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Old 19th Jul 2016, 1:03 am   #401
emeritus
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Default Re: 405-Line VHF Aerials 2013 to the present day.

The mast at Baddow came from Canewdon.

The article "Fundamentals of Radar" that appeared in the October 1945 Wireless World says that the wavelength originally used by the Chain Home (CH) system in the late 1930's was in the range 10 to 13 metres (20 to 30MHz if I have done my sums right!). For coastal artillery range finding and protection against low-flying aircraft, the "Chain Home Low" (CHL) system used a shorter wavelength of 1.5 metres and a correspondingly smaller antenna array of "about 4 wavelengths by five. ".

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Old 19th Jul 2016, 8:59 am   #402
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Yes, I've seen lots of period references to vehicle ignition interference but have never seen any regarding CH. Apparently AMES Type 1 used four frequencies in the range 20 to 55MHz and later just two frequencies in the range 20 to 30MHz.

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Old 19th Jul 2016, 11:13 am   #403
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Re posts nos. 392 & 296

The combined Band I & III aerial could be a Belling & Lee, but just having looked through a J. Beam catalogue dated 1972 it could also be a J. Beam. Certainly the catalogue's (stylised) drawing shows an aerial with the same non-even Band III director spacing as in the photo. Also, to my mind, the Junction Box more fits a J. Beam design than a Belling & Lee. A higher resolution photo would resolve the dilemma !
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Old 19th Jul 2016, 11:22 am   #404
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Emeritus,

In Malvern there is a display of some photographs taken of equipment developed at TRE during the Second World War. One of the photos shows a 4 x 8-element radar array whose dimensions certainly look to be consistent with a 1.5 m wavelength.

The interesting point is that this radar array is shown positioned on top of the Great Pyramid at Giza ! (apparently to cover for a visit that Churchill made to Egypt)

(The 'photo display is next to the supermarket Waitrose)
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Old 19th Jul 2016, 3:11 pm   #405
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Quote:
Originally Posted by Heatercathodeshort View Post
Quote:
Originally Posted by ntscuser View Post
Quote:
Originally Posted by Focus Diode View Post
Spotted this nice arrangement in Hexham earlier today, note the folded BI dipole.
The Band I element spacing is correct for 75 Ohms but wouldn't the Band III aerial be closer to 300 Ohms?
It is interesting to note that a number of early Band 3 receivers had provision for 300 ohm balanced feeder on Band 3 only. J.
Ah, that might explain it then. Thanks
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Old 20th Jul 2016, 11:07 am   #406
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Re my post no. 403:

On double checking I find I've mentioned the wrong J. Beam catalogue. It should have been the 1967 one. However there is scope for puzzlement here. In the 1967 catalogue there is indeed a stylised drawing of the aerial, but there is also a larger drawing showing two add-on band III elements attached to the junction box (ie a different aerial structure). The 1972 catalogue shows an actual photo but it does not have the director spacing we are discussing! J. Beam's model number for the aerial is DP5.
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Old 30th Jul 2016, 11:33 pm   #407
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Here's one that has seen better days, spotted on the Isle of Wight last week. It's on the roof of the Spar grocers at Wooton Bridge on the A3054. Despite the IOW being notorious as embodying the England of the 1950's, it was the only one seen in a week's touring round the island. Not the best quality, as I had to grab the shots from a moving car.
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Old 1st Aug 2016, 10:11 am   #408
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Looks as if the mount has been screwed into the fascia board; must be a good bit of timber to have stood that aerial 'towing' at it for around 40 years.
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Old 1st Aug 2016, 10:22 am   #409
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Re no. 407 - Looks like an Antiference junction box to me.
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Old 18th Aug 2016, 4:34 pm   #410
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Spotted this afternoon in the village of Cranleigh Surrey. I don't expect the array will be with us for much longer. It appears most of the roof is being replaced but you never know. Lined up with channels 1 & 9 from CP and BH. John.
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Old 27th Sep 2016, 3:49 pm   #411
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Two in one place! There's a combined BI/III array on the roof of the Castle Hotel in Devizes; as well as leaning somewhat, each of the two BI elements is lacking a 'leg' so it looks more like a stretched swastika than a H.

It points pretty much due-West so I'm guessing they got BBC1 from Wenvoe and ITV from St Hilary or Stockland Hill.
The BIII dual 6x6 is still intact. Attached pic is from Google Street View; I hope to take a better pic when I'm next in Devizes with my DSLR.

