Noise – Quick and Easy things you can do

This is a copy of the Talking Tech Power Hour on the Sandton Repeater on 27 April 2022 at 19:00 CAT, entitled “Quick & Easy Things You Can Do Today To Reduce Noise In Your Shack (and a few you shouldn’t)”

Click Link to download a PDF version –> Noise Discussion ZS6STN 

Outline Starts Here:

Good evening. Thank you for the privilege to modulate your airwaves for a few minutes. My sincere thanks to the Chair, Matthew, and all the other important guests, many of which I know and have met before e.g. Justin / Henry & many others and all the listeners.

Special mention to SK Willy Wilson F.I.L. who rescued me from raging teenage hormones when I was a young man. As an experienced radar tech his favourite saying was RF is art, not science. Wise man.

Also the invaluable inputs from Ian White, GM3SEK, and Bob Brehm, AK6R, and others who took the time to publish some of their knowledge.

Disclaimer: I’m only sharing my own personal experiences and opinions and while I hope you can find some useful hints tonight, you are solely responsible for your own results and you should at all times check our own data and keep safe.

  • Talking Tech Power Hour 1/

I was asked a while ago if I would like to share a few words about noise, a popular and sometimes emotional topic amongst amateurs.

Now I’m not an expert. I have burnt my fingers and/or or given up all hope too many times. But I have learnt a few lessons.

As an ex-electrical engineer I hate to admit this but occasionally I’m going to tell small white lies when I’m explaining something, to make it easier to understand.  Sometimes I might also sound (pun intended) controversial in order to highlight a particular issue. It is all in good fun.

So let me start with a very controversial point: We (hams) are making the most noise ourselves!  (at least 10dB more than the noise floor!)

Now before you hunt me down and poison me like Putin, let us go back in history a little bit – all the way to when radio started. Isn’t it true that the very first transmissions were created by – horror of noisy horrors – spark transmitters? Didn’t they deliberately create noise in the hope that someone else could hear them?

  • Talking Tech Power Hour 2/

The spark gap radios wanted their desirable noise to be stronger than the ambient or background noise. And this is an incredibly important point.

–> As long as your desired noise is stronger than the ambient noise, you can proceed to try and decipher/decode/interpret it.

This is critical: In order for you to hear and understand the sending party, you would search for his noise where it is higher than the background noise.

So take another more modern example: When you leave your cell phone too close to the car radio it will respond with a brrrrrrrrr. Is that intelligible? No, it is noise, unless you can interpret it. You must apply the right decoder (or demodulator) to the noise before it becomes useful and turns into information.

Therefore: The first principle of radio is that we create noise is the very thing we create (use) to communicate.

 

Yes, we shout harder.

  • Talking Tech Power Hour 3/

Which reminds me of the delightful story of the two guys who went camping. In the middle of the night they are woken up by a lion that is trying to rip open the tent and they are starting to run away with the lion in full chase of course.

Soon the guy in the back says to the guy in front: “Why are you running so fast?”

And the guys in front, without breaking stride, replies: “I don’t have to run any faster. I only have to run faster than you.”

This is the principle: You don’t have to be the loudest or the most powerful signal. You only have to be 10dB above the noise floor.

  • Tonight’s Focus Areas

I would like to use the first few minutes just to point out the environment in which we operate. It is really important to check out how we got to where we are and what is happening around us.

Then we will move on to look at how a little knowledge can go a long way to help us, but that it can also cripple us or confuse us. Shine some light on S/N

This discussion wouldn’t be complete without revisiting  two of the basic electrical formulas: Ohms Law and EMI  and how they help us.

Finally we can move on and talk a little about the specific things you can potentially try to improve matters.

Finally my disclaimer: You are on your own and I’m not responsible if you fall of ladders or do other silly things.

  • Focus Area One: Spectrum 1/

In the beginning when only a few stations could made the sparks fly, ether wasn’t considered a constrained resource.

Today, RF Spectrum is a valuable and scarce resource and the pressure to get more spectrum is immense. Mobile is pushing hard for more spectrum – and they have money. Just read the news on how many billions ICASA got for the auction of mobile spectrum. The “Golden Rule” applies – the guy with the gold makes the rules

Being a constrained and global resource, users are licensed or permitted. An amateur license is a privilege granted to experiment with all modes and types, not just to talk on 40 or play hamnet (*). As amateurs we have been granted a few generous slices of that valuable spectrum, but there is no guarantee that we will be able to keep it or that intruders will not encroach on it.

We can expect over time to experience much more push-back from industry and less sympathy from other competitive demands

Use it or lose it! Experiment more and talk less!

  • Focus Area Two: Knowledge 1/

When the sparkies started their sparkling experiments, they probably didn’t know how (or have the tools) to measure anything.

