Stratux making more EMI than it used to

[Ergonomicmike]

1. Stratux version: 1.2r1-0360e

2. Stratux config:

   SDR

   • [ ] single
   • [X ] dual

   GPS

   • [X ] yes
   • [ ] no type: VK-162

   AHRS

   • [ ] yes
   • [X] no

   power source: Anker E5

   usb cable: Anker

3. EFB app and version: iFly v9.8.7

   EFB platform: Andrioid KK

   EFB hardware: Asus Zenpad

4. Description of your issue:

This isn't a code issue, per se. But something changed in the Stratux code that is making more RFI now. (I'm gonna guess it's the faster psuedo-AHRS.)

About a month ago, the squelches on both our COMMs (King KX-165 and KX-155) started "breaking." (That is, started letting noise thru.) We noticed it on Tower (118.4 MHz), Ground Freq (121.8 MHz), Guard (121.5 MHz) and Unicom (122.8). Whether it does it in the 130's, I don't know.

Tonight I had the brainstorm to reboot the Stratux in flight. As soon as I hit the reboot command, the noise in the COMM stopped! When the Stratux came back on line, so did the noise.

This started in early February. So that would be coincident with the Feb 3 sh updates.

This is a Pi 3. No copper foil shielding like I had on my old Pi 2. Aside from the software, nothing has changed in my config. The Stratux is where it's always been. The antennas and SDR's have been where they've always been, etc.

I don't think that the developers can really code around EMI. More like the Project might start thinking about shielding the box if others report similar problems with their COMMs.

[merricke]

@Axtel4 Without the wire cage. I concentrated on getting the Pi's 125 carrier attenuated, never made a comprehensive test later. I saw a significant improvement when grounding the heat sinks and another drop with the wire rat's nest. My plane's radios are back to normal, not breaking squelch and no extraneous noise on the freq's I use. The early power supplies I had were a main source of noise, I believe. With the better power supplies I haven't experienced any noise problems.

[GitUser275]

"No, the levels stay constant at the high level when both 1090 and 978 are selected to off."

I repeated the test this morning. I see that the signal at the 978 SDR reduces when it is selected off with the GUI. The signal at the 1090 SDR does not reduce when it is selected off with the GUI. I did repeat the test several times this morning, with and without a GPS connected, and the results are consistent. 978 signal is controlled by UI on/off but 1090 signal is not controlled by UI on/off.

As observed yesterday - if both are selected off, then the Stratux is booted, the low level signal is seen at both SDR.

I suspect my observations of yesterday were invalid because the GPS USB connector prevented close positioning of the probe over 978 SDR. In today's test I moved the GPS to a different USB port to allow close contact of the probe with either SDR.

[Axtel4]

@GitUser275 Have you happened to connect the SA directly to the SDR antenna port and swept the frequency band? Also tried connecting the SA to the antenna port through a directional coupler and a Sig gen to the coupled port with injecting an in band signal and sweep the frequency band?

[GitUser275]

"Have you happened to connect the SA directly to the SDR antenna port and swept the frequency band? Also tried connecting the SA to the antenna port through a directional coupler and a Sig gen to the coupled port with injecting an in band signal and sweep the frequency band?"

Simple answer to both - No.

I'm willing to investigate what is transmitted by each SDR but you'd need to specify what frequency range you are interested it.

I don't understand your proposed use of the directional coupler. Typically an SA with TG and directional coupler are used to characterize S11 of an antenna system and I have made such measurements on my station antennas. Why would you want to connect the coupler to the SDR antenna port? What are you expecting to measure?

[cyoung]

Here's a sweep up to 3.2 GHz with the SA connected directly to the antenna ports, as suggested by @Axtel4. v1.4r3, dual band unit with internal GPS, in the white ABS case ("pre-built" configuration). This is important since the pre-built config has the antenna feed looped over the top of the Pi, so there may be some noise coupled onto the antenna feed from that (maybe the Wi-Fi stuff).

Magenta is baseline (Stratux off, SA input not connected to Stratux). Blue is peak hold while connected to the port and Stratux on (with uptime 2 minutes+). There's a peak at 345.6 MHz from something outside of Stratux, not sure what.

