Christos: The Brainerd 995x on the bench right now goes to 70MHz with better than -115dBm MDS. It goes to 79MHz with additional loss in sensitivity, at 79MHz, it's about -105dBm. At 80MHz, it's about - 100dBm.
The board under test stops working around 82MHz. This is because the DDS output LP filter on that board is of lower value. A higher DDS LP filter would let it go higher. Remember, the DDS on the 995X board is running at twice the received signal. So, 80MHz receive has the DDS running at 160MHz. I think the LP filter that I put on that particular board is limited to around 160MHz. With the clock 125MHz, and the PLL set to 4, the DDS clock is 500MHz. You should be able to get a fairly clean DDS output close to 200MHz with a carefully tuned DDS LP filter. That would mean close to 100MHz QSD operation, if the DDS is limiting it right now. I'm not sure where the QSD, clock logic, and other stuff will actually stop functioning on the Brainerd AD995x board. Keep in mind, this was a simple test with a sig gen to see how high it would go. I did NOT check QSD diff phase & gain, or other parameters for this testing. There are more spurs and other garbage as you go higher in frequency. You need to cherry-pick the actual LO freq to minimize them. This is one reason I'm going to experiment with using an Si570 to drive the AD9912 DDS on the Brainerd AD9912 board. If I can intelligently tweak the combination of Si570 freq, DDS PLL multiplier, and AD9912 output freq, I think we can get around some spurs. (top posting to keep message flow) Terry WB4JFI --- In [email protected], "Christos Nikolaou" <[EMAIL PROTECTED]> wrote: > > Hi Terry, > > How high can the 995x actually go? > Although the parts on it seem to have something like 350MHz or so > limits, I could not get it go beyond 60MHz. > > 73 > <snip>
