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Old 24th Apr 2019, 11:12 am   #1
SteveCG
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Default Triax UHF Aerial - info

Dear All,

A few years ago I was given a Triax UHF aerial whose lashings had finally failed. The question I'm asking is what Channel range did it cover?

I don't have a camera to take a 'photo but here is some information on it:

It is a (Triax nomenclature) "18 element" design, which has a six element barred reflector and a 'squashed' folded dipole, and 11 plain directors.

It is end mounted, with the boom split into two equal lengths making a total length of 1360mm.

The reflector element width is 420mm. The outermost director length is 130mm.

It has a printed circuit balun in the junction box.

The aerial was originally pointed at the Ridge Hill transmitter and I reckon dates from the early days of dual analogue/digital transmissions.

I've looked up Triax's recent catalogue and the only 18 el design of a similar style uses a centre mount trombone system.

The aerial is probably a Wideband design, but if so was it a 21-68, or was it a 21-60 design since Triax's Danish home-land only used TV upto channel 60.

I must say the dipole size made me wonder whether it could be a group E design.

Perhaps somebody has a Triax UK catalogue from about 2005, that may answer the question?

Last edited by SteveCG; 24th Apr 2019 at 11:14 am. Reason: layout and information correction
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Old 24th Apr 2019, 11:42 am   #2
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Default Re: Triax UHF Aerial - info

Anything in this 2007 catalogue?
http://www.instalsat.pl/files/Hirsch...gue%202007.pdf
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Old 24th Apr 2019, 2:23 pm   #3
SteveCG
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Default Re: Triax UHF Aerial - info

Unfortunately not, Frank. Interesting though in other ways!

BTW, I omitted to give the tip-to-tip length of the folded dipole of the Triax aerial. It is 228 mm. Oh, and when I called the dipole 'squashed' perhaps a better description would have been 'pinched-upto-the-boom-in-the-centre'.
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Old 24th Apr 2019, 3:05 pm   #4
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Default Re: Triax UHF Aerial - info

There is a 'colour code' used by some manufacturers to identify channel-groupings of UHF antennas; see

http://www.digitaluk.co.uk/reception_guide

Not sure if this would have been applicable when your antenna was made, or if Triax followed it!
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Old 24th Apr 2019, 3:26 pm   #5
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Default Re: Triax UHF Aerial - info

Sadly as far as I can tell Triax did not go in for the colour code - every plastic part on mine is blue, as is the plastics colour of all the other Triax aerials I've seen 'in the wild'.
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Old 24th Apr 2019, 9:27 pm   #6
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Default Re: Triax UHF Aerial - info

As well as the colour code, look for a letter, A,B,C,D,W etc.
A is 21 to Ca.31, B 32-44, C 45 to 68 or something like that. W or WB is 21-68, and there are other spreads within the 21 - 68 range.
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Old 25th Apr 2019, 10:10 am   #7
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Default Re: Triax UHF Aerial - info

The element sizes ought to let you estimate the bandwidth. The reflector width will be around or a bit bigger than a halfwave at the lowest frequency. The shortest director will be somewhat shorter (maybe -10% to -20%) than a halfwave at the highest frequency.
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Old 25th Apr 2019, 11:28 am   #8
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Default Re: Triax UHF Aerial - info

Just dug out my old data maps and says Ridge Hill 22 = BBC1, 28 = BBC2,
25 = ITV, 32=CH4. Channel Group A, Power = 100kw.
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Old 25th Apr 2019, 12:19 pm   #9
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Default Re: Triax UHF Aerial - info

Indeed John, those were the pre-digital channels. In the early days of dual analogue/ digital operation channels up in the group C/D range were used for the digital programmes. So one might expect a Wideband (ie 21-68) aerial, however Triax, being Danish, certainly sold aerials that only went upto 60 - presumably because in Denmark the UHF TV allocation only went upto 60 (as was true in Germany as well). So could this aerial have been of that era?

I think Triax may have had a range called 'super gain' - which look very similar to their current 'Digi' range.

And no, there are no letter codes on this aerial.
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Old 25th Apr 2019, 12:34 pm   #10
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Default Re: Triax UHF Aerial - info

Hi, I donít have any data on this brand, so unfortunately Iím not able to give a definitive answer. I would have thought there would have been some identification makings but I suppose if there were any they could have fallen off or just faded.
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Old 25th Apr 2019, 12:56 pm   #11
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Default Re: Triax UHF Aerial - info

Indeed John, it is all a bit of a puzzle. Studying some of Triax's pictures closely it may be that the rigger just did not bother to use the trombone mount supplied with an 18element aerial and so the use of just an end-mount for this size of aerial was never Triax's intention and hence a red herring for me...

