Given the bandwidths of the devices involved (GBPs in the low megahertzes) and the normal stray capacitances in circuitry not specifically built for VHF and UHF use, it strikes me as unlikely in the extreme that there's much of anything above 20 MHz on the rails, unless you're living right next to a big 50 MHz repeater station. And if that's the case, a couple of ferrite beads and a silver-mica cap or two (too small to have any effect at audio frequencies) will take care of THAT.
Oscillations and noise DO happen on PS lines, but a 20 meg scope is more than adequate to pick them up (remembering, of course, that the 20MHz spec isn't a brick wall). A spectrum analyzer is a nice thing, but you've already confirmed that the noise on the line is negligable.
Here's a fun experiment for you, which will save you the five-figure cost of a spectrum analyzer- capacitively couple the PS lines to a set of headphones, then run music or your test signals through the CD player. Listening to the rails is very often an effective way to see what's going on. Buffer the 'phones, if you like, but they're really a pretty insignificant load compared to the source impedance of the rails. If you can't hear anything (that's GOOD!), stick an amplifier between the rails and the 'phones.
Oscillations and noise DO happen on PS lines, but a 20 meg scope is more than adequate to pick them up (remembering, of course, that the 20MHz spec isn't a brick wall). A spectrum analyzer is a nice thing, but you've already confirmed that the noise on the line is negligable.
Here's a fun experiment for you, which will save you the five-figure cost of a spectrum analyzer- capacitively couple the PS lines to a set of headphones, then run music or your test signals through the CD player. Listening to the rails is very often an effective way to see what's going on. Buffer the 'phones, if you like, but they're really a pretty insignificant load compared to the source impedance of the rails. If you can't hear anything (that's GOOD!), stick an amplifier between the rails and the 'phones.
Re: DC is DC .. Not
Can't resist it. I must agree with SY. I also looked at the laundry list, and I have no idea what to do with it. A lot of "observations", unsubstantiated, opinion. Is OK, but it doesn't really help me to design better supplies.
Patwen, you are sure that if you had a spec analyzer, you would see fireworks. Well, that saves you getting one, really. How can you look at it with a scope, and then say well, looks OK, but that is just because I don't have a spec analyzer. You saw DC, so there is DC.
Bad water makes bad wine? Water is H2O, what is bad water?
DC is DC, what is bad DC?
My point is that you are so prejudiced that you ignore your measurements because you are you convinced that it MUST be there. How can you ever make progress if you fool yourself all the time?
Don' take it personal, but either you are serious in your hobby, or you are just playing around. That's OK too, but expect to keep going around in circles instead of going anywhere.
Jan Didden
patwen said:Hi SY,
yes, I did see flat line on my "20MHz" scope, but I can sure you that life above 20MHz is much more "interesting".
And if I have a spectrum analyzer. wow, I can sure that power rail is not steady as rock, instead I expect to see firework displayed to them.
So DC is NOT DC... and power supply does make a huge difference.
Actually, we are not "amplifying" a signal, instead we are using the power on the power supply to "replicate" the input signal and get an output hopefully similar to the input one.
Good water make good wine, bad water make bad wine. It is that simple ... (of course not, but the basic is the same)
Can't resist it. I must agree with SY. I also looked at the laundry list, and I have no idea what to do with it. A lot of "observations", unsubstantiated, opinion. Is OK, but it doesn't really help me to design better supplies.
Patwen, you are sure that if you had a spec analyzer, you would see fireworks. Well, that saves you getting one, really. How can you look at it with a scope, and then say well, looks OK, but that is just because I don't have a spec analyzer. You saw DC, so there is DC.
Bad water makes bad wine? Water is H2O, what is bad water?
DC is DC, what is bad DC?
My point is that you are so prejudiced that you ignore your measurements because you are you convinced that it MUST be there. How can you ever make progress if you fool yourself all the time?
Don' take it personal, but either you are serious in your hobby, or you are just playing around. That's OK too, but expect to keep going around in circles instead of going anywhere.
Jan Didden
When is DC not DC
Actually far from it in my experience.
A 'scope is a very good tool for verifying abscence of oscillations (I've never had oscillation at lower levels than a 'scope's resolution) and measuring DC levels, but the sensitivity of audio circuits to low level noise is often suprising. Most 'sopes have nowhere near the resolution necessary, and can't show discrete frequencies within the melee.
