Lack of coordination?

M0TAZ

Tonight noticed a Link 11 signal on top of a designated HFDL frequency.

Also some 3 frequency modem/data link on top of a STANAG signal?

G8JNJ

Hi Dave,

I've also thought that at times the military don't seem to have particularly good frequency co-ordination.

However they do have a fairly comprehensive frequency management systems. NATO has it's Frequency Management Sub-Committee based in Brussels and the UK, Australia, New Zealand, Canada and the USA also has the Combined Communications-Electronics Board (CCEB). Both of these use fairly sophisticated frequency planning tools and maintain frequency databases.

So why do some allocations look so chaotic ?

I think the answer is propagation and the required coverage area. In the 4-5MHz region the required communication is likely to be relatively short distances maybe up to 200km or so. If the wanted signals are strong enough to give adequate S/N in the region they are intended for then everything is OK.

As the intended coverage areas of the transmissions differ, if you try a few other web sdr's in different parts of the world, the chances are that some of the signals you see will be much weaker and others a lot stronger.

So if you are outside the intended coverage area then signals may clash, but inside the intended coverage area hopefully the wanted signals will be dominant.

Regards,

Martin - G8JNJ

M0TAZ

Thanks, Martin, I found the HFDL issue interesting, as it's an international "safety critical service" you would have expected this to be a prohibited frequency. I know some countries don't subscribe to the same rules, maybe that has something to do with it as well. Take your point on propagation, I guess it makes the best use of the resources.

Ta Dave