"Contractor" UHF TV aerials

[SteveCG]

Before the digital TV age most UHF aerials on rooftops were of the "Contractor" variety. The usual clue was the same sized flat plate reflector irrespective of the aerial's Grouping.

Come digital, come the fancy (and expensive) designs. However now that the first flush of digital is well and truly over, still I have not noticed a re-emergence of the cheap-and-cheerful designs. I was wondering why. Any thoughts folks?

My musings were that the earlier aerials were from the TV rental days. Or possibly that what was in-the-back-of-the-van for TV shops is different from the vans of the more specialist riggers today. (There can't be many independent TV shops left now).

For me an irony is that, with Digital, ghosting is no-longer the problem that it was with Analogue, yet the contractor aerials were not very good in that department!

[paulsherwin]

Riggers generally fit a wideband aerial nowadays, as frequency rejigging can mean a grouped aerial has a short life. They also like to fit more upmarket aerials because they make more margin on them.

Many houses in my area have been fitted with quite sophisticated wideband aerials in recent years, despite the fact that a very basic loft aerial is perfectly adequate (the transmitter is only a few miles away and can be seen from the end of the street).

[Andrew2]

We live about 18 miles from Winter Hill, line-of-sight all the way. Signals are strong and reliable. Our rooftop aerial is a simple 'contractor' 11 ele and has been there for about 25 years, as has the coax.
Across the road is a row of bungalows, almost all of which are occupied by elderly couples and widows. A few years ago as the DSO loomed, these houses began to sprout enormous, gold-coloured, multi-boomed aerials that looked like they'd do excellent service in radio astronomy.
I know one of the old ladies and when I casually mentioned her new 'radio telescope', she showed me the flyer that had come through her door a few weeks previously. It was disgraceful - 'you may lose one or perhaps all of your favourite TV channels if you don't get a digital TV aerial installed before the switch-over' or words to that effect. I think she paid about £180 for the installation. Blimmin' cowboys. I bet you could light bulbs from it...

[julie_m]

They're selling the sizzle, not the sausage. It's about convincing the customer that they need a fancy new aerial to receive good pictures on digital TV. Despite the fact that the system was designed from the outset to be highly resistant to multipath effects and transmitted in the same frequency band. And so the new aerial has to look the part, even if its performance can be nothing special.

[Lloyd 1985]

I was quite surprised when we moved to our new place in Coningsby that I can use one of those wire loop aerials supplied with some colour portable TVs from the 90's to receive all the digital channels! I was going to bin them all before we moved as they were completely useless for anything when we lived in Daventry. Looks like the 2 big aerials I bought with me will be redundant in my new workshop! One is a £4.99 loft aerial from Argos in the mid 90's, the other is a much newer yagi thing with built in signal booster.

Regards,
Lloyd

Riggers generally fit a wideband aerial nowadays, as frequency rejigging can mean a grouped aerial has a short life

So that's why http://www.aerialsandtv.com/ recommend a log periodic. It works a treat here some 20 odd miles away from Crystal Palace. I replaced the old TV aerial (which had fallen off the chimney) with a threesome of VHF/DAB and TV aerials a few years ago, they all point the same way as Wrotham is nearly in line with CP from here. I did it one Christmas, rather cold but Christmas dinner tasted wonderful!

[SteveCG]

Interesting comments folks. Where I live the main transmitter is Ridge Hill (Gp A - in Analogue days, Wideband in the changeover period, and essentially back to Gp A nowadays). So there are many Wideband designs - some of wonderous complexity - adorning the local roofs. Yes, I can imagine phasing a few of them up and looking for signals from the Radio Astronomy source Cygnus A. However I find that a humble Antiference 13 element Gp W Trucolour does the job in my loft just fine, even now with Ridge Hill back to Gp A only. In fact it is diplexed into what had been my VHF/FM only downlead - so there a few dB losses there (2 diplexers - Antiference UF23 - , one in the loft, one downstairs). My point in mentioning this is that I could easily have used a 10 el Contractor and still got a signal well over the minimum.

From examining samples of Contractors I came to the conclusion that quite a few 'designs' had a fixed element spacing irrespective of Group (rather like the fixed size, flat plate reflector). So in Gp C/D they were probably not too bad - matching to the downlead is a different matter. Whilst in Gp A, at the bottom of the band, they worked better with the reflector removed ! (The reflector being of such a width that it was acting as a director on Ch 21). This situation for digital would not be noticable, but for analogue in a hilly area...

