Some thoughts and observations on the RSP1a and EMI

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Some thoughts and observations on the RSP1a and EMI

Postby Nulluser00 » Sun Sep 02, 2018 1:57 pm

Some thoughts and observations on the SDRplay RSP1a and EMI, AKA RFI or Radio Noise.

I suggest anyone interested in understanding their EMI take a look at:
is the first of three pages that show one way to use a SDR for a RFI <EMI> survey.

I'd already developed another technique that has proven very useful to my coworkers and I. I've added some of the ideas nk7z presented to allow automated collection of data over several days.

NK7Z and I had different goals, I wanted to map out and pinpoint EMI sources, he wanted to log the EMI data from one location over an extended time span and derive conclusions about the probable source of the EMI. There are strengths and weaknesses to each approach and I suspect both need to be combined in most locations to be effective.

I've been interested in "radio noise" every since my I bought my first SW when I was 10 years of age.

I couldn't understand why the DX-398 worked just fine in the nearby city park but inside our home all those distant stations were buried by "Radio Noise."

Our next door neighbor was retired EE who took an interest in a very confused 10 year old boy. She helped me install a decent antenna, explained why there was so much noise in and near our home, my parents were software consultants and there were always computers, printers, servers, routers etc turned on and producing "radio noise." She explained there were two types of "Radio Noise," man made and natural. She also explained the proper name for "Radio Noise" was EMI, "ElectroMagnetic Interference."

It was easy for her to demonstrate EMI, all we had to do was approach any of the computers or accessories with the SW radio. The EMI even wiped out commercial FM stations!

A few months later my parents moved the bulk of their hardware to a small office park and the "Radio Noise" around our home markedly decreased.

I was impressed by our neighbor's knowledge and followed her career path and went to university to become an EE. I debated on specializing in some form of "radio," but realized that would be a very limited market tied to larger cities, I decided to go for "power generation, distribution, instrumentation and measurement."

I've just completed my master's and have been accepted in the college of engineering Ph.D program. My research and thesis will be on EMI with emphasis on "The impact of EMI on ELF~HF communications."

Don't get me wrong, I am almost as far from an expert as one can be, most of what I've learned has been from trying to solve my homegrown EMI issues.

The "Instruments and Measurement" classes along with general electrical theory have been the most useful "formal education" I've received.

After my parents and younger sister died in a house fire caused by the HVAC company failure to properly bond the CCST, corrugated stainless steel tubing, to the residential service electrical ground, I moved to Central Kentucky to be near my extended family.

I have been dismayed by how few SW, ham radio, or business band, antenna installations have any relationship to "approved and safe practices." I won't lecture, but I'll say losing your family because an electrician was too lazy or cheap to take the time to properly ground a natural gas tube has been an education I could well have done without. My family died for less then an hour's labor and ~$20 in wire and connectors. Take a hint from me, the insurance money isn't as nice as having your family.

I work part time for my aunt, a PH.D EE, licensed Master Electrician and an Extra Class Amateur Radio licensee. She owns a small engineering consultancy that specializes in "electrical infrastructure design, renovation and project oversight." We do everything from help plan new power plants, power plant upgrade and renovation, electrical distribution, high tension line routing, rerouting, electrical sub station design and installation, down to electrical wiring for new developments.

All of my coworkers are amateur radio operators. While they've just about given up to converting me to the dark side, becoming a ham, they are wonderful data base of practical experience and have never hesitated to help me understand the practical, real world, consequences of man made EMI.

Theory is theory, all nice and neat, and the real world is real, and very messy.

The consultancy just upgraded their computers and I've ended up with some HP Elitebook notebook PCs. I've adopted a HP2730p for my EMI survey work. The metal case reduces the EMI footprint to acceptable levels.

While I've designed and fabricated a nice selection of EMI probes, the one that has been most helpful for large area EMI mapping has been a "E-Field" active antenna. There are many designs publicly available and I am not claiming my choice is the best, but it works.

As an professor in Introduction to Engineering Principals told us "Perfect tomorrow is the enemy of good today."

I use PA0RDT's design, it uses a J310 and 2N5109 transistors, a handful of discrete components and offers acceptable performance. The main weakness isn't necessarily the PA0RDT design, but the fact all "E-field" active antennas are extremely sensitive to EMI caused by common mode current. I suggest anyone remotely interested in weak signal reception look up and study, and I mean study, think about, Common Mode Chokes by W1HIS. Any netsearch will return several hits. W1HIS made the document freely available.

My initial HP2730p/PA0RDT/RPS1a survey system was, to be charitable, rather awkward. One of my coworkers, our IT goddess, suggested mounting the PA0RDT electronics inside a hard hat and mount the actual antenna on top of the hat. She works with ARES and has experimented with a 2M HT feeding a hat mounted antenna. Her argument was it leaves your hands free. Since my hands were busy with the HP2730p, I adopted her idea.

It wasn't too difficult to mount the PA0RDT electronics and antenna on the outside of a plastic hardhat and line the interior with aluminum foil to couple the 'ground' of the antenna to my body.

[Least anyone try to kid you about trying to block alien mind control rays, laugh at them, everyone knows it requires gold foil.]

The PA0RDT "E-Field" antenna doesn't require a large antenna. I've found a 5" thin spring works fine.

I've added a USB GPS to allow recording the precise location and tie this to screen or audio captures.
We routinely use laptops in the field and use neck strap carriers to allow easy data entry and retrieval.


