As pointed out "PreEmphasis/DeEmphasis" and "PreDistortion" are two different things. So it is important to keep this in mind. To describe the process a little bit better it the introduction of "DeDistortion" would help. While DeEmphasis was done at the receiver end DeDistortion is done at the transmitter end by the amplifier. Just using one part of Distortion (or Emphasis) would really not reflect the true signal that is going into the microphone. As any amplifier stage is adding distortion it is appropriate to call the procedure done in the SDR (the ones that are capable of) PreDistortion. The DeDistortion in the amplifier gives you a much better approximation of a true linear amplification. Just ADDING Predistortion and not adding or better SUBTRACTING the proper amount of Dedistortion sure would make and leave the signal distorted.
3rd order IMD in the range of -60 dB and with careful design even more is possible. Consider this: the best receiver doesn´t help if a lot of average or below average quality signals are around and splattering into your "communication channel". The same is true if someone with a radio that creates a lot of phase noise is next to you - your radio can have a clean oscillator signal with low phase noise but still the other dirty signal will go into the equation. So after it has been acknowledged that high phase noise oscillators are a NO GO these days the next consequent step would be to clean up the transmit signal in terms of intermodulation. If someone tuning a motorcycle or a car he better not only tunes the engine for power but also adapt the brake system the chassis and everything else affected to handle the more power. 73 Roger, DL5RBW -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Jim Brown Sent: Sunday, May 19, 2019 2:09 AM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] K4 and Predistortion On 5/18/2019 4:01 PM, Phil Kane wrote: > Those > of us with engineering backgrounds knew that what I was referring to > as "pre-distortion" was the pre-emphasis / de-emphasis curves commonly > used in FM broadcast audio chains. All of which emphasizes the need for using the right words to describe things. The word "distortion" is most commonly used to describe non-linearity, not frequency response. And, BTW, that pre-emphasis/de-emphasis is a Standard, not just "commonly used." You know the Regs far better than I, but I suspect it's there too. As I'm sure you know, it was also common practice to go FAR beyond that, with multi-band dynamics processing and the tricky stuff that Bob Orban was doing. The engineering "rule of thumb" was that if you could see the modulation monitor needle move, you weren't doing enough.:) I did some research on the Orban FM processor, which I published as an AES Paper in 1986. http://k9yc.com/AESPaper-TDS.pdf 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
