Well when you have your experimental results we can compare them.
I have ruled out "microdiodes" and insulation effects. The other theory is that it has to do with the wire draw direction, one of these days I will get samples where I have that information, then I can do those tests.
I also ruled out contamination by the drawing die as today they are made from industrial diamonds.
Now the levels are very low, but they are consistent.
Ed this is well known to anyone designing 20GHz backplanes, 50 Ohms isn't. The uniformity of dielectric value and thinkness can cause a spacial variation of propagation velocity, L , and C per unit length. The transition parasitic from the termination at each end can be different. Board manu's are not always good at the stripline dimensions either. Those cheap Pomona 1 meter RG58 cables will measure as much as +-.5 % of 50 Ohms from batch to batch.
Experiment - easy take a good TDR set up and pinch or bend the cable. There is no surprise that reversing an RF cable has a different SWR (I assume you are doing the usual fiddling in the last digit).
BTW for the record I disagree with your post #105, there is no evidence for directionality or cable distortion. There is only evidence that a particular cable could have an uneven twist rate or poor shield coverage that varies along its length, etc. or anyone of several other problems. There are several good discussions going on about incursion, ciculating ground/supply currents and such. Remember batteries don't help, class A/B amplifiers generate rich harmonic supply/ground signals. At the -140dB vs. -150dB level all of these possibilities need to be addressed or NO conclusions beyond in situ with this set of stuff this is the data I got.
EDIT - The best anyone would fess up to was 50 +-2 Ohms, my experience verifies this. I assume you have seen some of the ultra high quality coax's they usually are very stiff, after a few months of mangling I would not expect ordinary cables to be very uniform anymore.
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Scott,
I have shown my method. If you review it I think you will find the possibilities you raise have been addressed. Which of them do you think will cause a change in distortion due to direction?
But you are welcome to disagree. If you ever come by give me a bit of notice and I will set it up for you to play.
As to RF cable issues. Scott I have wired stadiums using TDR results to assure quality for more than 25 years. I also have installed broadcast transmitters, small mistakes there can be very large problems. The point I made was that today's RF network analyzers can show you that connecting a cable one way vs the other can have advantages.
Now if you want to do an exhaustive study as to which phenomena are causing the issues you are welcome to do so. I will just continue to check and label the cables that I use.
Last weeks issue was a football stadium. The antennas have adjustable gain preamps built in. The connecting cables were under 40'. The operators worried that the wireless microphones would not cover the distance so they set the antenna preamp gains to maximum +15 db. Suffice it to say the microphones did not work. Of course it also requires a swing stage to get to the antennas!
(With the stadium mounting height using pads to get the level down so as not to saturate the receivers front end doesn't work as the antenna preamp is overloaded!)
ES
Don't hold your breath. As I said, experimental data without understanding contains no information. Given the choice between data and understanding, in an area well known to science for quite a long time, I would choose understanding.simon7000 said:
Apparent very low levels of something which should not exist often indicate experimental error. Measuring low levels of anything is hard, so only very good experimenters can do it reliably. By 'very good' I don't just mean good at experiments but also good at understanding the underlying theory so they can eliminate or compensate for various confusing effects which may mimic a real signal. This is how raw data gets turned into information.simon7000 said:
As we said, this says precisely nothing at all about audio cables.simon7000 said:
Depends, I might disagree. I assume you realize SWR is not a property of the cable but the cable in situ. With a network analyser and the two pieces of gear that you are going to install the cable between you could measure the 4 sets of S parameters and compute the best connection. Using only the network analyser and the cable could be a waste of time.
You haven't shared the difference or even what you consider better. I assume you're not talking about tuned loads or mega-watt tuned antennas the concept of cable there is different. I picked up a scrap of Comcast's long haul coax by the side of the road, solid fire hose that I would have a hard time connecting to a network analyser.
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You tango with Elvee here, so this link will give you some boost, as it is close to your line of thinking (you know the road to Heaviside’s Volume)
The Telegrapher's Equation
George
Actually a few days playing with a network analyzer, a bunch of cables and different sources and loads is quite eye opening. I handle signals from receiving 10 mW wireless microphone signals to kW transmitters. My idea of better is increased system range.
Interestingly on small transmitters used for hearing assistance systems SWR is really not much of an issue in transmission range. (I will not discuss this farther as there is a bunch of good information of this on the web... along with the usual nonsense.)
Hard line is rated by diameter. I have leftover spools of the teflon version, the unjacketed and the jacketed. It comes in 1/2 mile lengths and the plant that makes it is 1/2 mile long! The length is the maximum distance cable companies can send signal without the need to amplify it.
So if anyone has a need for the stuff let me know. (Shipping ain't cheap!)
And that is why I let other folks (That includes a few noted physicists, engineers and even folks with nice shiny medals) play with the test setup. Let me know if you will be around here and I can set it up for you. maybe you just might increase your understanding.
OOOH, OOOH... I have some shiny medals!!!
Can I play??
I mean, high school track means sumptin, no??
jn
Snide remark. I am sure he has won some real awards after a long time in the field.
Your both wrong..
I did indeed aspire to win the Senior woodchuck award for soldering. Alas, such was never to be. I failed...
Ed, don't worry bout it. JC's havin fun..
cheers,
john
Still no information, sigh. Show significant difference in ERP with a simple end swap. Ed you keep flogging the magnitude of what you do as an end in itself. I'm sure you have done lots of good stuff like JC just saying it over and over does not teach anyone something new or make your statements anymore correct.
Different sources and loads, why? How much off of match termination would anyone operate seriously? Eye opening - telecom pun?
EDIT - In thinking about it I'm amazed, you can demonstrate repeatable improvements in rate/reach by swapping the ends of a cable when I can go from 2 bars to 5 bars by stepping 4 feet to the side.
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They must piggy-back on the oil tankers. The QR series 1" -2" coax seems to come in 3700, 3000, or 2700 foot lengths with the spool sizes setting the standard for shipping.
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