I think there was a label on the boom - there is a patch at the shortest director end of the boom which looks suspiciously the right size - but not longer legible.

Last edited by SteveCG; 25th Apr 2019 at 12:58 pm. Reason: Added info
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Old 30th Apr 2019, 11:29 am   #12
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Default Re: Triax UHF Aerial - info

Sometimes, if the first director is significantly shorter than the adjacent dipole, that can indicate a wideband aerial. If it is a wideband, then it would likely have poor gain at the lower UHF channels in Group A as used by Ridge Hill - a reputable installer would (should) have used a Group A antenna at the outset.
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Old 30th Apr 2019, 12:41 pm   #13
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Default Re: Triax UHF Aerial - info

John, indeed so if they were doing the installation for Ridge Hill now. However in fairness I suspect this aerial is from the early digital days at Ridge Hill when some Group C/D channels were used as well as the Group A analogue set.

Either way apart from a dubious printed circuit balun (the corrosive effect of a nest of spiders??) I've been trying it out on the Channel 52 and 54 multiplexes from the Mendip transmitter. It is fringe reception but I've been listening to Smooth Radio which is programme 718 on the ArqB multiplex on chan 52, using a Thompson Set-top box. The STB quality readout was 6 yesterday and 8 today (with better propagation due to the settled weather). Indeed a Antiference set-top log periodic also worked today. Aaah, happy Dxing.

Last edited by SteveCG; 30th Apr 2019 at 12:42 pm. Reason: text change
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Old 20th May 2019, 12:53 pm   #14
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Default Re: Triax UHF Aerial - info

A good friend took the 'photo of the Triax aerial type I've posted here. The aerial is on a property adjoining the Lidl car-park in Malvern Link.

The aerial is pointing towards the Malvern TV relay, which is situated on the East side of the Malvern Hills about a mile or two away.

As you can see, it is mounted using a 'U' boom support. However the one I had was mounted at the reflector end of the boom using the same pole clamp as was used in the 'photo.
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Old 20th May 2019, 6:03 pm   #15
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Default Re: Triax UHF Aerial - info

That picture looks like an A group. It is not an 18 element aerial. The reflector counts as ONE element whether it is made of several rods or a flat sheet of ali mesh. It looks like a 12 element.
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Old 22nd May 2019, 11:34 am   #16
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Default Re: Triax UHF Aerial - info

Winston_1.

No, I am very confident it is a wideband design. However I agree with you concerning the number of 'elements' it has. To me, long used to Antiference's and other makers nomenclature, this Triax aerial would be a 'TC 13' if it were to have been an Antiference product.

Last edited by SteveCG; 22nd May 2019 at 11:37 am. Reason: data correction
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Old 22nd May 2019, 11:42 am   #17
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Default Re: Triax UHF Aerial - info

Looks like a TC18 to me. Malvern would be a C/D I think, but the larger reflector suggests a wideband. The blue plastic of the connector box is very tasty to some birds, we have replaced many with holes pecked in them. That and aerials where the box has come open, so not a model that we have installed for some time. Our mainstay is the Televes 1121.
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Old 22nd May 2019, 2:39 pm   #18
SteveCG
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Default Re: Triax UHF Aerial - info

Well, Triax have called it an '18 element' aerial - but as I've said it is really a 13 element aerial in other maker's nomenclature.

Malvern was originally classed as (one of the few) group D sites (ie ch 48-68), whereas group C (ch 53-65) was more common being one of the three main original groupings. Riggers found that quite a few group C aerials just could not do the top channel - and that this was true even after C was rebranded (but not redesigned) as C/D by quite a few makers. The Malvern Tx did not really provide a signal for Malvern itself - rather it was intended to serve parts of the Severn valley and in particular Worcester City.

The topography of the transmitter with the Hills behind it, and not on top of them, meant that it was possible to receive a very strong signal in Malvern itself but it was highly ghosted. This was because the main beam of the Tx was virtually horizontal whereas significant parts of Gt Malvern were lower in height than the transmitter site and so received less of the direct signal but still received the full Hills reflected/scattered signal. So you see quite a few aerials straining to get an (un-ghosted) signal from distant Sutton Coldfield.

When digital TV first started from the Malvern Tx the digital signals were down in the Group A part of the spectrum - hence the need for a wideband aerial. Also with the analogue ghosting problem up in the Group D part of the spectrum a directional aerial was needed; hence the number of elements on this slightly overkill Triax aerial, for the signal strength at the receiving site of the 'photo.

Last edited by SteveCG; 22nd May 2019 at 2:40 pm. Reason: added info
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