Arie Kleingeld PA3A wrote: > > > If we distort our SSB audio by compression etc, then let's hope that the > sideband filter will limit the bandwidth. (I don't know where the > compression or whatever is done in a K3). > But if the PA distorts the signal even more, there is no filter to limit > this within a few kHz. > So I think the IMD measurement might be important. > > Let the guru's speak..... > > OK, that's true about any compression that happens before the filter. But ALC compression certainly happens after. I think that any laboratory IMD measurement will be carried out without any ALC at all. In any event, ALC should not have an effect on a laboratory IMD test since the two tones are not varying in amplitude, unlike a real SSB or PSK signal. So the laboratory IMD test bears little relationship to the real world.
I think that the characteristics of a transmitter's ALC may have more effect on the signal than any laboratory IMD figure. To give an example: in the Rev 2 K2 firmware, a modification was made to the ALC characteristic in data modes that allowed ALC to be used to control TX power without introducing unacceptable IMD products. This suggests to me that complex characteristics of the ALC will have more effect on signal width in real-world SSB operation than small differences in PA linearity that are reflected in the IMD measurements that only relate to the transmission of two constant amplitude tones. Too slow ALC and the PA could clip, causing severe splatter. Too fast and it will operate like compression creating many IMD products. But I am not an expert and am interested in what they have to say to this hypothesis as well. ----- Julian, G4ILO K3 s/n: 222 K2 s/n: 392 G4ILO's Shack: www.g4ilo.com Zerobeat Ham Forums: www.zerobeat.net/smf -- View this message in context: http://www.nabble.com/K3-Transmit-IMD-tp16501433p16523434.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
