50 ohms is a compromise between maximum power transfer and minimum attenuation, as mentioned in page 9 of Network Analyzer Basics (http://cp.literature.agilent.com/litweb/pdf/5965-7917E.pdf)
Regards, Roberto EB4EQA -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Attila Kinali Sent: martes, 07 de febrero de 2012 21:59 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Why a 10MHz sinewave output? On Tue, 7 Feb 2012 12:19:11 -0800 Chris Albertson <albertson.ch...@gmail.com> wrote: > Related question: Assuming I'm using 10MHz sine wave. What's the > best physical cable to use? Is there any good reason to use 50 ohm > cable? What about 75 ohm? I looked at a schematic of my counter > and it looks like the 10MHz signal hits some high impedance chip > inside. RG6 seems like the way to go. It's double shieled and > lots of cable TV parts could be used. There is no particular advantage in one or the other, at least not for most applications. It's tradition that measurement and (most) RF gear uses 50R, while TV and radio uses 75R. (there was once a reason for this, but i don't know it). When it comes to low frequency stuff (ie everything below a couple 100MHz) i would stick with 50R cable and connectors. Cheap cables aren't too bad for lab stuff. Although for time-nutty needs you might want to choose the ones with better shielding. When you go to higher frequencies (especially above 1GHz) i'd rather use 75R sat cables + F connectors. These are available in good qualities at low price. What you should not do is mix different impedances, as this will result in energy reflected back to the source, which might or might not damage it. But you will definitly have increased jitter due to the reflections. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? _______________________________________________ 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.