Take any PSU that looks like a flat line on a 'scope and attach it to a spectrum analyser and you'll be amazed at the range of harmonic content just within the audio band!
A spectrum analyser will reveal a lot more, but I'd not take any note at all of steady state (i.e. unloaded) noise figures. Dynamic performance is all, IMVHO, and factors such as output impedance, settling times, line rejection and the bandwidth of those parameters are all critical factors.
For digital circuits, with often high levels of high frequency induced noise achieving stability and performance across the necessary B/W can be difficult.
Current paths have to be considered too - adding some good low-ESR capacitance to a noisy line means greater current flows in the 0V return. If this is shared with any other lines there may be more work required as a result otherwise you can shift a problem from one place to another.
This latter problem could be manifesting itself in the thread originator's circuit - wider bandwidth, better perorming reg. resulting in greater errors in resultant circuit, through poor layout?
Fred,
Re: Jung reg's
That's actually incorrect - the newer AD825-based designs actually increase o/p impedance in exchange for bandwidth and stability through lower Gm front-ends.
They sound better though, as the impedance trace is flatter, and the dynamic performance of the error amp is better.
A.
Actually far from it in my experience.
A 'scope is a very good tool for verifying abscence of oscillations (I've never had oscillation at lower levels than a 'scope's resolution) and measuring DC levels, but the sensitivity of audio circuits to low level noise is often suprising. Most 'sopes have nowhere near the resolution necessary, and can't show discrete frequencies within the melee.
Take any PSU that looks like a flat line on a 'scope and attach it to a spectrum analyser and you'll be amazed at the range of harmonic content just within the audio band!
A spectrum analyser will reveal a lot more, but I'd not take any note at all of steady state (i.e. unloaded) noise figures. Dynamic performance is all, IMVHO, and factors such as output impedance, settling times, line rejection and the bandwidth of those parameters are all critical factors.
For digital circuits, with often high levels of high frequency induced noise achieving stability and performance across the necessary B/W can be difficult.
Current paths have to be considered too - adding some good low-ESR capacitance to a noisy line means greater current flows in the 0V return. If this is shared with any other lines there may be more work required as a result otherwise you can shift a problem from one place to another.
This latter problem could be manifesting itself in the thread originator's circuit - wider bandwidth, better perorming reg. resulting in greater errors in resultant circuit, through poor layout?
Fred,
Re: Jung reg's
That's actually incorrect - the newer AD825-based designs actually increase o/p impedance in exchange for bandwidth and stability through lower Gm front-ends.
They sound better though, as the impedance trace is flatter, and the dynamic performance of the error amp is better.
A.
jean-paul said:
Sorry, beg to differ. The original thread was that somebody *claims* that there are differences etc. Quite a difference. In fact, this person was so prejudiced that he refused to accept his own scope measurements. I call that fooling yourself.
I like to work according to the scientific method, that means that is someone makes a claim it can be falsified. Meaning, you can verify it against observations. If someone claims that adding a 1k resistor somewhere in an amp decreases THD by half, I can go and add the same 1k in the same amp and verify that THD does or doesnot decrease by half.
If someone claims that substituting an 1085 by a 7805 drastically changes the sound, I have nothing to falsify that, because the next guy will claim the opposite, and the next guy the opposite again.
I readily accept that this change can make one believe that the sound changes. But, if you're serious, be critical, be doubtful (because a lot of info points the other way), try to find other ways to find out if there is a technical basis for it, etc. You will learn and will succeed in making better supplies, because you can work to an identified goal.
I often wonder why I get so exited by these things. It must be because audio is such a wonderfull hobby, and nothing gives me more satisfaction than making an improvement AND FINALLY UNDERSTANDING WHY THAT IS SO. Fooling yourself doesn't help here, on the contrary.
Sorry for rambling on, just had to get it off my chest. Forget it.
Jan Didden
Subjectivity
Re-reading the original post I can't help but feel that the 1085 may be working better, but results in other problems within the player / system as a whole being revealed.
I've had this happen a number of times, which is why it's hard to find absolutes. I know that if a circuit I fit one of my reg's too sounds worse, whilst the reg measures fine in-circuit the problem will lie elsewhere.
Try an LM317 adjustable and see how that works...
A.
