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Old 30th Nov 2023, 7:30 pm   #961
Mr Hoover
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Quote:
Originally Posted by G6Tanuki View Post
Here's a Band-III ITV antenna spotted on the roof of "The Strand" Hotel in the centre of Calne. Apologies for the less-than-perfect photo, I only had my phone with me and not the rather better DSLR.

It points North-East-ish as far as I can work out.
That would have been aiimed for Membury Channel 12.
One of the later Band 3 transmitters, I think it relayed Midlands
not Southern.
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Old 30th Nov 2023, 7:50 pm   #962
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Default Re: 405-Line VHF Aerials 2013 to the present day.

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Quote:
Originally Posted by G6Tanuki View Post
Here's a Band-III ITV antenna spotted on the roof of "The Strand" Hotel in the centre of Calne. Apologies for the less-than-perfect photo, I only had my phone with me and not the rather better DSLR.

It points North-East-ish as far as I can work out.
That would have been aiimed for Membury Channel 12.
One of the later Band 3 transmitters, I think it relayed Midlands
not Southern.
Yes I can imagine it being for Membury, given the horizontal polarisation.

Membury relayed Midlands ITA [ATV/Central] from Lichfield - which was always a disappointment because people in the Membury coverage-area really were not interested in the news etc. covering places like Nottingham and Derby and Newark and Crewe which were rather a long way away.
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Old 23rd Dec 2023, 11:35 am   #963
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Having a cycle round delivering Christmas cards yesterday, I spotted this one.

Sandy Heath is our local transmitter.

This image from Google Maps is from 2016, It's got much more of a lean to it now. Will it still be hanging-on next Christmas?

SR
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Old 17th Feb 2024, 1:35 pm   #964
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Default Re: 405-Line VHF Aerials 2013 to the present day.

This 'X' aerial for ch2V Holme Moss in North Manchester is in remarkably good condition, photo is from August last year but I saw it to-day and it doesn't appear to have suffered much from the recent storms.

I assume it is being used as an FM radio aerial; the Band III aerial aimed towards Winter Hill appears to have been replaced with a UHF one but the X was never taken down. Being fairly close to Holme Moss we usually have pretty reliable VHF-FM reception with indoor aerials, but this house is in the shadow of an old mill chimney which might frustrate reception a bit.

I have never seen a vertically polarized 'H' aerial in the area; the few that do still exist have all been changed to horizontal polarization and have been significantly shortened. Perhaps 'X'ers are more effective in their unmodified state as FM aerials.
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Old 17th Feb 2024, 8:42 pm   #965
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Default Re: 405-Line VHF Aerials 2013 to the present day.

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I have never seen a vertically polarized 'H' aerial in the area; the few that do still exist have all been changed to horizontal polarization and have been significantly shortened. Perhaps 'X'ers are more effective in their unmodified state as FM aerials.
The mast would also have carried a vertical Yagi for Ch 9 pointing at Winter Hill
This was probably removed after 1969 when all three channels were available on UHF.
The Antiference Antex has survived, in my opinion, not because a new use was found for it, rather, it was too much trouble to remove.

It's certainly a survivor!
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Old 17th Feb 2024, 9:36 pm   #966
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Default Re: 405-Line VHF Aerials 2013 to the present day.

I think these X shaped aerials for band I have only been used in the UK, I never saw one in France or other continental Europe country.
I always wondered how they were constructed, in which direction they were directive and if one branch of the X was a dipole and the other a director or reflector or something else...
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Old 18th Feb 2024, 12:12 am   #967
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Default Re: 405-Line VHF Aerials 2013 to the present day.

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I always wondered how they were constructed, in which direction they were directive and if one branch of the X was a dipole and the other a director or reflector or something else...

Yes - I'm no TV aerial buff, but I've wondered the same about X-aerials since a teenager! Perhaps one of the specialists here could briefly explain...

Mike
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Old 18th Feb 2024, 9:56 am   #968
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Default Re: 405-Line VHF Aerials 2013 to the present day.

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Originally Posted by Graham G3ZVT View Post
The mast would also have carried a vertical Yagi for Ch 9 pointing at Winter Hill
This was probably removed after 1969 when all three channels were available on UHF.
The Antiference Antex has survived, in my opinion, not because a new use was found for it, rather, it was too much trouble to remove.

It's certainly a survivor!
The mast has two UHF Yagis on it; the ch9 Yagi might have been taken down to make room for the second UHF Yagi.
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Old 18th Feb 2024, 10:12 am   #969
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Default Re: 405-Line VHF Aerials 2013 to the present day.

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Quote:
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I always wondered how they were constructed, in which direction they were directive and if one branch of the X was a dipole and the other a director or reflector or something else...

Yes - I'm no TV aerial buff, but I've wondered the same about X-aerials since a teenager! Perhaps one of the specialists here could briefly explain...