I must admit to not knowing the digital transition width now in terms of S/N between no signal and a perfect signal. I reckoned it was about 2 dB in the 2K carrier, 16 QAM era. It impacts upon the minimum performance that any of these aerial systems must achieve. But considering that a rule of thumb for the analogue era was about 6 dB increase in RF S/N for a one picture point improvement in picture S/N quality, then one can actually get away with a lot nowadays with a Contractor!

[Nuvistor]

Good information about the move of transmitters from above 700Mhz. Section 4.20 gives some figures on signal levels.
http://stakeholders.ofcom.org.uk/bin...rch_report.pdf

Frank

[G6Tanuki]

Originally Posted by merlinmaxwell

So that's why http://www.aerialsandtv.com/ recommend a log periodic.

I rather like *long* log-periodics.

Round here [rural south Wiltshire] terrestrial TV signals have always been problematic: we have lots of low-power 'infill' transmitters many of which now only carry a pathetically-constrained subset of the Muxes you'd expect.

They're also al vertically-polarised.

It's quite common to see houses with a pair of big "bling" wideband Yagis correctly horizontally-polarised and aimed at the big transmitters [mendip, hannington] along with a similar antenna - also horizontally-polarised (see below) - aimed at one of the local (VP) infill-transmitters.

(round here, terrestrial-TV-viewing people dream of one day being able to get London ITV)

Other houses I've seen just have a small horizontally-polarised antenna aimed at the local infiller but with an obvious masthead-preamp to make up for the cross-polarisation loss. I guess riggers are happy to point a HP antenna at a VP transmitter, show the customer a 'marginal' signal, then bung in a masthead preamp and charge another £100.

[dglcomp]

Yes, the whole digital aerial thing was a massive con, especially because while the TV signal is encoded digitally the signal coming out of the mast is still an analogue waveform and also because most transmission sites have been able to continue without a change of transmit antenna (I'm primarily talking relays as very few of the main sites did not have a new transmit antenna).

At my grans (Crewkerne in Somerset, with her house at one of the highest points) a perfectly good freeview signal could be had pre-DSO from Mendip using the loop antenna on an old Fidelity TV! (which seems to work better than the new maxview indoor antenna on the newer LCD TV)

The other 2 TV's both have their own aerial in the loft and both get a perfect signal (Level+Quality at 99%) even though one is most definatly not a modern "digital" aerial but one that looks nearly as old as BBC2 and none of the cabling has ever (IIRC) been replaced, the TV downstairs will even work fine when the freeview recorder is in standby mode and the RF loopthrough is supposedly disconnected (one of those super slim echostar units).

[Scimitar]

Surprised at the amount of misinformation here. Certainly there is no such beast as a "digital"aerial, but the word tends to be used as shorthand for a tested and certified device. Analogue is great, degrading gracefully it is surprising what a rubbishy aerial system will do and "Mrs Jones" is perfectly satisfied provided she can see her soaps.
Digital is a different beast, if the signal performance is inadequate or interference too high for perfect service, then you get nothing. THAT is why the contractor aerials thankfully died out, even at the sheds. Nothing to do with profits at all.

Contractor aerials do not have a balun which is the first issue. That means that the screen of the cable becomes part of the aerial system and sensitive to all the electrical noise being generated in the house. As the user of such junk would have bought purely on price, said user would also be perfectly happy to feed it with poor quality cable, sometimes not even double screened, let alone the heady hights of the WF100 specification laid down **.

Contractor aerials are made to as cheap a build as possible. Before the digital changeover, I was being offered contractor aerials at £2 each in small quantities. First puff of wind and the reflector (such as it is) falls off. The rivited or often self tapped directors come loose very quicky, leading to potential breakup.

As a dealer and installer with premises, even if I personally didn't care about customer service, they would soon find me to insert such rubbish where the sun doesn't shine. And they would be well justified. Of course "white van man" will get away with it.

** The specification for cable is not just for its RF properties but also for electrical safety. This is why it is mandated by building regulations for all new builds now. Sadly we still come across buildings, including a 250 room care home that we are working on that has been wired with non compliant and unsafe RG6. Clearly some accountant spotted that it is a fraction of the price and used the "sizzle" argument above to justify it.

Sadly for them, even ignoring the safety implications, some of the more distant points will now never work.

[Nuvistor]

One problem we found in the 60's and 70's was poor quality coax. Look at some early 50's coax cable and the screen was very dense, it made the cable more difficult to work with but the electrical characteristics were excellent for that time.

The first job I had they put me on a van with a 'rigger', quite large rental company, early 60's . The 12 months I did saw cable go from pretty good to very poor, the screen was just a few whiskers. The riggers loved it, quick an easy to install.

