This might be one for Ian Nock‍ from the IET Multimedia Communications Network to answer!  ?

Well I cannot better Denis McMahon‍ 's technical description but I can probably add an opinion.


Firstly it is amazing how many things are done because of habit and based on old training, as well as what is requested. I can certainly believe that installations like as described are done because of old approaches.


The reality though is that more and more people are leaving the antenna sockets unused through the deployment of IP based video and audio delivery, whether via Smart TV, OTT dongle or 'Smart Speaker'. The main advantage being that these devices provide content on demand whether it is live or recent - no different for 'TV' or 'Radio'. The second advantage is related to what Denis mentions - that the strongest wireless signal inside many homes today is WiFi, and through that you have a very steady video and audio delivery that covers 90+ of homes. In my own home, I can barely receive six radio stations on FM, DAB has missing stations and intermittent reception but my WiFi is strong and steady with a much broader range of content availability. Even when away from home and mobile, I have better delivery quality that matches my usage via my smartphone over its IP connection... I am afraid to say that I believe traditional broadcast RF transmission and reception is living on borrowed time compared to the utility of IP delivered content.

Back in a more youthful era of my life I used to notice X shaped aerials now and again. They seemed to be more common in older suburbs with terraced houses than anywhere else, and I wondered what they were used for. Enquiries revealed that they were aerials for the old 405 line TV broadcasts on VHF band 1. It had been switched off many years before I was even born so the aerials were long defunct but nobody had bothered to take them down. This also explained why many of them were in a decrepit state even with completely missing elements.


Therefore just because an aerial is mounted on the side of a building doesn't in any way imply that it is still being used. I wouldn't be surprised if countless omnidirectional FM aerials on houses were installed decades ago but are no longer in active use.


Omnidirectional FM aerials were one of those 'wonderful' products from the 1960s and 70s (when FM radio still had an air of luxury about it) with the advantage of being able to receive broadcasts from all directions in exchange for a gain slightly above 0dBi. Well, if you want an aerial that approximates an isotropic then don't expect a gain any higher than an isotropic! They had a secondary advantage of being easy for consumers to install as almost no alignment was necessary.


More recently, a local housing association decided that it would not provide terrestrial TV aerial sockets in some of its apartments and instead it had a communal satellite dish that could receive both Freesat and Sky. It resulted in a mixed reception (pun intended) with some tenants being very pleased with being able to receive more TV channels than on terrestrial and not having to install their own satellite dish if they wanted to watch satellite channels, but other tenants were unhappy and uptight about having to buy a Freesat receiver if they just wanted to watch terrestrial channels. I believe that the decision to have satellite rather than terrestrial TV sockets in the apartments had something to do with circumventing issues associated with the analogue switch off but I'm not 100% certain of this.


There seems to be some unwritten social rule in Britain that terrestrial TV aerial sockets must always be provided even if nobody uses them. Does the same rule also apply to FM radio sockets which is why omnidirectional aerials still continue to be installed on apartment buildings even though their performance is quite poor?

Ian Nock:

Well I cannot better Denis McMahon‍ 's technical description but I can probably add an opinion.


Firstly it is amazing how many things are done because of habit and based on old training, as well as what is requested. I can certainly believe that installations like as described are done because of old approaches.


The reality though is that more and more people are leaving the antenna sockets unused through the deployment of IP based video and audio delivery, whether via Smart TV, OTT dongle or 'Smart Speaker'.

...

I am afraid to say that I believe traditional broadcast RF transmission and reception is living on borrowed time compared to the utility of IP delivered content.

Thank you, Ian, for your reply. This makes a lot of sense. I can think of other branches of engineering where things are done in a way that is "traditional" rather than take best advantage of new methodology. I imagine that many "radio" sockets connected to a communal system will remain unused, as new technologies gradually take over from FM radio.


I likewise am making increasing usage of digital TV and radio, and IP schemes - Amazon Prime is now looking promising after a shaky start. Wi-fi is now more reliable than it used to be, delivering a stronger signal from the hub. I have also wired my house with Ethernet connections to various key points, to obtain an even-faster signal. A drawback of IP delivery is that it sometimes fails for short periods of time. Terrestrial or satellite broadcasting is more reliable in this respect. I don't think these more-traditional systems will disappear for a while yet.

Denis McMahon:

My guess is that the connoisseurs of quality sound radio would use the digital services available on either Freeview or Satellite, as I do. Casual listeners would go for DAB, where quality is compromised by the ever-increasing range of programmes, at the expense of bandwidth.

There is an article about this in E&T https://eandt.theiet.org/content/articles/2011/11/analogue-switch-off-aint-going-to-happen/

Denis McMahon:

Terrestrial or satellite broadcasting is more reliable in this respect. I don't think these more-traditional systems will disappear for a while yet.