Mike
Director and dipole, they worked extremely well, they were introduced I think around 1949 and I think claimed to pickup less ignition interference than H or dipoles. Quick to assemble and quite robust.
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Old 18th Feb 2024, 12:49 pm   #970
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Default Re: 405-Line VHF Aerials 2013 to the present day.

X's had a very sharp null at the rear,
giving a very good front to back ratio.
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Old 18th Feb 2024, 1:30 pm   #971
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Default Re: 405-Line VHF Aerials 2013 to the present day.

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X's had a very sharp null at the rear,
giving a very good front to back ratio.

Yes, but which side was the "front" and which the "back"? Presumably these were mounted "in line" with the direction of the transmitter, but which elements were the dipole, director(s) and reflector(s)?

When I was experimenting with these as a teenager, we lived in an area of insanely high signal strength (line of sight to North Hessary Tor), and the various orientations of the X-aerial made absolutely no difference - or indeed whether it was just lying on the ground. In fact, you got a full-strength signal with just a screwdriver blade touching the aerial socket, so experimentation with aerial orientation was impossible. But I always wondered where the optimum would theoretically be.

Sorry if this is all "infants" level stuff!

Mike
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Old 18th Feb 2024, 2:22 pm   #972
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Default Re: 405-Line VHF Aerials 2013 to the present day.

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Quote:
Originally Posted by Mr Hoover View Post
X's had a very sharp null at the rear,
giving a very good front to back ratio.

Yes, but which side was the "front" and which the "back"? Presumably these were mounted "in line" with the direction of the transmitter, but which elements were the dipole, director(s) and reflector(s)?

Mike
https://www.worldradiohistory.com/UK...ch=%22antex%22
Page 409

The shorter directors face the transmitter.
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Old 19th Feb 2024, 10:20 am   #973
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Default Re: 405-Line VHF Aerials 2013 to the present day.

I would have thought the back would have been the longer rods acting as a reflector the front acting as director.

Peter
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Old 19th Feb 2024, 10:50 am   #974
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Default Re: 405-Line VHF Aerials 2013 to the present day.

The ad of #972 refers to patent numbers 35957/46 and 12178/49. These are actually patent application numbers, but patent database websites such as espace or the UK patent office's web site should identify the granted patent numbers and provide downloadable copies. Just packing to go off for a few days do no time to do it myself. The Patent Office had a huge backlog of applications to deal with after the war, and legislation had to be passed to extend the time for granting.
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Old 19th Feb 2024, 11:09 am   #975
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Default Re: 405-Line VHF Aerials 2013 to the present day.

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I would have thought the back would have been the longer rods acting as a reflector the front acting as director.
I think that's what he said, the shorter rods go towards the transmitter so the longer rods are the reflector, away from the transmitter.

The shorter rods are the active element. There is no director. It's a 2-element beam.

For added fun, they can be made with equal length rods, the centre connection of the reflector being done with a small inductor to manipulate the effective electrical length of the reflector and play games with its phase shift.

You can also use the two upwards rods together against the two downwards rods together as a balanced vertical dipole. The divergence of the paired rods causes them to act as a broader-bandwidth element. Think of a cage-dipole but with only 2 conductors forming a roughly tapered element.

Then a horizontal dipole can be done by changing things around.

It all depends on what's going on in the little connection box!

For TV use, only the 2-element beam mode makes any sense. Had a lecturer who used these things as examples to knock students out of their comfort zones.

David
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Old 19th Feb 2024, 11:27 am   #976
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Default Re: 405-Line VHF Aerials 2013 to the present day.

The X didn’t have a reflector. The 2 shorter rods were a director and faced the transmitter. The longer rods at the rear were the active dipole.

Were Xes ever used for horizontal polarisation?
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Old 19th Feb 2024, 11:46 am   #977
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Wright aerial description of the X aerial describes the driven element behind the directors, I.e. no reflector.
That is how I remember them from the early 1960’s and they worked very well, the theory behind them is beyond me. I can only say they worked well.
http://www.wrightsaerials.tv/aerialp...ient/024.shtml
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Old 19th Feb 2024, 12:12 pm   #978
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Antex 'X's were/are indeed director- dipole systems. However other makers also produced 'X' designs which may have been dipole - reflector types.
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Old 19th Feb 2024, 2:18 pm   #979
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Default Re: 405-Line VHF Aerials 2013 to the present day.

I have no recollection at all of the connection box, but perhaps David is right, and "It all depends on what's going on in the little connection box!"

Perhaps the connection box could be wired for either dipole+reflectors or dipole+directors. And pity the poor rigger trying to decide which to use!

Mike
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Old 19th Feb 2024, 6:43 pm   #980
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Default Re: 405-Line VHF Aerials 2013 to the present day.

The one I took apart was definitely an active element and reflector, but I don't remember it being an antiference job. It's such a general purpose structure, you can set one up as almost anything.

Thanks for filling in a gap! I hadn't thought of driven element and director without a reflector because a reflector alone gives more F/B ratio than a director alone.

David
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