FM Aerial installation Q's

[PJ]

Hi

I'm planning on installing an FM aerial and using it to "feed" some sockets around the house. I don't have TV so it will be FM only.

I've already worked out which aerial is suitable. It's a small Ron Smith aerial and a fair amount of the planning is done. I do however have some questions which some here might be interested in answering.

(a) Can you recommmend a source of low loss coax cable? Ron Smith (Luton, Beds) sells it and that is the most likely source on this occasion, but I don't think Ron Smith will be selling it for very long as he is selling off the last of his stock as the Ron Smith business is shut down unfortunately :( I am going to get all I need for the first part of my coax installation but there'll be more in the future for more sockets and so it would be good to know of a different source. For all I know the stuff in the big DIY stores is very low loss of course but no doubt someone here can inform me.

(b) In the past I've always just put the coaxial plugs on the end of the cable without solder but soldering is recommended in what I've read so far for good stable connections. I can easily work out how to solder the inner of the coax, but do people solder the outer (shielding) and if so what to? Are there plugs better suited to soldering?

(c) My next question is about burying the cables in walls. Do people normally just chisel a trough in the wall, put the cable in it, and then fill it, effectively sealing the cable in, or do people use a conduit of some sort?

(d) I've looked at some amplifiers at the Maplin web-site. Although the signal strength is good in my area I might be splitting the signal up quite a lot as my house gets more populated with radios. It looks like the mast head amplifiers are only for UHF, judging by what's available at Maplins, is that the case that mast head amps are for TV only? Does anyone have any experience of amplifiers suitable for FM? Is there a source for them other than Maplins on the net?

(e) Years ago someone told me that even if a radio doesn't have an aerial socket an external aerial can be used by simply using a crocodile clip to attach the cable inner to the aerial of the radio. Is this true? It seems to make sense to me actually.

(f) One of the radios I will be supplying with this small network is the new Tivoli Clock Radio. Lovely it is too! I notice that with the American instructions there is a paragraph on the subject of grounding an external aerial this is to provide protection some protection against voltage surges and built-up static charges. They even have quite an elaborate diagram including things like an "antenna discharge unit" and a "power service grounding electrode system". Is this grounding of the aerial something to be concerned about?

You might be amused to know that included in the instructions for the Tivoli Clock Radio is this bit of advice:

"Do not place this product on an unstable cart, stand, tripod, bracket or table. The product may fall, causing serious damage to a child or adult, and serious damage to the product."

[Robin Prater]

Although I would not disagree with a word of your good technical advice I must take issue on your description of DAB as crap! I have had digital radio for three years, in London we have 50 stations to choose from and I would not go back to listening on FM. My advice would be to buy a DAB receiver put up a good Band III aerial and enjoy real quality sound.

Robin

[Gnube]

Well ok, but I'm not far from Luton, where the supplier mentioned by the OP is, and to be honest, we're NEVER going to have 50 stations on DAB around here, and I'd be surprised if we could even get DAB at all inside the next 10 years. The rationing of resources has never worked that way before, and I'd be glad to be wrong if I am, but experience suggests that's how it will be.

The BBC has announced no certain plans for local radio after the big switch off, and I am pretty sure that's because they don't have any. I'd be really glad to be wrong about that too. Not holding my breath about it though.

I'd like to go get DAB tomorrow, but I can't see any point, they have yet to make AM or FM work "well" here yet. I understand DAB is technically more demanding still. Having it happen sounds pretty unlikely then, given track records to date! I think I better go and re-research all this as it looks like something you could not make up, but had all the same! ;O)

Take Care, Gnube {too thick for linux}

[tony sayer]

In article , Robin Prater writes

Don't see it that way. DAB has been seriously degraded by the BBC and commercial stations because they have lowered the bitrates. This has had an adverse effect on the overall sound quality which has now gone from what could have been excellent, to what can now only be described as mediocre. The only DAB station that can hold its own is radio 3 which is at 192 K/bits most of the others are at 128 K/bits or even less sometimes, radio 4 is even in Mono at times!.

In fact the whole systems badly flawed as the encoder in use, MP2, has now been superseded by better ones so the tech is already 10 years out of date. But if it suits you then that's fine but the sound of Terrestrial DAB annoys me intensely. FM isn't perfect either but is far more natural than what DAB is but a lot of the time FM is adjudged as poor, and this is only due to insufficient aerial signals. I would only regard DAB as fit for portable use and for in car, as a serious medium for home delivery its poor, Satellite is a much better option or if you only want the local and main BBC channels then FM still manages to outshine them provided its fed with a clean signal...

