Tagged: interference

SDR# FM Co-Channel Canceller Added

A few days ago the developer of SDR# added a very useful AM Co-Channel canceller plugin, and just today he has also added a new FM Co-Channel canceller. A Co-Channel canceller allow a user to remove an interfering station, allowing a buried station to be received cleanly. This is especially useful for DXer's where strong local and weak distant overlapping stations are likely to be received at the same time. The plugin works with all SDR# compatible SDRs including the RTL-SDR.

On a related note, we wanted to point out that recently the Airspy website and downloads have been getting flagged by some antivirus software, however we believe these detections to be false positives caused by the very frequent update schedule of SDR#.

SDRSharp FM Co-Channel Canceller

Over on Twitter we've seen a couple of videos from @K7al_L3afta demonstrating how well the new FM Co-Channel canceller works.

Using a HackRF to Investigate Why WiFi on the Raspberry Pi 4 Doesn’t work when Running HDMI at 1440p

The Raspberry Pi 4 launched with it's fair share of problems, but a new problem seems to have been recently discovered and documented. It turns out that the Pi 4's WiFi stops working when running at a screen resolution of specifically 1440p.

Suspecting interference generated by the HDMI clock, Mike Walters (@assortedhackery) used a HackRF and a near field probe antenna to investigate. By placing the near field probe on the Raspberry Pi 4's PCB and running a screen at 1440p resolution he discovered a large power spike showing up at 2.415 GHz. This interferes directly with 2.4 GHz WiFi Channel 1.

An article by ExtremeTech article notes:

There’s a giant spike that could easily interfere with Channel 1 of a Wi-Fi adapter. So why is this happening? Because a 2560×1440@60Hz has a pixel clock of 241.5MHz and has a TMDS (transition-minimized differential signaling) clock of 2.415GHz, according to Hector Martin (@Marcan42). And what frequency does the RBP4 use for Wi-Fi? 2.4GHz. Which means… outputting on HDMI over 1440p can cause interference in a Wi-Fi channel.

The ExtremeTech article also notes that this problem is not unique to the Raspberry Pi 4 only. It turns out that USB 3.0 hardware is to blame, and this problem has occurred before with USB3.0 hard driver and on some MacBooks.

While the interference appears to be localized to the near field around the Pi4 PCB, we suspect that you could use TempestSDR to remotely eavesdrop on the Pi 4's video output if the interfering signal was boosted.

Using an RTL-SDR to Investigate GPS Interference Problems on Drones Caused By HD Cameras

Over on YouTube Drone and Model Aircraft enthusiast channel Paweł Spychalski has uploaded a video showing how he determined that cheap HD cameras that are commonly used on hobbyist drones can cause locking issues with the on board GPS. He writes:

You might believe it or not (today I will prove it, however) that HD cameras, especially cheap ones, can be responsible for GPS problems on your drones and model airplanes. The majority of HD cameras (RunCam Split, Runcam Split Mini, Foxeer Mix, Caddx Tarsier) generate RF noise on different frequencies. Some of them on 433MHz, some on 900MHz, but most of them also at around 1GHz. Just where one of the frequencies used by GPS signal sits. As a result, many GPS modules are reported to have problems getting a fix when the HD camera is running.

In the video he uses an RTL-SDR and SDR# to demonstrate the interference that shows up when a cheap HD camera is turned on. He shows how the interference is present at almost all frequencies from the ISM band frequencies commonly used for control and telemetry to the 1.5 GHz GPS frequencies.

GPS vs HD cameras - it's all about RF noise

SDR in the Local Newspaper: Investigating an RF Dead Spot for Car Key Fobs

Reddit user [SDR_LumberJack] writes how he was recently featured in his local newspaper [Part2] in Ontario, Canada thanks to his efforts in helping to hunt down the cause of an RF deadspot with an SDR. He began his journey by reading a story in his local newspaper called the [Windsor Star]. The story was about locals having found a ‘dead-spot’ for car key-fobs. In the dead-spot key-less cars wouldn’t start, key-fobs wouldn’t unlock cars, and alarms would go off.

Being intrigued by the story [SDR_LumberJack] investigated by driving around with an RTL-SDR, HackRF and a laptop running SDR#. Eventually he found that there was what appeared to be a WBFM Broadcast radio station interfering at 315 MHz. This frequency happens to fall into the ISM radio band that used by car remotes and key-fobs. The exact source of the interference hasn’t been nailed down just yet though.

While it’s possible a broadcast station is at fault it is also possible that his SDR was just overloading, causing broadcast FM imaging. Perhaps a WBFM filter could be used to prevent signal imaging that could interfere with the investigation.

Hopefully [SDR_LumberJack] will continue his investigation and we’ll get an update on this story.

If you’re interested, back in 2016 we posted a very similar story about the exact same thing happening at a car park in Brisbane, Australia. The conclusion to that story was that the dead-spot only occurred in particular locations in the car park, and this was due to the shape of surrounding building causing the RF signals to reflect off the walls and distort the signal.

SDR_LumberJack in the local newspaper
SDR_LumberJack in the local newspaper

Showing what Solar Power Inverter Interference Looks Like

Over on YouTube user ALI6359 has uploaded a video showing what severe interference from a neighbors poor quality solar power inverter looks like on his RTL-SDR dongle. An inverter converts the DC power produced by solar panels into AC power which is used by common household equipment. Inverters typically use switching techniques to convert the power, and this can cause RF noise if the inverter is poorly designed and not shielded.

