Hi If you decide to optimize the transformers, it’s pretty easy to do:
Bought in bulk (like by the pound) ferrite binocular cores (two hole ferrite beads) are quite cheap. The last batches I got were sub 10 cents each. You can get them in a variety of sizes and compositions. Obviously bigger is going to be more expensive than smaller. A surprisingly small number of bifilar turns through one of these is plenty to make a good broadband transformer. Think in terms of 4 to 8 turns. Yes, if you get the ones that are too small to see or work with, they are cheaper still. They also don’t handle a couple of watts of RF plus a few hundred ma of DC. The hand made ones are pretty rugged …. You can put them on a network analyzer to see what’s going on. A signal generator and a power meter is perfectly fine for doing the testing. A tracking generator on a spectrum analyzer also is great. For most uses they fall apart for loss before much else goes wrong. Bob > On Nov 24, 2014, at 2:39 PM, Joseph Gray <jg...@zianet.com> wrote: > > 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. _______________________________________________ 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.