Philaredditor: Silverliner Vs cause RF interference in audio equipment

This story comes to us from a post by Reddit user /u/alexdingley on the /r/Philadelphia subreddit, which can be found at The short version: the Silverliner Vs are producing a lot of radio frequency interference in the catenary that is rendering the recording studio in his home unusable. It’s unclear if this can get brought to the FCC, but if it can, then either SEPTA, Hyundai Rotem, or both are in serious trouble. And even if the FCC doesn’t care, it’s still bad and should be fixed.

I reproduce the full text of the original explanation here, with obvious speech recognition and style errors (but NOT technical errors) corrected, after the jump:

I intended just to provide a little bit of context for the sound were listening to, but I realize now that I have spent a while telling the whole and complete story of this problem. If you’re a local musician who lives within a football field of any Regional Rail lines, you might want to read this.

Just to provide some background: I have a background in audio engineering, and I’ve run a somewhat successful project studio out of my home the last several years. Within the last 18 months I started noticing that my guitar amp was picking up some terrible interference. At first I assumed it was my old guitar, which is a 1970s Fender. After taking the guitar to get looked at, and having the amp looked at, it became apparent that the problem was not repeating itself whenever I took my equipment somewhere else. As it turns out my equipment is perfectly fine, and other people’s guitars when they came over to record at my apartment would experience the exact same noise that I’d been picking up. It ruined several recording takes on an album that I was working on with a band.

After that, I noticed that my record player was picking up the exact same noise, and it would show up as songs would … I would occasionally hear this burst of noise. It seemed to come and go in hard stops happening for a few seconds or sometimes as long as a minute.

I’ve lived in my building, which is [adjacent] to SEPTA lines for the regional rail system for about five years now. The overhead power lines that [power] the trains are about 15 feet outside my window, yet I’ve been recording in my apartment ever since I moved in and only recently started noticing this issue. For quite a while, I didn’t suspect the trains at all. I assumed that something in my apartment was giving off radio-frequency interference. The noise was always the same frequency, so I assumed if I look hard enough I would find the offending device.

I have some signal testing equipment from my old job as a home stereo installer. As I began to look around my apartment for the source of the noise, I could not consistently find the signal. Sometimes the noise was constantly present in short bursts, and other times it would seem like there was no noise to be found at all. One day while I was holding my signal detecting (a Tempo brand inductive amplifier wand) device and I turned towards the window the signal became so loud on the amp that I realized whatever the source was was outside my window.

I went outside, and walked down the street, staying near the train line, and testing the signal with the inductive amplifier wand. It was loud as all hell, and the signal was present up to 300 feet away from the tracks.

I wrote an email to SEPTA’s help line, assuming that something was just wrong with the shielding on their power lines. I figured that this must’ve been something that just came up from old tired equipment or some sort of damage to the power lines that was now allowing radio frequencies to escape the system. I did not expect a response.

Oddly enough, they wrote me back.

The funny thing is, they were suffering from the exact same problem I was. An engineer at SEPTA explained to me that the problem I’m describing sounded an awful lot like a noise that had been happening on their speaker systems in all of the train stations and inside all of the trains for several months.

A few weeks later I was riding on SEPTA’s Regional Rail system in an area far from where I live. As I was riding the train, which was one of the older SEPTA trains, the engineer on board was making an announcement about the next stop. As he spoke, the noise I’d been hearing at home through my guitar amp and through my record player came out of all the speakers on the train so loudly that we could no longer hear the engineer announce the stop.

I began corresponding with the SEPTA engineer who clued me into the fact that this is a problem that they were trying to solve. He explained to me that the new trains they had purchased seems to handle electricity differently than the old trains they’ve been using for many years. The overhead lines on all septa regional rail run on 600 V of DC current. The old trains turn that current into AC inside the train for the outlets and the lights, and somehow that’s different from how the new trains handle things. I’m not an expert in electrical theory (so forgive any misuses of terms here) but my understanding of the difference is that the new trains return excess DC voltage back to the overhead power line. The AC to DC transformer on top of the train is actually operating at a frequency that’s becoming audible in the radio spectrum.

At any rate the new trains cause radio interference at two very distinct frequencies that will show up on any unbalanced amplified signal within a few hundred feet of an active train line. The engineers explained to me that the frequency is generated when the new trains are either accelerating or decelerating on the train line.

As the engineers at SEPTA were trying to solve the problem for themselves, they became very interested in demonstrating the frequency problem to the engineers who built and designed the new SEPTA trains. I invited them to come to my apartment last September to demonstrate the issue for them. Prior to having them out, I recorded 10 hours of my guitar sitting next to the window plugged into an amplifier as the normal weekday train schedules right. I put the MP3s in one hour blocks up on a private server and linked it to the SEPTA engineer. He downloaded the files and confirmed for me that exactly what I was experiencing was absolutely being caused by these brand-new trains.

When SEPTA engineers came out they also brought an independent consultant, and an engineer from Rotem… that’s the company who made the trains.

