On 03/05/2014 09:18 PM, Bruce Perens wrote: > On 03/05/2014 07:48 PM, Mel Whitten wrote: >> The HPSDR has now implemented predistortion and soon I think Walter K5WH, >> who is very active on FreeDV will have it for his TX. Perhaps, he'll share >> his experience with predistortion with us in the near future. >> > From what I've read, predistortion linearization does two things: > > 1. Model the inherent phase error of the amplifier and correct it by > applying an inverse phase change to the input signal. > 2. Model the amplitude compression caused by "soft" saturation of the > amplifier, and increase the amplitude by the amount necessary to negate > this compression.
You will also need to compensate for non-linear effects as you move into compression. An interesting challenge is to come up with a way to characterize a typical ham transmitter with inexpensive means, like a cheap and reasonably linear receiver that can capture samples (and maybe make EVM and ACP measurements) on an fdmdv signal. It would be amusing to compare the behavior of a PA with tubes to the "modern" transistorized stuff, when you drive them into compression. Anybody have a schematic for a 20m PA with cheap and easy to replace finals? I have a feeling that experimentation with predistortion may involve burning up a few of those... Regards, Jan ------------------------------------------------------------------------------ Subversion Kills Productivity. Get off Subversion & Make the Move to Perforce. With Perforce, you get hassle-free workflows. Merge that actually works. Faster operations. Version large binaries. Built-in WAN optimization and the freedom to use Git, Perforce or both. Make the move to Perforce. http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
