Recent content by Paul Sw

I watch this thread often and contribute rarely. I find the technical level fairly low with lots of misconceptions and technical errors. However the posts in this thread by sar104 and N107RW are the exception. They show an exceptional understanding of both the physics involved and the detailed...

I sometimes use my i-pod mini with a P3S. It works fine with no noticeable lag. The screen is not as bright as on my i-phone 6 so in bright sunlight I use the iphone. For evening of overcast days the larger size of the mini is an advantage for my old eyes. Paul

Yes, 15 years ago they were able to get 1 cm accuracy with differential GPS using phase tracking. Perhaps you did not look at the second reference, it has 2016 references. Of course it does not apply to DJI drones and we should end the discussion on this forum. I was just commenting on your...

Nigel, Look at these references or Google NASA JPL GPS or similar. JPL News Release - NASA Navigation Work Yields Science, Civil, Commerce Benefits GIPSY-OASIS By using differential GPS and keeping track of phase it is possible to get sub cm accuracy. It is not yet practical for weapons...

The only way to get mm accuracy is to track phase of the downlink from the satellites. This requires that the two receivers also are phase locked to each other. In your demo with two Garmin units side by side there is no phase reference between them. Thus the only accuracy improvement is that...

Good, I knew the rumor wasn't true.

A lon-lat system is defined which is tied to the solid Earth. That is the system a GPS receiver reports in. The absolute accuracy of a position measurement is about 5 meters. When you launch your drone the stored “home” location is only as good as this 5 meters. When you return home it is a...

Davis and Nigel are both correct. Placing two recievers side by side does not give an indication of the GPS accuracy. In fact the atmospheric phase correction, one of the largest error sources, is identical in both recievers. If you came back an hour later you might read a error of several...

With selective availability off (it is probably off permanently) and no Wide Area Augmentation (WAAS) the actual position of an object will be within a circle with a 30 meter diameter centered on the calculated GPS position 95 % of the time. WAAS is a system developed by the US Federal Aviation...

A couple of comments on Nigel's excellent discussion on GPS. There are not really two separate US GPS systems. There is only one GPS system. Organizations with the proper credentials (military for one) have access to the precision codes which have higher accuracy than the civilian codes that we...

The reason a satellite TV antenna needs to be accurately pointed is the much narrower beamwidth. K-band with a wavelength about 2 cm is often used for satellite TV. Referring to my post #24, the beamwidth for a 40 cm diameter TV reflector operating at 15 GHz is 60 x 2cm/40 cm = 3 degrees. This...

You are exactly correct that the dipole must be at the focal point. I was really responding to post #19 where he thought the gap between the dipole and reflector created noise because of out of phase reflections.

The windsurfer is just a parabolic reflector and becomes part of the antenna system. It concentrates the beam in one direction instead of the donut shape from the stock vertical dipole. The distance from the dipole to the reflector should be ¼ wavelength or about 3cm. The wave travels ¼...

You guys are really touchy... I was just trying to point out that in addition to the RC antenna being perpendicular to the line of sight it is also necessary to have both dipoles parallel to each other. An impossibility when flying directly overhead. The latter did not seen to be common...

Sky Hog, you are quite right about reflections and degrees of cross polarization response in both antennas. However, what people are overlooking is the range we are talking about...less than 400 ft. Even if it were legal or advisable to fly straight up one kilometer, I doubt if the data link...