1090 port: Peaks at 85.33 MHz @ -85.83 dBm 115.20 MHz @ -84.95 dBm 230.40 MHz @ -81.82 dBm 345.60 MHz @ -78.71 dBm (external noise) 1540.27 MHz @ -79.82 dBm 1902.93 MHz @ -80.04 dBm 2184.53 MHz @ -69.04 dBm 2410.67 MHz @ -65.25 dBm

978 port: 85.33 MHz @ -85.83 dBm 115.20 MHz @ -84.77 dBm 230.40 MHz @ -81.82 dBm 345.60 MHz @ -78.71 dBm (external noise) 1540.27 MHz @ -79.57 dBm 1902.34 MHz @ -80.04 dBm 1958.40 MHz @ -75.69 dBm 2184.53 MHz @ -69.04 dBm 2410.67 MHz @ -65.25 dBm

[Axtel4]

@GitUser275 Looking at the output of the SDR antenna port will show if there is any LO leakage or oscillations being emitted from the SDR. Stray signals radiating for the antenna port would require other mitigation efforts that shielding the SDR.

Using the directional coupler and the external generator allows the measurement of the generation of intermod products at the front end of the SDR in the presence of strong nearby signals. For example, if the SDR has ESD clamping diodes at the antenna port, a strong signal entering the antenna port could cause the creation of intermod distortion across the PN junction of the clamping diode. I've also seen radiated intermod products created at the output of receiver preamps in the presence of strong signals.

A better method would be to inject the signal though a circulator, but most home labs don't have one available so a directional coupler is substituted.

[Axtel4]

@cyoung

Thanks. That is an interesting look. As stated above, one of the potential interference sources is unintentional radiated emissions from the antenna port. The 115.2 MHz signal appears to be a reoccurring theme. I wonder if the received noise at that frequency is affected if a dummy load is placed on the SDR antenna port?

[GitUser275]

@Axtel4

I understood why you wanted the antenna port scan but was not aware of that technique for evaluation of front end intermod. I'll try to find some references. Maybe you can point me to some?

I don't think I want to send my time evaluating RTL based receivers though. I don't expect much for $15.

[GitUser275]

I had a quick look at 125.0 radiated signal using a hand held receiver. The initial observations were puzzling then I found out that my DVR and my Roku 3 both radiate quite strongly at 125.0 and were mixing with 125.0 signal radiated by Stratux.

With DVR and Roku powered down I found that 125.0 from Stratux is killed immediately by Web UI shutdown command. I don't know what is stopped at shutdown so I don't know if that observation is significant.

Touching various parts of the Pi with a finger (ESD strap in use) I found there were very localized areas where finger contact caused almost complete attenuation of the radiated 125.0 signal. I found no obvious change in signal when the heat sinks were touched or grounded. 125.0 did not seem to change significantly when both antennas were removed and replaced with 50 ohm terminators.

This was only a quick look. Priority today is to get a few IAP in the log before my currency expires.

[merricke]

@GitUser275 Dirty world we live in; my wifi router puts out a carrier at 120. Interesting that your grounding of the heat sinks had different results from mine: puzzling. Which components seem to benefit from the 'finger' grounding?

[Ergonomicmike]

(Cross posted this in Slack.)

Update: 3 min video of this, https://www.dropshots.com/ifly_user/date/2017-12-10/19:47:23 [See Warning below about clicking anything on the DropShots website.]

I did the (mostly) shielded Ammo Box text yesterday. Yes, there is noise being radiated from the antennas. That was the best case test for a Stratux. Everything in the box (Pi, battery, SDR's) with only 978, 1090 and GPS antenna outside.

BTW, it seems that the GPS cable is conducting and then radiating noise. So I might have to braid that.

Otherwise, with the braid on my power cable and most of the 1090 SDR, most of the COM noise is gone.

Now that the noise floor has dropped a bit, I'm finding that the 978 SDR is causing trouble. So am going to copper foil that today before flying tomorrow.

Warning: When I was checking to see if this video was viewable from another browser, when I clicked on "Play" I got a very believable message telling me I needed to update Flash. (Didn't do it.) Second time, I got redirected to another bad offering. So it seems that malware advertisers are using DropShots for evil purposes.

[cyoung]

What conclusions can we make up until this point and what remains to be investigated?

• 115.20 MHz emissions from SDRs.
• 125.00 MHz emissions from RPi.

In terms of shielding/reducing EMI, what has worked?

