RF Quiet Wall warts

And what do you do when the GPS band noise level increases, swamping the GPS signal. After all, the despread SNR is quite low to begin with.

Just what is going to happen on the ISM bands, such as 2.45 GHz when more and more devices are installed in that band. A specific WLAN link might work today at the desired distance, but what happens next week when one new devices are introduced ? The link range may drop significantly and there is really much you can do about it.

In the US, the problem is that WWVH at 60.0kHz also transmits BPSK data, the technology is tied up by patents. The patent holder, Xtendwave (Everset Technologies), was suppose to provide a suitable chip but hasn't done anything since it was introduced. Cut-n-pasted from something I posted to S.E.D. last year on the topic with a few additions and corrections:

(...) The mythical ES1000 chip: Patents and applications: and a whole bunch more patents and applications: Patent ownership is now in the hands of Grindstone Capital. See "Legal Events" at the bottom of the page on most of the patents. (click on "patent assignments" tab). Unless something has changed in the last year, at the current rate of progress, I don't know if we'll ever see PM chips. If anyone has some up to date info on the topic, I would be very interested.

Switching to BPSK offers a 10dB processing gain. Accumulating an hours worth of data will add maybe another 18dB of processing gain. Since most of the switching power supply noise and interference appears as amplitude modulation, switching to a phase modulated system will also add quite a bit of noise immunity. I recall seeing some info on the topic in the Time-Nuts mailing list, but I can't seem to find it.

The basic "interference" problem is that it takes a full minute to obtain one full frame, and two or three frames to determine that the received data is valid. Three seconds is a very long time to expect noise free reception. Simply flipping a nearby light switch will produce a small arc, which will disrupt reception.

A rather complex do it thyself WWVB BPSK receiver:

Some of my playing around with WWVB antenna polarization and orientation showing the effects of cross polarization: My comments on the photos:

The LORAN C system was turned off in the US in 2014 and in most of Europe in 2015:

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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

It isn't. You must be referring to the SNR before despreading. GPS is at 1575 MHz. It will not be affected soon by the kind of interference we are talking about.

That is what you get on ISM bands. Free spectrum but no allocation policy and no guarantee of interference-free use.

The part of the ISM band that overlapped with the 13cm HAM band has been declared receive-and-satellite-uplink-only here. (2400-2450) (to reduce the risk of interference from HAMs to WiFi)

You won't have long to wait for that to happen in the US. A few years ago, Lightsquared donated enough money to the Democrats to convince the FCC to allocate the spectrum they had won at auction to terrestrial cellular service. Unfortunately, the channels were adjacent to the GPS frequencies. Also unfortunately, GPS receivers have rather wide receiver front ends[1] making them susceptible to interference from nearby services. The outcry by GPS users was sufficient for the FCC to table the matter and for Lightsquared to back off, for a while.

Well, they're back as Ligado Networks: They've spent the last 5 years doing "research" and are offering a new grand plan to any company or organization that had previously protested their scheme. They've also continued to "support" the proper political party and office holders. Since the FCC is no longer interested in what the public needs, I predict that Ligado will get approval to use their frequencies. Since the FCC is no longer in the enforcement business, I can also predict that any interference reports will be ignored. Say goodbye to GPS in metro areas.

My guess(tm) is that they will use terrestrial repeaters to extend coverage, exactly like Sirus/XM does. These are NOT low power devices and are intended to fill in coverage holes that are inaccessible by satellite. The problem is that most of metro coverage for Sirus/XM comes from these repeaters, not satellite. I expect much the same from Ligado where the satellite system is simply an excuse to build a terrestrial network.

Yep, it's a problem. The surest sign of success is pollution and WiFi is certainly successful. The unlicensed outdoor long range links are the most susceptible. It's impossible to get any kind of long range link on 2.4GHz. 5GHz is still possible, but only with high gain antennas to provide the best possible SNR and to reduce interference from the sides and back. I don't know how long that will last. There are a few such links that have already moved up to the next available band at 24GHz.

