XL-1 RF Issue with Police Cars Resolved

[James Emory]

A few years ago, I had experienced the following issue while using the Sony PD 150 & 170 with portable 2-3 watt radios but never with the XL-1 until the spring of 2005. Whenever I would get back from shooting news I kept hearing this clicking noise throughout my footage but it was intermittent. Only a few months ago I figured out where the intermittent noise was coming from in my audio after finally looking back and isolating it to only happening when I was shooting around police cars and never any other type of normal environment. Our police cars were recently outfitted with new GPS locator tranceivers around 2005 or shortly after. Now it could also be newer and/or more powerful radios because as previously stated this didn't happen when I was around police cars in my area before 2005. So, if you are experiencing strange clicks in your audio and are around law enforcement vehicles or officers with high powered portables on their sides, that's probably what it is. I now try to avoid doing interviews near the police cars, at least near the trunk where the transmitters are located, but sometimes I don't have a choice. I'm thinking it's the GPS systems though. They must have to emit some serious power to uplink to the satellites. Below is an interview with a police officer where you can actually hear the clicks.

XL-1 RF Interference Audio Issues (5.22 MB)

Relevant Threads
http://www.dvinfo.net/conf/showthread.php?t=35565

http://www.dvinfo.net/conf/showthread.php?t=36046

[Boyd Ostroff]

Not likely to be the GPS. GPS is a one way system that only receives satellite signals which are always out there in the air. There is no "uplinking" with GPS.

I had a problem recording a performance with my Sony PDX-10 a few years ago. All of a sudden a two way radio cut into the audio loud and clear. Sounded like a trucker or maybe a taxicab, but the street was several hundred feet away from my camera location in the theatre. Weird...

[James Emory]

There has to be some signal that is being sent because that is what tells the satellite where you are so it can perform its calculations. The GPS system in their cars is not just for 911 or the station to track the cars' movements. The officers in the cars have the ability to pull up a map of the city and see where all cars are in real time too. So, that system would have to be two way if they can send and receive a signal.

[Boyd Ostroff]

I'm sure that is accomplished by the GPS in the cars sending data over regular terrestrial radio back to a computer somewhere. The GPS in the car locates its position by receiving satellite signals (in fact that's why they are called GPS receivers), then it transmits the position to a computer which can display each car's position on a map.

The OnStar system also transmits your position to a central station, but I think they use cellular communications whereas the police probably have some other kind of digital radio transmission. That may be what causes your interference, but not the GPS'es themselves.

Believe me, the GPS system consists of satellites which only broadcast signals, they don't receive them back from you. See http://gps.faa.gov/FAQ/faq-gps.htm#1

The user equipment, often referred to as “GPS receivers”, captures and processes L-band signals from the satellites in view for the computation of user position, velocity and time.

[James Emory]

I'll take yours and the government's word for it. It still doesn't make sense to me though. How does a satellite know where you are to then tell you where you are if your portable doesn't send it a signal first?

[Boyd Ostroff]

Does this help? http://en.wikipedia.org/wiki/Global_Positioning_System

A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites. Measuring the time delay between transmission and reception of each GPS radio signal gives the distance to each satellite, since the signal travels at a known speed. The signals also carry information about the satellites' location. By determining the position of, and distance to, at least three satellites, the receiver can compute its position using trilateration.[2] Receivers typically do not have perfectly accurate clocks and therefore track one or more additional satellites to correct the receiver's clock error.

[James Emory]

A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites. Measuring the time delay between transmission and reception of each GPS radio signal gives the distance to each satellite, since the signal travels at a known speed. The signals also carry information about the satellites' location. By determining the position of, and distance to, at least three satellites, the receiver can compute its position using trilateration. Receivers typically do not have perfectly accurate clocks and therefore track one or more additional satellites to correct the receiver's clock error.

Okay. So the receiver does all of the work by calculating it's position relative to the information the satellites send it at that given time.

