These observations are interesting:
https://www.audioshark.org/power-conditioners-regulators-24/measuring-ac-power-line-noise-11713.html
Just an extract of this very informative thread... :
«The Emtech is no longer being made. However, you can find some used ones on the eBay. The Enteq is useful for rudimentary demonstrations. However, it is not a good device for a comprehensive study of power line noise. First, it is has no standard references settings. You plug it in - you adjust the gain with the knob until you get a approximate 100 reading on the meter. This is arbitrary - not a measurement where you could compare two different power lines and certainly not compare readings between locations. It is however useful for a quick before and after of the same power line. You must be careful NOT to touch the gain control between readings and the readings should be taken very close together since power line noise is dependent upon the radiated RFI/EMI noise in the environment.
A Fluke Model 43 power line analyzer is relatively inexpensive but it doesn’t measure noise.
For actual scientifically accurate readings you need a spectrum analyzer that is specifically setup to do power line readings. We several including the Audio Precision Analyzer with power module installed. If you have a PC based spectrum analyzer DO NOT plug it into your power line! If you don’t know what you are doing - don’t do it. You must take very specific precautions when connecting measurement devices to a live power line.
The Enteq only detects and rectifies frequencies to around 700KHz which means is it completely insensitive to some of the most harmful noise frequencies - those in the 1MHz to 10MHz ranges. But hey it is inexpensive, easy to use and it is nice to be able to "hear" some of the stuff that is on your power line. Your dedicated power lines, rhodium plated outlets and large gauge wires in the wall in no way immunize you to power line noise. Power line noise is picked up from radiated electromagnetic waves all around you. This includes AM and FM radio, wifi, cell frequencies and the list goes on. Furthermore noise reduction is always "localized". That means that just because you have a power conditioner that reduces conducted noise does not mean that the noise doesn’t re-introduce itself farther down the line. So if you have some form of power conditioning at the electrical panel, the radiated noise will be picked-up by the in-wall wiring that acts like an antennae. This means you WILL have noise on the power line at the wall outlet. This is why we talk about the "distributed power conditioning" approach to noise reduction.
We are actually working on consumer level device that is more a modern and elaborate version of the Enteq. It will detect a broader range of frequencies and they will be calibrated so that absolute readings can be taken. This will allow you to see if you have a low, medium or high level noise on your line. And it will allow people to compare noise levels at different times of the day and at different locations. »...........................................................
«I have several of the Alpha and the Stetzerizer units. Personally, I prefer the old Entech unit. Entech was actually a very technically advanced group of engineers. Both the Alpha and Stetzerizer are similar in that they have a bandwidth that extends quite low for measuring RFI/EMI. They drop down to 15-30 kHz in there measurements. While this may seem to be an advantage it actually has a fatal flaw. Both aggregate noise from about 15 kHz to around 10 MHz and lump them all together in a single reading. Some frequency bands are more important to the performance of audio equipment specifically our research indicates the the most harmful frequencies are in the 100 kHz to around 1 MHz bands and then secondarily from 1 MHz to 10 MHz. Interestingly, I believe that the Entech engineers knew this and designed their device to be sensitive in the frequencies from 300 kHz to 700 kHz range. This makes the Entech particularly useful for finding noise sources in the specific ranges that are most noticeable in the context of music systems.
I have done direct side-by-side comparisons using all of the units listed. I would then plug a device into the power line that we ’know’ produces particularly harmful noise effects as measured by our power and spectrum analyzers. In many cases, the Alpha and Stetzerizer would barely change their relative readings while the Entech would go off the charts. This is because the Entech is more narrowly focused and the other two are less so.
And then conversely I would connect filters that reduce power line noise in a known manner as verified by the power and spectrum analyzers and in many of these cases the Alpha and Stetzerizer would show only as small or marginal difference while the Entech would show a much larger and significant difference.
Look these are all very inexpensive devices and all of them can be useful. But they have severe limitations from a technical point of view. I found the most useful for the hobbyist to be the Entech. As I said earlier, we are developing a device that will be much more useful and will show noise in specific bands much like the old audio spectrum displays. This is being developed for our medical division where this device will be quite useful in identifying specific types of noise pollution in hospitals. I hope this is helpful.
BTW, I have three of the Alpha units and would be happy to sell two of them at less than what we paid for them. Just PM me.
Caelin Gabriel President Shunyata Research