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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

You mean 3 minutes. With DCF77 there is more possibility for checking as there are parity bits and also the values are in BCD and have a limited value range within that (e.g. minutes field can only be 00..59)

Usually a receiving system has "some idea of the correct time" and can determine with reasonable certainty if a received datagram is correct. Receiving multiple datagrams of course can improve that certainty, but they do not have to be consecutive for that.

Still, it can be tricky to obtain a clean datagram under conditions of interference.

But that is as it should be! With the limited number of channels available, it should be considered criminal to try to setup an outdoor long range link without using high gain antennas with small sidelobes.

Oops. Side effect of talking on the phone while writing all that.

The current AM WWVB coding does not include any parity bits: The new PM WWVB encoding includes 5 parity bits and repeats one LSB: More than you probably wanted to know about the protocol used:

The most common AM time receiver chips by C-Max use an algorithm that requires 2 or 3 sequential successful frames before the clock will be updated: See the "compare both telegrams" box in the flow chart:

There is no storage in the C-Max chipset. There are receivers with storage capabilities, but those use the storage for error correction and accuracy improvement by accumulating previous frames.

Tricky? no. Expensive? maybe. Messy? probably.

For example, how hard would it be to throw together a diversity reception system using two DCF77 receivers that are geographically separated? With data arriving at the screaming rate of 1 bit/second, there's plenty of time to perform computation on the probability that the bit is a one or a zero. The disk drive manufacturers do that because the data from the head looks more like garbage than data. Lots of other error correction tricks can be used, all of which require storage of previous data and adequate computation time.

Incidentally, a problem with using WWVB as a reference is that it doesn't really make a good stabilized clock oscillator. There were WWVB disciplined oscillators available: but they were replaced by GPSDO's long ago.

--
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 am referring to the despread SNR. Going from the 1.023 MHz chip rate to 1 kHz carrier gives about 30 dB processing gain. The GPS data is transmitted at only 50 bit/s, with a further processing gain of 13 dB.

Detecting this 50 bit/s will require a few dB positive SNR.

Counting backwards, the on-air SNR in 1.023 MHz bandwidth must be better than -40 dB.

Just add a large number UWB sources and the noise level will increase all over.

Criminal? Are you planning to prosecute someone for failing to use good engineering practices? I wouldn't mind seeing that because it would put most of my competitors in jail.

Actually, the FCC "encourages" users of point to point links to use big high gain antennas. Part 15.247 describes how the gain of a directional antenna can be increased by 3dB for every 1dB drop in transmit power. That grinds out to a 24 dBm transmitter and a 24 dBi antenna, which produces 48 dBm EIRP or 62 watts EIRP.

Note that the interference problem with high gain antennas and point to point links is along the line of sight of the antenna, not to the sides or back. Along the line of sight, the gain of the antenna is highest. It's very likely that some other wi-fi transmitter is located along this line of sight, usually behind the intended other end of the wireless link. I have a 400ft link between my house and one of the neighbors. When I first set it up, I failed to notice that a local mountain top radio site was directly in line with my antenna. The mountain top is about 8 miles away and is full of interference sources. Nothing would work until I reduced my antenna gain and moved the link.

Incidentally, for point to point wireless bridges, I like to use Ubiquiti PowerBeam PBE-M5-400 radios at about $100/end. There are 3 different sizes of antennas and some options to deal with the side lobes. As long as I pick my channels carefully, I don't have much trouble with interference from other users of the 5GHz band. The built in spectrum analyzer software is a big help.

Fun and games:

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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

But the average GPS receiver is indicating a typical despread SNR of 30-50dB on an antenna with clear sky visibility so there is quite some margin! Not "quite low" in my opinion.

Here the typical DCF77 clock is a crystal-referenced digital clock with synchronization to the DCF77 signal. The battery-operated clocks synhronize once per hour or twice a day. At the time they receive the datagram they know what to expect.

All the receivers I am still using are old and are simple AM receivers with an AGC that kicks in on local interference and requires several seconds to recover. When I would want to build a receiver today, I would just tune a ferrite antenna to 77.5 kHz, and connect it to a suitable sound card (with 192 kHz sampling rate), and do it all in SDR technology. Easy to do both AM and BPSK.

