PilotAware
British Forum => General Discussion => Topic started by: barrieslinger on December 14, 2015, 09:31:25 am
-
After a short first flight with my PAW, we got very bad interference over the radio(Set to 122.6) at a level that could not be squelched out. Interference was in the form of regular pulses. Intensity appeared to vary, there was a lot of radio traffic and sensitivity of radio changed if it was receiving a carrier prior to someone talking but in quiet periods noise pulses were regular.
To confirm that it was the PAW we removed power from it and all was good, added power and the interference return when the PAW had booted. All worked fine as just an ADS-B receiver, there is no ARF connected to the PAW. We are powering from one of the recommended USB battery. I suspect the interference is coming from wifi. Are there any suggestions on how this interference can be corrected?
Thanks
Barrie
-
Wifi operates on very different frequencies (~2400 MHz and ~5000MHz), it will not easily interfere with our radios at 118-136MHz.
What will interfere is the Raspberry Pi computer itself. Bare computer boards are notorious for causing interference spikes at random frequencies. Even a change in software can make the spike disappear.
There are a few things you can do to suppress this interference
- Use a grounded all-metal housing for the RPi.
- Use shielded cables in and out of the RPi.
- Add ferrite RF suppressors on cables in and out of the RPi.
- Create distance between the RPi and the COM antenna.
-
After a short first flight with my PAW, we got very bad interference over the radio(Set to 122.6) at a level that could not be squelched out. Interference was in the form of regular pulses. Intensity appeared to vary, there was a lot of radio traffic and sensitivity of radio changed if it was receiving a carrier prior to someone talking but in quiet periods noise pulses were regular.
To confirm that it was the PAW we removed power from it and all was good, added power and the interference return when the PAW had booted. All worked fine as just an ADS-B receiver, there is no ARF connected to the PAW. We are powering from one of the recommended USB battery. I suspect the interference is coming from wifi. Are there any suggestions on how this interference can be corrected?
Thanks
Barrie
Can you try plugging something else into the battery pack so see if it's the PAW or the power unit?
Some battery packs use boost/buck converters to adjust the LiPo power from the battery (normally around 4v) up to the 5v needed, some of those are pretty effective noise generators.
-
Hi Barrie,
Its interesting you mention 'regular pulses', I had seen this previously with an ARF, but you also mention there is no ARF attached.
What is the period of the 'regular pulses' ?
I have not see any intereference issues without an ARF attached, and even with the ARF moving a short distance from the transceiver, semed to cure the problem.
Thx
Lee
-
After a short first flight with my PAW, we got very bad interference over the radio(Set to 122.6)
Was this at White Waltham? - if so, was the interference observed on the ground or when airborne - I've noticed some wierd interference of the type you mention in the Yak at certain parts of the airfield, nothing to do with a PAW. Very odd, and quite localised (it could of course be some bizarre new Russian electrical quirk).
-
Hi SCS, JC, Lee and RC
Will try and plug alternative load into battery.
Distance RPi to com aerial about 3 ft.
Will time pulses when I visit airfield tomorrow.
Will also borrow hand held transceiver to check out interference.
Plane was from Sherburn flying near Selby.
Ferrite beads seem a useful thing to have so will get some.
Will not attempt metal package until I have ARF in final form.
Thank you all
Barrie
-
For anyone looking to develop a metal housing for the PAW, this may be of interest......
https://www.youtube.com/watch?v=-DmaHUBhR_w&feature=youtu.be (https://www.youtube.com/watch?v=-DmaHUBhR_w&feature=youtu.be)
http://skaarhoj.com/free-stuff/schaeffer-scripts/ (http://skaarhoj.com/free-stuff/schaeffer-scripts/)
(http://skaarhoj.com/typo3temp/pics/4fb5dcf08b.jpg)
https://www.youtube.com/watch?v=Xnk0urpyfpg (https://www.youtube.com/watch?v=Xnk0urpyfpg) - this video shows cut-outs and pcb mounting.
I have used Front Panel Express and Schaeffer for a number of 2D panels (e.g. switch and circuit breaker panels for my a/c instrument panel) and very good they are too.
I have not used this new Skaarhoj scripting for enclosures / housings, but it looks pretty comprehensive.
Steve
-
It doesn't necessarily need to be metal to shield the noise.
