Using Ohm's law for creating a multiplying mixer?

[Nils Beyer]

I'm a hobby electronic technican. So, don't expect anything based on
facts. ;-))



U = R * I
| | |
FO = F1 * F2


If it's possible to convert F2 to a current, perhaps using a resistor,
and convert F1 to a resistance, perhaps using a transistor (what's nothing
else but a current controlled resistor), then it must be possible to
multiply these two frequencies using Ohm's law, or am I wrong?

Sth. like that:
---------------

+5V
O
|
R1 |
___ |/
F1 --|___|--| T1
|>
| R2
| ___
?? FO --o--|___|-- F2
|
.-.
| | R3
'-'
|
---
-

R1: converting V(F1) to I for controlling T1's resistance
R2: converting V(F2) to I
R3: build a voltage divider


Cheers,
Nils

 

[James Meyer]

I'm a hobby electronic technican. So, don't expect anything based on
facts. ;-))



U = R * I
| | |
FO = F1 * F2


If it's possible to convert F2 to a current, perhaps using a resistor,
and convert F1 to a resistance, perhaps using a transistor (what's nothing
else but a current controlled resistor), then it must be possible to
multiply these two frequencies using Ohm's law, or am I wrong?

Yes, you are mistaken. Frequencies have very little in common with Ohms
law.

Sth. like that:
---------------

+5V
O
|
R1 |
___ |/
F1 --|___|--| T1
|>
| R2
| ___
?? FO --o--|___|-- F2
|
.-.
| | R3
'-'
|
---
-

R1: converting V(F1) to I for controlling T1's resistance
R2: converting V(F2) to I
R3: build a voltage divider


Cheers,
Nils

If the circuit above is operating in a linear fashion, there will be no
multiplication of frequencies. There will be only addition so that FO=F1+F2 and
not F1*F2.

Multiplication will happen if F1 and F2 are passed simultaneously
through a non-linear element.

+5V
O
|
| The voltages of F1 and F2
.-. need to be high enough
| | R3 to cause currents to flow
'-' only during part of their
|----- FO 360 degree cycles.
R1 |
___ |/ The transistor is then
F1 --|___|---| T1 operating in a non-linear
___ | |> fashion and multiplication
F2 --|___|- | will happen.
|
R2 |

 

[Activ8]

Yes, you are mistaken. Frequencies have very little in common with Ohms
law.


If the circuit above is operating in a linear fashion, there will be no
multiplication of frequencies. There will be only addition so that FO=F1+F2 and
not F1*F2.

Multiplication will happen if F1 and F2 are passed simultaneously
through a non-linear element.

+5V
O
|
| The voltages of F1 and F2
.-. need to be high enough
| | R3 to cause currents to flow
'-' only during part of their
|----- FO 360 degree cycles.
R1 |
___ |/ The transistor is then
F1 --|___|---| T1 operating in a non-linear
___ | |> fashion and multiplication
F2 --|___|- | will happen.
|
R2 |

'cept for this simple mixer, one signal is often fed into the
emitter.

And the op's further confused, possibly, on what really goes on in
der mixer, i.e., the multiplication of the two signals ( if it were
a true multiplier ) results in a number of components which include
F1 + F2 *and* F1 - F2, not F1 * F2 ... it's x(t) * y(t)

Actually, the multiplication in this case is a result of the
addition of the two voltage signals. Taking advantage of the b-e
diode's square law simplification, I = a[Vdc + x(t) + y(t)]^2, you
end up with among other things two sine waves being multiplied which
yields two sines of the sum and difference.

A

 

[Frank Bemelman]

I'm a hobby electronic technican. So, don't expect anything based on
facts. ;-))



U = R * I
| | |
FO = F1 * F2


If it's possible to convert F2 to a current, perhaps using a resistor,
and convert F1 to a resistance, perhaps using a transistor (what's nothing
else but a current controlled resistor), then it must be possible to
multiply these two frequencies using Ohm's law, or am I wrong?

