Hi

If you fix one of the inputs then you violate the basic definition. 
You then get a *different* definition of linearity that is not the same
as the original definition. 

Bob

On Mar 17, 2022, at 9:43 PM, Tom Lee <[email protected]> wrote:

Ok, now really look at what you wrote. If you were to double A, leaving B (the LO) fixed, what happens to the output? 
-- 
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu
On 3/17/2022 18:38, Bob kb8tq wrote:
Hi

The output is A multiplied by B, that does not meet the definition of 
a constant times any input, 

Bob


On Mar 17, 2022, at 9:21 PM, Tom Lee <[email protected]> wrote:

Bob,

Show me that a multiplier, as used as a mixer, fails to meet your defnition.

--Tom

-- 
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 3/17/2022 18:12, Bob kb8tq wrote:

Hi

At least when I took the course in school on this stuff, the basic definition
of “linear” was indeed that the output was the input times a constant. Anything
other than that was “non-linear”. This is at the root of the conversation about
mixers being non-linear. If that *is* you definition of linear then mixers must
be non-linear.

Bob


On Mar 17, 2022, at 9:09 PM, Tom Lee <[email protected]> wrote:

Think about how one actualy uses a multiplier as a mixer, Bob. The input-output relationship of relevance is that between the IF output and the RF input. That is supposed to be linear, right? That is, the output should be a constant times the input, just as you yourself stated as the requirement.

--Tom

-- 
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 3/17/2022 17:45, Bob kb8tq wrote:

Hi

If you accept the definition that a “linear” circuit *only* produces
the input times some constant ( = the gain ) then anything that
multiplies must be non-linear.

If you look at a different definition, then of course, they can be linear.
It’s just a mater of what your base definitions are.

Bob


On Mar 17, 2022, at 8:13 PM, Tom Lee <[email protected]> wrote:

(Just to clarify, this was posted in response to Bob Nickels, not to Mike St. Angelo -- sorry for the confusion, Mike!)

--Tom

-- 
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 3/17/2022 12:16, Tom Lee wrote:

I wish people would stop repeating the claim that mixers are inherently nonlinear. That’s completely false. It is true that nonlinear things can produce mixing, but that’s a side effect, not an inherent property!

Good mixers have to be linear. You want the IF output to be proportional to the RF input.

We treat mixer nonlinearity in much the same way as we treat amplifier nonlinearity. It is an undesirable property and considerable effort is expended to minimize it.

Tom

Sent from my iThing; please forgive the typos and brevity


On Mar 17, 2022, at 11:39, MICHAEL ST ANGELO <[email protected]> wrote:

Bob,

Enjoyed that article and the one about the Si5351 Quadrature oscillator. Have the tried feeding the Si5351 to the SA612 instead of an Epson? It gives the the ability of easily changing frequency.

The SA612 and Si5351, what a pair for experimenters.

Mike N2MS


On 03/17/2022 1:05 PM Robert Nickels <[email protected]> wrote:



On 3/17/2022 11:10 AM, Phillip Carpenter wrote:
Can you please share the circuit diagram of your universal converter board that you used with the BC-453 receiver?

I've added an article about it to my website: https://tinyurl.com/mrj7rndd

The 4.7uH/100pF values shown work for 40 meters, or calculate your own -
I use a 10uH fixed inductor and 150-180pf capacitor for 75-80 meters.

73, Bob W9RAN


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