The engineer from the train manufacturer was attempting to disprove that the trains were what was causing the issue. He suggested all manner of other causes for the interference I was getting. He suggested that it might be other devices in my apartment, or a poorly maintained electrical power system in my old apartment building. In an attempt to eliminate all variables that he was mentioning, we threw the breakers in my apartment and shut down all of my power. We then plugged my guitar amp into the uninterruptible power supply from my computer. While running my guitar amp from nothing more than a DC battery we were able to continue to demonstrate the noise problem. The engineer from the manufacturer of the trains then suggested that I simply notch out (using EQ) frequencies to eliminate the noise from all my guitar playing.

Since the noise only comes in short bursts and is quite unpredictable, using an EQ to attempt to eliminate the noise is really an inadequate solution.

The SEPTA engineers actually had a filter box built for them that they plug-in to all the amplifiers and all the train stations now. This box is effectively a two frequency equalizer meant to snuff out the noise so that it doesn’t bother the speaker systems in the trains and in the train stations.

In an attempt to make peace with me for causing all this trouble, SEPTA gave me one of these boxes. I also have an email with the schematic drawing of what’s going on inside that box, and the explanation for the box’s existence.

After several months of me following up with them asking if they come up with a better solution to stop the noise from occurring, SEPTA has stopped returning my emails and calls. It’s become clear that my only solution now is to move. I have to leave my apartment, which I love very much. I live in a very cool old building that allows me to make all kinds of noise without ever bothering my neighbors. This apartment is also really really affordable, and trying to find a place to live that’s quite as nice and quite as affordable and very well isolated sonically has been next to impossible.

I want to know if I’m the only person who’s really been affected by this, or if there are other people who’ve noticed this problem as well. Perhaps there are other individuals of experienced it and not realized what the cause was.

I know that there are recording studios and music venues all along SEPTA rail lines throughout the greater Philadelphia area, so I have to wonder if this is hitting more people.

Mr. Dingley also follows up with further comments and explanations at the Reddit thread.

There are a few minor nitpicky points about the technical details that look like lost-in-translation errors, as far as I can see. The overhead lines are 11kV AC 25hz, not 600V DC, and have been ever since the Reading Company installed them. The change from the Silverliner IIs, IIIs, and IVs, to the Silverliner Vs, is that the older railcars use silicon-controlled rectifiers to convert the AC to DC, while the Rotem-built cars use newer semiconductor technology fed directly from AC. That enables the Silverliner Vs to regenerate electricity while braking and return the power to the grid.

That regenerative braking system is a welcome improvement, as it reduces electrical demand for a big environmental win, and saves SEPTA a lot of money in the process. But it looks increasingly like it may be creating the unwelcome RF interference. (One commenter has reported similar issues on Metro North/ConnDOT’s M-8 fleet.) The frequencies being broadcast are in the audible spectrum below the 9kHz threshold that the FCC cracks down really hard on, but serious FCC repercussions are not out of the question, hence why the Rotem engineer was so eager to find something, anything else to be the cause.

Even if the FCC is willing to let this slide, SEPTA should not. At the very least, it should be a good neighbour to the people who live along its lines, but SEPTA may also be on the hook for damages, especially now that its knowledge of the extent of the problem is public. SEPTA may have an obligation to go after Hyundai Rotem through the legal system to fix the filtering problem, or to pay for the repairs. If so, it should act vigorously to protect the public purse.

As a final note, someone at SEPTA was willing to go out of their way to help Mr. Dingley with their mutual problem, and indeed provide quite a bit of technical assistance and expertise. Unfortunately, they seem to have reached the end of what they can do for him without doing serious surgery on the 120-car Silverliner V fleet. That spirit of assistance should be commended, and should not be wasted. Alex Dingley should not have to move because of an unforeseen defect of the Silverliner Vs; SEPTA and Rotem need to work together quickly to fix this for him, and all the other neighbours of the Regional Rail system.

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  1. SEPTA’s overhead power system is not 600VDC, but 11,000 VAC at 25 Hz. If it were me, I’d be looking at the AC inverters Rotem used in the cars….

    1. I already noted that in my long postscript. A followup comment by Mr. Dingley says that the catenary is acting as a 4 mile long antenna; I think the issue is noise in the regenerated current, but we do need corroboration.

  2. I’ve heard this noise at literally every train station in my area for the past few years, I had no idea it was from the SLV’s.

  3. Some other considerations I’d be looking at: who else uses these kinds of AC inverters? Are there similar problems in e.g. France? Spain? The UK? Denmark? Japan? China? (Germany, Switzerland, Norway, and Sweden all use DC power.) Could the problem be being exacerbated by the variable-tension catenary? That is, would a conversion to a constant-tension system, such as is being done in the Raceway project between Trenton and Metuchen ameliorate the antenna effect?

  4. SEPTA knows what they are doing and they guy did move thank god. He whined way too long. SEPTA is not in trouble with anyone and if the fcc has a problem with the dumb noise, they should start by taping up our governor’s mouth and the crap that he says, along with crazy daryl metcalfe and michele bachmann. This is pale in comparison.

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