[merricke]

The schemes I described earlier for 125.0 (RPi) cleared my com problems on the freq's I normally use (118.02, 121.4, 124.5, 119.9). Any reports of problems on ATC freq 120.0? 115.20 is a nav freq. Any reports of interference from these VOR's (compiled from airnav.com): VOR’s on 115.20 HPB HOOPER BAY VOR/DME HOOPER BAY, AK EED NEEDLES VORTAC NEEDLES, CA SAC SACRAMENTO VORTAC SACRAMENTO, CA EKR MEEKER VOR/DME MEEKER, CO PIA PEORIA VORTAC PEORIA, IL NHZ BRUNSWICK TACAN BRUNSWICK, ME MKG MUSKEGON VORTAC MUSKEGON, MI CBM CALEDONIA VORTAC COLUMBUS, MS VCN CEDAR LAKE VOR/DME MILLVILLE, NJ FFO PATTERSON TACAN DAYTON, OH JFN JEFFERSON VOR/DME JEFFERSON, OH HIO HILLSBORO VOT PORTLAND, OR FLO FLORENCE VORTAC FLORENCE, SC ELP EL PASO VORTAC EL PASO, TX Location VBI SIOUX NARROWS VORTAC KENORA, , CANADA

[merricke]

I wonder if the new pi.3.+ with a faster processor speed and a metal cap over the chip might attenuate or move the interference out of our band.

[jmlras]

Hi All, Glad to talk with the aviation guys! I'm a LM'er, C130H / J, prod support guy, Dobbins AFB

My interest is in radio astronomy utilizing the Rpi 3, we've noticed unusual spikes in the freq rand of 1420 MHz on the negative redshift -390 khz below the 1420 plus a few smaller spikes as well on the baseline. From your conversation, it does seem to point to the pcb etc. and the need for some serious shielding. I've attached two scans. Would be interested in your thoughts. Thx Jeff (Whitesboro, Texas)

[jmlras]

Another fix was found when a monitor was turned off. In this case an hdmi, the -380 pulse dissapeared.

If I have entered this discussion in error, I apologize.

[cyoung]

testing image for RPi3B+. I did some informal trials with a handheld radio and noted that the Pi3B+ seems to output less noise on 125.00 MHz. Some of the redesigns on the Pi3B+ were specifically for EMI reasons. Worth testing further.

[jmlras]

Thanks so much cyoung for your efforts. Will be trying clam shell ferrite suppressors on the cables. One input I received was the use of the usb cell phone block transformers. The person found that the emi filter beads that were supposed to be on the Rpi power supply pcb were not installed during assembly in China.

Our primary frequency of interest lie within the microwave (L band) area. Our IFs are usually at 10.7 MHz. and 70 MHz. I will also be enclosing the pi in a emi box within the next couple of weeks.

[cyoung]

The person found that the emi filter beads that were supposed to be on the Rpi power supply pcb were not installed during assembly in China.

That's an interesting finding. Do you have a picture of that board? Where did he get it from? Where are those components located on the PCB?

[jmlras]

Hi,

Bruce Randall, a long time electronic tech/eng from SC. He is also a radio astronomy and amateur radio guy. Very gifted with electronics ( brandall@ comporium.net )

Tell him I recommended him.

Jeff

*Best Regards,Jeffrey M. Lichtman, KI4GIY*RADIO ASTRONOMY SUPPLIES

http://www.radioastronomysupplies.com http://www.radioastronomysupplies.comPhone: 954 554-3739 Fax: 954 343-1108Skype Contact: jeffrey.lichtman777 (by appointment)

“The most beautiful experience we can have is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. Whosoever does not know it and can no longer wonder, No longer marvel, is as good as dead, and his eyes are dimmed. "

• Albert Einstein *

On Tue, Apr 3, 2018 at 2:34 PM, cyoung notifications@github.com wrote:

The person found that the emi filter beads that were supposed to be on the Rpi power supply pcb were not installed during assembly in China.

That's an interesting finding. Do you have a picture of that board? Where did he get it from? Where are those components located on the PCB?

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/cyoung/stratux/issues/573#issuecomment-378369651, or mute the thread https://github.com/notifications/unsubscribe-auth/AkKCbAoTWgaNepACMIISZKJeEsjXjlRLks5tk864gaJpZM4MaFl4 .

