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London ambulance radio system fails in heavy rain
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5N0AFJ/A View Drop Down
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Posts: 156 		Post Options Post Options   Quote 5N0AFJ/A Quote  Post ReplyReply Direct Link To This Post Topic: London ambulance radio system fails in heavy rain
    Posted: 16 July 2010 at 16:40
London ambulance radio system 'fails in heavy rain'
 
I thought the following BBC news article would interest some here - here's the link to the news article http://www.bbc.co.uk/news/10608021
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G6URM View Drop Down
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Posts: 88 		Post Options Post Options   Quote G6URM Quote  Post ReplyReply Direct Link To This Post Posted: 17 July 2010 at 19:17
ah so the much vaunted airwaves system may not be so robust as they thought ?? - typical of the high up's to deny there is any problem - the crews probably know different though - but who ever listens to the troops on the ground ??
BRETT - G6URM - PLYMOUTH

it's a wonderful hobby amateur radio - i have friends all over the world - none in this country - but all over the world

tony Hancock : -the radio ham
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GW4KJW View Drop Down
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Posts: 272 		Post Options Post Options   Quote GW4KJW Quote  Post ReplyReply Direct Link To This Post Posted: 20 July 2010 at 15:27
Originally posted by G6URM

Emergency Preparedness - spanning the gap between "it won't happen to me"
and "we're all going to die!"


Or in Dad's Army terms, between L/Cpl. Jones's "Don't Panic!" and Private Fraser's "Doomed! We're all doomed!"
Gareth GW4KJW
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Posts: 88 		Post Options Post Options   Quote G6URM Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2010 at 08:36
Originally posted by GW4KJW


Originally posted by G6URM

Emergency Preparedness - spanning the gap between "it won't happen to
me"
and
"we're all going to die!"
     
Or in Dad's Army terms, between L/Cpl. Jones's "Don't Panic!" and Private Fraser's "Doomed! We're all doomed!"


LOL - yep got that one off a emcomms forum in the states - which i have been following as the whole emcomms thing is like soooooo political over there its untrue - anyways i digress

having been away from the front line of real emergency work for some years now - i have not had a chance to use the new system - but i doubt it is as good as made out , certainly i wonder if its any better than the old 70 MHz FM system we used to have - pretty good most of the time but absolute c**p in deep valleys and some other locations on the moors ( Dartmoor ) - many was the time we had to either shift position or relay via another appliance - however it did have advantages as we could also "cop a deaf un " and blame comms problems

ah the wonders of modern technology
BRETT - G6URM - PLYMOUTH

it's a wonderful hobby amateur radio - i have friends all over the world - none in this country - but all over the world

tony Hancock : -the radio ham
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2e0elw View Drop Down
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Posts: 10 		Post Options Post Options   Quote 2e0elw Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2010 at 10:34
So is it digital communications that are affected by the 'heavy rain' or all radio frequencies, and are there specific radio waves that can get through the inclemental weather better than others? The satellite systems used to be affected quite badly with heavy rain, snow, sleet and of course, strong winds with debris ;)
Elwyn 2E0ELW
Coventry RAYNET
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G1HUL View Drop Down
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Posts: 603 		Post Options Post Options   Quote G1HUL Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2010 at 10:50
Digital comms are "just RF", so affected in the same way.

Problem is that to the user, failure is instant - known as the "digital cliff-edge". You get 100%(ish) quality, or nothing as the signal drops below the decoder threshold. If you've got a digital TV, think what is happening when the screen breaks up. It's only about 1dB difference between all or nothing.

With analogue systems, fading isn't so obvious and the human ear is very good at decoding the "noise" of poor RF conditions.
Jim, G1HUL
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Posts: 88 		Post Options Post Options   Quote G6URM Quote  Post ReplyReply Direct Link To This Post Posted: 21 July 2010 at 12:09
Originally posted by 2e0elw

So is it digital communications that are affected by the 'heavy rain' or all radio frequencies, and are there specific radio waves that can get through the inclement weather better than others? The satellite systems used to be affected quite badly with heavy rain, snow, sleet and of course, strong winds with debris ;)


basically the higher in frequency you go the worse it gets - sat TV on 11 GHz is very prone to it but then you have to realise that ANY frequency above 1000 MHz is very easily stopped by things like trees etc ( what i call a "tree db attenuator" ) once you get into the very high microwave regions "water absorption" ( of signals ) can become a problem

however to a lesser extent this is true down to 400-500 MHz as well and even the path loss at 2m is considerable in areas with say a lot of hills or valleys - so add in the effect of weather on virtually any frequency and you have variables ( imo )

and of course in big cities - we have to add in steel frame buildings etc all of which can reflect or absorb signals so if you have a system that's digital as described "drop out " is virtually inevitable

at the end of the day "digital" is about saving bandwidth and making more money from the rest /whats freed up - for marginal paths /conditions - i agree analog is way better - probably because we humans are basically analog creatures - our hearing is analog till it reaches the brain where its converted to electrical impulses ( if i remember my biology correctly ?? ) - and we have the ability ( with practice ) to fill in the blanks caused by noise the same as we can actually make sense of sentences w th l tt rs mi ing
BRETT - G6URM - PLYMOUTH

it's a wonderful hobby amateur radio - i have friends all over the world - none in this country - but all over the world

tony Hancock : -the radio ham
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