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Posted by Richard on April 15, 2009, 6:24 pm
On Mon, 13 Apr 2009 14:54:47 -0400 (EDT), David Clayton
>How many "geeks" these days know what a SWR is let alone what to do about
>it?
I do. But then again, I'm a balding grey-haired 72-year-old "geek."
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
On Wed, 15 Apr 2009 18:24:43 -0400, Richard wrote:
> On Mon, 13 Apr 2009 14:54:47 -0400 (EDT), David Clayton
>>How many "geeks" these days know what a SWR is let alone what to do about
>>it?
>
> I do. But then again, I'm a balding grey-haired 72-year-old "geek." 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.
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
>I do. But then again, I'm a balding grey-haired 72-year-old "geek."
>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.
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
On Thu, 16 Apr 2009 15:11:36 -0400, Scott Dorsey wrote:
>>I do. But then again, I'm a balding grey-haired 72-year-old "geek." 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.
>
> 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....
"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
On Fri, 17 Apr 2009 18:06:15 +1000, David Clayton wrote:
>"This is expensive high-tech equipment, so don't force it - just hit it
>harder!" :-)
Au contraire!
[from my signature date file]
> All parts should go together without forcing. You must remember that the
parts
> you are reassembling were disassembled by you. Therefore, if you can't get
them
> together again, there must be a reason. By all means, do not use a hammer.
> --IBM maintenance manual, 1925
--
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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