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Old 6th Sep 2021, 11:37 am   #1
Edward Huggins
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Default Radio Caroline on 648kHz - More.

Since my last Thread I've been in touch with the Caroline's Chief Engineer and he has updated me on some of the topic raised:

BANDWIDTH
The upper limit is currently 7kHz or 7.5kHz, at the time of writing he could not confirm. I quote him: "Using our DSPx processor with its digital filter, we are 40dB down at 9kHz which is the stipulated EBU/Ofcom requirement. There is no specific EQ curve such as NRSC, but the processor does have multiband limiting which will tend to enhace quieter HF parts".
He laments the fact that many new AM sets only have an upper limit of 3kHz, let alone 4.5kHz. Given they are often software driven, he cannot understand why more Radios do not use signal-strength-driven variable bandwidth filters.

TRANSMITTER
They are currently using an RCA "Ampliphase" 50kW transmitter, the same as used for Big Ls "Tower Of Power" (Radio London) that needs "10kW of power just to get the filaments/heaters and blower motor working - very inefficient". However there is a new Transmitter with increased power being planned for the Winter to give more Natiowide coverage. But they will not be tweaking the audio processor on this because "many contemporary recordings do not take kindly to agressive AM audio processing".

I hope Members will find this "from the Horse's mouth" update of interest.
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Old 6th Sep 2021, 11:52 am   #2
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Default Re: Radio Caroline on 648kHZ - More.

Quote:
Originally Posted by Edward Huggins View Post
TRANSMITTER
They are currently using an RCA "Ampliphase" 50kW transmitter,
Surely not? Their current power is 1kW from a Nautel Transmitter.

http://www.radiocaroline.co.uk/#648_am.html
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Old 6th Sep 2021, 12:13 pm   #3
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Default Re: Radio Caroline on 648kHZ - More.

Yes, I'd be astonished if they were running anything like 50kW at the moment, and as for increasing power further, they would need to go to 100kW to get a meaningful improvement from 50kW. Ofcom are never going to allow those sorts of powers for what is basically a hobby station, even if finance could be arranged. There must be a misunderstanding somewhere.
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Old 6th Sep 2021, 12:17 pm   #4
Edward Huggins
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Default Re: Radio Caroline on 648kHZ - More.

You are quite correct as I saw that on their Website some time back. I got the impression that if it is an RCA - and which I did not expect to learn about - either On-Board or at Orfordness, then it is deliberately being under-driven for Ofcom compliance.
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Old 6th Sep 2021, 12:21 pm   #5
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Default Re: Radio Caroline on 648kHZ - More.

The RCA Ampliphase transnmitters are on board the Ross Revenge, a hangover from its pirate days. They're not used for transmitting even when using the studio onboard.

The statement made in the original post regarding transmitters obviously didn't come from Caroline's chief engineer.
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Old 6th Sep 2021, 12:25 pm   #6
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Default Re: Radio Caroline on 648kHZ - More.

I don't think they ever run a transmitter on the ship. They originate some programming from a studio on the ship, but the actual transmission is handled by the kit at Orfordness.

There may be a non-operational period Ampliphase transmitter on the ship - I've never visited it.

(Crossed with Graham)
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Old 6th Sep 2021, 12:54 pm   #7
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Default Re: Radio Caroline on 648kHZ - More.

Quote:
Originally Posted by paulsherwin View Post

There may be a non-operational period Ampliphase transmitter on the ship - I've never visited it.

(Crossed with Graham)
There is. I understand that the crystals have been removed so effectively they are 'amplifiers'.
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Old 6th Sep 2021, 1:29 pm   #8
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Default Re: Radio Caroline on 648kHZ - More.

https://www.bbceng.info/Technical%20...l_Issue_46.pdf

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Old 6th Sep 2021, 1:55 pm   #9
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Default Re: Radio Caroline on 648kHZ - More.

Whilst not in a position to measure or show the audio frequency modulation of 648Khz, my wideband am receiver is quite good at showing off an am radio station at its best.