Sth. like that:
---------------

+5V
O
|
R1 |
___ |/
F1 --|___|--| T1
|>
| R2
| ___
?? FO --o--|___|-- F2
|
.-.
| | R3
'-'
|
---
-

R1: converting V(F1) to I for controlling T1's resistance
R2: converting V(F2) to I
R3: build a voltage divider

It won't work. T1's resistance follows the F1 signal, changes
at the same speed of F1. Not a constant resistance that has
a relation with the frequency. The same applies to F2, it
is not converteted into a current.

If your F1 and F2 converters did work this way, you would have
gotten a signal U, not an FO yet, so you would still have to add
a voltage to frequency converter.

But your idea is okay, if you convert F1 and F2 properly, you
can use ohms law to get that 'U' which you can convert to F0.

 

[Activ8]

It won't work. T1's resistance follows the F1 signal, changes
at the same speed of F1. Not a constant resistance that has
a relation with the frequency. The same applies to F2, it
is not converteted into a current.

If your F1 and F2 converters did work this way, you would have
gotten a signal U, not an FO yet, so you would still have to add
a voltage to frequency converter.

But your idea is okay, if you convert F1 and F2 properly, you
can use ohms law to get that 'U' which you can convert to F0.

The F U theory, right?

 

[[email protected]]

On Mon, 24 May 2004 01:36:51 +0200, "Nils Beyer" <[email protected]> posted this:

Yes, you are mistaken. Frequencies have very little in common with Ohms
law.

<snip>

It would be better to insist on the realistic

V/Z = I

At the least qualitatively, right from the start, rather than the "unachievable"

V/R = I



Cheers
Robin

 

[Frank Bemelman]

The F U theory, right?

There is nothing wrong with the principle of the idea. Convert
one frequency to a resistance, another to a current, let those
work on each other, enjoy Ohms Law at work, and convert the resulting
voltage to a frequency again.

If it is practical, is another issue.

 

[Nils Beyer]

First, thanks to you all James, Mike, Frank and Robin for your replies.

I would really like to know how such a (F1->R)*(F2->I)-circuit would look
like.

You're right, Frank, if it would be practical, that's another question
but I would understand it then. I can't understand why a diode-ring-
mixer works:

1)


. |
.--------o--|>|--o-------.
!!( | ' | | )!!
-----. !!( --- .-. )!! .-----
)!!( A V )!!(
F1 )!! --. '-' --- .-- !!( F2
)!!( | | | . | | )!!(
-----' !!( | o--|<|--o | )!! '-----
!!( | | | ' | | )!!
'-|------|-------' .-|-'
| '-----------' |
| |
--- O
FO

This circuit works. I've tried it in LTSpice. But the input amplitudes
must not be larger than around 700mV.

I don't understand what the inductors are good for. I understand the
purpose of the diodes like that:

2)
___
F1 ----|___|----. . |
___ o----|>|----o----O FO
F2 ----|___|----' ' | |
.-.
| |
'-'
|
---

For what are in circuit 1) the inductors good for?

Or what's about that circuit:
http://www.b-kainka.de/bastel96.htm

It's said there, that the frequency of the xtal is mixed with the radio
signal. Where's the mixer there? And why does it work?

I've also tried to simulate a Gilbert-Cell-Mixer but it doesn't work.
Neither the basic circuit nor the inner-circuit of the MC1496. I've
attached the whole LTSpice-.asc-file if you want to simulate it, too.


My three problems are:

a) I don't like ICs. Of course they work well but I can't learn anything.
And fun is less as these ICs are _not_ _my_ _creations_.

b) I don't like inductors as it's difficult for me to get the right henry-
value. Don't to say anything about making transformers on my own.

c) I don't have any variable capacitors.

So the best thing for me would be using only resistors, capacitors, bjts,
fets, diodes.


My primary goal is to build a nice FM-Radio using the range 80-110 MHz.
And using a circuit that I _understand_. Not something like this:
http://www.somerset.net/arm/fm_only_one_transistor_radio.html


In that circuit I understand nothing. First the understanding then the
tricks. ;-)

For my FM-Radio-experiment, I'd like to use the quadrator-demodulation
principle. And a modular built.


