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H X & K aerials.

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H X & K aerials.

Post by colly0410 » Wed Dec 10, 2014 1:23 pm

When the UK used band 1 for TV you'd see a mixture of H, X & even the odd K shaped aerials on roofs where I spent most of my childhood. (Nottingham & East Derbyshire areas) Yet when I've been abroad just about all the band 1 aerials you saw were simple horizontal H's or multi-element yagi's, can't remember seeing any K or X's or any other shapes. Was it just a British thing to have weird shaped aerials?

 
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Re: H X & K aerials.

Post by Niall » Wed Dec 10, 2014 3:25 pm

I suspect it's a timing thing. Did the UK not have VHF TV earlier than much of Europe, before the Yagi was established as the best solution? Europe also IIRC kept VHF channels with no UHF alternative for longer, so the ones you saw in Europe would be in many cases newer installations. From the lack of use of X or K types in communications, I'm assuming the Yagi has overwhelming advantages.

I know some X aerials aren't in fact X - beams but the elements are actually the diagonally opposite ones, I think this was for additional bandwidth?

 
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Re: H X & K aerials.

Post by Panrock » Wed Dec 10, 2014 6:53 pm

I believe the vertical 'X' (and maybe the 'K') were supposed to be better at rejecting motor car interference from below than the 'H'. This wouldn't be the case if they were horizontal, so then this becomes a consequence of the main stations all using vertical polarisation in Great Britain. This was not the case elsewhere.

Steve

 
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Re: H X & K aerials.

Post by colly0410 » Thu Dec 11, 2014 6:29 pm

Interesting replies. Panrocks point about only being used with vertical pol seems valid. When I lived in Chester-le-Street (where horizontal pol was used) for a while in the mid 60's I can't remember seeing any horizontal X's or K's. When I lived in Bestwood Village near Nottingham we had a weird looking aerial, it was like a bent H, something a bit like this >-> where the top & bottom of the dipole & reflector were bent towards the transmitter, there was no band 3 part to it but it got ITV perfect..

 
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Re: H X & K aerials.

Post by Terrykc » Thu Dec 11, 2014 8:35 pm

colly0410 wrote:... When I lived in Bestwood Village near Nottingham we had a weird looking aerial, it was like a bent H, something a bit like this >-> where the top & bottom of the dipole & reflector were bent towards the transmitter, there was no band 3 part to it but it got ITV perfect..

I've seen one or two of those - I think they are very popular in the US, judging from various pictures I've seen.

However, I'm sure that those I've seen had the pointed end directed to the transmitter!

I don't think your Band III reception had anything to do with the shape of the Band I elements - just put it down to luck!

 
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Re: H X & K aerials.

Post by Synchrodyne » Fri Dec 12, 2014 6:34 am

I can’t say that I have seen any H or K aerials anywhere outside of the UK. In NZ we had vertical polarization areas outside of the bigger cities, such as Waikato-Bay of Plenty, which was covered by the rather large footprint of the Mt. Te Aroha transmitter, initially on channel NZ1 only, with the second program on channel NZ3 added in the 1970s. So it could have been a fertile area for the use of the X or K type – if in fact they had material advantages - but all of the outdoor aerials I have ever seen in this region have been either single folded dipoles or of the Yagi type (also with folded dipoles) – many still remain in place. I don’t think that I have seen a TV or FM aerial in NZ that did not use a folded dipole.

I have a vague notion that the X-form was used for mechanical as well as electronic reasons, being simpler and potentially more robust than a two-element Yagi. But then the folded dipole was also relatively robust.

I did see horizontal polarization aerials with vee-shaped elements (in plan-view) in the USA. The centre of the vee was away from the transmitter as compared with the ends of each element.

On chronology, whilst the UK was certainly early with the use of Band I, it was a relatively late starter with Band III, which had been used by the European countries from the inception of their respective TV networks in the first half of the 1950s, and in the USA from the 1940s. Germany I think was the first in Europe with UHF transmissions, followed by Italy. So the UK was a follower there as well, although its ultimate UHF program was more ambitious than most.

