[Milsurplus] US Navy Returning To CW Training

[Bob Camp]

Hi

On most systems ( = not in a country you have never heard of) holdover is specified
to be longer than 24 hours. Indeed since that’s a worst case spec (and for a few other 
reasons) something around 3 to 5 days is a likely number for a system that has been up
and running for a while. If the tower is in a hard to get to location, the holdover numbers
may be in weeks.

What happens when holdover time is exceeded? It’s not at all dramatic, your phone call 
gets just a bit more noisy. If you used long distance in the early days of digital, you know just
what the random ticks and clicks sound like. Since capture effect works, the only place 
you have an impact is at the RF fringe of the cell (and when there is an adjacent cell). 

If you are out in the sticks and there is only one cell system on your band / that you can hit, what happens?
Absolutely nothing at all happens. The codes drift. All the phones stay locked up to the tower.
No added noise. No problems. No disaster. The calls go through, nobody notices. 

So, a great big disaster? Nope, far from it, at least for cell towers. 

What about all those GPS’s in other applications? Well, no car navigates any more. 
People can no longer tag their photo posts with the location. All of the “normal” GPS stuff stops. 
Everybody gets on the phone and complains. Hmmm … everybody is complaining right around
*there*. Wonder where we send the truck to grab the jammer. If it’s airborne, where do we send 
the planes?

Bottom line, the jammer isn’t going to go on doing it’s thing for days and days un-noticed. The
world is not going to just sit there and blow bubbles while GPS is down. There will be complaints 
from lots of voters. Corrective action will be taken. 

A hammer and a bag of nails is a *much* better / easier / longer term way to take out a cell tower. 
Be sure to hammer fast !! The alarm is ringing somewhere ….

Bob
KB8TQ

> On Feb 9, 2016, at 3:04 PM, Francesco Ledda <frledda at att.net> wrote:
> 
> Actually, it is a little different.
> 
> When the GPS clock is lost, the oscillator enters a mode called Holdover.
> In this mode, the clock is held at the last good frequency.  It will remain
> in this mode, until the GPS clock returns.  The local oscillator has a
> prescribed frequency short and long term stability.  The network will work
> properly with a complete GPS outage. The synchronizes and desynchronize can
> operate properly with some frequency offset. This kind of technology was
> created in the late 80s (SONET).
> 
> F
> 
> -----Original Message-----
> From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
> Hubert Miller
> Sent: Tuesday, February 09, 2016 1:40 PM
> To: Milsurplus at mailman.qth.net
> Subject: Re: [Milsurplus] Fwd: US Navy Returning To CW Training
> 
> 
>  The telco office i recently retired from has two GPS systems for 
> supplying office timing, primary and secondary.
> I was told that if both GPS fail, the oscillator in the clock 
> distributor will run in free mode, undisciplined mode,
> or whatever it's called, for at least two weeks with reliable timing. 
> The clock distributor is in a 19 inch rack  by
> about 6 inches tall, but most of the card slots in it are distributor 
> cards, and the oscillator is only one or two
> slots, so that technology would fit in a cellphone site, i would think.
> The first GPS installed, maybe 15 years ago, was a big deal, antenna on 
> the building roof, coax, waterproofing
> entries and lightning protection. We had problems twice, once with 
> electrical failure and once with water entry.
> In those days, if i recall, timing was derived from a channel on an 
> optical circuit. The most recent GPS made me
> think of something you could buy off Amazon or Walmart even. After the 
> tech found a good window location,
> he glued the small plastic thing to the inside of the window, then the 
> rest of the coax was run inside the building.
> No more weather problems.
> -Hue Miller
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