Thursday 15 March 2018

Radio Caroline on 648kHz: great coverage with just 1kW

When I first heard about Caroline's plans to transmit on the Medium Wave, I was skeptical.

I couldn't see the point in running a community type radio station on just 1kW of power to cover a limited coastal region of East Anglia.

But I've changed my mind   ...Now I get it!

Back in 2017, Radio Caroline applied for an AM Community Radio License and here is their completed application form. It makes amusing reading because it basically implies that its listener base are a bunch of dinosaurs:-
"...aged predominantly from 45+ they will have little or no interest in current pop music..."
"They are not always at the cutting edge of technology...not always able to listen via computer or phone..."
"...tolerant of the limitations of... AM Mono radio..." 

I forgive them!

In fact the application is inspired, and it makes me wonder whether someone "inside" said "listen, this is what you will need to say to get this application through!"

The application also touches on transmitter power by noting that the typical max power for a Community Radio station is generally 20-70Watts ...and it then goes on to ask for something exceeding 1kW.

the reality

In an earlier post I was skeptical about the idea of Caroline as a Community Radio Service, but I've changed my mind. One reason is that I've been listening to Caroline on my car radio.

Here we are in West Sussex, and I can drive around local roads listening to a "Community Radio" station transmitting from Suffolk!

OK, the quality is not HiFi, and its a bit noisy, but just remember that I'm part of the target audience:-
 a technophobic dinosaur that can't use a smart phone or a computer, is tolerant of crackly AM mono radio and hates modern music!
My only failing is that I'm not part of the Suffolk community!

The truth is that Caroline is putting out a great day-time signal, and there are a number of reasons for this:-

  • Caroline's 1kW transmitter is hooked up to a mast at an ex-BBC transmitter site at Orfordness in Suffolk.
  • The site itself would have been well chosen back-in-the-day by the BBC for their World Service.
  • The mast (known as the "reserve 648kHz mast") is omni-directional, possibly over 100m tall and probably more efficient than any of the ship-mounted masts used by Caroline in the past.
  • With the recent closure of many medium wave transmitters (including the BBC) there seems to be no real day-time co-channel or adjacent channel interference.

Obviously at night, several powerful international stations spoil the fun (signals 'bounce' off the ionosphere after dark and are able to travel fantastic distances, Caroline included).

As regards to power, in the offshore radio days, Caroline on the m.v. Ross Revenge was using a 50kW transmitter into a 91m mast. I seem to remember that RNI (Radio Northsea International) had a 100kW medium wave transmitter ( a 10kW shortwave & 1kW VHF/FM transmitters), although I'm not sure they could run at full power due to insulation problems (salt water and electricity are a bad combination).

I think the Caroline organisation has been very smart in gaining this license. It may open the doors for future developments, possibly the introduction of a fully working Offshore Radio Museum.

what about the Ross Revenge?

The Ross Revenge was the third ship used by Radio Caroline and saw service during the 1980s.

It is currently used primarily as a tourist attraction, where visitors are ferried out to its location in the River Blackwater for a look around the ship and studio (...we are going out to the ship over the Easter weekend!).

However, the fully working on-board studio is increasingly being used for programs, where the audio is pumped out from the ship to the internet, for streaming directly to listeners, and also to the 648kHz transmitter at Orfordness for broadcasting.

Ross Revenge 1984.jpgThe Ross Revenge photographed in 1984 at anchor in the Knock Deep channel of the southern North Sea.
By Third ear - Own workCC BY-SA 3.0Link

Unfortunately the ship is now a registered hulk, which means it can't travel anywhere under its own power. But its a nice idea (although probably completely out of the question) that one day it might be made sea-worthy, so that it could sail from one UK location to another as a floating, fully operational museum.

Further reading:-

 OK, Caroline is no longer just 1kW

 Our visit to the Ross Revenge 

 The History of 648kHz 



  1. DAB+ on the Plymouth transmitter would reach a very large audience.

  2. I drove home from work in Edinburgh last night listening to it. Trying to find out if this is normal.

    1. I think you are doing particularly well from Edinburgh. I doubt if that could be relied upon regularly. At home in the Isle of Man, I can get it sporadically on 648, sometimes very clearly indeed, but it depends on the conditions. Other times it is completely unlistenable here. It seems to be very steady on the eastern side of the country, even quite far up North. Last year I drove across the Pennines and up towards Newcastle. It was afternoon to early evening and the station boomed in clearly on the standard car radio from around Huddersfield all the way to north of Durham where it started to struggle. No doubt with a more sophisticated receiver and directional aeriel you could stretch this a good deal further. As the article says it's AM so it isn't hi-fi by any means, but it is certainly more than comparable with what came from the ships a lot of the time. It is very impressive indeed with such low power. Well done to Caroline.

    2. I live in derby i can listen in the car on 648 a bit fuzzy sometimes better on the net.

  3. Caroline 648 was coming in pretty clear up here in East Yorkshire and very clear in Beverley ,but the signal has deteriorated recently for whatever reason ,I'd like to see Roger Days 4pm show on Caroline Flashback put out daily on 648 ,along with Mark Staffords weekly show ,Staffords World .

  4. I'm sure this will also be of interest:-

  5. I have to add, and point out, that most car radio aerials are somewhat deaf, due to there being a compromise for the more modern radio, where AM is an afterthought, for strong signals only, due to the small size, really meant for VHF and DAB.
    That said, I fitted an amplified base, and put my own telescopic rod at 750mm, which is 1/4 wave at FM, a 1/2 wave at DAB, and plenty big enough for AM.
    Reception is excellent for Caroline on AM here on the East Lincolnshire coast.
    The other stations are bound to be OK, due to the size of the aerial.
    David. G1ZQC (yes I am a qualified Radio Amateur.).

    1. Hi David, back in the mid 1970s I took one rod from a Band 1 ("X" shaped) tv aerial and attached it to the underside of my Austin Minor van using plastic clips. It ran inline with the exhaust, but on the other side of the car. I got fantastic results.

      You would have thought that the body of the van would screen most of the signal, but those medium wave lengths found a way to reach the rod. (It also stopped vandals snapping off my car aerial...which seemed to be a popular pastime back then).

      Good luck with the Ham Radio. I qualified for a license in 1972, but have never taken it up. I probably would have, if they had allowed me on 80 & 160, but didn't have the time or patience to learn morse.

    2. Very true but it is also important to have a big vehicle (made of metal) to increase the ground plane, I had both a ford transit and a citroen c1 the 648 signal was loud and proud in the transit but not so good in the C1.

  6. The Caroline Community served by 648 is more a special interest community than a local one, though broadly aligned to the main reception area of the good old offshore days, and is prepared (up to a limit) to accept “anorak-level” reception quality.

  7. I live in West Wales and get clear signal on 648kHz most evenings after dark. Although I'm part of the "target audience" I do have a smart phone and know how to work a computer. It's still great to listen on good old AM however!

  8. hearing Caroline on 648 day and night very good strong reception on my tecsun pl-660 portable radio+tecsun an-200mw loop antenna, Jon collins,moseley, birmingham, b13, uk 🇬🇧 😁

  9. Caroline will soon be using more than 1kw from Orfordness. as ofcom gave them the go a head to us more power around the 3 to 5kw mark as ofcom said they could not use 10kw. the talk is the new transmitter will be a 25kw one.