Signal penalty with aerial in loft

[Panrock]

In the 1960s and 70s we lived in Tonbridge, Kent and used separate loft aerials to receive Crystal Palace on Ch.1 and Croydon on Ch.9. Results on Ch.1 were excellent and Ch.9 just sufficient. My father wouldn't consider external aerials, thinking them ugly.

Data about how much loss roof materials accounted for seems hard to come by on the web. Are there any old charts, buried in the pages of Practical Television perhaps? And how did the loss vary with frequency?

Thanks,

Steve

[peter_scott]

https://www.aerialsandtv.com/loftaerials.html

https://otadtv.com/factors/index.html

https://www.ofcom.org.uk/__data/asse...ropagation.pdf

[Nuvistor]

The signal at VHF would be attenuated going through roofing tiles/slates but unless in a poor signal area would probably be ok.
One difficulty with loft aerials is when the signal has to pass through the walls of the house of the gable end or even worse in a semi or terrace house. Then the number of brick/block walls can considerably attenuate the signal.

Water tanks can also cause problems.

I have used a loft aerial for UHF for going on 50 years but the signal is through the tiles and I am line of site 8 mikes from Winter Hill which makes it much easier.

[paulsherwin]

It also depends on the roofing materials. Some ceramic tiles screen radio signals almost completely, while others are practically transparent.

[Panrock]

Thanks for the replies. Interesting about ceramic tiles. I guess there's a difference between the mechanisms of attenuation and screening, the latter presupposing at least a partial conductor(?).

[Refugee]

I guess it depends on the metal ore content of the clay the tiles are made from.
Then you have to check how much the signal drops when the weather is wet.

[emeritus]

Re #3, I cured my aunt's UHF reception problems by moving their loft multielement Yagi a few feet sideways so it pointed through the tiles rather than the coke breeze party wall. She had thought she needed a better aerial. Her tenancy agreement prohibited external roof aerials.

[ms660]

Some imported slates can have a high content of fools gold, Spanish slate in particular, I know this 'cos I've laid thousands of them.

Lawrence.

[G6Tanuki]

And wet roofing-tiles can add 10dB of attenuation compared to dry. . .

[Biggles]

On the plus side at least the aerial will be protected from the weather if it's inside the loft.The TV aerial at my parent's house is still going strong forty years after installation because it's inside. I suppose it all depends on the signal strength in the area whether you can get away with it or not. You may also have more trouble with reflections upsetting the signal if the aerial is mounted inside.

[Panrock]

Originally Posted by G6Tanuki

And wet roofing-tiles can add 10dB of attenuation compared to dry. . .

Is that at UHF though? I don't recall seeing much if any difference on low Band I.

Steve

[Graham G3ZVT]

Originally Posted by G6Tanuki

And wet roofing-tiles can add 10dB of attenuation compared to dry. . .

Maybe at around 500MHz. Much lower at VHF I would have thought.
As I remember, buildings were particularly transparent to Band I signals, and you had to try quite hard to get any ghosting.

[dglcomp]

My gran in Crewkerne live ~26mi from the Mendip transmitter and still get full signal/quality from a loft antenna (and a non-digital one at that ), she can even get the welsh PSB muxes from Wenvoe (which, of course, would have been the applicable transmitter for 405 line BBC One) and still gets a usable signal with the RF loop-through on the Freeview recorder turned off.
I do remember, though, that channel 5 was not always that good esp. in summer but given the lower power of Mendip's channel 5 transmitter/lower aerial height that's to be expected.

[Panrock]

Originally Posted by rambo1152

As I remember, buildings were particularly transparent to Band I signals, and you had to try quite hard to get any ghosting.

Severe, multiple ghosting was possible though, even on Channel 1 in extreme circumstances. I saw this when using a Sony TV9 with whip aerial in a flat in Central London.

Steve

[Nuvistor]

Yes ghosting could be a problem on B1 depending on the area of course.

[Bazz4CQJ]

I've used an aerial in the loft for a TV in one of the bedrooms. Considering that the one on the chimney stack pulls in a signal which "just manages", the one in the loft seems about the same. Could be that the external one, or its coax cable, has 'issues'.

B

[arjoll]

Originally Posted by rambo1152

As I remember, buildings were particularly transparent to Band I signals, and you had to try quite hard to get any ghosting.

When I was a student flatting in North East Valley, Dunedin, we had massive amounts of ghosting on band I (NZ channel 2) and III (NZ channels 4 and 10). We were only partially up the sunny (south-east) side of the valley, and signals would have been happily bouncing off both sides, probably not helped by Mt Cargill being off to the north-east of the valley.

[Panrock]

Presumably those NZ signals were horizontally polarised? One imagines that our vertically polarised signals bouncing off vertical objects would have been worse.

Don't know how much truth there is in that.

Steve

[SteveCG]

Panrock,

405 TV (Vert and Horiz) and VHF/FM (Horiz) reception in the Lake district suffered from more ghosts than lurk in the average cemetery...

[Hybrid tellies]

Apologies for the delay I meant to reply earlier.

When we lived in west Cornwall we used loft TV aerials. This gave us really good reliable VHF 405 line TV reception of BBC1 from North Hessary Tor on ch2 and ITA from Caradon Hill on ch12. Both transmitters were between 40-60 miles distance from our village. As I said reception was good and totally reliable with no signal degradation noticeable when our slate roof was either wet or covered in snow and ice which did happen occasionally.

When the UHF 625 line TV service started from Caradon Hill, BBC1 ch22, ITA ch25 and BBC2 on ch28, most people in our village needed a large 18 element UHF band 4 roof mounted aerial. Some cottages like ours were not permitted to install a rooftop aerial so we used a large 18 element aerial mounted in the loft. The quality of reception was ok, not as good as VHF 405 but it was adequate. But unlike VHF 405 reception the picture did become noticeably grainier during wet weather. Looking back I think the use of a mast head pre amp mounted near the loft aerial would have improved things.

Ref ghosting. My first encounter with ghosting came when we moved and lived for a while in the lower part of Helston. Because of the local hills my 405 line TV would only pick up BBC1 on ch1 from Redruth. Using an indoor aerial reception was ok but the ghosting was quite spectacular. I was quite surprised by this as I had been advised that the lower band 1 frequencies were less prone to multipath reflections than the higher band 3 and UHF channels.
How wrong they were I later learned that multipath or ghosting can be more of a problem at VHF than with UHF. It is something to do with increased absorption levels of most reflected surfaces, hills buildings etc, are much higher at UHF than at VHF.
One thing I am still not sure about is whether VP signals are more prone to multipath interference than HP signals or vice versa.