DCF77 and WWVB are only really suitable "network quality" time. The jitter on the demodulated AM signal is about 200us here. For purposes that require time in the microsecond accuracy range, like our simulcast NBFM repeater, GPS is a must.

THis is not "failing to use good engineering practices", this is simply "antisocial behaviour". Others should have their fair share of the channel usage as well.

That is quite a lot, we cannot have more than 1 Watt EIRP for unlicensed usage.

It of course still depends on the beamwidth of your antenna. The lower the gain, the larger the beamwidth and the more likely there is some other user in that beam.

You use those for 400ft links? That should give very good results at very low power. We build 30-40km HAMNET links using these, with

1 Watt EIRP only. We prefer to use the better -ISO variant. (less sidelobes, mechanically more sturdy)

But it does fix the problem of noise from switchers.

Other noise sources should be cleaned up too. But that doesn't mean we should ignore the "easy to handle" (in your words).

HF has unique propagation properties. It's a shame to throw those away.

Solution: we need VHF wallwarts, preferably in the two-meter region. That way only a small group of old-hat radio amateurs would be affected. ;-)

Cheers, James Arthur

I'm the one who knows all, knows what's best, and is always right, even when I'm wrong.

True. Until now, ham radio in the US has been a "sacred cow". It's unlikely to stay that way, but I don't mind enjoying it while it lasts. The limiting factor is the average age of the licensed ham radio population. "In some countries, the average age is over 80 years old with most amateur radio operators earning their license in their 40s or 50s." That's probably wrong, but close enough to make my point. When all the aging hams drop dead from brain cancers caused by a lifetime of RF exposure, the bands should then be clear enough to auction off to the highest bidder to be used for whatever acronym is then in fashion. This may be the reason why the FCC are not particularly anxious to do battle over a sacred cow. The merely have to wait.

You forgot to blame the internet. A local group recently bought an FM broadcast license and went on the air. Based upon some rather dubious research, they have more online listeners than OTA (over the air). It's also much the same with AM broadcast and OTA TV, where streaming and cable handle the bulk of the users. New technology, such as HD Radio (Ibiquity) was suppose to save FM from a premature demise. In the US, there are about 1,700 HD Radio stations out of 6,600 commercial FM and 4,000 educational stations. In my never humble opinion, the reason for the low uptake is techno-political. The station owners didn't want to take the gamble and switch to an all digital system. So, they opted for a hybrid mess that does a miserable job of digital and a tolerable job of analog. Anyway, if the FCC maintains it's generally poor batting average for new technology, we could very well see the premature demise of everything except cellular data.

That would be BPL. To the best of my limited knowledge, BPL is dead in the US. Note the large number of "concluded deployments" which is the politically correct term for bankrupt or shut down. The web site that the FCC was ordered to provide listing existing deployments has been down for at least 2 years. IBM continues to produce lurid press releases announcing the raising of this dead technology, just to see if anyone is still interested.

However, all is not lost for BPL caused interference. The HomePlug technology is basically just BPL for use inside a home or building. Merely go to your nearest electronics vendor, purchase a pair of these, and you too can trash the airwaves. Here's your chance to accuse me of being a hypocrite as I sometimes use these in place of CAT5 when expedient.

There's still quite a bit of HF traffic on the marine bands. Not as much as before but still plenty.

Wasn't that the argument used by industrial chemical companies after they polluted a river? Nobody ever drinks from the river, so it must be ok to pollute it. Can't have a few dead fish get in the way of progress.

--
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

If the problem is conducted, a ferrite may work, though at 100MHz, radiated emissions ten to dominate. The are certainly more problematic. Again, the fundamental is _rarely_ the problem.

Screw ill thought out "political solutions". They certainly aren't.

Again, the fundamental is *NOT* the problem with switching power supplies. If it is, you're doing something *very* wrong.

Don't you just love generalizations?