[jmlras]

brandall@comporium.net

*Best Regards,Jeffrey M. Lichtman, KI4GIY*RADIO ASTRONOMY SUPPLIES

http://www.radioastronomysupplies.com http://www.radioastronomysupplies.comPhone: 954 554-3739 Fax: 954 343-1108Skype Contact: jeffrey.lichtman777 (by appointment)

“The most beautiful experience we can have is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. Whosoever does not know it and can no longer wonder, No longer marvel, is as good as dead, and his eyes are dimmed. "

• Albert Einstein *

On Tue, Apr 3, 2018 at 2:40 PM, Jeffrey Lichtman < radioastronomysupplies@gmail.com> wrote:

Hi,

Bruce Randall, a long time electronic tech/eng from SC. He is also a radio astronomy and amateur radio guy. Very gifted with electronics ( brandall@ comporium.net )

Tell him I recommended him.

Jeff

*Best Regards,Jeffrey M. Lichtman, KI4GIY*RADIO ASTRONOMY SUPPLIES

http://www.radioastronomysupplies.com http://www.radioastronomysupplies.comPhone: 954 554-3739 Fax: 954 343-1108Skype Contact: jeffrey.lichtman777 (by appointment)

“The most beautiful experience we can have is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. Whosoever does not know it and can no longer wonder, No longer marvel, is as good as dead, and his eyes are dimmed. "

• Albert Einstein *

On Tue, Apr 3, 2018 at 2:34 PM, cyoung notifications@github.com wrote:

The person found that the emi filter beads that were supposed to be on the Rpi power supply pcb were not installed during assembly in China.

That's an interesting finding. Do you have a picture of that board? Where did he get it from? Where are those components located on the PCB?

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/cyoung/stratux/issues/573#issuecomment-378369651, or mute the thread https://github.com/notifications/unsubscribe-auth/AkKCbAoTWgaNepACMIISZKJeEsjXjlRLks5tk864gaJpZM4MaFl4 .

[jmlras]

Also, found a source for alum enclosures and pi parts. http://www.mpja.com/Electronic-Enclosures-Boxes/departments/105/

*Best Regards,Jeffrey M. Lichtman, KI4GIY*RADIO ASTRONOMY SUPPLIES

http://www.radioastronomysupplies.com http://www.radioastronomysupplies.comPhone: 954 554-3739 Fax: 954 343-1108Skype Contact: jeffrey.lichtman777 (by appointment)

“The most beautiful experience we can have is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. Whosoever does not know it and can no longer wonder, No longer marvel, is as good as dead, and his eyes are dimmed. "

• Albert Einstein *

On Tue, Apr 3, 2018 at 2:41 PM, Jeffrey Lichtman < radioastronomysupplies@gmail.com> wrote:

brandall@comporium.net

*Best Regards,Jeffrey M. Lichtman, KI4GIY*RADIO ASTRONOMY SUPPLIES

http://www.radioastronomysupplies.com http://www.radioastronomysupplies.comPhone: 954 554-3739 Fax: 954 343-1108Skype Contact: jeffrey.lichtman777 (by appointment)

“The most beautiful experience we can have is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. Whosoever does not know it and can no longer wonder, No longer marvel, is as good as dead, and his eyes are dimmed. "

• Albert Einstein *

On Tue, Apr 3, 2018 at 2:40 PM, Jeffrey Lichtman < radioastronomysupplies@gmail.com> wrote:

Hi,

Bruce Randall, a long time electronic tech/eng from SC. He is also a radio astronomy and amateur radio guy. Very gifted with electronics ( brandall@comporium.net )

Tell him I recommended him.

Jeff

*Best Regards,Jeffrey M. Lichtman, KI4GIY*RADIO ASTRONOMY SUPPLIES

http://www.radioastronomysupplies.com http://www.radioastronomysupplies.comPhone: 954 554-3739 Fax: 954 343-1108Skype Contact: jeffrey.lichtman777 (by appointment)

“The most beautiful experience we can have is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. Whosoever does not know it and can no longer wonder, No longer marvel, is as good as dead, and his eyes are dimmed. "

• Albert Einstein *

On Tue, Apr 3, 2018 at 2:34 PM, cyoung notifications@github.com wrote:

The person found that the emi filter beads that were supposed to be on the Rpi power supply pcb were not installed during assembly in China.

That's an interesting finding. Do you have a picture of that board? Where did he get it from? Where are those components located on the PCB?

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/cyoung/stratux/issues/573#issuecomment-378369651, or mute the thread https://github.com/notifications/unsubscribe-auth/AkKCbAoTWgaNepACMIISZKJeEsjXjlRLks5tk864gaJpZM4MaFl4 .