A very quiet (EMI) 5V SM-PWRS

My 5V rail supply, a home build job using a 5V step-down regulator which is being fed of one of my 12V rails is starting to hit its limit at about 40W. If I start up an additional Raspberry Pi the thermal protection activates and the regulator shuts down. Bugger.

Time for a new supply. I have an old (>25 years) AT switch mode power supply (SMPS) which had at one stage been put into service as a bench supply to supply +-5V and +-12V for projects. Since I have upgraded my bench supply this unit was sitting in a box ready to be ....

Anyway cutting a long story short I decided to use this SMPS as the unit to supply the shack with 5V. Now this unit is not the best when it comes to EMI and so I rummaged through my store and found a few items to make the supply as noise free as possible.

Below is the design of the whole supply. This AT-SMPS is a 200W unit. With a rating of 20A for the 5V rail (100W), about 60W more then the current supply. I'm now able to run a few more Raspberry Pi churning away in the shack.

The AT-SMPS has been stripped down to its bare bones and only the 5V rail is being used. Since I already have enough 12V power available in the shack I did not bother with the 12V rail.

All parts fitted nicely into the original case. Here are a couple of photos of the modification.

Here we see the filtering for the fan, a 220µF and a 0.1µF capacitor and a 10Ω resistor to slow the fan down a bit.

And the 5V output stage with the 135µH choke, the 2200µF capacitor and the 0.1µF capacitor to frame/chassis ground.

This is the little Schaffner FN610, a 10A single stage line filter. 10A is a bit overkill but is was the best size to fit into the case. Since the SMPS already had a single stage input filter I hope that an additional single stage would be enough.

Next I started to setup the test bench to see if I managed to quieten the unit down. 

This is a picture of the noise the SpecAn is picking up with only the mag-probe attached. Note the big spike in the middle at 148.7MHz is one of the local pagers. This pager is causing me endless grief. Working on a solution currently, though. 

Note, the Power supply is switched off.

The above picture shows the probe attached to the power cord of the SMPS.

The next picture is with the power supply switched on and the probe attached to the 5V rail.

Note: No load attached to the 5V rail.

The below shows the noise voltage as measure on the 5V rail with the mag-probe.

The next picture is with the probe attached to the 5V rail, SMPS switched on and a load (LED globe) attached. 

We can see that we have a bit of noise from about 13 MHz on wards. However, it is still less than 85 dB down. But we also can see that below 1 MHz  noise has increased, so let's zoom in, to have a better look.

So from about 200 kHz we see a steady increase of noise to about -18dBm at 10kHz. So the VLF spectrum will be still a bit noisy. However, from 200 kHz to 1 kHz the noise is less than -80 dBm and from 1 kHz the noise is below -90 dBm. So I'm happy with the result.

And the noise voltage between the negative rail and the frame ground measure with a 10x probe.

Conclusion

The VLF/ELF noise might be reduced further if a FN610-3 would be use as this unit has 4.5 time more induction than the FN610-10. Reducing the FAN speed has quieten the wind noises so the power supply is also acoustically quiet. The next few days will show if it is as good as the old 5V regulator (or better).

And yes, "Hot Glue" keeps everything in place.

NOTE: This can also easily be applied to a 12V SMPS or the 12V rail in any of the AT-SMPS. Make sure that you use appropriate electrolytic capacitors though (min 16V better 25V).

Appendix

Schaffner FN610

Differential and Common Mode Noise

SNR, a better way to give a signal report

Or why I believe a 59 report is meaningless!