-
Well, plastic ain't gonna stop much RF at 122MHz. You could use copper paint on the inside perhaps, but for a little more money you can have a very, very nice full metal housing. Fits like a glove and looks really professional.
http://lukse.lt/uzrasai/2014-10-raspberry-pi-b-case-is-now-available/
It does take a bit of modification if you plan to use an ARF shield (old or new alike).
-
The RPis can emit quite a lot of EMC, so this doesn't surprise me.
Best approach would be to put it all in a grounded metal box and use ferrites on the power supply lines to the RPi, as suggested above.
-
Questions that do not appear to have been asked: Does the interference only appear on 122.6MHz? Does the nature of the interference change/disappear on adjacent/distant channels? If it is RF-borne interference then a bit of tuning around can reveal much about the interference source and how (indeed if) it is getting into your radio.
Other questions that might help to pin down what is causing the problem include:
* Are you sure that the interference was being picked up as RF by the radio and not by induction into audio lines? That can happen very easily with unshielded audio lines close to noise sources in a small cockpit.
* What was the nature of the interference? Regular pulses (how frequent?) or random crud?
I spend a lot of my time as an air traffic engineer trying to track down EMC issues like these and they can often be quite intractable. The two starter questions are always "what exactly is generating the interference signal" and "where is it getting into my equipment". The answers are seldom simple! Often a new EMC problem turns out to be an issue with the equipment suffering the interference rather than the putative source of the interference.
-
It has taken a while to get back in the Yorkshire air.
Been for a 1.5 hr flight with much to my surprise no sign of interference.
Relieved but baffled.
Squelch setting on radio is rather critical in clearing noise but when optimized system is fairly silent.
When troubled by noise previously the RX indicator on the screen of the Garmin 530 flickered with the noise.
Sorry I am not adding much to the information pool.
Will investigate further.
-
not an answer to the root cause of interefernce but I did see some postings the other day where people have created some cavity filters for ADSB, and have given the PCB files, I was thinking of printing some as they are only PCB layered and I expect pretty small put this in line to the antenna and RT dongle..
https://www.reddit.com/r/RTLSDR/comments/1ce9p8/filter_for_adsb_reception/
-
Don't overlook the material specs. "The material needs to be 2 sided 62 mil FR4". If you use anything else, the filter will resonate on a different frequency.
-
interestingly, at the bottom of the comments there's an explanation that they are going for ranges far in excess of what PilotAware needs.
>100 miles is common without a filter, (far in excess of what is useful to us) it looks like they are seeing how far they can get out to the theoretical 480 mile edge.
I'm not sure we need such a filter for the operation of PilotAware. ;-)
-
On the SkyDemon forum there is a post that warns:
"You need to be careful using those 'TV tuner' dongles in the air. They use a local oscillator in the tuner and spit out masses of RF interference spanning from VHF frequencies up past 1.5GHz (GPS) and beyond. One I tried knocked out a GPS receiver from half a metre away. Not good..."
Not being a techie I have no idea what this means and it certainly does not reflect anything I have seen while flying with a RPI with PIAWARE with both GPS and ADS-B USB dongles...can anyone throw light on what the author is saying?
-
Virtually all receivers employ what is know as the "superheterodyne" (superhet) design. The incoming signal is mixed with a very low power locally created signal to produce an intermediate frequency where most of the signal amplification takes place. This locally created signal is known as the "local oscillator" and it is, in effect, an extremely low power transmitter.
Dongles like the one we use actually convert down to baseband where digital signal processing (DSP) is used to render the required signals. The superhet concept still applies, so in theory, at least, it is possible for interference from the local oscillator to occur. It is, however, an extremely improbable effect. It would only occur in the event of a fairly significant malfunction in the dongle's electronics, as the local oscillator should not be tuned to anywhere near any of the frequencies that we use. I don't discount it by any means but there are other places I'd be looking first.
-
Do Software Defined Receivers (SDRs) even have a local oscillator? I tried to find out what mine was for my Baofeng dual band handheld, but I drew a complete blank. I found that it too uses an SDR I believe.
-
Answering my own question, there's a guide here:
http://www.pentek.com/pildocs/8363/techother/DGTLRCVRHBK43.PDF (http://www.pentek.com/pildocs/8363/techother/DGTLRCVRHBK43.PDF)
Diagram on page 7 (compared with analogue receiver on page 6).