Cheers,

Steve

 
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Re: H X & K aerials.

Post by colly0410 » Mon Mar 30, 2015 3:06 pm

I wonder if the use of folded dipoles outside of UK was because of the wider bandwidth of 525/625 channels? 405 bandwidth was about 5 MHz, 525 about 6 MHz, 625 about 7/8 MHz & 819 about 14 MHz. Also some parts of the world (USA, Canada, New Zealand, Australia, others?) had more than one band 1 channel in use in any area. This didn't happen in the UK on band 1, only in band 3, i.e. Winter Hill, Belmont, others?

 
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Re: H X & K aerials.

Post by Synchrodyne » Sat Apr 04, 2015 2:38 am

Yes, I suspect that the greater channel bandwidth requirements at least in part drove the use of folded dipoles outside of the UK. Also, in New Zealand, Australia and the USA, 300 ohm balanced feeders were the norm for a long time, and folded dipoles probably would have provided better matching. NZ started the move to 75 ohm coaxial feeders around 1970 give or take, and anyway just ahead of the colour introduction. The changeover in the USA might have happened a little later than that, and for whatever reasons the US standardized on F-connectors, rather than the B&L type chosen for use in NZ and Australia. In all the countries it was normal to connect the aerial active element to the coax via a balun, so as to avoid degradation of the polar diagram. The apparent past UK practice of connecting dipoles (balanced) direct to coax (unbalanced) seems very strange, not to say inelegant.

Here in NZ, as far as I recall Waikato/Bay of Plenty was the only region where the main transmitter used Band I for both TV1 and TV2. The broadband aerials, covering channels NZ1 through NZ3 were visibly different. With a typical 3-element unit, there were significant length reduction steps from the reflector through the dipole to the director, as compared with the older channel NZ1-only aerials. By the way, more than a year out from our analogue switch-off, the local population of now-obsolete vertical Band I arrays around these parts seems to be little diminished; example attached.

In the USA of course, many areas would have had two, even three low-band channels back in the analogue days. In DFW we had channels A2, A4 and A5. Multi-element aerials covering lo-band, FM, high-band and UHF, all connected to the same feeder, were the norm.

Cheers,

Steve
Attachments
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Re: H X & K aerials.

Post by GlowingAnode » Sun Apr 05, 2015 9:28 am

Were "X" aerials used because they could receive equally well horizontally and vertically polarised transmissions?

Rob.

 
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Re: H X & K aerials.

Post by nuvistor » Sun Apr 05, 2015 2:46 pm

I thought the X aerial vertically polarised from Antiference which had the dipole/director were sold on better rejection of signals and interfence from below and the sides. However I also seem to remember that the also were advertised as much easier and quicker to install than the H aerials.

My first job was mate to an aerial rigger, we put many Antiference X plus 5, i.e an X aerial for channel 2 and a 5 element channel 9 aerial. The hinge connecting the two allowed upto a 270 degree adjustment to line up with the transmitters, only required one downlead. Only every used seperate ch 2 and 9 arrays if in a bad reception area.
I only remember using Antiference aerials, probably the company I worked for had a good deal, they were quite a large dealership with about 20 shops.
Frank

 
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Re: H X & K aerials.

Post by Panrock » Sun Apr 05, 2015 3:10 pm

It's interesting freeze-framing through old films showing street scenes, looking for television aerials. Last night I worked through an amateur film showing Holland Park, London in about 1950. I may have glimpsed two aerials, but if I did they were far off and indistinct.

Presumably in Holland Park, firstly the signal was strong so an indoor aerial would often suffice, and secondly in 1950 there were very few television aerials around anyway. I imagine things didn't really take off until the mid 'fifties, after the Coronation and the coming of ITA.

Steve

 
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Re: H X & K aerials.

Post by Terrykc » Mon Apr 06, 2015 10:59 am

GlowingAnode wrote:Were "X" aerials used because they could receive equally well horizontally and vertically polarised transmissions?

