Video Cameras characterization

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Daniel Wee
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Joined: Wed 25 Feb 25 2009 8:00 pm

Camera RFI impact on GPS

Post by Daniel Wee » Wed 03 Nov 03 2010 11:46 am

Camera RFI impact on GPS

It isn't yet common knowledge that the RFI from cameras can adversely affect GPS performance. The following test demonstrates an example of this:-
Before powering up the VSN500
SnapShot(29).JPG (55.77 KiB) Viewed 26767 times
After powering up the VSN500
SnapShot(31).JPG (55.45 KiB) Viewed 26767 times
The second screen capture was taken within seconds of powering up the camera and it is obvious how the GPS reception has degraded dramatically. At this distance, the RFI is being radiated directly more so than it is coming across the wiring.

Of interest to me is the impact of the various types of KX171, and in particular the RFI performance of the G2 compared to that of the original KX171 and the LVP model (both of which have similar RFI profiles). In our test, the KX171 (original) and the LVP have negligible or no measurable impact on GPS performance, even when place within 1cm to the GPS module (LS20031). The G2, on the other hand, degrades GPS performance up to 5cm away from the GPS module, though not nearly as bad as the VSN500 (and presumably cameras of the same design).
Before powering up the KX171 G2
SnapShot(19).JPG (55.26 KiB) Viewed 26767 times
After powering up the KX171 G2
SnapShot(20).JPG (54.96 KiB) Viewed 26767 times

Other cameras tested, such as the WDR700 also show degradation of GPS performance when in close proximity to the GPS module. In this test, most of the RFI would be direct radiation but in an FPV setup, it is highly possible that RFI is transmitted across the wiring and power supply as well. It was also found that different GPS modules performed differently in terms of how much they are impacted by the RFI. Some modules were still able to retain enough signal to lock even through RFI but the general accuracy is degraded.

In the light of these findings, the following recommendations are made:-

1. Keep as much separation as possible between the camera and the GPS module. Even 5cm is not enough separation in many cases. You probably need at least 12cm or more.
2. Where separation is not possible, use a camera with low or no RFI in the GPS L1 band.
3. Where and if possible, place an RF choke (ferrite toroids) on the camera cable as near the camera as possible - for cameras that are noisy (RFI-wise.)
4. Where and if possible, place, place an RF choke (ferrite toroids) on the GPS cable as near the GPS module as possible.*
5. Not all GPS modules perform equally. The one you are using may fare better or worse than another module or design.

*There are some people advising that the choke should not be at the GPS end and that is incorrect and wrong information. The choke should be as close to the GPS as possible.

Daniel Wee
3 November 2010
Daniel Wee
Site Admin
Posts: 2153
Joined: Wed 25 Feb 25 2009 8:00 pm

Resolution comparisons

Post by Daniel Wee » Wed 03 Nov 03 2010 2:46 pm

Res-test 005a.JPG
Actual scene
Res-test 005a.JPG (78.51 KiB) Viewed 26752 times
KX171 original
SnapShot(37).JPG (48.84 KiB) Viewed 26753 times
SnapShot(34).JPG (47.66 KiB) Viewed 26753 times
KX171 G2
SnapShot(33).JPG (50.92 KiB) Viewed 26753 times
SnapShot(35).JPG (58.72 KiB) Viewed 26753 times
SnapShot(39).JPG (46.4 KiB) Viewed 26753 times
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