I've got a pair of these wired up at the moment, as part of another project:

They just so happen to be running from a LISN, because I already know they're noisy as hell, but I CBA to fix them right now. ;-)

So, what the hey, let's turn on the speccy and entertain that thought, huh?

(No, I don't have log sweep, so this is in segments.) Tons of crap at the fundamental and low harmonics. Eww!

And yes, both are running pretty much spot on 200kHz. Kind of a silly choice, 140kHz would be much better suited. But there you have it, eh? Oh, but what about the rest of conducted --

Mid-band peak, about 84dBuV -- but still less than the 92dBuV fundamental (note different ATTEN settings).

So, if one were to take your words literally, your argument is pretty well f***ed. If /NO/ supplies have issues at fundamental, then the above plot doesn't exist, right?

But this is just one example, right? Maybe you don't literally mean "all", you're just calling out a stereotype, and you've worded it badly. Over several posts..

And what about radiated?

Well, I don't have antennas set up, of course, and you are welcome to question the veracity of "300MHz conducted". But, whatever, it definitely shows things. Here it is:

(The peak at 125MHz is related to the "another project". Actually, I'm not sure why it's so strong, it should be well within a metal box. Another thing to fix, it seems.)

Even if the mains wiring is particularly unlucky (-20dB or more?) in the VHF band, and even if a lucky wiring accident made this radiate egregiously at some frequency, it seems unlikely that those

Sure the radio amateurs are a dying breed. But contrary to your statement there is no scarcity of HF spectrum. In the past years, we got our allocation extended several times. The original user left, the space was unused, and re-allocated to ham radio. So I don't think the authorities are anxious to sell it to others, they could have done that instead of giving it to radio amateurs and they did'nt.

Over here, "official" AM radio has nearly died. The medium wave transmissions of the public radio stations have ceased, the frequencies were auctioned and some "higher profile commercial" stations took them and subsequently went away, some are still used by "radio nuts" and religious groups without a viable commercial plan and they often sit unused or used at only very low power. Now you can apply for an AM license as an individual for "community radio", a lot of them were taken but as I predicted the majority never went on-air. There is initial enthousiasm but after being faced with reality most of them throw in the towel.

And FM will go the same way. The official stations are transitioning to DAB+ (as a dying gasp, of course online is the future), and will stop transmitting on FM within a decade, the route will then probably be the same: issueing licenses to ever smaller operations and finally sitting unused or taken over by pirates. Or maybe even ham radio.

No, I don't mean the use of powerlines to transport internet to the home. Here, it is used to distribute internet and other local network traffic inside the home. E.g. when a subscriber decides to switch from traditional cable TV to IPtv, they get a fiber or VDSL router at their switchboard and they don't want to run a UTP from there to their TV set. So they get a set of two wall warts with RJ45 connector that send the IPtv signal via powerline, locally. (of course they would be much better off with a MoCA set using their existing coax, but these decisions are made by marketeers not technicians)

That is what I mean.

Our coast station on HF bands was shut down at least a decade ago.

Never heard that here...

The FCC allows this because some brilliant attorney

+++1

That's a false dichotomy, you know. There's no shortage of good designs that, in mass production, produce negligible RF with very minor layout or component changes from the 'junk emitter' wallwarts under discussion. In medical designs, for instance, there are some stiff ISO standards, and medical-grade power supplies are VERY quiet. Even at close range with a pickup coil, one Condor supply gave me NO indications, couldn't even find what its switch frequency was. It was pumping out a couple of hundred watts at DC.

There was a time when all the inexpensive computer monitors (remember the Heath/Zenith H19?) in town were doing the same crystal-controlled power handling, and one could find the RF in every street, every building, all over Seattle. You just couldn't pin it down to a single source. The FCC cracked down after a bunch of complaints came in.

What you need, is to complain to the FCC, and for the FCC to be sensitive to the complaints, and proactive in sending out vans to find the source... which means you WANT the FCC to be political, in that sense. Or, you want to get a retirement home in Green Bank, West Virginia.

Anything less than a federal agency won't have a van to do a survey with, and the FCC has the jurisdiction (so to speak) that speaks to the issue.