Rob, if you look back at the posts by colly0410 and Panrock you will see that they were only used with vertical polarisation.

I remember visiting the area around Beccles on the Norfolk/Suffolk border in 1959 before B III aerials started appearing for the new Anglia TV service that started later in the year and being fascinated by all the horizontal H aerials - and quite a few 3 element yagis on single story buildings - because the ends of the elements tended to droop slightly, giving the appearance of long legged insects swooping over the chimney tops!

 
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Re: H X & K aerials.

Post by Niall » Mon Apr 06, 2015 4:32 pm

I have dug out an X centre made by Aerialite.
This is the type where the coax centre is connected to the centre of one diagonal and the screen to the other.
I'm assuming that the rods would be 1/2 wave in total, i.e. 1/4 wave either side of centre.
So what we have is a pair of dipoles, one inverted with respect to the other?
Anyone have any info about theory of operation, likely performance figures etc.?
I am interested in trying it out on the Amateur 6 meter band.

I have tried an X beam on 11m many years ago but that was a conventional reflector / director arrangement.

 
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Re: H X & K aerials.

Post by Doz » Tue Apr 07, 2015 11:35 am

Niall wrote:I have dug out an X centre made by Aerialite.
This is the type where the coax centre is connected to the centre of one diagonal and the screen to the other.
I'm assuming that the rods would be 1/2 wave in total, i.e. 1/4 wave either side of centre.
So what we have is a pair of dipoles, one inverted with respect to the other?
Anyone have any info about theory of operation, likely performance figures etc.?
I am interested in trying it out on the Amateur 6 meter band.

I have tried an X beam on 11m many years ago but that was a conventional reflector / director arrangement.


Bit like an HB9CV?

 
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Re: H X & K aerials.

Post by Focus 2 » Tue Apr 07, 2015 5:57 pm

Terrykc wrote:if you look back at the posts by colly0410 and Panrock you will see that they were only used with vertical polarisation.


I seem to recall seeing a couple of horizontally polarised "X" aerials for the Grampian Durris transmitter in Perth many years ago. They're certainly very rare and have never spotted any for our horizontally polarised VHF transmissions in North East England.

BI folded dipoles, at least for our Channel 5, have been spotted however, such as the one I photographed in Hexham a few years back, see post #62 in the link. As a guess these were manufactured later, possibly 1970s installations?

http://www.vintage-radio.net/forum/show ... 777&page=4

Cheers,
Brian

 
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Re: H X & K aerials.

Post by ntscuser » Tue Apr 07, 2015 10:00 pm

Focus 2 wrote:BI folded dipoles, at least for our Channel 5, have been spotted however, such as the one I photographed in Hexham a few years back, see post #62 in the link. As a guess these were manufactured later, possibly 1970s installations?

http://www.vintage-radio.net/forum/show ... 777&page=4


The closely-spaced director was needed to bring the impedance down from 300 to 75 ohms. It did nothing to unbalance the signal though.

 
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Re: H X & K aerials.

Post by Niall » Tue Apr 07, 2015 10:20 pm

Doz wrote: Bit like an HB9CV?


I see what you mean. Presumably the phasing section isn't needed with the X because both elements are fed at the same point.

 
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Re: H X & K aerials.

Post by Focus 2 » Wed Apr 08, 2015 2:02 pm

Focus 2 wrote:I seem to recall seeing a couple of horizontally polarised "X" aerials for the Grampian Durris transmitter in Perth....


This should read BBC1 Meldrum ch4H of course :ccg

Brian

 
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Re: H X & K aerials.

Post by colly0410 » Wed Apr 08, 2015 3:13 pm

Been looking at FM aerials round here & they seen to be: A straight dipole, H, yagi with folded dipole or those halo things. No X or K or any other weird shape. I use a vertical FM dipole & get all the local & national stations perfect in stereo.

On the subject of baluns: I can't ever remember seeing a balun used on an aerial, neither of my UHF aerials (both in the loft) have got one nor my vertical FM dipole, just centre wire to one side & braid to t'other. How much signal would you lose by not using a balun?