Receiving an S9 signal doesn't automatically mean that the signal is clear and intelligible. The S-meter (or signal strength meter) gives us a snapshot of the signal strength, but it doesn't tell us anything about the Noise Level (NL) or the Signal to Noise-Level Ratio (SNR), which are crucial in understanding the overall quality of the received signal. A signal might be strong in terms of the S-meter, but if the noise level is similarly high, then the actual communication may be difficult or unclear. Most of today's operators will add an Audio quality report of 5, to make the report 59 which in amateur jargon means that the received transmission supposed to be of excellent quality e.g., an excellent signal. However, to often we hear stations giving a report of 59 or even 59+ only to go on to request a retransmission. Audio quality reports have a scale from 1 to 5 and are given by the operator. With 5 being excellent and 1 being very poor. This relies heavily on the operators HSP, and as we all have experienced, those "Audio reports are ...." well let's say that those reports are not very reliable.

For instance, if the noise level at the receiving station is S8, and the received signal is S9, the SNR would only be 6 dB. Which would mean that the signal is just slightly stronger than the noise. This could make understanding the transmission challenging, even if it shows up as S9 on the meter. On the other hand, if the noise level is low (say S3) then an S9 signal would be much clearer as the SNR is now 6x better i.e. 36dB vs 6dB. 

The Importance of SNR

SNR (Signal to Noise-Level Ratio) gives us a much better sense of how usable a signal is as it compares the strength of the desired signal to the current background noise. A high SNR means that the signal is much stronger than the noise, making it easier to decode and work with. On the other hand, a low SNR means the noise is almost as strong or stronger than the signal, which can lead to poor communication quality or to a completely unreadable signal.

To calculate the SNR we need two signals, the noise level  and the signal strength of the received transmission, both numbers need to be a power level (dB). And since the levels will be rather small we'll use the Decibel in milli Watts e.g, in dBm.

Determining the Noise Level

Determining the Noise Level (NL) of our receiving system is rather easy, all we have to do is tune to a channel where no signal is present and record the S-Value, as shown in the below picture. 

Next we tune to a channel with a transmission and note the recived signal, say S9+10 as depicted below.

Converting S-Values to Power

From the IARU Technical Recommendation R.1:

S1 corresponds to -121 dBm

S9 corresponds to -73 dBm

 And the steps between S-Units are in 6 dB increments. This means:

S1 to S2 = -121 dBm to -115 dBm (6 dB increase)

Above S9 we tend to add a dB value to the S9 value, i.e. 

S9 to S9+10 = -73 dBm to -63 dBm (10 dB increase) 

 

click to view larger file

So, to calculate the SNR:

1. Convert both, the received signal strength and the noise level into power levels (dBm).
2. Calculate the difference between the received signal and the noise level (e.g., SNR = Signal Power - Noise Level).

Using the above values:

Using the above graph we convert the received noise level of S4 to a power level of -103dBm and the received signal level of S9+10 to -63dBm. 

Using the below formula:

 

SNRdB = (Signal-LeveldBm) - (Noise-LeveldBm) 

  

SNR = (-63) - (-103)

 

SNR = 40 dB

This would mean that the signal is 40 dB above the noise level, which is a strong signal and would be very clear.

Conversely, if the received signal would be S9 (-73 dBm) and the noise level would be S8 (-79 dBm), the SNR would only be 6 dB.

While still a reasonable SNR, it would be somewhat noisier than the 9+10 example, and we might find that we would need to ask for a repeat transmission occasionally.

Potential Benefits of Using SNR instead of S-Meter Values

• More Accurate Representation of Signal Quality: 

SNR considers both the signal strength and the noise level, which gives a much clearer idea of the actual quality of the communication link.

• Increased Context: 

By reporting SNR, operators would have more information about whether the signal is being received clearly or if noise is impacting communication.

• Noise Awareness: 

Instead of just reporting a S9 signal, one could be aware of how much noise is present at the receiving station. This could help with adjusting the transmitting stations output power, e.g. increasing the output from 100W to 400W, which is a power level increase of 6dB and as such should, in principal, add 6dB to the SNR.

 

Remember bigger SNR = better signal quality.

Challenges

• SNR requires additional measurements: 

To report SNR, operators would need to be able to measure or estimate the Noise Level  (NL) at their location. This can be challenging if the equipment doesn't provide this information directly. Most modern SDR systems do have the ability to read signal strength as a power or voltage level.

