Question on negative peak limiting

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steve_qix:
Quote from: kc2ifr on November 18, 2008, 05:58:31 PM

Quote

I agree with Bill on processing at low level if If IF (and only if ) the transmitter is capable of passing a square wave (or close to one), and properly.

Steve,
Could u explain why this is? Im not talking about hard clipping.
Bill


Hi Bill,

Hard clipping is the discussion at hand and that's why I mentioned the square waves, etc.  Even soft clipping could be an issue - depending.  For normal processing, in theory, there shouldn't be any problems  8)

Regards,

Steve

w1vtp:
Bill, Steve

It might be educational to show a spectrum display of a pure sine wave versus one that has been clipped.  The problem as I see is it that once there is clipping in an AF mudulation signal there are a LOT more unwanted high frequency components to deal with IE:  splatter.  If we try to filter the high freq comp... that solves the broad band stuff but now we have a lot of junk cluttering the spectrum we WANT to hear.

First cup of "bean" hasn't kicked in yet but that's the way I see it right now.  Interesting thread.  I love this forum

Al VTP (Very Tired Person this morning) :)

K3ZS:
I use diode negative peak clipping only to protect the mod transformer.   I try to keep the mod level so that it only
clips rarely.    Any sharp clipping creates harmonics and splatter.   There was an article a few years ago that
"softened" the diode clipper with an added resistor in series with the zener string (this was the clipper using zener
diodes).

kc2ifr:
OK Steve,
I see.........never used clipping here......just heavy on the compression using this little box.
http://www.inovon.com/?a=2&s=1&i=1

So far its working GREAT. I use it with my 500.
I use the Urei modulimiter with the 4x1 and I love it also.
Scroll down on this page to see the BL40 Modulimiter....
http://www.uaudio.com/webzine/2005/august/index4.html
Both units are designed to be used with broadcast AM transmitters.

Bill

Steve - WB3HUZ:
Consider that the clipping is occuring at negative 95+ percent moduation. What is the power of any harmonics/distortion products at that point?


Quote from: w1vtp on November 19, 2008, 08:39:59 AM

Bill, Steve

It might be educational to show a spectrum display of a pure sine wave versus one that has been clipped.  The problem as I see is it that once there is clipping in an AF mudulation signal there are a LOT more unwanted high frequency components to deal with IE:  splatter.  If we try to filter the high freq comp... that solves the broad band stuff but now we have a lot of junk cluttering the spectrum we WANT to hear.

First cup of "bean" hasn't kicked in yet but that's the way I see it right now.  Interesting thread.  I love this forum

Al VTP (Very Tired Person this morning) :)

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