16th Sep 2022, 12:43 pm | #881 |
Dekatron
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Re: 405-Line VHF Aerials 2013 to the present day.
Yes, wooden dowels were sometimes fitted into elements to provide mechanical damping; without this, at certain wind-speeds the elements could be excited to mechanical resonance as a result of 'vortex shedding*'. Apart from an annoying hum conducted down the mast to the chimney [and causing night-time annoyance to occupants of the bedroom below!] the vibration could eventually cause mechanical failure. Weighting one half of the element removes the symmetry of the mechanical resonance about the feed-point, making it harder for wind-excited vibration to occur.
Some antennas used a length of cord threaded inside the element as a damper. * Search for "Tacoma Narrows" on YouTube if you want to see what uncontrolled vortex-shedding can lead to!
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17th Sep 2022, 10:57 am | #882 |
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Re: 405-Line VHF Aerials 2013 to the present day.
Thanks for the link, yes I remember seeing that before, quite spectacular. I noticed that in Caithness where they have wicked winds in the winter that most TV aerials are just a pole with a few bits of rod on, look a bit like a brussel sprout stalk.
The lighthouse keeper on the John O Groats road had a ham tower which was guyed about every five feet but only had wire antennas on it, one year he installed an HF tribander on a much shorter pole, the next year we went it was virtually tied in a knot. Peter |
8th Oct 2022, 10:19 am | #883 |
Pentode
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Re: 405-Line VHF Aerials 2013 to the present day.
Hi, I spotted this array in Sherborne, Dorset at the weekend. It looked to be in quite good condition still. I believe that’s a band I, band II and a band 3 on the same mast. There was a similar array further down the road but in a poor state.
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8th Oct 2022, 2:07 pm | #884 |
Hexode
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Re: 405-Line VHF Aerials 2013 to the present day.
Sherborne was quite a fringy sort of Vhf area.
The Band 1 and Band 2 are probably looking at Wenvoe (Ch5 Band 1). The double 6 band 3 should be at the same sort of angle for St Hilary Ch 10 but mechanically it's difficult. Maybe the aerial is getting a mix of St Hilary Ch 10 and Stockland Hill Ch 9 which had much lower erp towards London to reduce Co channel problems.Amazing how it has all survived! North Hessary Tor Ch2 and Rowridge Ch3 would also put in a fair strength there. |
8th Oct 2022, 8:17 pm | #885 |
Heptode
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Re: 405-Line VHF Aerials 2013 to the present day.
Taken today in Dumfries this town is full of them
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17th Oct 2022, 12:55 pm | #886 |
Octode
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Re: 405-Line VHF Aerials 2013 to the present day.
This thread has got me studying the rooftops! This is the only 405 aerial I have found so far, On a big old house in one of the older parts of Peterborough. The house is for sale so I don't know how much longer the aerial will remain, A lot of the bigger older houses get ripped out and made into flats so it may go.
In any case when I took the picture BBC 1 dipole was loose and seemed to be hanging on the connecting wire so it may drop before very long in any case. BBC1 channel 5 in Peterborough came romping in all the old sets I sold to mates at school needed no more than a bit of mains lead splitting out to make a dipole Anglia was a bit more of a challenge and UHF especially if the set had a valve tuner needed at least a loft aerial. |
17th Oct 2022, 2:12 pm | #887 |
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Re: 405-Line VHF Aerials 2013 to the present day.
I spotted this last week in Cardiff but didn't think to take a photo of it, so these images are from Streetview and aren't the best angles.
https://www.google.com/maps/@51.4714...7i16384!8i8192 https://www.google.com/maps/@51.4715...7i16384!8i8192 https://www.google.com/maps/@51.4714...7i16384!8i8192 I'm assuming it's FM (band 2) but not sure, so welcome comments. I'm not sure how well it would work mounted vertically against the side of the building and so close to a metal streetlamp. It is pointing approximately north west so about 45 degrees off for the closest likely transmitters at Wenvoe and St Hilary (which are both west of the location). Last edited by Paul Stenning; 17th Oct 2022 at 2:16 pm. Reason: Added another image |
17th Oct 2022, 4:42 pm | #888 |
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Re: 405-Line VHF Aerials 2013 to the present day.
