[time-nuts] NIST

Brooke Clarke brooke at pacific.net
Thu Aug 30 17:20:04 EDT 2018

Hi Bob:

I would disagree in that ease of jamming/spoofing is strongly related to wavelength.  That's because antenna efficiency 
goes down as the size of the antenna gets smaller than 1/4 wave.
So, it's easy to make a GPS jammer (1,100 to 1,600MHz) since a 1/4 wavelength is a few inches, something that  you can 
hold in your hand.
It's harder to make a WWV jammer (.5, 5, 10, 15, 20 MHz) since a 1/4 wavelength in in the range of  500 to 12 feet, 
something that can be mounted on a vehicle for the higher frequencies.
But it's extremely hard to make a jammer for WWVB (60 kHz) where a 1/4wavelength is over 4,000 feet.  This means an 
antenna that can be vehicle mounted will be very inefficient. Note this also means that it's extremely hard to make a 
Loran-C jammer.  Note that the WWVB and LORAN-C transmitters run very high power and the antennas are massive.

This also means that if someone makes a WWVB simulator for their house the signal at the next door neighbor's house is 
probably going to be too small to effect their clocks.

PS. Some decades ago I maintained a beacon transmitter "LAH" on 175 kHz where the rules for unlicensed operation limited 
the input power to 1 Watt and total antenna length to 50 feet.  Under these conditions the effective radiated power 
might be 2 milliwatts, orders of magnitude less if a portable system.

Have Fun,

Brooke Clarke, N6GCE
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.

-------- Original Message --------
> Hi
> When infastructure GPS *does* get jammed these days that source gets tracked down a lot faster
> than a month or so. Anything that goes on for more than a day gets booted up pretty high
> pretty fast. Indeed I’ve been in the middle of that more than I would have wished to be …..
> The same sort of RFI issues that take out GPS from a TV preamp  can equally well take out WWVB or WWV.
> With WWVB, there are a *lot* of 60KHz switching power supplies out there to create problems. There is nothing
> unique about any of these services in terms of being jam immune.
> The bigger issue with any of them is spoofing. A proper GPSDO will go into holdover when RFI jammed. I would
> *assume* the same would be true of a fancy WWVB device. I’m not at all sure that’s true of a real WWVB standard,
> they haven’t been for sale new for a really long time. If your time source is in holdover, you can go out and track down
> the issue. If it simply locks to the new signal …. not so much.
> There is a subtle distinction in some of this. Newer systems do indeed want time. Older systems were generally after
> frequency. The only WWVB standards I’ve seen were aimed at frequency (and frequency holdover) rather than time and
> time holdover. Getting reasonable (1 to 10 ppb) frequency from WWVB is a very different task than getting the sort of time
> that modern systems are after.
> Bob
>> On Aug 30, 2018, at 2:46 PM, Scott McGrath <scmcgrath at gmail.com> wrote:
>> The port of Long Beach CA was jammed wrt GPS for several months by a malfunctioning 29.95 TV preamplifier on a boat.
>> GPS was completely unusable when this unsuspecting guy was watching TV on his boat.
>> He had quite the surprise when the coasties with guns showed up.
>> The fact is civillian GPS Is trivial to jam and jammers can be bought ‘under the counter’ at any truckstop along with illlegal linear amplifiers.
>> On Aug 30, 2018, at 12:58 PM, Peter Laws <plaws0 at gmail.com> wrote:
>> On Mon, Aug 13, 2018 at 8:52 AM Peter Laws <plaws0 at gmail.com> wrote:
>>> I have yet to hear anyone make a case for retaining the HF system that
>>> isn't backed by nostalgia.
>> Still looking for this.  Most of the "OMG IF WWV GOES AWAY MILLIONS
>> WILL DIE" posts (elsewhere, not here ... quite ...) are the type of
>> hysteria that is usually reserved for, I don't know, the EMP folks.
>> :-)
>>> As for solar flares taking out the various GNSSs ... wouldn't a solar
>>> flare only take out the vehicles that were on the "sunny" side of the
>>> Earth?  Wouldn't the (approximately) half of the SVs that are in the
>>> Earth's shadow be unaffected?  Serious technical question - I have no
>>> idea.
>> One of the responses to my initial message pointed out that the
>> effects of solar flares and CMEs take a while to get from Sol to Sol
>> III and don't arrive all at once, so potentially all GNSS spacecraft
>> could be affected.
>> Since then, I've been poking around for papers on the effect
>> (observed, potential, theoretical) of these events on the Navstar or
>> other GNSS constellations but am not having much luck.  I assume it's
>> because I'm not putting the right magic incantation into the google
>> machine.
>> Anyone got some cites?  Looking for the effect of solar flares and
>> CMEs on the spacecraft themselves and not how the GNSSs can be used to
>> measure the effects on the ionosphere, etc (those seem plentiful).
>> IOW, I'm curious about the resiliency of the systems to solar events.
>> I did note that at the time of the 1989 solar event that took out a
>> lot of Hydro Quebec's grid, only the "Block I" experimental GPS "SVs"
>> were in orbit.  Well, maybe a couple of the later ones - the
>> operational constellation started launching about a month before that
>> flare.
>> As I said initially, I'll be sad if WWV* goes away but it won't affect
>> my life in any measurable way that I can see.  I mean, other than the
>> mantle clock slowly losing time.
>> -- 
>> Peter Laws | N5UWY | plaws plaws net | Travel by Train!
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