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Old 15th May 2015, 10:52 pm   #41
WaveyDipole
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Default Re: Station broadcasting on 1431khz

Ian, I only saw the top of it, but yes, the top of the antenna I saw looks consistent with those examples you posted both in terms of the horizontal elements being at the very top of the antenna and their length relative to its height. The latter was a bit difficult to gauge as I couldn't see its entire length, but just guestimating based on the height relative to what would be ground level behind the building. The building was just one storey high, so its conceivable that the top of a 10m high antenna would still be visible above the roof of the building. I obviously mistook the horizontal elements for Yagi's, but from my vantage point I thought I saw what would be 4 rods assembled at right angles.

Interesting point about requiring 20w to 50w to generate 1w of radiated power. You mention that the antenna is limited to 10m in height, which would be very short for the wavelength being transmitted, loading coil notwithstanding. If my math is correct then a half wave would need to be about 105m long! Such a length would be rather impractical for most sites, including hospital sites such as this. By being so short though, it would seem that efficiency is relatively low as based on the input requirement above, the radiated power efficiency would seem to be only between 5% and 2% which seems quite low (but perhaps normal at these frequencies)?

Google estimates that my home location is around 9.3 miles by road from the Hospital. I dare say, that as the crow flies (do they really fly in straight lines?) this is probably nearer 8 so is still well within the 10 miles that you say would be covered easily. As I mentioned, the terrain is relatively flat and the transmitter is located on elevated ground. Generally there is no significant background noise on this part of the band either so I usually get good reception. Curiously though, the signal seems to be very weak at the moment. The Eddystone is barely picking it up and the other radios are struggling. This is the first time that I noticed it has been that weak.

Last edited by WaveyDipole; 15th May 2015 at 11:09 pm.
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Old 15th May 2015, 11:01 pm   #42
Ian - G4JQT
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Default Re: Station broadcasting on 1431khz

Quote:
Originally Posted by WaveyDipole View Post
Interesting point about requiring 20w to 50w to generate 1w of radiated power. If, as you mention, the antenna is only 10m high, it would be very short for the wavelength being transmitted...
Yes, the antenna is very inefficient, but relatively easy to construct and install, although not as easy as an FM RSL antenna!

A more efficient AM antenna for this type of establishment would not be practical for various reasons, and the range is therefore more or less self limiting to the the Ofcom range - which from memory is something like 2 miles in urban surroundings and 3 to 4 miles in open country for an AM RSL station. But that obviously depends upon various parameters too.

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Old 16th May 2015, 12:29 am   #43
paulsherwin
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Default Re: Station broadcasting on 1431khz

Please stay on topic folks.
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Old 31st May 2015, 4:49 pm   #44
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Default Re: Station broadcasting on 1431khz

The 1431Khz Smooth Radio transmitter at Reading has been closed down as well as the local Absolute transmission on 1233Khz. Apparently the land owner did not wish to renew the lease with Arqiva. Because of Smooth's licence agreement with Ofcom Smooth has had to switch of theie 1485Khz transmitter at Newbury.

So now on 1431 if you are hearing Smooth it's coming from their Southend transmitter which I can now hear clearly most evenings here near Bristol. There are also 7 1W LPAM stations dotted across the country.
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