• S-meter and SNR are still subjective: 

While SNR is definitely more meaningful than just reporting an S-value, it still depends on the equipment's ability to measure signal strength and noise level accurately. Again, most SDR systems are very accurate.

Conclusion

Reporting 59 without any context of the noise level doesn't provide the full picture. Shifting to SNR as a primary metric would give operators a much better understanding of the quality of the received signal. It would not only account for the signal strength but also how well the signal stands out from the noise in the environment, leading to clearer communication and fewer misunderstandings.

Incorporating SNR reports into amateur radio communication could definitely improve clarity and signal quality perception. Perhaps this is something more operators could adopt in their day-to-day operations.

Most SDR (Software Defined Radio) already have the ability to report the signal strength as a power or voltage level. A few lines of code and the SNR could additionally be displayed.

Appendix

NOTE: The SNR changes with the receiver bandwidth however, for the purpose of a quality/signal report it is not nesseary to include the receiver bandwith. 

See https://vk5hw.blogspot.com/2022/02/lets-talk-about-receiving-signal-that.html

• HSP  = Human Signal Processor (normally found between the ears)

• IARU Technical Recommendation R.1
• Signal Level Strength Meter Calibration and IARU Standards
• Understand SINAD, ENOB, SNR, THD, THD + N, and SFDR so You Don't Get Lost in the Noise Floor 
• Signal strength and readability report
• Noise Counter-measures
• What is your S-Meter actually indicating
• S-Values are they useful
• A little history about S-Points
• How to achive receiver bliss

Is my NOISE FLOOR (NF) really worse than yours ?

Well, let's answer that question first so you can move on to better things in life. And the answer is:

No it is not, because I use an S-Value indicator (S-Meter) that follows a Standard! The so called 6dB per S-Point (6dB/S) standard!

And that's it, 73 and catch you on the bands (as they say).

Oh, hello you are still here. So, it looks like you would like to know a bit more about this phenomena. Well, then read the below or maybe this "What is your S-Meter Really Displaying".

As far as I know, most Amateur Radios Transceivers from the three main manufactures, ICOM; YAESU and KENWOOD seem to display a 3dB/S scale below S9 (-73dBm). 

So if I read a Noise Floor (NF) of S3 on my S-Meter, which by using the 6dB/S standard would be -109dBm or -2.0dBμV NF.  And my QSO partner, i.e. you, is stating a NF of S2 which, using the applied 3dB/S scale would be a NF of -94dBm or -13dBμV.  

So is my NOISE FLOOR really worse than yours?

Let's have a look at the below two Tables, the left one is scaled in 6dB per S-Value i.e. my S-Meter and the right in 3dB per S-Value like your S-Meter. 

Received Power (Zin = 50 Ω)	Signal Strength S-Value 6dB step		Received Power (Zin = 50 Ω)	Signal Strength S-Value 3dB step
-121 dBm	1		-97 dBm	1
-115 dBm	2		-94 dBm	2
-109 dBm	3		-91 dBm	3
-103 dBm	4		-88 dBm	4
-97 dBm	5		-85 dBm	5
-91 dBm	6		-82 dBm	6
-85 dBm	7		-79 dBm	7
-79 dBm	8		-76 dBm	8
-73 dBm	9		-73 dBm	9

Doesn't that shed some light on this (issue)?

According to the IARU Handbook (Ver 9.0) Paragraph 4.1.3 S-Meter Standards:

1. One S-point corresponds to a level difference of 6dB.

2. On the bands below 30 MHz a meter deviation of S-9 correspond to an available power of a CW signal generator connected to the receiver input terminals, of -73dBm.

3. On the bands above 30 MHz a meter deviation of S-9 correspond to an available power of a CW signal generator connected to the receiver input terminals, of -93dBm.   

It has been a Standard for quite a while, but it seems that it has not been adapted widely.

