Low Frequency Radio Transmission for long distance.

On Tue, 19 Apr 2016 23:25:45 -0400, rickman Gave us:

He is almost as bad as Donald Trump with his claims of "good management" and always jacking off at the mouth about his schooling.

They are not proud of him... at all.

They're not ear rings.

Let's not think about that.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

AlwaysWrong strikes again. GPS is received well below (~26dB) the Earth's noise floor.

Hog rings?

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Nope. The various space probes (Voyager 1 and 2) probably have the weakest signal "out there". Dig out your handy 8GHz receiver and try your luck. This is 10 years old, but still interesting: See calcs starting on Pg 12.

True, but a negative SNR (signal to noise ratio) doesn't mean that the GPS signal can't be decoded below the noise floor: The theoretical processing gain for GPS is 43.1dB, which leaves sufficient SNR to demodulate a BPSK signal. There's an example of the calcs on Pg 176-177 here: The example produces a signal that is 26.7dB above the noise after despreading.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Obviously. It wouldn't be of much use otherwise.

No mention that NASA tracked this with some of the early Microdyne

1100 series receivers. They were still in service 30 years later, having required no repairs.

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Handheld and car and cell phone GPS receivers use tiny antennas in noisy environments. GPS works in wrist watches. There is lots of signal.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Enough, obviously. Lots? Not so much.

Tiny antennas mean lots of signal.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Ok, you get bragging rights for having worked on or with the receiver.

30 years continuous duty is a very good record. Are you sure NASA wasn't rotating spare receivers every few years? Methinks it unlikely that one receiver would have lasted 30 years (dry electrolytics, tantalums, control lubrication, xtal aging, drift, calibration, etc).

Is it this one, or one of the later versions with a similar model number?

The DSN (deep space network) downlink is at 8.4GHz for data and imaging. The command channel downlink is at 2.2GHz, which is barely within the range of the Microdyne 1100-AR. Ok, that works: See Pg 10.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I beg to differ. For GPS, most antennas are circular polarized patch antennas, either RHCP, LHCP, or both. These are sold in various sizes, usually plated on a ceramic substrate. As the patch becomes smaller due to using higher permeability ceramics, the usable bandwidth and gain of the antenna becomes smaller. If you just need L1 reception for civilian location and timing, you can use a really tiny patch, such as 12x12mm. However, if you want L1, L2, Glonass, and WAAS, you'll probably need a 36x36mm patch. Anyway, tiny GPS antennas means less signal.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I was wondering how small a GPS antenna can be purchased. This looks like the smallest at 3.2x1.6x1.1mm:

The gain specified is about 1dBiC, which is quite good for such a small antenna. It's better than the smallest patch antenna that I could find at 10x10x4mm: which has a CP gain of -4.45dBiC.

So, perhaps smaller is better, depending on geometry and antenna type (unless the data sheets are lying as usual).

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

The problem with urban canyons is that the signal from every satellite will propagate through reflections from buildings. Thus, the pseudo-code distance to each satellite is larger than in an open field. The calculated fix point is at a longer distance from each satellite, i.e. deep under ground level.

When the reflected path length varies constantly when the receiver moves, you might not be able to calculate the fix point all the time.

Despite this, the signal strength might still be sufficient.

Sufficient for what? If you can't get a good fix, it throws off all the calculations giving not only altitude errors, but lat/lon errors since the sats all travel different distances. It's not the same as all the signals traveling an arbitrarily longer but equally longer paths (similar to using an outdoor antenna with a long cable). Each sat travels a path with an arbitrary additional length added. This is hard to correct for and gives errors in lat/lon/alt and even time.

If you are moving, the path to the sats is changing and much like multipath with FM stations, it is hard to lock to any given sat.

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Rick

I guess we have very different definitions of "lots", but we won't get into the definition of "infinity". ;-)

Communication is not occurring. ;) I take John's meaning to be that in order for a tiny antenna to work adequately, there has to be lots of signal (uV/m) available.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Sufficient to get a location fix. The urban canyon and indoor reception problems are largely solved by HSGPS (high sensitivity GPS). etc... Once locked, the receiver can produce satellite delay data at a high rate. Depending on signal strength and reflections, many of these fixes will be garbage data, but a substantial number of them will result in usable locations. The catch is that in order to do that, quite a bit of processing horsepower is required. That's easy enough in a smartphone, hand-held GPS, or GPS tracker. Not so easy in a GPS watch, sports device, or animal tag, which are limited by available battery power. Incidentally, the iPhone 3GS and later have HSGPS chips.

Actually, it's fairly easy if you have a large number of independent location fixes. Just built a histogram or some kind of correlation function and take the number that appears the most. Having the satellites move around the sky is actually an advantage. If the satellites were at a fixed location in the sky, and the GPS receiver were in a static location, such statistical methods of detecting multipath errors would fail because the multipath would always produce the same timing delays for sequential fixes. However, because the satellites and possibly the receiver are all moving constantly, the chances of getting two identical delays are zilch, making statistical analysis and correlation possible.

So, what's the catch with HSGPS? Well, to get a 2D location, you need data from 3 different satellites. 3D requires one more. That's fairly easy in open country, but not so easy in the urban jungle. Also, delays from satellites directly overhead are useless. More simply, it only works when you have 3 or more satellites directly in view between the buildings. That works so-so in most urban jungles, and doesn't work at all in my dense forest for 150ft and higher trees. Indoors is much the same problem. You have access to the satellites in the sky only through doorways and windows. If the glass is metal plated with Low-E film, no RF gets through. There are also some issues about accuracy.

Yes, but once you have an initial location fix, subsequent fixes go much faster. Using HSGPS techniques, even faster.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558