 
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Re: H X & K aerials.

Post by ntscuser » Wed Apr 08, 2015 3:44 pm

colly0410 wrote:On the subject of baluns: I can't ever remember seeing a balun used on an aerial, neither of my UHF aerials (both in the loft) have got one nor my vertical FM dipole, just centre wire to one side & braid to t'other. How much signal would you lose by not using a balun?


Assuming the aerial is balanced for 75 ohms you don't lose any signal, in fact you gain some in the form of interference!

Since half of the signal will now be travelling down the outer braid it defeats the whole purpose of using a shielded cable. This is less critical for short runs or indoor aerials but still leaves you prone to impulse interference from domestic appliances and nearby vehicles.

 
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Re: H X & K aerials.

Post by nuvistor » Wed Apr 08, 2015 10:55 pm

I thought the J Beam UHF aerials such as the MBM46 used a balun. I have one in my loft working since 1970 with the same coax.
Antiference had the "Trumatch dipole", the claim was the shaped dipole resulted in a good match and an unbalanced feed point.
Anyone confirm my thoughts?
Frank

 
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Re: H X & K aerials.

Post by ntscuser » Wed Apr 08, 2015 11:20 pm

nuvistor wrote:I thought the J Beam UHF aerials such as the MBM46 used a balun.


Yes but they had to use a 4:1 impedance matching transformer in any case as their unique active element had a nominal impedance of 300 ohms. :)

It's still a good idea to use a balun even if the nominal impedance is 75 ohms and the impedance matching is 1:1. Digital receivers are particularly sensitive to impulse interference.

 
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Re: H X & K aerials.

Post by nuvistor » Wed Apr 08, 2015 11:38 pm

Thanks for that, OK on the 4:1, I did not know the impeadance of the MBM 46 dipole just knew they matched 75 ohm unbalanced coax well and used them on all our colour TV set installs for the first few years of colour TV.
I presume it is cost cutting that stops the use of 1:1 baluns, but I agree they should be part of the aerial installation.
Frank

 
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Re: H X & K aerials.

Post by Synchrodyne » Sun Apr 12, 2015 12:17 am

I’d guess that cost was a factor that mitigated against the use of aerial baluns in the UK. I suppose that non-use of baluns could be put in that bucket of cost-driven poor engineering choices along with mean level agc, lack of black level restoration, lack of mains isolating transformers, vision bandwidths well below those which were transmitted, and so on.

The use of resistive type splitters rather than the better hybrid kind, which was normal in the USA, may also have been cost-driven. In New Zealand and Australia, both kinds are found, the result of there having been both British and American influences at work. American-style 300 ohm balanced ribbon cable feeders were the norm for monochrome era, but when 75 ohm coax arrived, it was with Belling & Lee connectors.

Balance-to-unbalance matching at aerial/feeder interface does not seem to have garnered much attention in the text books of the 1950s and 1960s, although impedance matching was usually treated in some detail. One has the sense that there was something of a “near-enough-is-good-enough” approach at work. That is conveyed by this Belling & Lee advertisement from 1952:

WW 195208 p.A69.jpg


To be fair, though, B&L did acknowledge the existence of a balance-to-unbalanced condition.

Cheers,

Steve

 
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Re: H X & K aerials.

Post by Niall » Sun Apr 12, 2015 8:08 pm

Don't know about the cost aspect, one of the things I noticed coming back to amateur radio a couple of years ago was the tremendous emphasis on baluns which were virtually unheard of up to the 80s. Looking back at old aerial designs and articles, baluns were never used, now they are almost always there. I wonder if it is something to do with the availability of toroid cores in various sizes and materials which again were never seen in the past, now they are used as transformers and filters in most rf circuits.

Actually, over the same timescale, toriodal power transformers have also gone from rare to ubiquitous.

I do wonder how much difference a 1:1 balun actually makes in most cases. If it does nothing more than introduce loss into the feedline, it will make the SWR look better!

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