Although my current project doesn't have the strict requirements that many of you have, I thought I would mention part of it, due to the recent talk of distribution amps.
I am putting one of the FE5680A's that I bought a while back into a permanent home. I have a nice box from a gutted HP microwave mixer that is just about the perfect size. I also have two surplus RGB video distribution amps rated for 100 MHz. After changing out the 75R resistors for 50R, I will mount the bare board in the HP box, along with the rubidium. Since the video amp BNC's are not isolated, I thought I'd better do that while I was at it. Being frugal, I used a heat gun to remove several transformers from old 3Com Etherlink III ISA cards. As most of you know, there is a single 1:1 transformer for the 10Base-2 and a dual 1:1 transformer module with low-pass filters for the 10Base-T. After removing the parts, I thought I'd characterize them on the spectrum analyzer. It was a good thing I did. Some of the transformers were obviously bad and had wacky curves. (the Ethernet cards were pulled from a scrap pile.) All of the dual transformer modules were within about 2 dB of each other. The -3 dB point being around 15 MHz and dropping to about 20 dB down or more at 30 MHz. The single transformers were of two types: square and oval with two flat sides. All of the oval transformers were almost flat out to 50 MHz (I didn't test higher). The square transformers were odd. Their -3 db point was around 8 MHz and then things gently sloped downward about 30 degrees for quite a ways. Being that both styles of transformer were being used for the 10Base-2 connection, I assumed that they should behave similarly. Rolling off at 8 MHz doesn't sound good for a 10 Mbit speed. The finished project isn't going to be anything fancy. I just wanted to make a semi-portable standard. I will divide things down so I also have 1, 5 and 10 MHz TTL outputs, in addition to the 10 MHz sine. Later, I may also incorporate a DDS that is locked to the 10 MHz to give me programmable sine and TTL outputs. I also spent all weekend tweaking both of the rubidiums via the serial port. Both of them had a zero offset programmed. Using a scope and triggering on my Z3801A, I slowly dialed things in until I got as little drift as possible. One rubidium needed to go low and the other high. BTW, using the calibrator program from VK4XV made things much easier when talking to the rubidiums serially. Joe Gray _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
