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[email protected] · December 4th 12, 09:49 PM posted to rec.radio.shortwave

On Tuesday, December 4, 2012 4:22:53 PM UTC-5, Michael Black wrote:
On Mon, 3 Dec 2012, wrote:

We don't have any analog tv broadcasting since 2009 over here,in NYC. If

WWV and its sisters like WWVB or WWVH cannot be used due to the phase

modulation- I think the Canadian CHU still uses simple AM modulation or

something very close to it.

The problem with CHU is that it's not on an exact MHz frequency, so you

won't be able to adjust your 100KHz calibrator to that

I suppose it matters less now since you can easily divide 10MHz or 100KHz

down to 10KHz that will have a harmonic on CHU's frequencies, but it used

to be a big issue, and people who rely on 100KHz calibrators are likely

those unwilling to mod the receiver to get 10KHz.

But of course, if you're using a 100KHz calibrator, some phase modulation

isn't likely to be a problem.

Wait a minute. I WWV and WWVH have phase modulation (excrpt

whatever comes from propagation), it's WWVB that was mentioned. For a lot

of purposes, WWV is good enough, and on exact multiples of 1 MHz. The

issue is that due to propagation, it comes and goes, and can pick up

distortion along the way. But for those who were beating their 100KHz or

such calibrators against the carrier, it was good enough. The ability to

beat absolutely was hindered by the frequecy response of the receiver

(which made it harder to hear the really low beats) and once the beat is

really slow, it takes time to figure out whether you are too fast or too

slow.

Which is why WWVB was seen as the frequency standard ifyou needed

something better. If you could receiver the signal, you'd have a reliable

frequency standard, since it was groundwave (not bouncing off the

ionosphere where other issues come in). For a long time, WWVB was only a

frequency standard, initially that's all it was, then of course the

decoders to get the time took up so much circuitry that you wouldn't see

clocks that sync'ed up except in the lab. It's only the last ten or so

years where you could cheaply get "atomic clocks" and the time became

important. (And despite the low frequencies, WWVB was used because the

signal was always there, unlike WWV where the signal would fade. The

"World's Most Accurate Clock" from Heathkit used WWV, but apparently

adjusted the internal clock so it even kept good accuracy when WWV was not

receivable.)

Technically with the right receiver, you could get a 60KHz frequency out

of a WWVB receiver that was really accurate, while trying that with WWV

would fail due to fading and such. No transfer oscillator need, that

100KHz calibrator, though 60KHz isn't too useful a frequency reference in

itself.

The phase modulation on WWVB is recent, like sometime this fall. It

reflects the demand for all those "atomic clocks" since it's a secondary

method of sending the time on the carrier. Just like FM is noise-free

because you can put limiters in, the same with phase modulation, and in

plces that are at the farther edges of WWVB's pattern, phase modulation

would be more distinct since it won't be confused by interference from

other things like switching supplies that are generating "am noise".

I guess they've decided that "atomic clocks" in every household are more

important than a frequency standard, and at least nowadays there are other

methods to get accurate frequency, though less so for the hobbyist.

Let's not forget all those ads in the magazines for Hammarlund recievers

where crystal manufacturers and broadcast station engineers would plug the

receivers for profeesional use. Up until a certain time, WWV and WWVB was

used by a lot more people as a frequency standard (and WWVB for those who

needed something more), and they'd use off the shelf shortwave receivers

for that.

Then it become possible to get an expensive but still within reach Cesium

standard. Who can forget that wave of articles in the seventies about

getting a frequency standard from the color subcarrier frequency in color

tv? It wa accurate because it was set by the cesium standard at the

network. ANd then it soon faded because local stations started getting

their own cesium standards, and they weren't necessarily calibrated to the

extent of the ones at the network. They stopped using the network

standard. I may have garbled this, but there wa a point when it became

possible to get some standard that was better than a crystal oscillator

but wasn't as absolute as the atomic clock at the time stations.

The point is that the time stations became less important with time. Yes,

they are still fun and useful for the hobbyist, and WWVB is certainly

getting much more use via all those home "atomic clocks" than when it was

"merely' a frequency standard, but professional needs are being met

other ways (an indeed, professional needs often need something better

now).

Wikipedia says that there will be no phase modulation of WWVB for a

period each day, at 7 and 1900 UTC, it says for 30 minutes but it's not

clear if that's each time or 15 minutes each time. So you have some time

with an accurate frequency source, but not something that can be locked

too constantly.

Michael

Very much so. WWV +CHU+ several others are still broadcasting around the clock. What about GPS signals? They must be extremely accurate,considering how many uses this service provides worlwide.