You just made my point by showing suppressed carrier and opposite sideband values. The values you state are ok for properly operating transmitters but how about non-properly operating transmitters? If the FCC sends you a notice that you are transmitting a readily heard suppressed carrier you need to check your rig if you are using AFSK and determine if the carrier suppression is faulty. If you are using FSK that uses either direct frequencies or mixing of two RF frequencies, you only need reply that your tranmitter operates in such a fashion that it does not use/generate a 'suppressed carrier'. The same goes for the unsuppressed SSB. That is one reason why there are different emission designators for the two methods.
I never said that properly operating transmitters don't have harmonics and spurs that may be stronger than the mixing products in an AFSK signal. That is not what was being discussed and is another issue entirely. The elimination of undesired mixing products of 5+5.001 mHz signals require a totally different approach than that of eliminating undesired mixing products of 10+0.0001 mHz signals. That is the point I am making and why I wanted to indicate that they are not equivalent. Each method has its own set of issues that one must deal with and they are very, very different. In fact, there is no reason FSK signals can't be generated directly. I am experimenting with an AD9851 DDS using a FAR Circuits board and have used it to make a dual conversion receiver. I am starting work on a CW/SSB transceiver. There is no reason this DDS can't generate HF RTTY FSK signals directly at the operating frequency under software control. Is this functionally equivalent to a J2 AFSK type signal? Would a spectrum analyzer with a 90 db range show the same footprint at the operating frequency? You obviously understand these issues, but many do not. It is not appropriate to create misunderstandings among those that don't. There is enough misinformation floating around the internet as it is. Just do a search on baud versus bit rate. To me it's kind of like telling folks that gnats and bumblebees are functionally equivalent because they are both insects and fly. Someone should point out the inaccuracies from broad generalizations like this. Jim WA0LYK --- In digitalradio@yahoogroups.com, "expeditionradio" <[EMAIL PROTECTED]> wrote: > > > jgorman wrote: > > > > This is misinformation that can be harmful to newbies or folks that > > don't have the knowledge of about how the two different types of > > signals (FSK versus AFSK) are generated. > > > > At the most basic level, if you look at the math involved in > > generating the two types of signals, i.e., FSK versus AFSK, you will > > see that AFSK has signal components close to the operating frequency > > that FSK doesn't have. These components are commonly called 'opposite > > sideband' and 'suppressed carrier'. Depending on the quality of the > > transmitter and the method of SSB generation, AFSK will have these > > components more or less suppressed but they are still there. > > > Sorry, but I didn't see any "misinformation" going on there... > Practically speaking, FSK generated by frequency shifting an audio > tone into an SSB transmitter is more FSK at the RF spectrum than it is > AFSK. > > A properly adjusted SSB transmitter is simply a means of heterodyne > with the "Local Oscillator" suppressed (phantom carrier) and the > "Image" suppressed (unwanted sideband). Typically we see -50dB or so > of suppression with modern SSB rigs. > > Let's put this in practical perspective for typical ham rigs: > > Transmitter power 10 Watts. > Suppressed carrier (L.0.) = 100 microwatts. > Rejected sideband (image) = 100 microwatts. > > Transmitter power 100 Watts. > Suppressed carrier (L.0.) = 1 milliwatt. > Rejected sideband (image) = 1 milliwatt. > > Transmitter power 1000 Watts. > Suppressed carrier (L.0.) = 10 milliwatts. > Rejected sideband (image) = 10 milliwatts. > > It seems like my neighbor's plasma TV set radiates more RFI than > my undesired sideband does :) > > There are often harmonics and spurious from most common transmitters > that are 15 or 20dB stronger than that... even when you are running > Class C with CW or a diode-shifted oscillator FSK modulator :) > > There may be hum and noise when a computer sound card is used to drive > the audio of an SSB transmitter... but if an attenuator is used or a > properly set up audio interface, the noise floor is usually better > than -60dB below the desired signal. > > Of course, there are some ops who use other software programs that > generate strange sounds and music while they are transmitting with > their soundcard, but IMHO, these should be characterised more as > operator error than unsuppressed noise. :) > > Bonnie VR2/KQ6XA > Hong Kong, etc. >