No matter what though, I didn't have that audio issue until after they got GPS in their cars. One thing I didn't mention earlier was that the county police cars don't have GPS and I don't have that issue when around them. But as I also stated the city police cars could have also gotten stronger radios or ones on a frequency that conflicts with the XL's circuits. Who knows? I've only had one occurance where the picture jumped like with the Sonys. I wonder if I turned off OIS if it would still happen? I was planning to see if I could do a process of elimination test by placing my camera near a police car with only one system at a time in operation to see which one was causing the problem. Until then, I have to keep my distance or put up with it. One more interesting note is that another shooter on one story was using a newer GL-2. I had him place his GL-2 near a car making that noise in my camera and it didn't happen with his. So, maybe Canon has improved the RF shielding in their latest cameras.

[Don Palomaki]

GPS is part of the system but not the whole system. They probably call it GPS Tracking (or something like that) as a marketing thing because the the system, as installed, uses GPS to determine the unit's location, and then uses a separate transmitter built into the system to send the units ID and location back to the dispatch office. Without the GPS there is no reason for continuous chatter from the car back to dispatch. Kind of like cell phone keep up an frequent hand-shaking chatter back to the local cell tower that can break into some radio receivers, land line phones, etc.

On RF interference, reminds me of a reception I shot with a friend a few years ago. The DJ had a cheap wireless system, and the local police chatter was breaking into his system. He ended up using our wireless because it was not bothered by the police radios.

[Boyd Ostroff]

FWIW, here's a company which makes a variety of vehicle tracking systems: http://www.advantrack.com/hw_gps_tracking_overview.htm

And this one is a little scary... http://www.pimall.com/nais/gpssnitchit.html

[James Emory]

I believe I've confirmed that something producing strong RF signals from our city police cars is definitely affecting my XL-1 cameras in a very bad way. I experienced this with a third XL-1 recently with only one to go and I think it's ruining my cameras. Not only is it creating clicks in the audio and making the image jump as described earlier but it's also interfering with the way my cameras are recording by resetting the timecode causing intermittent TC drops creating banding in the image and sometimes not even recording content even though the code is rolling. I have two other XL-1's that don't work reliably now, as far as recording to tape, because of the timecode/recording issue and I just pulled out my third camera. It was working fine like the others but during and after shooting around those police cars recently, it too breaks code and is now unreliable. I only have one left before I'm totally disabled. The common factor with all affected cameras is that they began malfunctioning after being in close proximity to these police cars. What in the world could that RF energy be affecting in the cameras to cause recording issues?

[Bob Hart]

If the Police car is phoning home to update a central computer with its current location as determined by its GPS, then there will be a regular periodic transmission and it will likely be as powerful as the car's own radio.

The in-car computer systems, are they simply passive, receiving periodic data updates or are they also a two-way data system? In that event, a periodic phone home might be also be going on.

If digital settings stored info on a camera is being corrupted, a data uplink would be my wild guess. I don't know if your Canon is like JVC but if it is then likely there are stored adjustable settings which you the user don't have access to.

(In my ignorance I can only describe this generically - is it called firmware? In this instance, it might just be that your camera's firmware is being updated corruptly and from then, maybe a limited memory is being incrementally filled with junk data, which might cause the timecode glitches.).

I wonder if restoring factory presets will fix your problem, or to an extreme, if the camera has a memory battery, removing then replacing the battery and re-booting the camera from scratch might do something?

[James Emory]

Originally Posted by Bob Hart

... I wonder if restoring factory presets will fix your problem, or to an extreme, if the camera has a memory battery, removing then replacing the battery and re-booting the camera from scratch might do something

I hope that it's as simple as a factory reset. Are you talking about replacing the watch battery that maintains the meta data like the time and date? Someone at B&H said to remove and then replace reinstall the data battery and that might reset an IC,capacitor or something else vital.

[Don Palomaki]

Call Canon tech support, see if they have had similar reports from other areas, and if there is a solution.

[James Emory]

I will definitely be giving Canon a call. I noticed something yesterday when shooting near a police car again. I've always known that their radios trigger their RADAR transceivers because when they key up the radio, the RADAR unit on their dash beeps. Yesterday though, when shooting by that car, the window was down and when I heard that click described above, I also heard the RADAR unit beep simultaneously with that click. So, that leads me to believe it's their radio units and probably not the GPS. All I know is that I've got 3 XL-1's that are screwed up now with only one good one left and I'm not too happy about it. :(

[James Emory]

Here is a relative thread about what else I thought the timecode breaks and banding was being caused by.