Interesting Paul,
That aerial does not appear to have a 'TV' look about it. DAB radio comes to mind but as I'm not familiar with the area, I'm probably completely wrong! John. |
17th Oct 2022, 5:20 pm | #889 |
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Re: 405-Line VHF Aerials 2013 to the present day.
It's much too big to be for DAB.
I wonder if it could be a low band mobile radio antenna for something like a link back to a taxi company??
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17th Oct 2022, 5:41 pm | #890 |
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Re: 405-Line VHF Aerials 2013 to the present day.
The ground floor is a Chinese grocery store and there are no known taxi companies at that address or the address of the side entrance, but of course they could still have an office or something upstairs. Having said that, every taxi company I know of here uses mobile apps for their drivers now, not two-way radios.
It looks more like a 3 element FM aerial in style, but I don't know what size they would be to estimate whether this is about that size from the photos. It's probably not 405-Line TV though. |
17th Oct 2022, 6:27 pm | #891 |
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Re: 405-Line VHF Aerials 2013 to the present day.
I was wondering what was downstairs. In my mobile radio 1980s past I came across quite a few unconventional (and Unlicensed) installations. Like a taxi company using Italian CB radios on 46MHz.
Unlicensed back-links were surprisingly common, whether for taxi companies or pirate radio stations Always think of the obscure when the obvious has been exhausted.
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17th Oct 2022, 7:45 pm | #892 |
Nonode
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Re: 405-Line VHF Aerials 2013 to the present day.
There was an old system of community alarms on 107.9875 prior to the extension made
to Band II in 1989. |
18th Oct 2022, 12:30 am | #893 |
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Re: 405-Line VHF Aerials 2013 to the present day.
Here is a mysterious VP UHF aerial on a bungalow near here.
https://www.google.co.uk/maps/@53.52...7i16384!8i8192 Not a TV aerial for sure
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18th Oct 2022, 2:25 am | #894 | |
Hexode
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Re: 405-Line VHF Aerials 2013 to the present day.
Quote:
https://www.freeview.co.uk/help/cove...ostcode=M250DT
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19th Oct 2022, 11:26 am | #895 |
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Re: 405-Line VHF Aerials 2013 to the present day.
That aerial in Cardiff is a bit of a mystery. Whatever it was or is being used for its performance is going to be degraded with its position near the side of the building. The aerial does not look that old but the coax run looks a bit shabby.
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19th Oct 2022, 11:32 am | #896 | |
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Re: 405-Line VHF Aerials 2013 to the present day.
Quote:
One next door to me never been changed, looks wide band.
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Frank Last edited by Nuvistor; 19th Oct 2022 at 11:40 am. |
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20th Oct 2022, 9:44 am | #897 |
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Re: 405-Line VHF Aerials 2013 to the present day.
There is an 'X' aerial in very good condition I passed on Tuesday in Wilmington Devon. Its half way down a long hill with its back to the transmitter which I think would have been North Hessary Tor I think it was to long for Wenvoe but it didn't have a clear view in that direction either. It's amazing how the Band 1 signal would bend into what you would think would be inaccessible places.
Peter |
20th Oct 2022, 7:44 pm | #898 | |
Hexode
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Re: 405-Line VHF Aerials 2013 to the present day.
Quote:
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21st Oct 2022, 11:21 am | #899 |
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Re: 405-Line VHF Aerials 2013 to the present day.
True but it must have been late arriving because all the early band one aerials were facing Dartmoor or Wenvoe, the one in question is facing Dartmoor or rather straight into the hill above Honiton
I passed it again yesterday and it is actually a 3 element complete as in your picture. We moved here from Kent in 1970 and had just gone through the conversion to UHF, down here we were back on 405 again for a couple of years. Stockland hill wasn't on the eraly list of 405 transmitters as seen on the first superhet TV's i.e the bush TV22. Although we are in Dorset we can see Stockland hill from here but you can't from wilmington, not from the village anyway. Peter |
21st Oct 2022, 12:05 pm | #900 |
Hexode
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Re: 405-Line VHF Aerials 2013 to the present day.
Stockland Ch9 went on air in Spring 1961
when Westward TV launched.Power to the East was much lower to avoid co channel problems with London. North Hessary Tor Ch2 was a little later than Wenvoe Ch5 which started in 1952. |