M1) RF Amp:
+5V
O
.-------o
| .-.
.-. | |
| | '-'
'-' o-----O ARF
|| | | /
RF ----||----o----|<
|| | >
o---.
.-. |
| | ===
'-' |
o---'
---

M2) Phase Shifter:

ARF ----o------------.
| |
.-. |
| | R1 === C1
'-' |
|---O -45° o---O +45°
| .-.
=== C2 | | R2
| '-'
| |
--- ---

R=R1=R2
C=C1=C2

1
R = -------------- with F=99.2 MHz [WDR2 ;-)]
2 x PI x F x C


M3) Mixer:

.---.
+45° ------| X |------O NF
'---'
-45° --. |
| |
--- |
ARF

M4) NF Amp:
_ _
.---. | \ .---. | \
NF ------|LPF|------| >------|LPF|------| >------O TRALALALALA
'---' |_/ '---' |_/



Automatic gain control would be cool and nice, but I don't know how
to do that. Does anyone of you know whre to get information and example
circuits for AGC?

Tuning (selecting radio frequencies and stations) would be changing the
phase-shifting circuit using a potentiometer as R for example, or?

So, my main problem is the X-mixing-circuit...


Cheers,
Nils




<- snip: Mixer_Tests.asc ->
Version 4
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SYMATTR Value 100k
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SYMATTR Value 1N4148
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TEXT 800 24 Left 0 !.param rser 25
TEXT 800 48 Left 0 !.param hen 1mH
<- snip: Mixer_Tests.asc ->

 

[Jan Panteltje]

If you want any selectivity, in you FM radio, you will HAVE to use
a tuned circuit.
Even if you mix down from say 100MHz with a 90MHz osc. to a 10MHz IF, you
still have to get rid of the 80MHz input, it will also give 10MHz IF.
The lower the IF (as seen today), the more difficult this becomes.
One could perhaps use a very sensitive PLL at 100 MHz and use its error
voltage for the audio...
JP

 

[Frank Bemelman]

First, thanks to you all James, Mike, Frank and Robin for your replies.

I would really like to know how such a (F1->R)*(F2->I)-circuit would look
like.

You're right, Frank, if it would be practical, that's another question
but I would understand it then. I can't understand why a diode-ring-
mixer works:

Neither can I I know how an AM detector works, and that's about
it. Are you skipping chapters in your book ? ;-)

[snip]

It's said there, that the frequency of the xtal is mixed with the radio
signal. Where's the mixer there? And why does it work?

Try this mixer in LT-spice, just for fun:

5V 10000Hz sine -----1K------.
|
5V 9990Hz sine -----1K------.-----|>|---.---------.--- OUT
| |
=== 22uF 1K
| |
GND ____________________________________|_________|____

a) I don't like ICs. Of course they work well but I can't learn anything.
And fun is less as these ICs are _not_ _my_ _creations_.

b) I don't like inductors as it's difficult for me to get the right henry-
value. Don't to say anything about making transformers on my own.

c) I don't have any variable capacitors.

Yes, I sometimes try to boil potatoes without water too. It doesn't
always go very well

[snip]

 

[Activ8]

There is nothing wrong with the principle of the idea. Convert
one frequency to a resistance, another to a current, let those
work on each other, enjoy Ohms Law at work, and convert the resulting
voltage to a frequency again.

If it is practical, is another issue.

Let me try that again. That's the F [yo]U theory, right ?

 

[Nils Beyer]

Try this mixer in LT-spice, just for fun:

5V 10000Hz sine -----1K------.
|
5V 9990Hz sine -----1K------.-----|>|---.---------.--- OUT
| |
=== 22uF 1K
| |
GND ____________________________________|_________|____

Mmm, 10Hz at output.

There's something you want to say, right? ;-)
But I can't see it now.

Yes, I sometimes try to boil potatoes without water too. It doesn't
always go very well

Yep, I think I'll have to fiddle around with that components even if I
don't like them. But are they so really neccessary like potatoe water?

No way to build a FM-radio without varicaps, inductors and ICs?


Heel veel dank, en meer suggesties zijn zeer welkom...


Cheers,
Uri

 

[Frank Bemelman]

Mmm, 10Hz at output.

There's something you want to say, right? ;-)
But I can't see it now.

