Hi.

I'm just starting to try to learn a bit about electronics, and have
what may be a dumb question.

How can I reverse the polarity of an analogue signal - say, an FM
radio signal? And would I need to convert it to a digital signal
first?

I know something like an oscilloscope can do it, but I mean, something
I can include in a circuit.

Any help would be greatly appreciated.

On Sat, 29 Nov 2003 19:44:03 GMT, wrote:

Hi.

I'm just starting to try to learn a bit about electronics, and have
what may be a dumb question.

How can I reverse the polarity of an analogue signal - say, an FM
radio signal? And would I need to convert it to a digital signal
first?

A simple inverting amplifier setup with an op-amp at unity gain should
do the trick. Depending on exactly what frequency range you needed
you may need a special op-amp to do this. You don't need to convert
to digital anywhere in the process.

If you can be more specific about what you need, I'm sure you can get
more specific information from somebody in the group. I don't know
much about op-amp models, except that a run-of-the-mill 741 won't do
the trick for FM frequencies. Now, if it's an audio signal AFTER the
FM has been demodulated, the 741 should be fine*.

(* I'm sure there's an op-amp that has lower distortion, but, meh...)

On Sun, 30 Nov 2003 12:17:33 GMT, Philip A. Marshall
wrote:

On Sat, 29 Nov 2003 19:44:03 GMT, wrote:

Hi.

I'm just starting to try to learn a bit about electronics, and have
what may be a dumb question.

How can I reverse the polarity of an analogue signal - say, an FM
radio signal? And would I need to convert it to a digital signal
first?

A simple inverting amplifier setup with an op-amp at unity gain should
do the trick. Depending on exactly what frequency range you needed
you may need a special op-amp to do this. You don't need to convert
to digital anywhere in the process.

If you can be more specific about what you need, I'm sure you can get
more specific information from somebody in the group. I don't know
much about op-amp models, except that a run-of-the-mill 741 won't do
the trick for FM frequencies. Now, if it's an audio signal AFTER the
FM has been demodulated, the 741 should be fine*.

(* I'm sure there's an op-amp that has lower distortion, but, meh...)

Oh, and i've actually heard of CMOS inverters being used for this.
just put a large (several megohms) from the input to the output, and
be sure to couple the input and output in with capacitors. I'm not
sure what the gain would be, I'm curios to see if anyone here can give
me specifics of this implimentation...

On Sun, 30 Nov 2003 12:28:33 GMT, Philip A. Marshall
wrote:

A simple inverting amplifier setup with an op-amp at unity gain should
do the trick. Depending on exactly what frequency range you needed
you may need a special op-amp to do this. You don't need to convert
to digital anywhere in the process.
...
Oh, and i've actually heard of CMOS inverters being used for this.
just put a large (several megohms) from the input to the output, and
be sure to couple the input and output in with capacitors. I'm not
sure what the gain would be, I'm curios to see if anyone here can give
me specifics of this implimentation...

Thanks for that. Most of it went straight over my head, but I'll try
and chase it up.

Being a newbie, I hope this isn't the equivalent of of a left-handed
hammer, a bucket of air or a "long weight". :-)

A simple inverting amplifier

i've actually heard of CMOS inverters

I hope this isn't the equivalent of of a left-handed hammer


Start he
http://images.google.com/images?hl=e...oogle+Sear ch

wrote in message . ..
On Sun, 30 Nov 2003 12:28:33 GMT, Philip A. Marshall
wrote:

A simple inverting amplifier setup with an op-amp at unity gain should
do the trick. Depending on exactly what frequency range you needed
you may need a special op-amp to do this. You don't need to convert
to digital anywhere in the process.
...
Oh, and i've actually heard of CMOS inverters being used for this.
just put a large (several megohms) from the input to the output, and
be sure to couple the input and output in with capacitors. I'm not
sure what the gain would be, I'm curios to see if anyone here can give
me specifics of this implimentation...

Thanks for that. Most of it went straight over my head, but I'll try
and chase it up.

Being a newbie, I hope this isn't the equivalent of of a left-handed
hammer, a bucket of air or a "long weight". :-)

Better slow down here. Before jumping to breadboarding CMOS and op amp
circuits, you must better define what your after. "Reversing the polarity
of an analog signal" won't buy you much. It will still sound the same out
of a speaker. A quality scope will have an 'invert' switch to flip the
polarity 180 degrees but that's not really that exiting. As for the suggested
polarity reversal of an FM signal, again not much will happen here. Apart
from the dificulty in handling the 88 - 108 MHz frequency band (its kind
of high) the nature of frequency modulation of the carrier and the way its
demodulated at your radio makes the recovered audio signal immune to
'polarity reversal'. There are other modulation methods (i.e. phase
modulation) that WOULD be affected by monkeying with the polarity. You
need to read more books. Electronics can be fun so enjoy.

Philip A. Marshall wrote in message . ..

Oh, and i've actually heard of CMOS inverters being used for this.
just put a large (several megohms) from the input to the output, and
be sure to couple the input and output in with capacitors. I'm not
sure what the gain would be, I'm curios to see if anyone here can give
me specifics of this implimentation...

If resulting gain is much lower than the invertors gain, Vgain =
Rfeedback / Rin. Otherwise gain is less. Its a handy enough trick.

Regards, NT