Also, on the white building further down the street - just behind the streetlamp with the strange pineapple-like thing (CCTV camera globe?) on it, is another combined BI/III antenna - again, more photos will follow in due course.
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Old 28th Sep 2016, 10:09 am   #412
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Would've thought St.Hilary would be too far East yet I remember a house in Devizes receiving much better Wenvoe UHF reception than in Chippenham. Would certainly appear to be for Ch5 Wenvoe and Ch10 St.Hilary therefore. A brilliant photo, thanks for uploading it.

As for Stockland Hill I never received this on VHF in Chippenham. North Hessary Tor ch2 was weak but useable. In Devon the results from Stockland Hill ch9 were poor, suggesting it operated on reduced power. Tor ch2 was superb though.

The dome thing is a CCTV camera I believe.

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Old 30th Sep 2016, 11:17 am   #413
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Hi, Stockland Hill on Channel 9 had a very directional signal,quite low power to the east to reduce interference with Croydon,there's some info on it here..
http://itv1963.retropia.co.uk/catego...coverage-maps/

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Old 30th Sep 2016, 12:32 pm   #414
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Stockland hill beamed a high powered signal in two directions, one NW towards North Devon and SW for south Devon. Radiation was reduced to the east to avoid co channel problems with Croydon and to the N and NE to reduce the overlap with St Hilary's coverage area.
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Old 3rd Oct 2016, 8:05 pm   #415
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Default Re: 405-Line VHF Aerials 2013 to the present day.

I was back in Devizes today and managed to get some photos of the second aerial I mentioned: as can be seen, the BI "H" is mounted on a side-arm from the main mast, and has lost half its dipole.

The BIII 9-element antenna's dipole is still there - unfortunately it's hidden behind the mast of the UHF aerial.

Also spotted in the locality is what looks like a horizontally-polarised 2-element BIII aerial - picture enclosed complete with a convenient pigeon to give a sense of scale!
At first I thought it was a BII FM broadast-aerial but the elements look too short. I'm wondering if there was at some time a local low-power 'infill' transmitter in the Devizes area?
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Old 3rd Oct 2016, 8:37 pm   #416
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Default Re: 405-Line VHF Aerials 2013 to the present day.

I should think ATV Membury ch12H would've been well received in Devizes.
Excellent photos.

Cheers
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Old 5th Oct 2016, 7:22 pm   #417
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Quote:
Originally Posted by Focus Diode View Post
I should think ATV Membury ch12H would've been well received in Devizes.
Indeed - but the 2-ele pigeon-loaded antenna was - if anything - directed west-south-west.

Looking at it in detail, it seems rather 'modern' - what 1960s-era BIII antennas had little caps on the ends of the elements that had not degraded and dropped-off in the intervening decades??

I'm suspecting it might have been an early-90s point-to-point antenna used with first-generation BIII commercial digitally-managed 'trunked' radio network.
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Old 6th Oct 2016, 5:54 pm   #418
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Default Re: 405-Line VHF Aerials 2013 to the present day.

I like the vintage street light "arm" too!
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Old 17th Oct 2016, 11:18 am   #419
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Here are a couple more photos of the "Castle Hotel" combined BI/III antenna in Devizes I mentioned a few weeks back, also two photos of half a mile away where in Long Street there's a rather nice classic BI "H" still standing.
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Old 14th Dec 2016, 7:34 pm   #420
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Default Re: 405-Line VHF Aerials 2013 to the present day.

Here are a few photos I took in Hungerford today.

A 2-element BI vertically-polarised antenna [with a bird on the boom] pointing at London, with a 2? el horizontally-polarised BIII pointing at Membury. I think the BIII antenna was originally a 3-or-more-ele but the last director(s) are missing. The coax from the BI dipole hangs freely in the air on its way to a mast-mounted combiner.

A little 2-ele horizontally-polarised BIII pointing at Membury. Membury would have been near enough line-of-sight from here so no real gain would have been needed.

A dipole-for-BI and 7-ele-for-BIII pointing at London. One of the BIII directors has slid down through the clamp. This is an example of the cost-cutting approach where the BI dipole was used as the BIII dipole because it was roughly 3/2-wavelength. This particular antenna is located high up on the side of a hill so presumably got enough of a BI signal to not need any reflector/director.

More to come....
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Last edited by G6Tanuki; 14th Dec 2016 at 7:47 pm.
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