In the video ALI6359 shows strong interference all across the VHF spectrum. He also writes in the video description that the interference also occurs all over the entire HF band. He writes:

This is what happens if you or your neighbours install a dodgy quality solar power system. i am using a uhf phased array antenna facing away from the source of interferance but i am picking up very strong interferance. just touching the antenna connector of the rtlsdr is enough for the interferance to show up. i once had a HF upconverter (stopped working now) it used to show very strong interferance through the enitre HF band. the solar inverter certainly fails the part 15 FCC requirements.

In a previous post we also showed how interference from Ethernet over powerline adapters can destroy the entire HF band as well.

HamRadioScience: Why Apple’s iMac May be the Best PC for SDR Applications

Over on on the HamRadioScience blog, the author has uploaded an article that makes the case on why Apple iMac PC’s may be the best choice for SDR receivers (at least for HF frequencies). In the testing he uses an SDRplay and Elad FM-Duo to show that the plastic case of the SDRplay does not affect the picked up RFI. He shows that when the SDR’s are connected to an iMac the interference from RFI on HF frequencies is minimal. However when connected to a Core i5 PC, there is significant amounts of CPU and monitor noise generated.

The differences in generated noise probably come from the fact that the iMac is probably much better shielded with an aluminum case and that they have high build quality standards for their monitors. The author suggests that an alternative to using an iMac could be to build your own PC, ensuring that dual chamber metal enclosures are used, which ensures that the power supply is isolated in its own separate steel compartment.

RFI is visible with the SDRplay in SDRuno when using the PC. But no RFI is seen with the iMac.
RFI is visible with the SDRplay in SDRuno when using the PC. But no RFI is seen with the iMac.

Solving the Mystery of a Keyless Vehicle Entry RF Deadspot in a Carpark with a FUNcube Dongle

The Brisbane Times ran a story today that discussed an interesting RF phenomenon that was solved using a FUNcube dongle software defined radio. The Funcube dongle is a SDR similar to the RTL-SDR. The issue was that vehicle wireless entry keyfobs would not work at a particular location within an outdoor shopping centre car park.

The story goes like this – First a user on a local Brisbane subreddit message board posted about how he had noticed that his cars wireless entry keyfob would not work when he parked in a certain area of the shopping area car park. The user wrote:

I walked out to my car from Bunnings, and there was a new HSW Maloo parked in front of me with the owner staring at his key fob and shaking his head.

I said “let me guess, car won’t open?” and he said yeah, and he’d been trying for about 5 minutes. I said that I’d had the same thing happen to me a few months back in the same spot, and then went to open my car.

Nothing. No beep, door stayed locked. Looked around and there was another couple trying to get into their car as well (late model C Class).

It took about 5 minutes of me trying the door every 20 seconds or so before it opened. HSV owner was still there when I left. The only thing he and I could think of causing it was the mobile phone tower in front of Aldi.

After reading the post, user u/riumplus decided to go out to the same spot with his Funcube dongle SDR and see if there was any interference that might explain the issues. But he found no such interference. However, when he pressed the wireless entry on his own keyfob he noticed reflections from the main transmission that were coming from the buildings walls. He wrote:

So I pulled out my SDR and I did a complete frequency sweep from 100kHz to 2.2GHz and… also nothing. Everything completely normal. Nothing on that frequency, nor anything odd anywhere else on the spectrum. Couldn’t see any of the usual potential harmonics from RFID or standard WiFi gear. Here’s the output at 433.3MHz(forgot to grab a screenshot centred right at 433.92Mhz but it was also empty, as was 315MHz).

Here’s where it gets interesting – I noticed that that location is almost in the middle of the car park between the three buildings, and they all have large amounts of metal flashing on their fronts. On a whim I watched the output when I pressed my own keyfob. And what do you know, I could see distorted reflections from my own signal bouncing off these buildings right back at me. My guess is that this is what was causing you issues!

It may sound counter-intuitive, but next time it happens try cupping the keyfob in your hand to weaken the signal. It should still be strong enough to trigger your car to open, but then the reflections will be weak enough they won’t cause you trouble.

So it seems that the layout of the buildings caused a focal point for reflections at that particular location which affected some wireless keyfobs.

The location in the carpark of the deadzone.
The location in the carpark of the deadzone.

Updates to Shielding the RTL-SDR with an Aluminium Case

A few weeks ago we posted about will1384 who had bought an aluminium case from Ebay and was using it to shield his RTL-SDR. After running multiple tests, will1384 discovered that the aluminium case was actually not helping with shielding performance at all. Oddly his results showed that the aluminium case was actually increasing the amount of noise received. Will has been updating his imgur album with noise analysis results from rtl_power scans over the entire spectrum.

In his latest tests he tried a metal outlet box as the case and saw improved results over the aluminium case. His conclusions seem to indicate that the aluminium box is not a good EMI shield. We’re not sure why he found these results, but one theory might be that because the aluminium case is anodized, it has a non-conductive surface, which might cause poor grounding.

RTL-SDR in a Metal Outlet Box
RTL-SDR in a Metal Outlet Box