Well, it was not much different from your circuit you used as
an example to show your understanding of diodes. There are
many ways to build a mixer, and there are good reasons for
inductors and variable caps in radios, whether you like them
or not. I have no desire to build a radio myself, but if I
did, I would do some reading about such circuits, and try to
understand it. And probably quit after the 3rd chapter and
go out to buy a radio But don't let that keep you from
trying...

 

[Frank Bemelman]

There is nothing wrong with the principle of the idea. Convert
one frequency to a resistance, another to a current, let those
work on each other, enjoy Ohms Law at work, and convert the resulting
voltage to a frequency again.

If it is practical, is another issue.

Let me try that again. That's the F [yo]U theory, right ?

Yes, I understood the F*** Y*U but I don't see the joke here.
I was about as serious as I get

 

[Rich Grise]

You're right, Frank, if it would be practical, that's another question
but I would understand it then. I can't understand why a diode-ring-
mixer works:
<SNIP CIRCUIT>
This circuit works. I've tried it in LTSpice. But the input amplitudes
must not be larger than around 700mV. ^^^^^

I don't understand what the inductors are good for. I understand the
purpose of the diodes like that:

2)
___
F1 ----|___|----. . |
___ o----|>|----o----O FO
F2 ----|___|----' ' | |
.-.
| |
'-'
|

I think there's more to it than that - if you look at the V spec,
that's right about where a diode is turning on - i.e. its
nonlinear range. This nonlinearity is what mixes the signals,
AIUI.

For what are in circuit 1) the inductors good for?

Coupling, and making it balanced, I think.

 

[SioL]

No way to build a FM-radio without varicaps, inductors and ICs?

Even with the simplest designs you need at least one coil and variable cap or a varactor diode.
But the results are total crap (regenerative receiver).

I suggest using real coils-caps in a superhet. The intermediate frequency transformers are standard
and relatively easy
to get. You can take them out of an old receiver. The rest of the coils are just 4-5 turns of 1mm
Cu wire so are very easy to construct.

Disasemble an old transistor radio to get the variable caps. Or use varactor diodes, relatively easy
to get.

I strongly suggest starting with AM first.

SioL

 

[Activ8]

"Activ8" <[email protected]> schreef in bericht
On Mon, 24 May 2004 09:33:41 +0200, Frank Bemelman wrote:

"Nils Beyer" <[email protected]> schreef in bericht
I'm a hobby electronic technican. So, don't expect anything based on
facts. ;-))



U = R * I
| | |
FO = F1 * F2


If it's possible to convert F2 to a current, perhaps using a resistor,
and convert F1 to a resistance, perhaps using a transistor (what's
nothing
else but a current controlled resistor), then it must be possible to
multiply these two frequencies using Ohm's law, or am I wrong?

Sth. like that:
---------------

+5V
O
|
R1 |
___ |/
F1 --|___|--| T1
|>
| R2
| ___
?? FO --o--|___|-- F2
|
.-.
| | R3
'-'
|
---
-

R1: converting V(F1) to I for controlling T1's resistance
R2: converting V(F2) to I
R3: build a voltage divider

It won't work. T1's resistance follows the F1 signal, changes
at the same speed of F1. Not a constant resistance that has
a relation with the frequency. The same applies to F2, it
is not converteted into a current.

If your F1 and F2 converters did work this way, you would have
gotten a signal U, not an FO yet, so you would still have to add
a voltage to frequency converter.

But your idea is okay, if you convert F1 and F2 properly, you
can use ohms law to get that 'U' which you can convert to F0.

The F U theory, right?

There is nothing wrong with the principle of the idea. Convert
one frequency to a resistance, another to a current, let those
work on each other, enjoy Ohms Law at work, and convert the resulting
voltage to a frequency again.

If it is practical, is another issue.

Let me try that again. That's the F [yo]U theory, right ?

Yes, I understood the F*** Y*U but I don't see the joke here.
I was about as serious as I get

And I'm Ted Nugent. Joke? More like word play.

But it really *is* an F U theory with the U being anyone who gets
suckered in to trying this out or rather using the above circuit to
demonstrate the concept, cause it will mix (no, multiply), but the
explaination won't fly.