[ntp:questions] CHU/IRIG audio drivers

David L. Mills mills at udel.edu
Mon Jan 29 19:12:58 UTC 2007


Max and others,

An essay:

This discussion is actually about your page linked from your message.

You bring up VOACAP, which is specific to antenna configuration at both 
the transmitter and receiver, as well as the 10-cm flux, which at this 
time of the sunspot cycle is miserably low.

You mention CIRAF zones, which is ironic since CHU 7335 is presently 
victim of IHFB broadcasters in Central America. The broadjammers have 
essentially chewed up all the spectrum from 7100-8100 in ITU Regions 1 
and 3 (Europe and Asia) and 7300-8100 in Region 2 (North and South 
America). The band 7350-8100 was once allocated to the Fixed Service, 
but as a practical matter the band has been heavily infested with 
broadcasters even before reallocation.

The band 8100-9040 belongs to the Maritime Mobile and Aeronautical 
Mobile Services. The next slot above that is 9040-9400 allocated to the 
Fixed Service. Broadcasters have poached there as well. In any case, 
that's probably too high for the current 7335 users.  There is a small 
slice 6765-7000 allocated to the Fixed Service worldwide but the FCC 
considers it an ISM band. It's unknown how Canada allocates it, but do 
we want CHU in an ISM band? There's nowhere to hide.

A very solid case can be made for the Maritime Mobile users to give up 
some spectrum. Once upon a time Morse telegraphy was the medium of 
choice, but most maritime coast stations have abandoned that mode and 
rely either on Marisat or SITOR, which is much more spectrum efficient 
and the operators don't need Morse training. Using an archaic ITU 
footnote, the maritime coast frequencies are often poached by US 
military stations using encrypted teletype. An especially egregious case 
even now is the poaching of the WWV protected band at 5 MHz by 
broadcasters that camp on the edges of the protected band and splatter 
sidebands over the WWV signal. Is there no shame?

I once complained to the FCC Maryland monitoring station about 
interference on the 60-kHz WWVB signal. They and the Maine monitoring 
station triangulated to a location in Quebec. They told me they had no 
jurisdiction and directed me to the State Department. So, adjacent 
channel splatter on 5 MHz coming from Costa Rica? Gimme a break.

In principle, CHU could join the IHFB consortium and fight VOACAP wars 
with the other broadcasters for frequencies, with a gentleman's 
agreement to protect the 7335 frequency. Problem is at night the 
adjacent channel splatter takes out CHU now.

As for western Canada, I hear you. You propose a system similar to how 
European countries manage their national mediumwave/longwave networks. 
They heat up a national loudenboomer on a protected longwave frequency 
near the center of the country (Radio Luxembourg come to mind?) and spot 
several lower power, mediumwave transmitters to fill in the outskirts of 
the coverage area. The problem is, even if the outskirt transmitters are 
synchronized by one means or another, coverage at places nearly 
equidistant from two or more transmitters is very problematic.

CHU has another problem. Unlike WWV and WWVH that were designed to 
coexist on the same frequencies, the CHU signal design of not conducive 
to cochannel frequency sharing. It might be simpler to retail CHU 
modulation via VHF FM broadcast subcarrier in selected metropolitan 
areas, like the BBC does in Singapore. Using the NTP audio drivers, and 
inexpensive FM subcarrier demodulators, no special purpose equipment 
would be needed.

Obviously there must be a lots of noise going on in Canadian politics on 
this issue, since the problem must certainly have been anticipated on at 
least the last two WARCs, but only announced recently in public. Western 
Canada is about as far from Ottawa as Eastern US is from Fort Collins, 
so the propagation conditions should be about the same. There will be no 
joy in the high latitudes of Canada and Alaska due geomagnetic unrest, 
so HF service might not be an option anyway.

The precision time and time interval (PTTI) folks have toys far better 
than anything that can be done at HF. CHU has expensive, redundant and 
precise timecode generators and transmitters that can deliver time 
accurate to 0.1 ms, as claimed on the CHU web. The NTP audio driver can 
deliver that level of performanc, even if the fractious ionosphere 
wanders up and down some 0.3 ms or more.

There is a fundamental problem which is often overlooked. Who are the 
true customers of the HF services? The CHU web site mentions the NTP 
audio driver, but does not mention CHU receivers that might be available 
from other sources. I can't find any commercial purpose-built CHU 
receivers, but Google came up with another CHU audio decoder 
http://www.rossi.com/chu/ similar to the NTP audio driver, but designed 
to operate standalone. Are they the only CHU sources?

The easiest option would be to re-license as a broadcaster and try to 
hold on to 7335. Next best, move 7335 just below 7000 might be the 
easiest option.

Dave

Max Power wrote:

> Have you seen:
> ??????????????????????
> http://CBC.am/CHU.htm
> ??????????????????????
> 
> CHU can be improved upon, at least to the point of having 2 transmitter 
> sites.
> 
> This at least would allow for transmitters at some sites to be turned off 
> while others are turned on -- allowing for the upgrade to pay for itself 
> with respect to the power bill.
> 
> 
>>I've just gone through a round of audio driver upgrades for the WWV and 
>>CHU radio services and the IRIG signal. The documentation has been 
>>rewritten as well. I'm hoping that the CHU upgrade might find users in 
>>Canada to support the continued operation of CHU with three frequencies, 
>>even if the 7335 kHz frequency is moved. As it is, that frequency is 
>>clobbered from sundown to sunup by broadcasters that should be using the 
>>Internet.
>>[...]
>>In addition to the accuracy improvements, the radio drivers have better 
>>behavior under marginal signal conditions, especially the 
>>maximum-likelihood UART and majority decoder used in the CHU driver. As we 
>>are at the nadir of sunspot cycle, propagation conditions have been truely 
>>awful, but does present the opportunity to improve the algorithms to 
>>separate weak signals from real trash.
>>
>>To Canada (my father was born there): get the CHU thing running and make 
>>sure the NRC knows it.
> 
> 
> 




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