[tony sayer]

In article , Owain writes

Beg to differ:-)))....

I think that the future of home reception is via satellite delivery. What's needed now are better satellite receivers..

[Dave Plowman]

Yes. Although R3 and 4 are still ok on DAB IMHO.

I'd say the finest broadcast sound quality readily available to all is probably NICAM on TV. Good FM reception can be much more difficult to achieve - and costly.

You were ahead up until now. ;-)

Vinyl has inherent distortions that cannot be overcome. And that's before the physical wear and damage problems. It also requires great compromises as to what can and can't be cut satisfactorily which invariably means altering the master recording to suit. CD, for example, doesn't.

I'd say that many who aren't committed Hi-Fi types would be satisfied by DAB - it suffers from non of the reception problems that plague both FM and AM. Can have some of its own, though.

I'd say the reason they have reduced the audio quality to cram in more choice is that it hasn't exactly been a success, numbers wise. But at least the option is there to later restore bitrates to where most would find acceptable.

[Dave Plowman]

As a general comment, DAs for FM use are rarely satisfactory.

[tony sayer]

In article , Dave Plowman writes

Have you any reasoning for that assertion Dave?..

[The Natural Philosopher]

Yes. 60db S/N ratio at best on FM, up to 75 on vinyl, and better than 80 on CD and no scratches..:-)

[Dave Plowman]

Most good receivers approach the maximum theoretical sensitivity, so adding untuned gain before them will do no good. Passive splitting works just as well. You might get a VHF distribution system to work tolerably well for clock radios on local reception, but that's about all.

Of course I could be wrong, but I've yet to actually witness for myself one that does work as well as without.

[tony sayer]

You can up that to about 70 odd these days with the right modulator and tuner. Bit academic all the same..

[Andy Hall]

Very happy, thanks for asking..

.andy

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[tony sayer]

In article , Dave Plowman writes

Well I can tell you that they do, and they do it very well provided that they aren't overloaded. I have a Labgear unit that has the FM input supplied with a 5 element Triax aerial that is aimed midway between the local TX at Madingley and Peterbourgh and its fine.

The main purpose of the amplifier section is to overcome the splitter or divider losses. In fact its performance is very good indeed and this is not too far removed from the performance of the amplifier systems we use in the "day job", VHF comms radio, which have up to 16 outputs and cost about 700 quid!....

[Colin Blackburn]

On the general theme of aerial installations is there a reasonable way to wire in several aerial points off one aerial without a distribution amplifier, ie just using a splitter or splitters. Say I want four sockets, should I split near the aerial or run a single co-ax as far as possible before splitting? There would only ever be one socket in use at once but I can appreciate that long 'stubs' may cause various problems on the line as a whole.

Colin

[The Natural Philosopher]

Thats true if the front end receiver noise figure is no better than the boosters which is likley on a decent tuner.. However it is good for crap radios - as you point out - and does no harm and may overcome interference pickup in the cable if the local signals are weak.

I tried with and without a 10db booster - no audible difference ona good tuner - but the 10 db booster does at least feed the 10 coaxial cables...whereas a passive splittter to do that would have introduced significant losses.

I thimk you meant as well with, as without..

I';d say the labgear amp I am using is pretty neutral. Doesn't make it better, doesn;t make it worse. Its there to buffer and distribute not to amplify tho.

[tony sayer]

In article , Colin Blackburn writes

Yes what you state with long stubs will be problematical. Use a distribution amp a good one can be had for about 20 quid and then look forward to many years of use with good clean signals. A splitter will work but it divides the available signal....

[Colin Blackburn]

As I live off the grid I was checking the possibility of solutions not requiring power. Not specifically because of the power but more the convenience of not having, say, to turn on a DA in one room to watch the TV in another---my assumption is that for most people the DA is hidden away and permanently on, not something I can have easily.

I guess at the same time I wire in the aerial cables I could wire in a switch in each room with an aerial point so that the DA can be turned on from anywhere---this could get complicated!

Colin

[Dave Plowman]

I'll bow to those with superior knowledge, but still maintain that the average installation using commonly available bits just doesn't work properly - at least in the way an average UHF TV one does.

[Andy Hall]

Another option could be a mast head type of amplifier, but not fitted at the mast head, then followed by a splitter. These can be powered with 12v and at a few tens of milliamps. Would that be more suitable than a mains type of device?

.andy

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[Andy Hall]

Could that be because you are in a high signal area, though Dave? Admittedly Wrotham is a bit further away than Crystal Palace and Beulah Hill, but is a high power site....

I wonder whether the wideband noise starts to have more of an impact under high signal conditions.....

.andy

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