Well, I certainly have to agree, Tom, if the signal on the desired sideband is just a single shifting tone. Might get messier if an sudio stage or A/D is driven into limiting and producing harmonic distortion at audio, I guess.
73, Charlie, K4OTV -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Tom W8JI Sent: Monday, December 30, 2013 10:56 PM To: [email protected] Subject: Re: Topband: Digital mode spurious issues Thanks everyone for the suggestions. I'm going to have to install some software to identify some of the signals. >I would think that IMD products in a high-level PA that is over-driven > beyond good linearity limits could add some junk in the "undesired > sideband"? FWIW > IMD **requires** two or more signals at once, and does not appear anything like sideband leakage. This was a single shifting tone, and the lower frequency signal went the opposite way but the same amount as the main signal with shifts. That is classic for inadequate sideband suppression. There are multiple problems with using SSB to transmit audio tones and "thinking" it is a pure digi mode. 1.) things like this do not show on almost all digi waterfalls because they are out of passband of the other fellows receiver. 2.) SSB carrier, noise, and opposite sideband suppression is limited by the radio quality 3.) output purity is also limited by audio input purity, which includes audio line issues 4.) most digi operators do not have the low noise antennas most DXers have, and cannot hear some fairly strong signals. They are often on digimodes because of that! 5.) radios have terrible SSB transmitter performance compared to even fair receivers, so the transmitters often set the adjacent channel interference levels Placing digimodes near weak signal areas is not very wise frequency planning, but there is nothing anyone can do about it. _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
