The KX-171 from Cameray, apparently comes in a number of variants. The datasheet suggests at least twelve possible variants, of which three (six if you count PAL and NTSC separately) major ones are now available in the FPV market. These are:-
1. KX-171 (traditional), runs from about less than 7V to 12V @90mA
2. KX-171LVP (NGHobbies), runs from 4.4V to 5V @150mA
3. KX-171 G2 (RangeVideo), runs from about 8V to 12V @60mA
Physically, all three cameras look identical except for text on the backplate. The first two are very similar except for their power supply specifications, but the third one, the G2, is a different beast altogether - utilizing a different CCD as well as power supply system. In order to get the low-down on all these three and to see if the G2 with improved resolution, retains the low supply noise of its predecessors, I ordered all three cameras to run these tests.
As we are doing some relative noise testing, all three cameras are re-tested using the same configuration with a 433MHz helically tuned antenna as the primary sensor. What this means is that it will pick-up noise better in the UHF band as this is the band of our primary interest. Markers are set for 435MHz (UHF), 1.575GHz (GPS), and 1.11GHz which is somewhere in between the two. The total span of the test is from 150MHz to 3GHz. We could have gone quite a bit higher but are constraining the test to a more relevant portion of the RF spectrum. The cameras were tested at the rated voltage, as well as the minimum operating voltage - which is defined as the voltage below which the picture starts to degrade noticeably.
RF Emissions Profile
The KX-171 (traditional) yielded the following spectrum profile, which we will use as the baseline for testing the other two cameras:- As can be observed, there is some RFI, concentrated mostly in the UHF and below range. In practice, this level is only noticeable because of the sensitivity of the spectrum analyzer and the EMI/RFI sensing setup.
Then comes the KX-171LVP:- The RFI levels appear to be slightly lower but in the same sort of range. One can surmise that for all intents and purposes, these two cameras are in the same class as far as RFI emissions go.
Compare this with the KX-171 G2:- Just a cursory glance reveals a completely different RFI profile compared to the previous two cameras. Not only are the levels different, but the RFI covers a much broader spectrum, all the way up to nearly 3GHz. Testing at the minimum operating voltage usually show a slightly lower RFI level (no more than 5dB).
It is interesting that while the G2 has a lot more RFI, the actual increase at 435MHz is actually quite small, lower in fact that the first two cameras. Where there is a real increase would be in the GPS L1 band where it was previously completely clean but now has a significant level of noise. It is likely that this camera won't be a problem for UHF LRS systems but whether it will be a problem for GPS reception is something we will have to investigate. The current draw profile suggests that these cameras utilize linear regulators so much of the noise is coming directly from the video circuitry itself but propagated through the supply lines in particular.
We will next test the image quality that these cameras put out to see if the IQ gains (if any) warrant putting up with the higher noise levels of the G2.
The sensor for the G2 is purportedly better than the other two. To start with, the CCD itself has a higher resolution of 752(H) x 582(V) for PAL and 768(H) x 494(V) for NTSC. This is a significant improvement over the other cameras' 500(H) x 582(V) for PAL and 510(H) x 492(V) for NTSC. That improvement, however, is confined more to the horizontal resolution with vertical resolution remaining virtually the same. In theory, this should yield better clarity in the horizontal (about 50% better) and should be noticeable in images. The reason vertical resolution wasn't improved much is probably due to the vertical rate limitation of PAL and NTSC. Even so, the G2 gives a 480TVL (NTSC) and 520TVL(PAL) so you should also see a corresponding increase in resolution in the vertical as a result of this. In this case, the PAL cameras will be far better in terms of resolution, compared to NTSC ones. Where you are likely to see the enhanced resolution of the G2 is in diagonal lines which are rendered more smoothly, compared to the "stepped" or "jagged" look of the lower resolution variants.
Resolution isn't the only difference though. The SONY Ex-View 1/3-inch CCD sensor also has different light handling. The following three images demonstrate the widely different low-light handling capabilites of the three cameras:- It is quite apparent that the G2 is out performing the other two cameras and that the LVP is better with low-light than the original KX171. There were at least two dead-pixels on the G2 sensor, though, but this is not uncommon for this type of sensor and would be unnoticeable in daylight. If was going to fly at night, the G2 would represent a pretty good choice judging from the test images. It should be said that the LVP isn't doing too badly as it does look closer to what the actual scene looks like, whereas the G2 looks enhanced in brightness.
*In the test, I did not refocus the optics for the best infinite focal-length, except for the original KX-171 which had pre-focussed. This could account for some differences in the far field detail in the captured images.
The follow are daylight tests of the three cameras. The pictures should give you some idea of the key differences, both in colour/saturation and resolution:-
Surprisingly, the first thing that struck me wasn't the added resolution of the G2 but the somewhat over-saturated colours. In this respect, the LVP actually performed very well, giving the closest colours to the actual scene if somewhat muted. The G2 colours looked artificial by contrast, while the original KX171 was clearly lagging behind. The improved resolution of the G2 comes into its own with the indoor shot where you have a lot more details and where you see less colour fringing and moire compared to the original KX171. I would have to give this one to the G2 although the LVP held its own quite respectably.
RFI impact testing
See next post.
If I were to pick one of these cameras, it would be a toss-up between the LVP and the G2. The older KX171 is clearly, well, old. The LVP stands out in low RF noise performance, while still holding its own in image quality. The 5V supply can be an important feature for some users too, although the current draw is on the high-side (150mA@5V) compared to the lower current draw of the G2 (60mA@7V). The low light performance is not that great either. The G2, on the other hand, is a fantastic low light performer, has much better overall resolution and good indoor colours. The outdoor colours are a little bit to strong but this may be correctable in post-editing. There was a patch of blur-ness in the lower right of the image which could be due to the optics (lense) or sensor alignment. More significantly, the G2 puts out a more noise than the LVP and across much bigger spectrum (although slightly less noise in the UHF), including the GPS L1 band. Another important consideration is that the LVP costs only USD65 compared to the G2's USD95 (see links at the end of the post). If I were going to do night flying, I would get the G2 without question, but short of that - the LVP looks like a more attractive solution.
2 November 2010
http://www.rangevideo.com/index.php?mai ... cts_id=207
http://www.nghobbies.com/cart/index.php ... cts_id=549