mode you will hear much more loud... cause it's dedicated demodulator there... with e.g. germanium diodes (old stuff radio like you posted).

My question is: why use FM if you look for amplitude modulation ?

When you talk about BFO you mean there's some frequency mixing somewhere and this will be detected by FM radio as frequency (variant) modulation ... and thus amplitude modulation residual information is just a part of what you are looking for?

Kind regards,
Max

Yes, of course, this is the reason for to use the IR beam instead the BFO MD. You generate the tone and you can adjust the system for to leave stable and sensitive.

I use FM mode because is very more clean than AM. If you don't use the IR or loop for to generate the tone, or BFO MD, or I-B MD in conjunction FM radio, only the FM radio, well also works only the FM and don't know why! Also any RF clean receiver... For example, I bought a wireless bell and I use the receiver part (only for check if this can be useful), well also works.