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Thread: RF (radio frequency) tests performed on my system.

  1. #11
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    Quote Originally Posted by AJSki2fly View Post
    Perhaps Mr C.would lend you one so you could repeat the test with a grounding box connected. Very interesting
    That's a good idea. I'd be happy to an impartial viewer/listener
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  2. #12
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    Quote Originally Posted by Bigman80 View Post
    That's a good idea. I'd be happy to an impartial viewer/listener
    Same here
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  3. #13
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    Test 6, and 7 didnt surprise me Alan, that is what I would expect from most things with a clock, good on you for doing the test though, hopefuly it will give folk interested in this thread a bit more insight.
    I remember reading somewhere years ago that; if all of a sudden all radio frequencies became visible, there would be so many, that we wouldnt be able to see!
    Quote Originally Posted by Firebottle View Post
    This testing is with Grounding boxes in mind, just to see what the background RF levels and emissions are from stereo kit.

    Radio Frequencies cover a very wide frequency range, the test equipment I have goes right up to 1GHz.
    That is 1000 MHz or to put another way 50000 times the audio bandwidth.

    RF energy is very pervasive, it is all around us and is induced into anything metallic. Even a screened lead will pick up RF on its outer braid.

    The test kit is known as a spectrum analyser and shows the frequency along its X axis with the logarithmic amplitude on the Y axis.
    The X axis is linear so shows frequencies from Zero to 1GHz, so each graticule line is 100MHz.

    The Y axis shows signals above the noise floor mush at the bottom of the screen, at about 20uV. This is ten times lower than a low output moving coil cartridge to give a context.

    Test 1.
    A 1 metre whip antenna connected to show the background RF level.



    Test 2.
    A probable ground box lead connected, made from some RG58 coaxial cable.




    A test lead was made to connect to only the outer shell of an RCA socket and used for subsequent tests.
    Test 3.
    Test lead connected a CD transport output. Transport mains OFF.



    Test 4.
    As test 3 but CD transport mains ON.



    See the slightly raised mush up to about 430MHz.

    Test 5.
    Test lead connected to a SPDIF input of Bel Canto DAC3, mains OFF.



    Test 6.
    As test 5 but DAC3 mains ON.



    Look at all those clock harmonics

    Test 7.
    Test lead connected to XLR output of DAC3, mains ON.




    Test 8.
    Test lead connected to spare input of KIN preamp, mains ON.

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  4. #14
    Join Date: Oct 2012

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    Yes I did think after seeing all those harmonics that the clock must be on the good side> You don't get a spectrum like that without fast edges.

    I had Tony around this afternoon and we did some more testing with a box and cables in various connection arrangements.
    Unfortunately we drew a blank with being able to see anything happening, on the spectrum analyser or a 200MHz scope

  5. #15
    Join Date: Jan 2008

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    Quote Originally Posted by Firebottle View Post
    Yes I did think after seeing all those harmonics that the clock must be on the good side> You don't get a spectrum like that without fast edges.

    I had Tony around this afternoon and we did some more testing with a box and cables in various connection arrangements.
    Unfortunately we drew a blank with being able to see anything happening, on the spectrum analyser or a 200MHz scope
    Alan

    Despite not being able to see anything on your spectrum analyser, did you experience an improvement in sound quality from your home system, as you had at Tony's?
    Steve.

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  6. #16
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    Are your scopes able to focus/magnify in on the audio band and surrounding area? Say from 5hz to 30khz?
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  7. #17
    Join Date: Oct 2012

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    Yes I have had a very good improvement to the sound quality, I bought the box and leads a few days ago. Whoopee

    The scope was used to view the eye pattern coming from the CD transport, the spectrum analyser can't focus in that low in frequency.

  8. #18
    Join Date: Mar 2017

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    I wonder if it is possible to measure THD+N using something as simple as a calibrated mic and software such as REW?
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  9. #19
    Join Date: Jan 2008

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    Great afternoon at Alan's lots of scratching of heads swapping of test probes cabilbration and more head scratching but more importantly music after brainstorming

    Even was accused of having a quantum slingulaity finger

    However the bottom line was predictable which is why Alan is still listening to music I suspect even the vinyl sounded pretty good

    Long day 350 miles but Alan is a very genial host also good to bounce a few ideas off

    Alan already has his own RTZ box so I am sure there will be more to follow from the man himself at some point in the future
    Last edited by Mr. C; 07-02-2019 at 23:08.
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  10. #20
    Join Date: Oct 2012

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    I'm Alan.

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    I put my RF hat on last night and had a think about how the grounding box cables are made.
    The construction will effectively create a balun that can reflect an impedance connected to the end of the cable.

    The length of the cable (balun) will determine where impedance nulls and peaks will occur across the frequency range. This is the theory so the test is to find out if the grounding box actually has an impedance.
    This impedance is relative to free space (RF/antenna engineers will understand this). The impedance of free space is 377 ohms, though this could be thought of as a construct as it is calculated from the theoretical capacitance and inductance of free space, or a vacuum if you will.

    What is really needed is a Network Analyser to measure the reflected impedance but I don't have one.
    The next best thing is to use the calibration signal of the Spectrum Analyser which is a 50MHz square wave, so displays frequencies at 50MHz intervals across the screen.
    I quickly made an adaptor so the grounding box cable could be connected directly to the Spectrum Analyser.



    The spectrum was monitored with and without just the lead connected, no difference was found. When the grounding box was connected to the other end of the cable a difference was observed, but only to the bottom 4 frequencies, namely 50/100/150 and 200MHz.

    The differences were small but repeatable so the Analyser was set to display to 200MHz and at its maximum vertical resolution of 3dB per graticule line.

    Display with/without just the cable connected:



    Note the respective levels of the four spikes.


    Display with cable and grounding box connected:



    Note the 50 and 150MHz responses have increased and the 100 and 200MHz responses have decreased.


    OK what does this tell us? It doesn't tell us what the impedance is as that is beyond the scope of the test.

    It does confirm that the grounding box has an impedance at RF.
    Last edited by Firebottle; 08-02-2019 at 14:06.

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