Does anybody know if any DAB pirate radio stations exist in the UK? In London the FM band is absolutely packed solid due to the number of pirate radio stations which operate in the area but the pirates don't seem to have moved into DAB yet. Therefore pirate radio creates an additional market for FM radio receivers and antennas, and could be prolonging FM broadcasting (from a user's perspective) even if the legitimate radio stations migrate to DAB and switch off their FM broadcasts.


Pirate radio is a subject that the IET probably only has a limited knowledge of along with even less of an understanding of the motives behind why people establish and listen to pirate radio stations.

Arran Cameron:

Back in a more youthful era of my life I used to notice X shaped aerials now and again.  .  .


Omnidirectional FM aerials were one of those 'wonderful' products from the 1960s and 70s (when FM radio still had an air of luxury about it) with the advantage of being able to receive broadcasts from all directions in exchange for a gain slightly above 0dBi. Well, if you want an aerial that approximates an isotropic then don't expect a gain any higher than an isotropic! They had a secondary advantage of being easy for consumers to install as almost no alignment was necessary.


More recently, a local housing association decided that it would not provide terrestrial TV aerial sockets in some of its apartments and instead it had a communal satellite dish that could receive both Freesat and Sky. It resulted in a mixed reception (pun intended) with some tenants being very pleased with being able to receive more TV channels than on terrestrial and not having to install their own satellite dish if they wanted to watch satellite channels, but other tenants were unhappy and uptight about having to buy a Freesat receiver if they just wanted to watch terrestrial channels.  .  .


 

Yes, one still sees old X and H aerials, and multi-element Band 3 aerials from the ITV 405-line era. To send someone up onto the roof to take them down costs the householder money, for which he gains no real benefit, so that is why some remain deteriorating. Not many householders have the ability or the inclination to this job themselves.


But I do notice new buildings going up and new aerials being installed on them so not all circular aerials are relics from the past. The installation in the picture I provided seems fairly shiny and recent.


In theory, the horizontal gain of a circular omni aerial cannot be as much  as a single dipole vertically polarised. A horizontal single dipole has the same sensitivity perpendicular to it as a vertical single dipole, but its sensitivity tails off sinusoidally to next to nothing as we move round to a direction longitudinal to it. The sensitivity of a circular dipole can be no better than the mean of this. Bear in mind that the horizontal single dipole has sensitivity also in upward and downward directions (so is more affected by interference from aircraft). This also applies to a circular aerial. The vertical dipole has relatively little sensitivity to the (useless) vertical  directions and maximises its sensitivity horizontally. Based on this theory, my calculations indicate that the circular omni aerial has a gain of -2 dB relative to a single dipole vertical. Yagi arrays can achieve positive gain of several dB.


Serving a community with a single satellite dish does seem a good idea; one can receive all the terrestrial channels, the Sky subscription channels, radio, alternative BBC and ITV regions - the lot. But yes, tenants would need the Sky box or at least a Freesat receiver. As I said earlier, the provision of some terrestrial services, particularly FM radio, seems somewhat perfunctory.


As for single domestic users, my neighbour has removed all his terrestrial aerials and uses a satellite dish for everything. I have Sky but am not ready to do this just yet. Sky is very good but pricey. Extending Sky services to other rooms hikes up the subscription even more, whereas for terrestrial all you need is a distribution amplifier and some coax wiring. Satellite dishes are vulnerable to snow. One winter mine became snowed up, cutting off reception. Since it is not far from the ground I was able to clear the snow with the aid of a stepladder. If this happened to a dish high on a roof it would be a choice of going onto a snowy roof - dangerous and not recommended - or waiting for nature to take its course. Terrestrial aerials are not affected by snow.


I have taken down my Band 2 FM sound aerial but I reckon terrestrial television will be with us for a while yet.

Arran Cameron:

. . . Does anybody know if any DAB pirate radio stations exist in the UK? In London the FM band is absolutely packed solid due to the number of pirate radio stations which operate in the area but the pirates don't seem to have moved into DAB yet. Therefore pirate radio creates an additional market for FM radio receivers and antennas, and could be prolonging FM broadcasting (from a user's perspective) even if the legitimate radio stations migrate to DAB and switch off their FM broadcasts. . .


 

 

An interesting point. It is not difficult for a pirate broadcaster to set up a station - just start to transmit on a "spare" frequency. To set up a pirate digital station seems theoretically possible but a whole lot more complicated. It would mean setting up digital multiplex, capable of accommodating many radio services. This would be technically difficult and expensive. Since pirate stations are in competition it might be difficult to get others to share the enterprise.


That's my guess, anyway. Let's see what happens.