Ham Radio In Any Neighborhood

From these amateur radio pages, one can get my enthusiasm for ham radio. I am finally to the point I am going to install my stealth magnetic loop antenna in my HOA regulated backyard. I spent nearly two years building the loop itself and perfecting the control mechanisms and PLC controller.

However… I’ve got a problem.

Millionths of a Volt

Surrounded by Damn Noise

The sensitivity of a good radio receiver is what makes continental and intercontinental (DX) ham radio possible. In among the slight noise common to radio are faint signals of people speaking from around our globe. It is the sensitive equipment that is capable of receiving these weak signals, filtering them, amplifying them, and make them intelligible.

Most hams use relatively low power to communicate with each other. Ham radio by law is limited to 1,500 watts peak input power applied to the antenna feedline. But for most hams, the power output used is between 100 to 500 watts. That’s enough to make QSOs (contacts) to the far corners of the globe, as far away as South America, Europe, Russia, China, or Australia. The emphasis is not on high output power, rather the transmission methodology, the antenna, and the receiver.

A receiver’s specs include sensitivity as well as selectivity. Ham receivers are capable of receiving signals down to 5 to 10 microvolts on a very narrow bandwidth. The problem is even though a receiver can filter out adjacent noise as well as conditioning the received signal, it has trouble filtering out random radio waves on the same frequency.

However… There is a more recent issue that has arisen and is plaguing the worldwide ham community.

In an email I send to the MagLoop Group.io, I talked about the supposed clarity of ham radio. I told them of my dilemma about all the noise on the bands. They responded talking about noise traps and antenna placement. This did give me some hope. But after some investigation, I found my situation is not unique. Apparently, most hams have the same problems with noise as I do

The difference between the time in 1965 when I heard ham radio for the first time and now is significant. Today we are inundated with something called switch-mode power supply noise or QRM.

These hideous things generate a significant amount of broad-spectrum electromagnetic noise. This issue is a more recent phenomenon – within the last 20 years. With all the electronic devices we now have in our homes, there is a lot of generated spurious noise clogging the airwaves.

Switch Mode vs. Linear

Up until early Y2K, most power supplies used a large transformer to step down the current for use in electronic devices. These devices emanated no RF noise because they used a chunk of iron and copper to reduce the voltage. But because everyone wanted cheaper more efficient power supplies that were light weight, we as a society adopted switch-mode to save size, weight, energy, and costs.

A switch-mode power supply is a device that produces low voltage DC current. These devices rectify and filter the incoming AC mains power into DC. It then employs a switching circuit that modulates this DC current at a very high frequency (10 to 50kHz) and passes this through a tiny transformer which steps down the voltage. With the high frequency of a switching circuit, resistance is very low enabling the use of a very small inexpensive transformer. The output of the transformer is then rectified and filtered to DC making it useful for powering the various low power electronic devices. The problem comes with the sudden sharp on-off switching of the high frequency which generates noise on a number of harmonic frequencies.

These switch-mode power supplies can be found in just about every device we now have in our homes. These include appliances, HVAC, TVs, DVRs, tablets, laptops, alarm systems, smart speakers, the plethora of wall-wart chargers we use, and so on. This now also includes LED lighting.

The question then arises, doesn’t the government regulate the production of these power supplies? Well, they use to. But because these devices are low-power and most people no longer rely on RF to receive their news, information, and entertainment, the regs have become laxed.

Preamp off, gain at 1/4..

It is not the noise of one power supply that is the issue, rather the proliferation of these devices. It is the noise of thousands similar to white noise that raises the noise floor. 

There are no standards as to how a power supply is to be designed and manufactured. As a consequence, each has its own characteristic signature. And when a ham lives in a neighborhood with tens of thousands of these things… Well, you get the picture.

So, how do we get rid of the noise? The answer for a lot of hams is in their antenna placement, getting it up high enough.  Many seek to live somewhere far from any neighbors - at least 1 km or 3280 feet from the nearest neighbor.

My God! What a disappointment.

So, if I knew then what I know now, what would I have done? I’m talking about HOA regs on antennas and now tens of thousands of noisy wall warts, appliances, TVs, etc., etc., etc. What would I have done. Bought a house far from… Or, not do ham radio? Because of HOA regs, I can’t put up an antenna high enough in the air.

I’ve already spent lots of time and money on building loop antennas and purchasing the necessary radio gear and all its paraphernalia.

Now what do I do?

In my home I can easily replace switch-mode power supplies with linear supplies, add RFI traps to everything, or totally turn off devices when not in use. But I can’t do anything about my neighbors who are within ear-shot of my receivers.

Again, what a disappointment.

I took a portable battery powered HF rig on a little hike. As I walked away from the various houses to a field, the interference cleared up to the point QSOs were very clear – without filtering.

This really sucks.

Every electronic device that has recently been manufactured and derives its power from a wall socket is going to generate extraneous noise. In the “Old Days” a manufactured switch-mode power supply had to meet US FCC or Canadian ISED regulations and were marked accordingly. But now…

Will this situation get worse?

It’s time for someone to design a software driven receiver that has enough artificial intelligence which can distinguish the difference between RFI and an actual harmonic signal.

September 3, 2022