Thanks for the reply JR. I dunno what I was thinking, I meant 8 X 50MHz, of course. I also experimented with 106,25 "can" oscillator and used 4 X multiplier (425MHz system clock), same results.
I have the LPF set for 200MHz. JR, the frequencies don't move in unison with the output frequency. These really do appear randomly so as they disappear too. So, based on your comment, I don't have a leakage problem then, pheewww... Some of the spurs are REALLY loud, on the Winrad display they go as high as -30db. I've noticed that none of the loud spurs will appear when using 1MHz steps, with using no smaller division than 1MHz. I've managed to find the highest spurs with 1Hz to 10kHz steps. Even with 1Hz step, they will appear really suddenly. For example at DDs output 10.300001MHz I may have really high spur and at 10.300002 the whole 48kHz Winrad screen is totally clean. I don't mind the small spurs, just that I didn't expect this high spurs, even with 8X50MHz. Should I give more details about my DDS solution to clear out )or reveal) any HW problems? -Janne, OH1GTF --- In [email protected], "jr_dakota" <[EMAIL PROTECTED]> wrote: >Another thing, you need to terminate the antenna input with a 50 ohm >resistor (Assuming they are 50 ohm filters of course) and then you >know for sure what you are seeing is internally generated > >JR > >A 50Mhz can and X4 is 200 Mhz ... If you have your low pass set for a >400 Mhz clock and you have a 200Mhz clock then most likely you are >seeing the Clock and/or one of it's images (Clock - output Freq or >Clock + output frequency) > >Do the spurs seem to move in unison with the output frequency? That's >usually a sure sign of clock feedthrough, 'normal' spurs appear to be >more random > >JR > > > --- In [email protected], "Janne Pulkkinen" <iami78@> wrote: > > > > I just finished my AD9954 board and I'm getting spurs on audio > > frequencies. I haven't been able to test the board with spectrum > > analyzer since there's no hams around with one... > > > > You can see the problem at: > > http://www.saunalahti.fi/johku76/pic/spurs.jpg > > > > Pictures of the project can be found www.oh1gtf.com > > > > First quick note about the DDS setup: > > I'm in the process of building a 425MHz reference oscillator, but > > since it's not finished, I'm using only a 50MHz crystal "can" > > oscillator and 4 X multiplier on the DDS. So, this way I'm having a > > 400MHz system clock. > > > > In the picture above, the antenna is not connected. Some kind of > > leakage can be detected, since when I connect the antenna some of the > > "spurs" disappear. By the way, some of the spurs, which don't > > disappear when connecting the antenna, don't have image rejection, so > > they are both visible on the screen, getting away off from the zero > > beat when adding frequency from the DDS. Some times when going with 1 > > Hz steps the "spurs" kind of jump in and disappear with every Hz. > > > > Is those audio frequency spurs a result from bad IQ signal or some > > kind of imbalance, or am I just having problems with grounding loops > etc? > > > > 73 Janne, OH1GTF > > >
