[sdiy] Ring Mod (was Re: Hadamard Transform Network)

[Neil Johnson]

Tom,

>> David G Dixon wrote:
>>> Also, if a "ring modulator" and a "4-quadrant balanced modulator" give
>>> exactly the same transfer function, then why can't the terminology by used
>>> interchangeably?
>>
>> They don't give the same transfer function, so you shouldn't
>> interchange the words.
>
> Further explanation please, Neil.

In the general case, discussed above, they don't have the same
transfer function.

> Like David, it was my understanding that a diode ring modulator gave the same sum and difference frequencies when fed with clean square waves like you suggested. In which case, it would be doing 4 quadrant multiplication in that limited case.
>
> Is that not right? Why not?

In the *specific* case of driving both with a perfect square wave
carrier yes they do produce similar outputs.  But that's a specific
case, and David's comment was a general case (no mention of
specifics).

The two main areas where they don't produce the same outputs are when
either of the carrier or signal has DC offsets (transformers are very
good at blocking DC), or when the carrier is not a square/pulse wave
(the diodes of the ring modulator add colour that don't get in a 4QM).
More on this topic in the MW thread (I appear on page 2):

https://www.muffwiggler.com/forum/viewtopic.php?t=127474

Neil
-- 
http://www.njohnson.co.uk