Excellent advice from Charles, especially concerning isolation criteria. Should you be looking to distribute a standard 10 MHz frequency to various bench instruments, I'd recommend that you take a look at Extron video distribution amps. Several models on Ebay right now, at reasonable prices. They have quite good BW (tens of MHz to several hundred MHz) specs, and since they are made for video, they have very low distortion and reasonable noise specs. Gain is usually unity, with +/- 30% adjustment. They have very robust output drive capabilities, since they are intended to drive long runs of coax. Return loss is usually in the -30 to -40 db range. They are almost always made for 75 ohm systems, but usually can be modified for 50 ohms by replacement of resistors inside the unit.
My $0.02 worth... Dave M ----- Original Message ----- From: "Charles Steinmetz" <csteinm...@yandex.com> To: time-nuts@lists.febo.com Sent: Saturday, March 16, 2019 6:11:05 PM Subject: Re: [time-nuts] Distribution amplifier for 10MHz Taka Kamiya wrote: > I am thinking about distribution amplifier of a sort. Not a kind with 8 or > more output but just 2 or 3. > * * * > But how do I do this on 10MHz side? I'd like to have minimal distortion (sine > wave) and high isolation. I acquired a few signal splitter and monolithic > amplifiers. Split first and amplify? Amplify first and split? Remember it's > only 2 to 3 channels. Amplifier module has too much gain, so I'll probably > have to use attenuators. > > Have anyone run into this kind of thing? Is there an existing design? > Anything anyone would like to share? I have previously posted some documents you may find helpful: <http://www.ko4bb.com/manuals/73.134.121.2/Tutorial_Distribution_Amplifier_Architectures_STEINMETZ_rev1.pdf> <http://www.ko4bb.com/manuals/73.134.121.2/Extron_ADA_6_modifications_for_use_as_10MHz_distribution_amp_STEINMETZ.pdf> The first one is a general tutorial on sine-wave distribution amplifiers that describes the various approaches and provides generalized design details. The second one is a "modification manual" that gives specific instructions for modifying one particular family of commercial 75-ohm video distribution amplifiers (found inexpensively on eBay) for optimal use as a 1MHz to 100MHz sine wave distribution amplifier [with way more outputs than you say you need -- but note that you may find your "needs" develop and expand if you have more outputs.] Finally, consider carefully how much isolation you really need. There are two basic kinds of "distribution amplifiers". The first is what the term is generally used for, while the second ("isolation amplifiers") is a specialized subset of distribution amplifiers with specific, enhanced performance requirements. Distribution amplifiers are intended to provide high-quality output signals to a number of instruments (e.g., a frequency counter and a spectrum analyzer) simultaneously. However, they are not expected to have their various outputs compared differentially or interferometrically with respect to delay time (phase), harmonic content, noise, etc. Output isolation figures are typically from 40dB to 80dB. Isolation amplifiers must be used when such comparisons are to be made, for example sending two copies of a signal down different paths and comparing them differentially or interferometrically at the downstream ends -- for example, to determine the residual phase noise of devices under test). These techniques are capable of much greater resolution and are used to compare signal parameters at levels very close to the metrological (or even the physical) limits, so much greater fidelity between the two initial copies is required. Isolation should be at least 125dB at the fundamental and first 11 harmonics, with other errors (phase noise, harmonic distortion, etc.) at similar levels. True isolation amplifiers are therefore substantially less forgiving to design and build than even very good distribution amplifiers, and most of us don't need them until we have reached at least the journeyman level of time and frequency analysis. My personal advice is to walk before you try to run. Build or acquire a very good distribution amplifier, and use it until your measurements are pretty much always limited by the DAs. *Then* augment your lab with a proper isolation amplifier. Best regards, Charles _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
