On Thu, Oct 20, 2011 at 2:30 PM, Dave Beumer WØDHB <d...@w0dhb.net> wrote:
> Ed > > > > Using a transmit profile with a 250Hz wide filter centered at 1500 will > help . > Well, actually, it won't. The only reason to run a narrower TX filter is if the signal being presented to the transmitter already has too much THD or IMD. With the flex radios that is not the case because the digital mode program is sending the signal in digital form to PowerSDR via VAC. Since it never gets converted to analog, there just isn't a need to narrow the TX filter. Now it is possible, if some program along the way (VAC or PSDR) has to do sample rate conversion, to get some artifacts in there but usually they are at least 60dB down. (In my case they were almost 80dB down.) Yeah, you can see them on the pan display but I can almost guarantee you that no one is going to hear them and they certainly aren't going to show up on the wattmeter. So, narrowing your TX filter might make you feel good but it doesn't really have any effect on the quality of your signal. And if you think you are reducing IMD, the bulk of the IMD is created in the PA just prior to reaching the antenna. Nothing you do with the TX filter is going to change that. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 br...@lloyd.com +1.767.617.1365 (Dominica) +1.916.877.5067 (USA) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