Signal Level Strength Meter Calibration and IARU Standards

NOISE COUNTER MEASURES, or how to make sure we can hear those new QRP stations!

I did live in a fairly, Amateur Radio Operator populated area (Canberra ACT) with quite a few Amateur Radio Operators close by. Some of them with the same transceiver outfit as me. There were of course slight differences. For instance, my antenna arsenal then comprised of a Multiband Vertical (Cushcraft R8), 40m horizontal loop, non-resonant dipole (ZS6BKW), a 1/2λ 80m inverted L, (RX/TX 80m and RX down to 200kHz) and then a few RX only E-Field and H-Field antennas (MiniWip clone and a Hermes Loop). Whereas most had rotary dipoles on 40m and some even had 2 element beam (Yagi/Uda) antennas. 

And yes, my QTH was on a small suburban block surrounded by houses, which were positioned higher than my Antennas at the back and to the right. To the left they started to climb up gradually and the only real take off was into the NNW at about 280 to 320 degree.

Yes, I've been lucky to be able to get these antennas into the air (I do do dishes and other chores around the house which does give me AR-brownie-points). 

Anyway, what I've noticed is that some of my local Amateur Radio colleagues don't seem to hear as well as I do. The complaint is about NOISE i.e., a noisy receiver.  I do understand that there are differences in antennas, antenna patters, antenna angle of radiation etc. but, most of the time those stations are being heard a lot better than me. However, when it comes to receiving, I seem to be able to hear station on the end of the contact a lot better. Well, It can't be the radio, as some actually have the same radio, an ICOM IC-7610. 

So what could it be? Why would I be able to hear stations a lot better? And I mean most often a lot better. (It could be that I have a better HSP with more HIPS 😏)

Maybe it is the way I use my receivers reception improvement arsenal and so I thought I'll share the way I use the tools my receiver provides to improve my listening pleasure.

So lets have a quick look at the way I conquer some of the noise.

Please note, that these are some of the things I do to help me overcome QRN and even some QRM. This is not a blurb about technical specs, even though I might throw some into the mix. This is more a HOWTO get the best SIGNAL to NOISE (SNR) performance out of your system, i.e. the system made up of the receiver/transceiver, the antenna and not to forget the antenna cable. Being able to receive and understand a station that does not move the S-meter up to the S9 point but still has reasonable good recovered audio quality even if the signal strength is as high as the band noise floor.

First up a disclaimer, I do not talk about the "OH NICE SIGNAL 59+20", sounding like John Laws and are > 3 kHz wide, no I'm talking about stations that are in or just above your received noise floor. And second, I refer to Single Side Band (SSB) but will show the effects on a CW signal to make it easier for me to show the effects.

We know that our receivers have BIG EARS. For instance the Minimum Discernible Signal (MDS) of my ICOM IC-7610 starts at about -122dBm and goes to over -140dBm [1]. Basically what that means is, that the radio is capable of hearing the proverbial fly fart. 

I would like to see the ambient noise floor at my QTH go that low but according to ITU P.372-12 the noise floor at my QTH should be about -91 dBm at 7 MHz (S6) (Note: an accurate S-Meter is required to confirm this). At the new QTH, here in VK5 land it is slightly better, by about 9dB.

Which is still a far cry away from -122 or even -140 dBm of which the IC-7610 is capable of achieving (sorry about the technical digression).

To show you what I'm talking about I've been taking some screen shots which show what can be achieved by applying the following, let's call them receiver-improvement-tools, to improve our receiving pleasure. The setup for the demonstration comprises a SDR-IQ withand the following software SpectraVue Ver. 3.39 and SBSpectrum Ver. 1.31. 

To have a steady signal I'll be tuning the radio to our local NDB (ground wave) at this frequency the noise is still high and the signal will be at a constant strength for the duration of the test. This makes it easier to show the effects of the applied countermeasure. 

So here is a list of the Tool Set I've been talking about.