I left and went to a small firm who cared about quality, the good stuff was available, along with a policy of J-Beam or Antiference aerials. That was what we requested the contractor fitted, he was a decent man and that's what he did. He admitted he kept the cheaper stuff but that's what some other of his customers wanted.

There must be a lot of poor quality cable out there, counting poor as in RF performance..

Apologies, another ramble from me.
Frank

[Peter.N.]

Believe it on not I don't have a digital aerial. When digi started I still used analogue for videoing and one day all I found on replaying was a lot of grain, I checked on the TV and two stations had disappeared and the others were just discernible, the digi picture was still perfect, I later noticed a length of coax hanging down the wall with nothing on the end, its still there and still giving a perfect picture, previously we needed a decent aerial to get a reasonable analogue picture.

In spite of all the warnings about poor digi signals I have in fact found that in the majority of locations it is far superior especially where ghosting was a problem so it seems that generally you need a less efficient aerial.

Peter

[Tractorfan]

Hi,
My first job after school in 1970 was for a local TV shop that also erected aerials. The two guys who ran it were the usual skinflints and they used unbranded 'contractor' aerials & cheapo co-ax. Even the plugs were nasty crimp-on types.
They bought the aerials in bags of bits and the uncle of one of the guys spent his retirement assembling them for us to install.
They seemed to work well enough around the Chester/north Wales area, and I sometimes wonder if any of them still survive.
Cheers, Pete.

[dglcomp]

The big problem that can happen with digital TV is that if you live very close to a transmitter the signal level received by the receiver is so high that the filters no longer are able to filter out other channels/frequencies so all they see is a massive jumble of different channels and therefore some form of signal attenuation is required (i.e. a lower gain antenna or an in-line attenuator). Remember years ago being on Granby Industrial Estate in Chickerell, Dorset which has a good view of the Weymouth transmitter, the place I was visiting got a decent (although can't remember how decent) TV picture from an Amstrad TV/Video which not only didn't have an aerial, it didn't have a usable aerial socket!

[Radio Wrangler]

When the Japanese 'MUSE' high definition system was being promoted, a large truck carried a demo system around the UK. (Large probably to fit in a player!) Punters were shown the HD telly.

They liked the large screen
They really really liked the 16:9 ratio
Very few were bothered about the increase in resolution, few could even tell.
Almost all asked if they'd need a new aerial.

Against the cost of one of these monsters, the aerial was trivial. But they were assured their ordinary aerial would be fine. The disappointment this brought made the demonstrators curious.

People weren't all that keen on getting one, but if they did, they sure wanted the neighbours to know!

Maybe there's an aspect of this in the bling antenna phenomenon?

David

[Aub]

What about "digital" headphones then? I think our ears are analogue aren't they?

Cheers

Aub

[Radio Wrangler]

Digital headphones are easily told from mere analogue ones... Gold on the jack-plug and a fiver on the price!

One of my pet tricks when giving a talk is to whirl round like a loonie, leap in the air, cupping both hands together, look into the cupped hands and announce that I've caught an electron. I pick a victi... em.. member of the audience. I show him the electron and ask him if it's a digital one or an analogue one.

David

[SteveCG]

So we have the irony that aerial systems are being installed for digital that are the ones that should have been installed for analogue - and those Contractor aerials and cheap downleads of the analogue era would in general just be fine now.

Would I be correct in thinking that digital is most prone to IMPULSIVE interference - hence the foil downleads? The higher the QAM the more prone? Impulsive interferenece hardly affected UHF analogue TV - VHF TV was a different matter.

[Nuvistor]

Had a bit of an experiment yesterday. I have a wide band aerial in the loft, unused, used to feed a bedroom. So I disconnected the MBM46 C/D and connected the wide band, it's about the same size as the MBM46.

Results, still 100% quality and strength but the AGC figure had changed by about 10%, meaning a slightly weaker signal. I also checked the local mux, Wigan is more or less in line with Liverpool so although being in Greater Manchester I get that mux not the GM one. The Local Mux for Liverpool is 2Kw ERP against the main muxes 100Kw.

Results show again 100%quality and signal and the AGC about 50% different to the main muxes, did not check it before the change. No pixelation or problems on any of the muxes.
The Liverpool mux is on ch56 Manchester on 57 but on 1Kw, I thought with being adjacent it could be the problem but ch55 has a 100Kw mux and it does not affect ch 56 so I presume the Manchester mux aerial is very directional.

I cannot check the HD channels on 31 and 37, I don't have a Freeview HD tuner. At least the aerial should be OK if they do move the channels below 700Mhz and it also gave the TV a work out, it's not been on for a month.

Obviously little to do on a Sunday afternoon

Screen shot of signal strength, note pre and post viterbi error correction

Frank