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

Mike HEQX mike at heqx.com
Wed May 17 02:43:36 CEST 2017

```There is a form of "AM" radio which is the version where the frequency
of the carrier produces side bands that are sums and differences with
relation to the carrier and the amplitude of the carrier is only related
to the relative amplitudes of the side bands. Is this what we are

Sometimes the definition of AM and FM get confused when talking about

Mike

On 5/16/2017 12:13 PM, Donald Tillman wrote:
>> On May 16, 2017, at 8:40 AM, Tim Ressel <timr at circuitabbey.com> wrote:
>>
>> But you bring up an interesting point: 4QMs multiply, but they produce x+y, x-y tones. Anyone got the math on that?
> High school trigonometry.
>
> Trig identity:
>     cos(a+b) = cos(a)cos(b) - sin(a)sin(b)
>
> Another trig identity, derivable from the first:
>     cos(a-b) = cos(a)cos(b) + sin(a)sin(b)
>
>     cos(a+b) + cos(a-b) = 2 cos(a)cos(b)
>
> Your multiplication operation is on the right, your sum and difference tones are on the left.
>
>    -- Don
>
> --
> Don Tillman
> Palo Alto, California
> don at till.com
> http://www.till.com
>
>
>
>
>
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```