Hi One of the things I’ve run into doing Rb’s this way is that the spurs out of the DDS are not always the same device to device. They also change a lot with small tuning changes. The result can be a very close in spur ( like << 1 Hz) that really rips up your ADEV since it passes through all the cleanup PLL’s …. It’s a rare occurrence, but it does actually happen.
Bob > On Jun 24, 2018, at 1:21 PM, <cdel...@juno.com> <cdel...@juno.com> wrote: > > Hi, > > I've repaired a few 5065A A1 synthesizer modules recently and lets just > say that they are not my favorite repair! > I decided to go back to a project I started a while back to try and > replace the A1 module with a DDS implementation. > I built up two different styles to evaluate. > > One I call the DDS-FE uses a synthesizer board removed from a dead > FE5650A > Rubidium module. It applies the 5Mhz input to a 74HC14 schmitt trigger > which > drives a 570A multiplier giving a 50Mhz output. This is applies to the > synthesizer board (AD9830A) which is configured for the 5.31XXXXMhz > output. This signal is > sent through a one transistor buffer amp with a tuned transformer output. > Frequency is adjusted via RS-232 (pretty much a one time adjustment) and > after > saving is nonvolatile. > > The second I call the DDS-BJ. It is a small board that Bert and Juerg > designed > that has schmitt trigger gate and 570 multiplier as well as an 8 pin PIC. > It multiplies the 5Mhz to 100Mhz. The 100Mhz is input to one of the cheap > Chinese > DDS (AD9850) that are available pretty much everywhere. The DDS is > configured > for a 21.24XXXX Mhz square wave output and divided by 4 on the board to > get the 5.31XXXX Mhz output. This is applied via series resonant LC > to the input to the buffer amp. Frequency is adjusted by an up and a down > > pushbutton and is nonvolatile. It is cleverly designed to allow the DDS > board to > plug right into the PIC board. > > First I installed one into a 5065A that had the super mod installed and > the > performance stayed the same. So that proved DDS was not degrading the > performance. > > Then I tried both styles in a standard 5065A that was performing well. > and then plotted the performance. I was a bit surprised that the DDS > units > gave better performance than the original A1! > > Either style fits easily inside the original module once the original > circuitry is removed. > Also you could install onto an L shaped aluminum bracket made to fit in > the A1 position. > > Attached is a combined plot showing the performance of each and also PIX > of the two DDS styles. > > Cheers, > > Corby<ORIGINALvsDDSA1.pngi.jpg><ddsbjpix.jpg><feddsrs.jpg>_______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > https://lists.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to https://lists.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