• RF-GAIN control
• RX-Attenuator
• AGC
• RX-filter bandwidth

If we apply any or all of the above appropriately we'll be able to dig out signals that are difficult/marginal to hear/understand. What we are doing is what is know in professional circles as the improvement of the Signal to Noise Ratio (SNR). It does not mean that the signal strength will increase, most likely the signal strength will be lowered. However, not only the signal strength will be lower but also the received noise. And, this is the aim of the game,  if we apply our toolset appropriately we will reduce the noise level more than the received signal! And as such we will have improved our SNR.

Let's start with our receiver bandwidth (RX-BW), some call it the channel bandwidth, e.g. the frequency span the receiver is listening too. Receivers have a basic RX-BW of about 3 kHz. And most Voice transmissions are with a 2.8kHz transmit bandwidth (TX-BW) (yes, yes I did say most).

Now if we look at those number we can see the we already have 200Hz unused RX-BW and this 200Hz is filling our receiver with noise (RX-BW3000-TX-BW2800=200Hz of noise) Imagine if the transmitted signal would have a TX-BW of 2.4kHz and we would receive the signal with a 3 kHz RX-BW. We would now receive 600Hz of additional noise. To improve the quality of the signal we would need to get rid of the 600Hz of noise. 

In the olden (Golden?) day's we added X-Tal filters to limit the ingress of additional noise (a quite expensive exercise let me tell you). However, this is were the new breed of SDR's shine, they use "software" to do the filtering and some of those software filters are exceptionally good. Additionally they are very flexible, with soft or hard skirts etc. You'll be able to adjust the RX-BW quite easily to adapt to the transmitted signal.

So by adjusting the RX-BW to the TX-BW we would improved the SNR by 600Hz.

On a good receiver S-Meter, one would be able to see that the noise floor has dropped and the signal has gone up. 

Let's have a look how that would look in real life.

The grey area is the noise that we are receiving. Looking at the bottom CW signal we see that we can see (hear) it but it is quite buried in the noise. Taking away the noise by limiting the RX-BW we are able to see that the signal becomes more darker, almost black. It is now popping out of the noise and listening to the signal it is more audible, e.g. clearer and more intelligible. If we widen the RX-BW again it becomes clearly visible that the signal loose's  its intelligibility, as it is fading back into the grey again (picture below).

For me reducing the RX-BW is one of the most effective ways to improve the received signal quality. Even if I receive a signal that does not limit its TX-BW to say 2.8kHz I always run 2.7 or even 2.1kHz RX-BW on SSB. I even go as low as 1.7 or 1.5kHz RX-BW if the going gets tough but that has mostly to do with adjacent channel QRM. 

If you tune above 7.2MHz at night you will find some US Amateur Radio Operators there between the big AM BC stations. And those narrow filters make it possible to hear those station without to much interference from those potent signals.

What we have done is we have limited the receivers SIGNAL+NOISE ingress e.g. we've improved the SNR. The net effect is that the SIGNAL we are interested in, SOUNDS clearer/louder.

 

Another tool in our receiver-improvement-tool is the Automatic Gain Control, the AGC. Most modern Amateur Radios have the ability to adjust the TIME CONSTANT (ATTACK TIME) of the AGC.

The below picture shows the AGC disabled and then enabling the AGC, the noise disappears and the signal pops up. It is worth while playing around with the AGC time constant. This is a bit of an art form and it is quite different between radios and the design of a radio. I have three different settings on my radio for different noise events/modes. I have a slightly faster AGC recovery time for thunderstorm/lightning QRN then I have for quite band conditions on 10m. Also I have different timing setups for different modes (SSB, CW, DIGI).

Switching the AGC off and riding the RF-gain can also improve our listening pleasure. Below you can see me adjusting the RF-gain manually (this is called riding the RF-Gain) to bring the signal out of the noise. However, as you can see from the above picture, a proper adjusted AGC does do a better job than I can do.

The next picture show a combination of AGC and manually adjusting the RF-gain.