Trust me, either purchase a commercial unit or make your own, you do not want to try walking, using the keyboard and touchpad while trying to hold the laptop. I never dropped a PC but coworkers have.

I've made a very detailed EMI map of the area around my home out to about 1 mile. Because EMI is like any other radio signal and follows the inverse square law, double the distance and quarter the signal, my EMI map has more data points closer to my home and fewer as the distance increases.

I've also walked the power line right of way to pinpoint noisy hardware out for around 6 miles.

A US Geological Topographic map can be your best friend when planning power line EMI hunts.


My coworkers and I have used a similar lashup to pinpoint cable TV/DSL leaks and to locate a bad telephone concentrator that was radiating broadband EMI and wiping out anything weaker then S7 from 100KHz~30MHz for several miles.

We used a work vehicle and an E-probe antenna designed by W0QE [
pole_amplifier.html] to make area EMI survey maps around all my coworkers homes. This should allow us to do monthly spot checks to see if the ambient EMI levels have increased.

It would be nice if the Android package supported the RSP1a, but the RSP1 is adequate for informal EMI surveys. We initially built a "go package" consisting of a Dell Android tablet, RSP1, PA0RDT "E-Field" active antenna on a wand and used it to do rough checks on electrical substations and other electrical infrastructure. This has been replaced by a Rohde & Schwarz portable spectrum analyzer. The "go package" proved the concept. We formerly contracted these tests out and have saved enough in 3 months to pay for the professional equipment and hire a part time hiking enthusiast.

Grace can walk any five of you into the dirt. She thinks nothing of a 10 mile stroll before breakfast.

The biggest advantage of integrated commercial EMI survey equipment is the ease with which non technical people can be trained to use it.

I'm not foolish enough to think my HP2730p-RSP1a/ "E-field" antenna can replace the
Rohde & Schwarz portable spectrum analyzer, but it is affordable and more then adequate from a hobbyist's perspective.

I checked the local used computer store in Lexington KY and the HP2730p is available for $125 with the snap on auxiliary battery that extends operating time to at least 5 hours.
The PA0RDT shouldn't cost more then $10~15 if everything is purchased new. The RSP1a costs ~$100.

Some testing has shown most residences have a few RF quiet locations in their backyard. So far there are no clear patterns; I mean locations I would have bet would have been very noisy were very quiet and the reverse was also true. The only way to be sure is to test several locations. I had hopped to come up with some general guidelines, but that appears to be impossible.

I realize suggesting the use of a traditional, non-SDR, SW radio is an anathema to SDR enthusiasts, but the truth is it is easier to do quick go/no go tests with a portable SW radio. I used a Sangean ATS-909X but Katio offers suitable radios that are quite a bit less expensive.

Use the SDR to pinpoint specific trouble frequencies, and the regular SW radio to quickly prove/disprove any given area.

Be prepared for some odd looks as you do EMI surveys. I've had the police stop and question me several times. My work ID and university ID have allowed me to avoid any unpleasantness.

So far.

I moved into the house my parents had intended to be their retirement home. It's in the middle of kinfolk, in a rural area with an agreeably low ambient RF noise floor. Shortly after I moved here the heat pump failed and I decided to replace it with a geothermal, ground coupled, heat pump. Our corporate attorney wrote an iron clad "This installation must meet all requirements of the relevant FCC rules and regulations." The HVAC company and manufacturer lost money on the installation. It was my first "up close and personal experience" with serious EMI. The variable speed pumps were an amazing source of EMI. After all the work I could still detect very low levels of EMI from the pipes buried ~6 feet deep. They used a mixture of tap water and antifreeze. The tap water was conductive enough to carry significant EMI. The solution required flushing the system with distilled water, refilling with a mix of distilled water and antifreeze. While the HVAC company is not terribly fond of me, the EMI is now so low the ambient RF noise floor is higher except on a few winter nights. For those super quiet nights I use the woodstove to keep the home warm.

I've taken what many might call extreme EMI mitigation steps. There is a 500A EMI filter on the AC mains just behind the KWH meter. Each circuit breaker HOT is bypassed to that circuit's neutral with an approved safety 0.1uF capacitor. I've replaced all the incandescent light bulbs with LED replacements. I had to add EMI filters in or behind each light fixture. I've replaced every switch mode power supply with linear power supplies. Every EMI source has a high quality EMI filter between it and the AC mains. I've used a lot of ferrite to knock what EMI remained down to insignificant levels. Such extreme measures probably aren't justified in most places because the EMI produced by your neighbors will be high enough to make quieting your homegrown EMI less then effective.

While my efforts might strike many as excessive or even obsessive, it has helped keep my mind off my losses and helped me gain a practical education in applied EMI mitigation and control.

It also prompted me to shoot for my Ph.D., which my aunt and cousins have been yammering for me to do.

Who knows, I might even learn something useful.


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Re: Some thoughts and observations on the RSP1a and EMI

Postby NK7Z » Sun Sep 30, 2018 6:28 pm

I just ran across this, thanks for the link back to my site! Have you been able to generate a heatmap of RFI yet? That is a project I want to either help with, or start...

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Re: Some thoughts and observations on the RSP1a and EMI

Postby NK7Z » Sun Apr 21, 2019 2:49 am

Thought I'd check back and see how your RFI location project is going?

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