I would question a cut off at 7.5Khz for whilst without a narrowband IF, say 3.5 Khz the sound quality is improved, it doesn't shout out anything extraordinary.

MerlinMaxwell very kindly illustrated sibilance on RADIO 4 198Khz whilst also showing the audio frequency limitations of the transmitted signal.

Should he read this thread, perhaps he could illustrate 648Khz warts and all.

Then, why not show off RTE 252.

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Old 6th Sep 2021, 3:22 pm   #10
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Default Re: Radio Caroline on 648kHz - More.

I visited the Ross Revenge in 2018 here are some photos of the old Ampliphase TX.
Mike
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Old 6th Sep 2021, 4:29 pm   #11
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Default Re: Radio Caroline on 648kHz - More.

As requested, a shot of my RSP DX and loop, very weak today (must be the sunshine) but looks like a shade under 5kHz.
Better make that 4kHz, I must learn to read!
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Old 6th Sep 2021, 4:50 pm   #12
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Default Re: Radio Caroline on 648kHz - More.

Many thanks merlinmaxwell for the 648 audio modulation graph. So that's why it's as good as you are going to get.

I wonder if you would do the same for RTE1 on 252Khz?

Reading reports on other sites suggests an analogue Optimod is in use but no mention of HF equalisation but it is "very bright." A technical term meaning I probably don't know what I am talking about!.

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Old 6th Sep 2021, 5:00 pm   #13
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Default Re: Radio Caroline on 648kHz - More.

As requested...

The other window is my loop aerial rotator showing the general direction it is pointed to.
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Old 6th Sep 2021, 5:43 pm   #14
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Default Re: Radio Caroline on 648kHz - More.

Thanks merlinmaxwell, that looks like 12Khz. Not quite FM but ideal to show off many of the radios with variable bandwidth and how they would have sounded "Back in the Day" when Brookmans Park was at its best.

Maybe not quite PC for The Murphy Day but I look forward to listening to the station next time I'm working on the stand.

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Old 13th Sep 2021, 3:18 pm   #15
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Default Re: Radio Caroline on 648kHz - More.

Caroline are reported to have acquired a 25kW transmitter.
Quote:
Radio Caroline, Have acquired a 25Kw transmitter, which they are going to install at there (sic) Orfordness site in Suffolk on 648Khz, permission granted by Ofcom, the regulator. The idea being to overcome interference man made, and to overcome the skip signals from Spain and Slovenia. The signal should be strong in the East, and South of England, and of course in NW
Europe. Should come to air sometime before the end of the year.
Mike Simmonds (2021-09-13)
mediumwave info

Rumoured at Digital Spy to be a Harris DX25.

Last edited by Pfraser; 13th Sep 2021 at 3:21 pm. Reason: Tidy and extend
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Old 13th Sep 2021, 3:31 pm   #16
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Default Re: Radio Caroline on 648kHz - More.

That is more than I expected, which was 5-10kW. 25kW should make it to London.
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Old 13th Sep 2021, 3:43 pm   #17
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Default Re: Radio Caroline on 648kHz - More.

Wish I was allowed to increase the output of my ham transmitter by 25 times, to overcome man made interference 😄.

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Old 13th Sep 2021, 4:05 pm   #18
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Default Re: Radio Caroline on 648kHz - More.

Quote:
Wish I was allowed to increase the output of my ham transmitter by 25 times, to overcome man made interference
You want the other end to do that.
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Old 13th Sep 2021, 4:38 pm   #19
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Default Re: Radio Caroline on 648kHz - More.

Slightly off topic (hope mods will allow) but last weekend i saw this for sale at an event i went too.
A radio Caroline Reel to Reel off the Mi Amigo.

Almost bought it !!!
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Old 13th Sep 2021, 5:26 pm   #20
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Default Re: Radio Caroline on 648kHz - More.

It seems an odd choice of recorder for a 60s professional AM radio station, even one with the shambolic history of the Mi Amigo. I'd expect them to be using something like half or full track Ferrographs at the very least.
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