I wish it would always be that easy.

Instead of ridding the RF-gain, most radios have the ability to add predefined attenuation. The below picture show similar results as using RX-BW limiting and predefined attenuation switched in and out.

Below is a good view of the AGC in action. As soon as there is no signal, the AGC increases the gain (darker grey), but as soon as the signal shows up the AGC reduces the gain enough for the signal to pop out of the noise.

So, as you can see we have a great arsenal of tools available to BETTER our receivers ability to get the desired signal out of the noise, or to phrase it more appropriately, to ease the HSP between our ears to only work on the SIGNAL and not needing to apply filters to remove the noise (remember the HSP has limited HIPS).

Please remember that I used a CW signal for display purposes only, this will work equally well for SSB and even for some DIGITAL modes.

On 7 MHz (40m) and below I use between 9dB and 24dB attenuation as atmospheric noise levels are high on these bands. Start with whatever you feel comfortable with. Next I'd setup the filter bandwidth to remove the higher pitched noises, the noise above 2.4kHz and then I adjust the filter to cut out the low rumbles, the noise below 100 kHz. My RX filters are set at 2.7 kHz, 2.1 kHz and 1.7 kHz for SSB, low cut at around 100 - 200 Hz for example, my 2.1 kHz filter bandwidth is setup as 200 - 2300 kHz. And last but not least, adjust the AGC to your liking. My preference SSB AGC settings are Fast 1.2, Mid 2.0 and Slow 6.0.

The AGC, RX-gain and RX-attenuation are basically controlling the overall system gain, which does includes the gain from your Antenna System (Antenna, Cable, ATT, LNA etc.).

The RX-gain/attenuation values will be different for a lot of situation it depends on a lot of factors i.e. the mode of operation, what antenna is being used, the frequency of operations, the operator mood, the time of day, band conditions etc. etc.

However, as you get more and more familiar with your radios rx-tool-set you will not only get more and more pleasure out of your receiver (station), you will also manage to finish more contacts with ease.

Remember, you will need to play around with the setting until you find a setting that sounds/feels right to you. The above are setting that work for me and should only be seen as a guide. Your environment, radio, antenna, HPS and HIPS are different. 

Let me mention a few more tools that some of the radios provide or are external items that would improve our listening pleasures. An additional AF filter (Equaliser) can help in reducing noise, Digital Noise Reduction Systems (NR), which most newer radios have built in. 

Note however, that some noise should be removed before it hits the AF stage of your receiver. Some of the digital (DSP) Noise Blankers are quite impressive and then there are the Notch Filters, either the automagic ones or the manual ones (the manual dual notch filter in the IC-7000 is quite amazing).

 

There is one (two) more thing(s) I would recommend and that is using a decent speaker or two if your transceiver has two receivers. And lets not forget a good set of headphones, which will bring the recovered signal directly, without any additional noise to the HPS. 

There are of course additional measures we could apply. Like the use of a low noise receiving antenna or the use of antenna diversity.

I worked my best DX with a noisy vertical as a TX antenna and a quieter RX antenna (see above my antenna arsenal).

73 and good DX.

Footnotes:

1. The sensitivity of the receiver is dependend on the size of it ears, e.g. the RX Channel Bandwidth. The smaller that bandwidth the higher the sensitivity, the better the SNR!

HSP  = Human Signal Processor (normally found between the ears)
HIPS = Human Instructions Per Second (it has been said that a man can only do one HIPS) 

DX   = Normally used to refer to a station on another continent. From the old telegraphy  abbreviation for Distance eXchange.

SBSpectrum V.1.31 by Peter Martinez G3PLX
SpectraVue V. 3.39 by RFSPACE Inc.
SDR-IQ by RFSPACE Inc.
DXing

NOTE: This has been reposted from my old VK1HW web page and was initially written in 2018.
© ¼ ½ ¾ ⅜ ⅝ @ π ω µ Ω ε η λ °