Re-reading the original post I can't help but feel that the 1085 may be working better, but results in other problems within the player / system as a whole being revealed.
I've had this happen a number of times, which is why it's hard to find absolutes. I know that if a circuit I fit one of my reg's too sounds worse, whilst the reg measures fine in-circuit the problem will lie elsewhere.
Try an LM317 adjustable and see how that works...
A.
it strikes me as unlikely in the extreme that there's much of anything above 20 MHz o
HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA !
I'm sorry but I couldn't help myself. I guess it is because I worked with EMI complience pretty extensively in my last Telecom gig. Let me put it this way:
1. Do you or any of your neighbors have a computer?
2....... television?
3 ..... digital audio components?
4. ..... Videogames?
5. ....... anything at all with a microcontroller in it?
Ingnore EMI at your own risk but it get's in everything and most audio circuits are highly non-linear at RF frequencies and will demodulate RF energy into distortion products right down to DC.
"And if that's the case, a couple of ferrite beads and a silver-mica cap or two (too small to have any effect at audio frequencies) will take care of THAT."
SURE THEY WILL, and with absolutely no negative effects on the sonics at audio frequencies. Man there is nothing to this audio design stuff, I don't know what every body is whining about!
Thank's for the great laugh. I was feeling a little blue but you cheered me right up. I do think that I will keep on listening, measuring, and experimenting though. A really good power supply for audio requires as much (maybe more) work as a good audio circuit. Don't take my word for it, read some about some of the results from the hundreds of people who have be investigating the subject for well over a quarter of a century now.
Power to the people,
Fred
P.S. For some interestng reading
http://131.109.59.51/techstuff/rectifiers.htm
Performance Verification of Low Noise, Low Dropout Regulators
http://www.linear-tech.com/pub/document.html?
pub_type=app&document=84
Understanding and Applying Voltage References
http://www.linear-tech.com/pub/docu...app&document=83
Voltage Reference Circuit Collection
http://www.linear-tech.com/pub/docu...app&document=45
REFERENCES AND LOW DROPOUT LINEAR REGULATORS
http://www.analog.com/technology/po.../pdf/fsect2.pdf
http://www.diyvideo.com/forums/show...page=15&highlight=power supplies&pagenumber=1
HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA !
I'm sorry but I couldn't help myself. I guess it is because I worked with EMI complience pretty extensively in my last Telecom gig. Let me put it this way:
1. Do you or any of your neighbors have a computer?
2....... television?
3 ..... digital audio components?
4. ..... Videogames?
5. ....... anything at all with a microcontroller in it?
Ingnore EMI at your own risk but it get's in everything and most audio circuits are highly non-linear at RF frequencies and will demodulate RF energy into distortion products right down to DC.
"And if that's the case, a couple of ferrite beads and a silver-mica cap or two (too small to have any effect at audio frequencies) will take care of THAT."
SURE THEY WILL, and with absolutely no negative effects on the sonics at audio frequencies. Man there is nothing to this audio design stuff, I don't know what every body is whining about!
Thank's for the great laugh. I was feeling a little blue but you cheered me right up. I do think that I will keep on listening, measuring, and experimenting though. A really good power supply for audio requires as much (maybe more) work as a good audio circuit. Don't take my word for it, read some about some of the results from the hundreds of people who have be investigating the subject for well over a quarter of a century now.
Power to the people,
Fred
P.S. For some interestng reading
http://131.109.59.51/techstuff/rectifiers.htm
Performance Verification of Low Noise, Low Dropout Regulators
http://www.linear-tech.com/pub/document.html?
pub_type=app&document=84
Understanding and Applying Voltage References
http://www.linear-tech.com/pub/docu...app&document=83
Voltage Reference Circuit Collection
http://www.linear-tech.com/pub/docu...app&document=45
REFERENCES AND LOW DROPOUT LINEAR REGULATORS
http://www.analog.com/technology/po.../pdf/fsect2.pdf
http://www.diyvideo.com/forums/show...page=15&highlight=power supplies&pagenumber=1
Really? I don’t think so. What a voltage regulator IC is in fact is an amplifier with large feedback. The output capacitor is part of the feedback loop. That means that a too good capacitor with low ESR (like the OSCON’s) can worsen loop stability. Different IC's react different, just as different amplifiers sound different.SY said:
A good way to judge the behaviour of a regulator is to use a pulsating load. Then look with an oscilloscope (in AC mode) at the output of the regulator. If you see an oscillatory reaction on the pulse load the ESR of the output cap is probably too low.
