Re: Sabotage attacks knock out phone service [Telecom]
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Posted by Richard on April 15, 2009, 6:24 pm
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 When I worked for Bell Labs designing broad-band microwave systems, we used return loss rather than SWR, because the numbers made it easier to visualize what was happening. We had to keep each individual echo to about 70 dB below the signal. This translated to a 35 dB return-loss requirement for each component. In SWR terms, that was 1.035. One day, we visited a manufacturer of waveguide parts: bends, transitions, etc. They were used to SWR's of 1.2, and couldn't believe that we were serious about 35 dB retun losses. But that's what it took to transmit 1860 multiplexed voice circuits with low intermod noise, and later 3 DS-3's using 64QAM modulation with adequate fade margin, over a 30-MHz wide 6 GHz channel 3000 miles from coast to coast. Dick Grady, AC7EL | ||||||||||
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Posted by David Clayton on April 16, 2009, 8:53 am
Please log in for more thread options Ahh yes, I recall building an audio return-loss bridge sometime in the late 1970's. I think I still had my 27Mhz SWR Meter until about 5 years ago.... (48 year old geek here.....) -- Regards, David. David Clayton Melbourne, Victoria, Australia. Knowledge is a measure of how many answers you have, intelligence is a measure of how many questions you have. ***** Moderator's Note ***** An _audio_ return loss bridge? Were you a roadie for The Police? Bill "This gives Roxanne's red light a whole new meaning" Horne Temporary Moderator Please put [Telecom] at the end of your subject line, or I may never see your post! Thanks! We have a new address for email submissions: telecomdigestmoderator atsign telecom-digest.org. This is only for those who submit posts via email: if you use a newsreader or a web interface to contribute to the digest, you don't need to change anything. | ||||||||||
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Posted by Scott Dorsey on April 16, 2009, 3:11 pm
Please log in for more thread options Yes, but back then, SOME waveguide manufacturers published tuning procedures which involved banging on waveguide sections with a hammer until the return loss hit a certain amount. Problem with that is that once you've bent it you can't easily bend it back.... --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." | ||||||||||
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Posted by David Clayton on April 17, 2009, 10:48 am
Please log in for more thread options On Thu, 16 Apr 2009 15:11:36 -0400, Scott Dorsey wrote:"This is expensive high-tech equipment, so don't force it - just hit it harder!" :-) -- Regards, David. David Clayton Melbourne, Victoria, Australia. Knowledge is a measure of how many answers you have, intelligence is a measure of how many questions you have. ***** Moderator's Note ***** This reminds me of one of my father's favorite phrases: "Never use force! Just get a bigger hammer!" Bill Horne Temporary Moderator Please put [Telecom] at the end of your subject line, or I may never see your post! Thanks! We have a new address for email submissions: telecomdigestmoderator atsign telecom-digest.org. This is only for those who submit posts via email: if you use a newsreader or a web interface to contribute to the digest, you don't need to change anything. | ||||||||||
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Posted by Julian Thomas on April 17, 2009, 11:28 pm
Please log in for more thread options On Fri, 17 Apr 2009 18:06:15 +1000, David Clayton wrote:Au contraire! [from my signature date file] parts them -- Julian Thomas: jt@jt-mj.net http://jt-mj.net In the beautiful Genesee Valley of Western New York State! -- -- The sad thing about Windows bashing is it's all true. | ||||||||||
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