RF (radio frequency) tests performed on my system.

[Firebottle]

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.

http://i65.tinypic.com/2h4hj4o.jpg

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

http://i65.tinypic.com/2r759q1.jpg


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.

http://i65.tinypic.com/6s45ea.jpg

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

http://i67.tinypic.com/6sualj.jpg

See the slightly raised mush up to about 430MHz.

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

http://i63.tinypic.com/x1iw4m.jpg

Test 6.
As test 5 but DAC3 mains ON.

http://i64.tinypic.com/2w2j8na.jpg

Look at all those clock harmonics :eek:

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

http://i68.tinypic.com/2j5ys7b.jpg


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

http://i68.tinypic.com/vx2bro.jpg

[Bigman80]

What does all that mean?!!!! Lol

[Firebottle]

It is the amount of RF that is picked up with various connections to bits of kit.

You are never free of it. All the spikes coming from the Bel Canto surprised me.

[Bigman80]

It is the amount of RF that is picked up with various connections to bits of kit.

You are never free of it. All the spikes coming from the Bel Canto surprised me.Ah I see.

Yes, RF everywhere!

[NRG]

....and that’s only up to 1Ghz, mobile phones at 1.9Ghz, 2.4Ghz and 5Ghz WiFi etc etc.

[Edward]

Very interesting Alan. Would your test equipment and methodology be useful in proving (or not) the improvement in SQ we both heard (separately) when trying out Tony's RTZ boxes at his place? I'd imagine that you would be able to show the RF reduction. But perhaps I'm being too simplistic?

[Lee Henley]

I popped into Alans house last night whilst he was doing these experiments with the spectrum analyser and it was quite interesting to see how much RFI is actually present within the room, I guess that all rooms would be similar? What effect this RFI has upon the sound is way above my electrical knowledge of putting a 3 pin plug on but Im interested all the same.

If by reducing the amount of RFI present within the room does have a desired effect on the sound then this will be something that I will definitely be looking at myself

[jandl100]

Now if only you had a Grounding Box to plug in - RF up, down or the same? :eek:

[Bigman80]

Now if only you had a Grounding Box to plug in - RF up, down or the same? :eek:

indeed!

[AJSki2fly]

indeed!

Perhaps Mr C.would lend you one so you could repeat the test with a grounding box connected. Very interesting:eyebrows:

[Bigman80]

Perhaps Mr C.would lend you one so you could repeat the test with a grounding box connected. Very interesting:eyebrows:That's a good idea. I'd be happy to an impartial viewer/listener

[Lee Henley]

That's a good idea. I'd be happy to an impartial viewer/listener

Same here

[anthonyTD]

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! :eek:
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.

http://i65.tinypic.com/2h4hj4o.jpg

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

http://i65.tinypic.com/2r759q1.jpg


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.

http://i65.tinypic.com/6s45ea.jpg

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

http://i67.tinypic.com/6sualj.jpg

See the slightly raised mush up to about 430MHz.

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

http://i63.tinypic.com/x1iw4m.jpg

Test 6.
As test 5 but DAC3 mains ON.

http://i64.tinypic.com/2w2j8na.jpg

Look at all those clock harmonics :eek:

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

http://i68.tinypic.com/2j5ys7b.jpg


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

http://i68.tinypic.com/vx2bro.jpg

[Firebottle]

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 :scratch:

[Snoopdog]

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 :scratch:

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?

[Edward]

Are your scopes able to focus/magnify in on the audio band and surrounding area? Say from 5hz to 30khz?

[Firebottle]

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

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.

[Edward]

I wonder if it is possible to measure THD+N using something as simple as a calibrated mic and software such as REW?

[Mr. C]

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 :stalks:

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

[Firebottle]

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.

http://i63.tinypic.com/v7txtd.jpg

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:

http://i67.tinypic.com/2vll8wy.jpg

Note the respective levels of the four spikes.


Display with cable and grounding box connected:

http://i68.tinypic.com/28ajmrn.jpg

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.

[anthonyTD]

I agree, it must have an impedance/load somewhere, otherwise it would disapate nothing, all very interesting, keep scratching your head, watch you dont get splinters though. :eek::D
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.

http://i63.tinypic.com/v7txtd.jpg

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:

http://i67.tinypic.com/2vll8wy.jpg

Note the respective levels of the four spikes.


Display with cable and grounding box connected:

http://i68.tinypic.com/28ajmrn.jpg

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.

[Gaz]

Are your scopes able to focus/magnify in on the audio band and surrounding area? Say from 5hz to 30khz?

Wow, are you a bat?

Most humans can only hear 20hz to 20khz

:lol:

[Edward]

Wow, are you a bat?

Most humans can only hear 20hz to 20khz

:lol:

Not at all Gary. I can hear from about 20hz to about 16khz. The point I was making, not terribly well I guess, is the possibility of stuff just outside the human audio band possibly impacting the human audio band (as supertweeters are often claimed to do). Also Alan's instruments were 'seeing' the full range up to 1ghz, not in or near the human audio band.

But I guess your :lol: recognised all this? :)

[Macca]

Seems to me that if we are going to consider that frequencies beyond the limits of human hearing can be <ahem> 'perceived' (despite the lack of any evidence to support this) then I don't see how some arbitrary cut off at any point in the frequency range all the way up into gigahertz can be consistent with this theory.

BTW The reason we can hear supertweeters is because they have output within the accepted range of human hearing. No mystery there.

[jandl100]

BTW The reason we can hear supertweeters is because they have output within the accepted range of human hearing. No mystery there.

Yup, listen to most 'supertweeters' on their own and you can easily hear them squeaking away. My guess is that they usually start at 8-10khz.
Bit of a cheeky con imho.

[walpurgis]

Suertweeters that have clearly audible output are being misused. They should roll in above the output from the main tweeter, usually somewhere above 20kHz.

The exception is use with the Celestion HF1300 which output cuts off abruptly at around 13.5 kHz. A supertweeter used above these will have output audible to some, when employed with the correct 12/18 db/oct intro slope.

[jandl100]

Sure, they should be properly integrated into the speaker design with a bespoke crossover - but I bet the vast majortity are simply used as add-ons plonked on top of the main speakers leaving them to squeak away and sound 'impressive' because of the accentuated upper treble.

[anthonyTD]

:)
Suertweeters that have clearly audible output are being misused.

[struth]

Sure, they should be properly integrated into the speaker design with a bespoke crossover - but I bet the vast majortity are simply used as add-ons plonked on top of the main speakers leaving them to squeak away and sound 'impressive' because of the accentuated upper treble.

depends on the supertweeter. some only work over a certain freq, and others need a cap of correct value in line

[walpurgis]

Most tweeters seem to roll off at the top by around 12db to 18db/oct, so intro slope of the supertweeter needs to match this. Both need to be down a few db in output at the response overlap.