You can make such a pulse load with a c-mos 555 timer as an a-stable multi vibrator running at app. 1 kHz and driving a power MOS-fet + load resistor. I build this with 9V battery power as a little test box. If you use such a test box on the DC power of a real amplifier, you can also judge the PSR of the amp. The lesser the 1 kHz comes out of the speakers the better the PSR is and probably also the regulator configuration.
Also keep in mind that good ceramic 100nf caps to ground close to the input pin and output pins are mandatory for most IC regulators to avoid oscillations. For low noise, use two electrolytic output caps with a small resistor (depending on the current need) in between.
For reasons of low noise and good pulse behaviour I personally stick with the old-fashioned discrete build regulators.
Seeing the replies, no wonders people still claim CD sound is perfect, CD transports don't make a difference, jitter is just something one dream about at night... etc.
Anyway back to regulators,
janneman>
"Bad water makes bad wine? Water is H2O, what is bad water?
How about H20 with impurity?
How about DC with noise? any kind of noise?
Untill one day there is power supply with zero output impedence, zero noise, zero load regulation, zero ... etc DC is NOT DC.
ALW>
"Re-reading the original post I can't help but feel that the 1085 may be working better, but results in other problems within the player / system as a whole being revealed."
I think this may be the problem I am having. If so, this will be damn hard to track down ....
Pjotr>
Will a 1KHz sin wave good enough to detect oscillatory reaction?
Thanks
Pat
Anyway back to regulators,
janneman>
"Bad water makes bad wine? Water is H2O, what is bad water?
How about H20 with impurity?
How about DC with noise? any kind of noise?
Untill one day there is power supply with zero output impedence, zero noise, zero load regulation, zero ... etc DC is NOT DC.
ALW>
"Re-reading the original post I can't help but feel that the 1085 may be working better, but results in other problems within the player / system as a whole being revealed."
I think this may be the problem I am having. If so, this will be damn hard to track down ....
Pjotr>
Will a 1KHz sin wave good enough to detect oscillatory reaction?
Thanks
Pat
Re: large capacitance after the regulator
I really don't think 1000uF is unreasonable after the reg in certain applications. The size of the capacitor will obviously have complex effects, but if you are optimizing for low noise (analog) or your load variation is above 100kHz (high speed digital logic) it can be helpful to make it large. You just have to read the datasheets and see what effect the size, and the ESR, have on the regulator. And sometimes you need to build it and see.
P.S. a certain well-liked designer advocates large downstream capacitance for analog circuits
I really don't think 1000uF is unreasonable after the reg in certain applications. The size of the capacitor will obviously have complex effects, but if you are optimizing for low noise (analog) or your load variation is above 100kHz (high speed digital logic) it can be helpful to make it large. You just have to read the datasheets and see what effect the size, and the ESR, have on the regulator. And sometimes you need to build it and see.
P.S. a certain well-liked designer advocates large downstream capacitance for analog circuits
your load variation is above 100kHz (high speed digital logic) it can be helpful to m
Or maybe not..... large value capacitors have larger series inductances and thus potentially higher impedances at high frequencies. I have found that caps in the 50uF to 220uF range work better on digital circuits. Look at the impedance vs. frequency graphs to be sure.
Read your data sheets.
Fred
Or maybe not..... large value capacitors have larger series inductances and thus potentially higher impedances at high frequencies. I have found that caps in the 50uF to 220uF range work better on digital circuits. Look at the impedance vs. frequency graphs to be sure.
Read your data sheets.
Fred
Jan, thanks for the reply. I've used a lot of your ideas and circuits over the years.
Your point about not verifying observations is key; it does indeed lead to a lot of chasing of one's own tail. I noticed people on other threads exulting over how much their sound improved when going from a fast silicon rectifier (very low Z) to a tube rectifier (very high Z). Or even worse, a mercury vapor tube, a horrific source of HF noise (I last used 866s in my high-power 8005-based transmitter and the PS alone screwed up every TV set in the house).
So what am I to make of this? That a power supply should have a high and nonlinear source Z? People claim that "sounds" better. Or a low source Z? Other people claim, just as fervently, that THIS "sounds" better.