Today we have a much better understanding of the parameters and I want to focus on noise.

Definition time: dB – it is a ratio of power or voltage etc.
Easy to add or subtract. 3dB is double, 10dB is ten times.

S/N Signal-to-Noise ratio, like the guys who ran away from the lion
you only have to be slightly louder than the noise, usually 10dB
R = V / I or the important variation: I = V / R – current in a wire is what
radiates the RF, either good noise or bad noise

Typically one might expect to see a figure in the region of 0.5 microvolts for a 10 dB S/N in a 3 kHz bandwidth for SSB – basis?

  • Focus Area Two: Knowledge 2/

When we started tonight’s talk I promised not to tell the truth, not the whole truth, and definitely not only the truth. So here is my layman’s explanation of how the S/N ratio can spoil your lunch.

Way back in the beginning when I started with my radios with the older analogue radios, the MDS (Minimum Discernable Signal) was maybe around 90dB or slightly better and the limitations were mostly receiver noise in the front end.

Recently I purchased a Xiegu X6100 (same as Matthew) and I was picking up noise that my Yaesu was oblivious to. After much wringing of the hands and digging deep into the specs I found that the X6100 has a MDS of 138 dB … that is so sensitive and almost GPS territory!

And remember – we still only need 10dB S/N to decode a signal

  • Focus Area Three: EMI 1/

Electro Magnetic Interference according to the professors that know everything, has three elements and all three must be present before you can have EMI. They are:

1: A Source    2: A Coupling (or Path)   3: A Victim

Be aware that you could be or are part of the problem in all 3 areas.

With RF, multiple paths or couplings are very common:

Radiative – air.  Conductive – wire.  Inductive – wires. Capacitive – wire.

A Source: It’s all your fault with that big antenna!

( I used to issue an award jokingly called: “Worked All Neigbours”)

  • Focus Area Three: EMI 2/

Are you a Victim? Definition: “… a disturbance (ed: noise) that acts on an unintended receiver”    -> no FUN!

RFI Sources:

Ham Antennas (not only the one you are transmitting on)

Radiating Coax (our favourite Tri-pole)

Electronic Devices (they have become ubiquitous)

Solar Systems (not always the culprit)

Grow Lights (yassss!)

HVAC motors (or at least the controllers)

In the lounge: Plasma TVs and LTE / Fibre Routers

Switching power Supplies (this is a big one)

Washer/Dryer or other kitchen appliances

  • Focus Area Three: EMI 3/

Electrical Theory

I (RFI Current) =  E (TX voltage) /  R (Choking resistance)   [I=E/R]

à Objective: Reduce the current ( I ) that causes RFI

In order of priority:

  1. Shut down the SOURCE (Set E to zero)
  2. Choke the PATH (minimize E, increase R)
  3. Protect the VICTIM (Set R very high)

Elaborate somewhat.

  • Typical RFI Manifestation
  • Focus Area Four: Actions 1/

Ask any Ham (Amateur) what to do about noise and you will get a quick simple answer. Oh, the answers are not always the same but they are quick and precise and described in great detail!

This reminds me strongly of another indightful story.

I graduated at the Univ of Pretoria in 1974 and the story also goes back to the same year – 1974 – when the physicist Richard Feynman delivered his commencement address at the California Institute of Technology. During his speech he mentioned “Cargo Cult Science” which is defined as a pseudoscientific method of research that favors evidence that confirms an assumed hypothesis. In contrast with the scientific method, there is no vigorous effort to disprove or delimit the hypothesis.

  • Focus Area Four: Actions 2/

Cargo cults are religious practices that have appeared in many traditional tribal societies in the wake of interaction with technologically advanced cultures. They focus on obtaining the material wealth (the “cargo”) of the advanced culture by imitating the actions they believe cause the appearance of cargo: by building landing strips, mock aircraft, mock radios, and the like. Although cargo cult sciences employ the trappings of the scientific method, they fail to deliver anything of value.

Feynman adapted the speech into the final chapter of his book “Surely You’re Joking, Mr. Feynman!”. He based the phrase on a concept in anthropology, the cargo cult, which describes how some pre-industrialized cultures interpreted technologically sophisticated visitors as religious or supernatural figures who brought boons of cargo. Later, in an effort to call for a second visit the natives would develop and engage in complex religious rituals, mirroring the previously observed behavior of the visitors manipulating their machines but without understanding the true nature of those tasks. Just as cargo cultists create mock airports that fail to produce airplanes, cargo cult scientists conduct flawed research that superficially resembles the scientific method, but which fails to produce scientifically useful results.

  • Focus Area Four: Actions 3/

Action 1: I’m going to quote Terry Mackenzie-hoy In Engineering News: “The first principle is that you must not fool yourself – and you are the easiest person to fool.”