-
The first few pages, before it drifts off into marketing spiel, is one of the best SDR receiver primers I've ever seen. Thanks Paul!
-
there is more than just the local oscillator to consider... the DSP uses clocks running very fast, which can often come out of the antenna port at a range of frequencies (lots of them all at the same time!). this is one of the issues with SDRs vs the traditional analogue technique.
It would be best to keep this as far away from your VHF as possible.
-
What Wobblewing says ^^^ is right. The problem with fast digital logic is that they create lots of spurious carrier waves, little transmitters that can interfere with your regular COM, your transponder and your GPS.
A clean analog local oscillator produces a single sine wave signal. This is usually not a big problem unless it sits exactly on the frequency you are trying to receive. A digital system on the other hand uses square waves. That means that besides the signal frequency, you will also find signals at multitudes of that signal frequency. Usually the odd multiples, so 3x, 5x, 7x etc. What that means is that if you have a clock somewhere at 1 MHz, you'll find signals at 3, 5, 7MHz etc. An entire comb of signals. In a DSP there are usually lots of clock-like signals, so lots of noise.
A good DSP (or any other digital) system will use proper shielding to keep that interference from escaping. Unfortunately the cheap consumer dongles use simple plastic casings and cheap cables that keep nothing in. The RPi itself is guilty as well.
What might help a bit is to use a metallic case that includes the dongle, and perhaps some ferrite beads on every wire coming out of that case. One of the other threads showed some 3D printed cases. Perhaps spraying them with metallic paint on the inside would be a good first start to fight interference.
-
Would an aluminum case for the Rpi help?
-
Yes, it probably would.
-
Had our first flights over the past couple of weekends with the ADSB PAW, and we have also had consistent interference on all the frequencies we used. We have powered it via a 12v socket hard wired in the aeropane, and then a plug in USB (3.1A) power supply, and having unplugged various components in turn, it seems clear that it is the PAW that is causing it and not the lead or power supply. More of a nuisance than anything, but still a bit annoying. I have used the same cheap plastic box as in the instructions, maybe metal will help?
-
Hi Rick
Just to confirm, are you hearing a 'click' every couple of seconds, or a white noise effect ?
also you say
a plug in USB (3.1A) power supply
Can you post a link to this, and do you ever power anything else (such as your iPad) from the
same supply and not get the same effect. Some of these are notoriously noisy.
Finally are you able to try powering PAW from a USB battery source, these give much less noise.
I would strongly suspect the USB power supply, and bear in mind this would only cause this issue when loaded, just plugging the USB power supply into the Auxillary socket, does not rule this out as your noise source, it mus have a load attached
Thx
Lee
-
Lee - it’s a white noise effect, and it was a USAMS twin port charger, one of these:
http://www.ebay.co.uk/itm/NEW-TWIN-USB-USAMS-DUAL-2-PORT-3-1-AMPS-UNIVERSAL-CIGARETTE-SOCKET-CAR-CHARGER-/121911798279?hash=item1c62826a07:g:NFIAAOSwYlJW1uxJ
We have only connected the PAW to this one which I bought because of the higher current requirement.
I will try sorting out a battery supply to check that out too. We also have 2 12v sockets in the aeroplane, and have another (different) usb charger in the other one which drives an Aware gps. What I should have done is to switch the chargers, and see if the USAMS one causes the same interference when connected to the Aware. I will check this out the next time I fly!
Do you have a recommendation for a good USB charging socket?
Thanks
Rick
-
http://www.charge4.co.uk/ Designed with pilots in mind
-
Lee - it’s a white noise effect, and it was a USAMS twin port charger, one of these:
http://www.ebay.co.uk/itm/NEW-TWIN-USB-USAMS-DUAL-2-PORT-3-1-AMPS-UNIVERSAL-CIGARETTE-SOCKET-CAR-CHARGER-/121911798279?hash=item1c62826a07:g:NFIAAOSwYlJW1uxJ
We have only connected the PAW to this one which I bought because of the higher current requirement.
I will try sorting out a battery supply to check that out too. We also have 2 12v sockets in the aeroplane, and have another (different) usb charger in the other one which drives an Aware gps. What I should have done is to switch the chargers, and see if the USAMS one causes the same interference when connected to the Aware. I will check this out the next time I fly!
Do you have a recommendation for a good USB charging socket?