Your point about not verifying observations is key; it does indeed lead to a lot of chasing of one's own tail. I noticed people on other threads exulting over how much their sound improved when going from a fast silicon rectifier (very low Z) to a tube rectifier (very high Z). Or even worse, a mercury vapor tube, a horrific source of HF noise (I last used 866s in my high-power 8005-based transmitter and the PS alone screwed up every TV set in the house).
So what am I to make of this? That a power supply should have a high and nonlinear source Z? People claim that "sounds" better. Or a low source Z? Other people claim, just as fervently, that THIS "sounds" better.
Patwen, a sine is not a very well idea, although it is possible. When you use a square wave pulse load, you are looking at the step response of the system in accordance with control theory. It is also easy and cheap to build with a few components. I don’t have it hand but if you want to experiment with, I can post a schematic of it. It is not a solution for the problems, but an analysing tool.
Fred, you are quite right to my opinion. Larger capacitors have larger inductance. In digital circuitry: If you use such large capacitors in combination with a 100 nF ceramic hf capacitor close to it, the inductance together with ceramic cap causes hf ringing on the supply lines. It is good practice in such cases to use 1 to 5 ohm resistors in series with the electrolytic cap to dampen the ringing. If you need a large capacitor, its is better to use a number of smaller ones in parallel to keep inductance low in such cases.
Capacitors on the output of a regulator are needed to keep the impedance low at higher frequencies. That is to say, from the point where the loop gain of the regulator drops to a too low value. Large values aren’t needed indeed. Large capacitors are something for after the bridge rectifier and for power amps and even then …
SY, what is good and what is bad? As always in electronics, every thing is connected to everything. Just as a large chain. But every bit counts, some bits count more and some bits count less. But let us start with proper engineering, it is difficult enough. Without it there is no floor to stand on and to be creative. Or is this just what you meant?
Fred, you are quite right to my opinion. Larger capacitors have larger inductance. In digital circuitry: If you use such large capacitors in combination with a 100 nF ceramic hf capacitor close to it, the inductance together with ceramic cap causes hf ringing on the supply lines. It is good practice in such cases to use 1 to 5 ohm resistors in series with the electrolytic cap to dampen the ringing. If you need a large capacitor, its is better to use a number of smaller ones in parallel to keep inductance low in such cases.
Capacitors on the output of a regulator are needed to keep the impedance low at higher frequencies. That is to say, from the point where the loop gain of the regulator drops to a too low value. Large values aren’t needed indeed. Large capacitors are something for after the bridge rectifier and for power amps and even then …
SY, what is good and what is bad? As always in electronics, every thing is connected to everything. Just as a large chain. But every bit counts, some bits count more and some bits count less. But let us start with proper engineering, it is difficult enough. Without it there is no floor to stand on and to be creative. Or is this just what you meant?
SY said:
I dunno SY.
Some time ago there was this guy starting a thread, asking a question, and got at least a dozen answers. Some of those were very valuable, clearly well thought-out and reasoned. Anybody in his right mind would be absolutely delighted with the concentrated knowledge and experience he got for free.
Not this guy. He just started a new thread, complaining that on the other one they gave him so many different answers, and pleaded if someone now please give him the RIGHT answer.
Go figure. It made me feel depressed.
Jan Didden
going from a fast silicon rectifier
the rectifiers low impedance is only during the conduction periode when charging the filter caps. The Impedance seen by the input is more a funtion of the input capacitor seen by the regulator. There seems to be some evidence that limiting the peak current charging the filter caps can have benificial effects on diode generated noise and transformer saturation during peak cuurent from the rectifier bridge. The is also a widely held believe that too large a value of filter caps can cause problems for the same reasons. Every body raise thier hands that thinks audio power supply design is a slam dunk........
For inquiring minds:
http://www.gensemi.com/appnotespdf/quik108.pdf
http://www.microsemi.com/micnotes/302.pdf
http://131.109.59.51/images/pdf/Calculatin_ Optimum_Snubbers.pdf
http://www.diyvideo.com/forums/showthread.php?threadid=3894&highlight=rectifier
Absolute power corrupts absolutely,
Fred
P.S. patwen
The LT1085 requires minmum load current of 10mA and probably more ouput capacitance for good perfomance. You have also told us nothing about input and adjustment terminal bypass capacitors that you used (I hope)
the rectifiers low impedance is only during the conduction periode when charging the filter caps. The Impedance seen by the input is more a funtion of the input capacitor seen by the regulator. There seems to be some evidence that limiting the peak current charging the filter caps can have benificial effects on diode generated noise and transformer saturation during peak cuurent from the rectifier bridge. The is also a widely held believe that too large a value of filter caps can cause problems for the same reasons. Every body raise thier hands that thinks audio power supply design is a slam dunk........
For inquiring minds:
http://www.gensemi.com/appnotespdf/quik108.pdf
http://www.microsemi.com/micnotes/302.pdf
http://131.109.59.51/images/pdf/Calculatin_ Optimum_Snubbers.pdf
http://www.diyvideo.com/forums/showthread.php?threadid=3894&highlight=rectifier
Absolute power corrupts absolutely,
Fred
P.S. patwen
The LT1085 requires minmum load current of 10mA and probably more ouput capacitance for good perfomance. You have also told us nothing about input and adjustment terminal bypass capacitors that you used (I hope)
But things like diode noise and transformer saturation are well-understood, quite measurable with that nasty ol' scope, and are factors only insofar as they cause the rails to be something other than constant DC under the conditions of the operation of the load circuitry. And the worst solid state diode I ever used was orders of magnitude quieter than an 866.
PS for audio a slam-dunk? No. Straightforward? Yes.
PS for audio a slam-dunk? No. Straightforward? Yes.
Re: your load variation is above 100kHz (high speed digital logic) it can be helpful to m
Certainly--it all depends on the parts and the application. As far as HF ringing--hard to determine without testing. Francios' investigations with paralleled caps seem to indicate that we can sometimes get away with these designs that look like complex resonances waiting to happen.
One thing that hasn't been discussed much is regulator noise...some of those parts generate quite a lot of it. Does a few mV of low-frequency noise matter in a digital or high PSRR design? It shouldn't. Does it matter in a low-PSRR or input stage? Maybe. Those smaller caps won't necessarily get rid of it. (don't trust 'em, but check out those 7805 datasheets--a lot of variation with noise depending on the manufacturer--I've seen 1% quoted!)
Any thoughts Fred?
Fred Dieckmann said:
Certainly--it all depends on the parts and the application. As far as HF ringing--hard to determine without testing. Francios' investigations with paralleled caps seem to indicate that we can sometimes get away with these designs that look like complex resonances waiting to happen.
One thing that hasn't been discussed much is regulator noise...some of those parts generate quite a lot of it. Does a few mV of low-frequency noise matter in a digital or high PSRR design? It shouldn't. Does it matter in a low-PSRR or input stage? Maybe. Those smaller caps won't necessarily get rid of it. (don't trust 'em, but check out those 7805 datasheets--a lot of variation with noise depending on the manufacturer--I've seen 1% quoted!)
Any thoughts Fred?
Fred,
oh yes. For instance using a small power resistor at the input of the PS's CRC filter just squishing the cap loading peak a bit more wide and flat reduces filter ripple measurably and makes a world of a difference sonically. Tried out fr several occasions also something as weird as a PS for a loudspeaker field coil.
SY,
second your suggestion to "listen" to the music on the PS rail. And to response of square wave pulse load like Pjotr suggested. I look at them at the scope too.
Very telling, to look at the scope how the PS responds to varying loads.
All,
Feeding the PS output voltage influenced by such signals to a spectrum analyzer sounds like a very good idea to me, just, my analyzer stops at 60kHz, audio only. Have to try that out, mayeven feel urged to buy that RF analyzer combo at the local surplus shop.
oh yes. For instance using a small power resistor at the input of the PS's CRC filter just squishing the cap loading peak a bit more wide and flat reduces filter ripple measurably and makes a world of a difference sonically. Tried out fr several occasions also something as weird as a PS for a loudspeaker field coil.SY,
second your suggestion to "listen" to the music on the PS rail. And to response of square wave pulse load like Pjotr suggested. I look at them at the scope too.
Very telling, to look at the scope how the PS responds to varying loads.
All,
Feeding the PS output voltage influenced by such signals to a spectrum analyzer sounds like a very good idea to me, just, my analyzer stops at 60kHz, audio only. Have to try that out, mayeven feel urged to buy that RF analyzer combo at the local surplus shop.
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