à Always check the facts.

Action 2: I’m going to quote Bob Brehm, AK6R, of Palomar Engineers who supplies ferrites to Amateurs: “When in doubt, add a choke.”

à Always use Chokes (ferrites).

Action 3: Never buy a box of ferrite rings (toroids) without knowing their exact characteristics. You will be disappointed. Aim for a choking resistance > 500Ω over frequency range used.

à Always buy from a reputable source

  • Focus Area Four: Actions 4/

Action 4: Speaking of which … I started with Ugly Baluns and they do have some choking effect, but are seldom sufficient.

à Always use a Current Balun – they have better choking.

Action 5: Dipoles are so … 1970’s …. but since many older people believe them to be superior (Cargo Cult remember), please do not deliberately turn it into a Tri-Pole

à Always use a Balun with your Dipole to prevent RFI feedback

Action 6: Consider ALL the other gear and equipment. While it would make matters much more simple if everything can be thrown at the Cheap Chinese LEDs (or solar or …). I wish I had a silver bullet.

à Always check every electrical apparatus for noise

  • Conclusions
  • The fight for spectrum is going to result in an ongoing escalation and conflict

–Our “rights” are not entrenched

  • Interference needs a source, a path, and a target

–Don’t leave the garden gate open

  • EMI Electromagnetic Interference is a complex topic with no simple answers

–Although the basics are well understood (by experts)

  • We have some very good tools to fight the interference
  • End Of Formal Presentation
  • What happens with more than one?
  • In Series – just add them

More beads = higher choking R (up to 30 MHz)

e.g. at 7 MHz:

5 beads = 400Ω

10 bead = 1000Ω

15 beads = 1600Ω

  • Extra Turns – SQUARE them

Ferrite resistance increase as (turns)2

  • If 1 turn = R, 2 turns = 4 x R,
    3 turns = 9 x R !!
  • More R = less RFI wire current = less RFI radiated from wire or induced into wire. (I=E/R)
  • General rule: choking R > 10X line impedance
  • (e.g. > 500 Ω for 50 Ω cable but 5000 Ω is 10x better)

e.g. at 7 MHz: 100Ω 900Ω 2500Ω

  • Is your Dipole a Tripole?
  • Coax outside of braid acts as extension of transmitting antenna and extra receive antenna
  • Choose choking resistance > 500Ω over frequency range used
  • Further Conclusions
  • There isn’t one silver bullet solution
  • There isn’t one super-supplier of toroids
  • Don’t buy a box of “rocks”
  • Don’t believe a word anyone “says”
  • Determine RFI interfering frequency & suspected path
  • Douse at RFI fundamental frequency
  • Choose best topology (slip, snap, ring) to fit the Path “Antenna”
  • Install ferrites – then retest for RFI suppression
  • Add additional ferrites or paths if RFI persists
  • The End – Thank you!
  • Further Reading 1/
  • Noise in HF radio systems definition: Typically the input voltage for a signal to noise ratio of 10dB is stated. For an HF radio communications receiver, typically one might expect to see a figure in the region of 0.5 microvolts for a 10 dB S/N in a 3 kHz bandwidth for SSB or Morse https://www.electronics-notes.com/articles/radio/radio-receiver-sensitivity/signal-to-noise-ratio-s-n-snr-formula.php
  • Very good copy and paste material (restaurant) https://kf6hi.net/radio/SNR.html
  • Good explanation of s/n over the noise floor of the receiver http://www.k0bg.com/signal.html
  • Refers to video https://qrznow.com/radio-receiver-signal-to-noise-ratio-snr-specification/
  • The moment your noise has some pattern – in effect becoming an interfering signal – all bets are off. (assume white noise)
  • http://play.fallows.ca/wp/radio/ham-radio/signal-noise-ratio-essence-radio/
  • Cargo Cult Science
  • https://en.wikipedia.org/wiki/Cargo_cult_science
  • Further Reading 2/
  • Common-Mode Chokes by Chuck Counselman, W1HIS
  • A Ham’s Guide to RFI, Ferrites, Baluns, and Audio Interfacing Revision 7 Jan 2019 Jim Brown K9YC
  • https://qrm.guru/the-truth-about-ferrites/
  • https://qrm.guru/category/qrm-kill-kits/
  • https://youtu.be/Ivr9VbSgjUU
  • https://youtu.be/p5vw3cq3DkQ
  • https://www.vkham.com/resources/reference-info/ferromagnetic-information
  • https://rrc.org.au/2020/07/10/some-ideas-for-rx-noise-reduction-and-a-mains-filter-for-your-radio-shack/
  • http://www.m0nwk.co.uk/mains-electricity-filter-for-emc-noise-reduction/
  • https://youtu.be/xF2wFJBpu_I (DX Commander)
Tags: