Low Frequency Radio Transmission for long distance.

What we have here is a failure to communicate.

The charitable way to interpret things is in a way that doesn't assume that one's interlocutor is a moron. ;)

Cheers

Phil Hobbs

Reread my words 5 posts up in the stack:

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Tiny antennas mean lots of signal.

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I said the same thing twice, namely that because tiny antennas work, there must be lots of signal. I said it shorter the second time. The meaning should be clear in both cases; the alternate interpretation that you suggest is obvious nonsense.

To do that, I would need to have recognized that there was a different interpretation. I simply read John's statement and took it at face value. I had not considered an alternative interpretation until your posting appeared this morning. Please note that my reply addressed the technical content of the issue, without a personal attack, as is all too common in this newsgroup.

We can debate whether John made a grammatical error, or whether I misinterpreted his statement. I would give it 50% blame for each of us. I probably should have asked for clarification.

I look at it this way. If John had dug a large hole in ground, and I walked into the hole, is it John's fault for digging the hole, or my fault for missing the hazard and falling into the hole? I believe that the law would consider it's John's fault.

My comment about ambiguity being aggravated by short one-line answers is a personal preference, not a criticism. There are plenty of times when one line comments are appropriate or necessary, such as when there's not enough time to offer any detail. The problem is that I don't learn much from one-line comments. I prefer to have some detail, explanations, derivations, logic, sources, examples, etc. Had some of that been supplied, the self consistency of normal writing would have easily shown which interpretation of "Tiny antennas mean lots of signal" was appropriate.

The equations relating signal reception to signal strength are pretty simple. Look it up sometime. It's not so much different from receiving satellite signals from the edge of the solar system.

I can't see that I made any errors. But your alternate interpretation, namely that smaller antennas deliver more GPS signal, could only be proposed by an idiot, which I assume I'm not.

The one-liner was an affirmation of a longer statement, a few lines up in the same post.

Getting a location fix is not the same thing as getting an *accurate* location fix. The urban canyon changes signal path lengths which are how location is calculated. It also changes time measured since the time of each sat has to be adjusted for the location of the receiver. Finally, each sat has to adjusted for Doppler shift which also depends on all of this, so frequency suffers.

I think it's amazing that a wristwatch or a cell phone can receive signals from a constellation of satellites, each less than 50 watts. A bunch of dish antennas on the roof wouldn't seem unreasonable to get a GPS fix.

Lol! We can only view your mental state from the outside where the reception is not so good.

A very small dipole (compared to wavelength) works surprisingly well compared to full sized dipoles, just a few dB down. The problem is that a very small antenna is highly reactive and the resistive part might be _well_ below 1 ohm. You have to transfer the available power to the receiver input. Typically you would have to tune out the reactance and increase the impedance that better matches the receiver input impedance. On UHF and above you really have to think about power match also on receiving systems.

The problem with such low impedance levels is that any losses in the antenna or matching network might be grater than the radiation resistance, causing additional losses.

Current antenna preamplifiers might have noise figures below 1 dB, while the noise figures were much higher (especially with some input protection in military devices) when the GPS system was designed. Thus current commercial equipment can tolerate not so good antennas compared to original military GPS receiver antennas.

The actual data rate from a GPS satellite is just 50 bit/s when there is a lock. Compare this to tens of megabits/s for a TV sat. The required receiver power is at least 60 dB down and the antenna capture area can be reduced correspondingly.

OK, but a signal that's orders of magnitude below the background noise can hardly be called huge.

Once you get one, the rest are easy. ;-)

Checking prices, the Casio OCW-G1000 series mentioned in the article sell for between $1,300 and $2,300 depending on model and vendor. Ouch.

Methinks one of the smartwatches with GPS might be a better deal: For example, the Moto 360 Sport is about 1/5th the cost at $240 to $300. Getting a VLF in the Casio watch does not justify the added cost.

I wonder how much it would cost to just receive the LF time signals?

modules starting at 8 pounds:

You missed the point of my post. Some people want to refer to the time signals as VLF when they are LF. VLF is 3 to 30 kHz. LF is 30 to 300 kHz. There may be some time signal somewhere in the VLF band, but the ones everyone uses are in the LF band.

Just the RF signal or the decoded data?

The RF you can do with a loopstick, narrow bandpass filter, and an oscilloscope. In theory, the Q of the BPF needs to be: 60,000Hz / 5Hz = 12,000 which is not going to happen with a passive filter.

Incidentally, you'll be doing all your work after midnight, when the VLF signals are strongest.

In the past Digikey carried C-Max chips, boards, antennas, etc. However, they haven't stocked anything from C-Max for at least 3 years: receivers: antennas: So why did I post these URL's? Because these pages are the best shopping list for necessary parts and pieces needed to do development without dealing with C-Max and possibly signing an NDA.

I did manage to find some receivers with antennas on eBay a few years ago. The price was rather high and supply limited because they appeared to be salvage from broken "atomic clock" products.

Instead, I just found an old "atomic clock" and ripped it apart to see how it worked: I suggest you start this way so that you are able to see what is considered a "normal" signal. You will need to find a way to permanently enable the receiver since it only turns on when the clock needs an update and propagation is likely to be favorable. Plenty of "atomic clocks" available cheap on eBay, most of which use C-Max modules that can be extracted:

You can also "see" WWVB with the common RTL-SDR USB dongle and an eBay upconverter board. Dongles and upconverters:

Video of what you see with WWVB: Note that the antenna used is a very small active antenna design by PA0RDT proving that you don't need a loopstick or big loops antenna:

I've also done some tinkering with using a sound card and a computah. The common 44 and 96KHz sound cards won't receive anything at 60KHz, but the newer 192 and 384KHz sound cards will. I borrowed a customers machine that had an M-Audio something 192KHz sound card, ran Spectrum Lab software: connected a clip lead to the audio input connector, and was able to see what I think was WWVB after midnight. The SNR of this system is horrible, but it works. At the time, the price of such cards was rather high. Hopefully, they've come down. I suggest USB to get away from the computah noise.

Notes on VLF loopstick design and C-Max receiver:

C-Max antenna design and tools:

All too true, but that's not how it works. One can always trade update rate for accuracy. You can do quite a bit of computation between the NMEA 0183 update rate of 2 seconds. If you take a large number of locations, toss out the obvious junk, and just average the remaining readings, you'll get a reasonably accurate location fix. It just might take a while longer. The theory is that given a sufficiently large population of satellite delays, the too high and too low errors will tend to cancel each other, resulting in an accurate result. Kinda like garbage in, valid results out. Much as I don't like this, it does seem to work. Also, there are some tricks that can be employed, such as favoring data from satellites with good SNR and steady signals.

I was doing something like that years ago when selective availability was still a big problem for GPS users. The accuracy was there, but the military insisted that the civilian signal be dithered. It took an order from then president Clinton to get rid of that problem. Meanwhile, the most common solution for surveying and DGPS was to simply record NMEA 183 location sentences for hours, average the results, and produce an accurate location. It worked. So, if you have time, you can improve accuracy.

With the urban canyon and indoor problem, sample time is an issue. Since everything is moving, the duration for which a given reflection path is stable will be very short, while the direct path is comparatively longer. It's still measured in milliseconds, but given a sufficiently fast receiver (as in HSGPS), the phase differences can be collected quite quickly. The (direct) path has the longest stable duration, produces the largest number of data points, which then favors a more accurate average location fix.

So what do these links have to do with VLF time signals? I see the PA0RDT antenna design covers VLF, otherwise I can't find any mention of VLF.