Thanks
Rick
http://www.ebay.co.uk/itm/Adjustable-DC-DC-Boost-Step-up-Power-Converter-Module-XL6009-Replace-LM2577-/272041588474?hash=item3f56f136fa:g:68gAAOSwiwVWRUaf
These work pretty well, but you have to wire them in (don't forget a fuse).. adding extra capacitor also helps keep the noise down. You need to use a multimeter to set the output voltage to 5V (or just a little higher, say 5.25V), then it's best to glue up the potentiometer with cyano so it doesn't readjust itself with any vibrations.
Cheaper than a £100+ power supply.
-
Lee - it’s a white noise effect, and it was a USAMS twin port charger, one of these:
http://www.ebay.co.uk/itm/NEW-TWIN-USB-USAMS-DUAL-2-PORT-3-1-AMPS-UNIVERSAL-CIGARETTE-SOCKET-CAR-CHARGER-/121911798279?hash=item1c62826a07:g:NFIAAOSwYlJW1uxJ
We have only connected the PAW to this one which I bought because of the higher current requirement.
I will try sorting out a battery supply to check that out too. We also have 2 12v sockets in the aeroplane, and have another (different) usb charger in the other one which drives an Aware gps. What I should have done is to switch the chargers, and see if the USAMS one causes the same interference when connected to the Aware. I will check this out the next time I fly!
Do you have a recommendation for a good USB charging socket?
Thanks
Rick
http://www.ebay.co.uk/itm/Adjustable-DC-DC-Boost-Step-up-Power-Converter-Module-XL6009-Replace-LM2577-/272041588474?hash=item3f56f136fa:g:68gAAOSwiwVWRUaf
These work pretty well, but you have to wire them in (don't forget a fuse).. adding extra capacitor also helps keep the noise down. You need to use a multimeter to set the output voltage to 5V (or just a little higher, say 5.25V), then it's best to glue up the potentiometer with cyano so it doesn't readjust itself with any vibrations.
Cheaper than a £100+ power supply.
I bought something like those to look at, before they rebranded their knock off LM2577 as something else to get round selling fake chips. Would I trust one of these in the air, no, there is a reason they are 99p and no doubt someone will find out soon enough.
I think I bought 5 for £2.99 or the like, 1 just passed the input voltage through regardless of adjustment. I might dig one out and pop it on the bench...
Those ones listed are actually down as boost onverters, so plugging one of those into an iPad will generate a few sparks. They all look the same so it can be pot luck what you get. You may have meant these ?
http://www.ebay.co.uk/itm/Boost-Buck-DC-DC-adjustable-step-up-down-Converter-XL6009-Module-Solar-Voltage/191777597596?_trksid=p2047675.c100009.m1982&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140328180637%26meid%3D9473a34b18de4af1ab63337625095938%26pid%3D100009%26rk%3D1%26rkt%3D10%26sd%3D272041588474
-
I have an Anker one which is now discontinued, but there's a new version. It's very quiet RF wise at least in my car and aeroplane. The car radio is quite sensitive to cheap USB chargers! It doesn't manifest as noise but as reduced sensitivity.
-
Lee - just to close out my interference issue, you were absolutely right of course, it was the plug in USB power supply. By trial and error, I have now found one that works fine with no interference. Thanks for the help!
-
Hi Rick
Great news, I saw a similar issue where I could not squelch out the receive when using a poor quality usb power adapter
Thx
Lee
-
Lee - just to close out my interference issue, you were absolutely right of course, it was the plug in USB power supply. By trial and error, I have now found one that works fine with no interference. Thanks for the help!
Rick, would you care to share the identity and source of your successful purchase? Several people I know are searching for the holy grail!
Mike
-
The unit that you need is an Anker Power Drive 2
Highly recommended
https://www.amazon.co.uk/Anker-PowerDrive-2-Port-Charger-iPhone/dp/B00VH84L5E/ref=dp_ob_title_ce
-
I can vouch for the Anker PowerDrive 2 - great bit of kit.
I have even run PAW and iPad Mini at the same time
-
Thanks, both.
Mike
-
Mike - this is the one that worked for us!
http://www.ebay.co.uk/itm/UNIVERSAL-TWIN-PORT-USB-12V-CAR-CHARGER-ADAPTER-CIGARETTE-SOCKET-LIGHTER-SILVER-/231853445396?hash=item35fb8ad114:g:-1oAAOSweW5VcmWU