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How far does a watt go...
the_radio_kid
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As i am assisting with an RSL radio station this year - how far roughly would 1 watt go at an aerial height of 10 metres (we have a10watt licence).... just curious to know
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I'm sure if a 1 watt tx was put on the moon, NASA could pick it up on earth, so it's down to the terrain, and the sensitivity of the receiver as well.
I did actually use to own a 10 watt FM transmitter, never used it in this country obviously (cough), but I (ahem) believe they will go at least 2 miles and probably more.
It's mostly goes on terrain and height of antenna, its abit like asking how longs a piece of string, in some circumstances 1 watt is just as effective as 5 watts or even 10 watts. Ideally stick the antenna out of the way of obstructive buildings / trees etc and choose somewhere with the maximised line of sight. I presume you are talking FM, otherwise if it's AM, things get more tricky.
FM - Height is the key, FM strictly works line of sight. Get a decent antenna with some gain to increase effective radiated power too and some decent coax so that the last milliwatt actually makes it to the antenna and radiates. Get a cut to frequency antenna at that and check it with a SWR meter to get mimium deflection, once you done that, take the SWR out of circuit. Plenty of web sites around that will give you step by step help - Good Luck
1 watt will comfortably serve a housing estate and, if decently placed, will reach beyond 1 mile for most radios, though it can sometimes cover exceptionally long distances.
10 watts will comfortably cover up to 3 or 4 miles with good line-of-sight to the transmitter. Any obstructions will reduce that. However, with a decent site, 10 watts can go for 10 miles and beyond. E.G. the Northside Radio 2001 RSL in Springburn, Glasgow, was received on people's portable trannies at homes in Paisley.
Another trick. Broadcast in mono. People's radios are much more sensitive for receiving mono signals, due to the lower threshold required to pick up a clean signal. A stereo signal will give listeners lots of hiss beyond 1 mile.
Stick a lightbulb on the top of Big Ben. Go and stand on the other side of the Thames. Can you see it? Maybe. Think of that as your TX, and sympathise with radios! I suppose you could go quite a bit down the road (next to the hospital), and you'd still see it - but the further you get, the less easy it is to see.
Anyway, according to Veronica, as a very sketchy guide:
50mW - 1 to 500 metres
100mW - 1000 metres
1W - 1.5 miles
12W - 7 miles
30W - 11 miles
100W - 30 miles
Im no expert but it does also seem to depend on the frequency in use, Does anyone remember the Susy Radio RSLs over the last few years on 531 from the Redhill area in Sussex? They were supposed to be using just one watt but they put a cracking signal out over a good part of the SE, I could even hear it on a car radio in Essex.
Sorry i meant Surrey not Sussex, I should know where Redhill is My Mother In Law lives there, Then again???
How right you are, Hang on i had better finish as the wife has just got up.
I picked up Radio Caroline's 1 Watt MW RSL here in Swansea under night time conditions and last year's RSL from Blaenavon in the South Wales valleys was picked up on the Isle of Skye.
It's frequency dependent, at SW you could get to the USA and Russia or further - at VHF a handful of miles - terrain dependent.
So our local ILR Metro is on 10Kw of power, so how far should that be able to travel if 100W is 30 miles?
I should imagine the only reason for Kilowatt licenses are for increased field strength in the TSA. 100 Watts might cover the distance, but 10 Kilowatts would give you the decent reception (theoretically, those figures make no sense!).
For example, and I REALLY don't know how this happened, but our 2nd AfanFM RSL was broadcasting on 25W from Mumbles Point (off the coast of Swansea) - now we had a very very clear signal for about 17 miles but the oddest thing happened.
Aberavon RFC, one of our major partners (plus we're the official radio station of the towns main Rugby club) were playing at the Millennium Stadium in Cardiff, we were covering the event, and I get a call from the head coach - "give us a shout out then - we've got you on the stereo outside the Millennium Stadium" - for some perspective, that's about 35 miles
But as our engineer says - it's the height of the aerial that gives you distance, power only gives you penetration
Craig
Yup I could hear it down in the new forest when I visited friends, I queried it then and some one on a forum assured me that they were running their licenced 1 watt.
Absolute crap ! I have since spoken to a few of my watery wireless friends involved with that experiment and found out that someone missed 'Kilo' out of the end of the statement. Probably because they were only issued with a 1 watt licence.
From experience 10 - 15 watts on the medium wave will cover 4-6 miles and be receivable on the average tranny. You will pick it up on a car radio a lot further afield. It will all depend on the aerial efficiency and ofcourse whether its a VHF or MF licence. I guess if its 1 watt its MF.
Another feature to look at is the coverage of some of the local hospital MF transmitters. These usually run power of 250mW - 1 watt
Good luck
Henry
It's not just the transmitter power that has an effect, it's the bandwidth of the receiver IF, generally the more narrow the receiver IF then the lower the S/N ratio and the more able it is to receive the weak signal. If you've ever experimented with PMR446 radios then you'll find from a hilltop you can talk to people upto ten miles away or more, despite the maximum power output from a PMR446 radio being set at 500mW.
It needn't have been a lot more than 1 watt, though. Spectrum International on 558 runs 1kW and covers a vast area - lamost double the size of Capital Gold (97.5kW) or LBC 1152 (23.5kW). That's because of the low frequency. 1kW on a higher frequency would barely cover half of the capital, hence why Premier (on 1332) using the same power, need multiple relays in the suburbs.
It really would surprise me to discover Susy Radio were using all of 1kW - it certainly couldn't be heard on a normal radio at all up in Warwickshire at the time, whereas Spectrum were quite listenable, although not exactly loud.
A couple of watts on 531 does go a long way, especially if its' anoraks with expensive receivers doing most of the listening, unlike such a power on a typical RSL frequency such as 1503. Not to mention the factor that during the day 531 is dead clear, unlike most of the channels given to low power AM stations.
Someone once told me that the Radio London RSL was heard in Nova Scotia.
Forget us enthusiasts et al with long wires and loop antenna, and midnight DX ing, and when you can hear stations from Canada and the USA on medium wave in the early hours, in real terms its short range local coverage.
Henry:)