Another FM aerial question

[ian_news66]

Seeing the other thread on FM and aerials has reminded me about something I've been meaning to find out about.

I would like to have a proper FM aerial installed on the roof. The thing is that there are two receivers that I would like to connect it to. One is in the lounge at the front of the house and the other is in the dining room at the back. One option would be to have the coax coming down from the aerial, eirther at the front or the back of the house, bring it into the house and then split it somehow. I'd rather avoid this option to minimise internal disruption. I was wondering instead how feasible it would be to have two separate wires coming from the aerial - one going down to the front of the house and the other to the back. Would this need some fancy splitter or something or could the two coax leads simply be wired into the same aerial. (I guess there's also the option of having two separate aerials but that seems a bit over the top.)

In case it's relevant, I get pretty decent stereo reception already with one of the receivers (its a hi-fi tuner component) even with the T-shaped bit of wire that came with it, so I reckon I'm in a reasonably strong signal areas. The other receiver gets weaker reception usually, but I think that is partly to do with there being fewer options in arranging its 'bit of wire' optimally because of how the room is organised. The latter would I think particularly benefit from a proper aerial but it would be a shame not to make use of it for the other receiver too.

Thanks.

Ian

[Mark Carver]

Yes, a good quality low loss spitter.

code: QQ69A

NO ! Certainly not, you cannot parallel up RF in the same way as 50Hz lekky :-) You have to use a proper RF splitter to avoid mismatches and reflections within the cables.

If the signal is weak (not a problem by the sound of your description) you should use an active splitter, or an amplifier in line *before* a passive splitter. Have a sift in the Maplins site. Anything that covers the frequency range of FM (88-108 MHz) will be suitable.

[Frank Erskine]

If you simply wire two cables in to the aerial you'll lose a lot of signal. Depending on the lengths of the cable, if you unplug one receiver you might lose reception on the other (an open-circuit cable of a certain length wired across another might act as a short-circuit).

You can buy a splitter to fit near the aerial, to feed two cables, but you obviously have to make sure it's quite waterproof (unless you live somewhere with no rain).

You will lose a bit of signal with a splitter, but probably a lot less than you would by simply wiring the two cables together (and it would be tricky physically to get two cables into the connection block in the aerial!).

[John Rumm]

That will do nicely, but make sure you put it in a nice waterproof mast mounting box. CPC do those (and while you are at it you may as well order the splitter fromthem since they will probably be cheaper for that as well)

[Mark Carver]

Indeed. In fact they do a mast mounting outdoor splitter for 8.20 inc VAT (+£5 handling if the order's less than £30)

[ian_news66]

Thanks to all who replied. It was all very helpful information.

Ian

[tony sayer]

You'll lose around 3.5 odd dB with a splitter, that is approximately half power. If your signals are good at the moment then I expect that you should be fine afterwards. Suppose if your going to do it then try and see. If your getting a rigger in then ask him to bring a splitter and an aerial so if the split results in unacceptable loss, then he can add on another aerial.

[John Rumm]

the last anti-ference one I saw was basically an inductive splitter PCB in a waterproof box, but there was no screening. This would not be so good for digital TV signals where impulse inteference can be a problem.

be a better bet...

They used to do a plain mast mounting box that would take one of the metal bodied splitters you linked to before - but I can't seem to find it in the (useless) online search!

[Mark Carver]

I've got Triax ones that are screened. The modern versions have F-Type connections.

sure who stocks them in the UK, Taylor Bros of Oldham probably. (another useless website, but a very helpful firm)

[John Rumm]

CPC have them (the link I posted above was for a Triax one - although I just noticed I actually posted the link for a switch and not a splitter

- but they have them as well)

(it was the anti-ference one that *may* not be screened)

[The Natural Philosopher]

I have never regretted bringing both aerials into a lab gear amplifier that gives about 10dB gain and takes 10 cables all over the house carrying TV and FM signals eto wall sockets..

[tony sayer]

Yes and that is a very sensible option. But putting an amp on a TV aerial to split it for FM isn't such a good idea. In fact avoid amplifiers unless they are distribution ones.

Front end overload by out of band signals is the reason, TETRA for one for example!....

[The Natural Philosopher]

That Labgear you recommended me Tony, has been flawless throughout.

Best piece of advice ever.

[nemo]

You can get splitting devices to run two receivers from one aerial in most dealers. I believe Argos may have them as well. They're not fancy. They're just small boxes with a few coils and capacitors inside that make sure the signal is divided between the two or more receivers efficiently without any reflected signals getting in the way.

Two separate cables from the one aerial is incorrect and would not give as good results as a proper splitter. It'd also be a waste of cable.

If you're in London, make sure the aerial is mounted horizontally and pointed at Wrotham where the transmitter is. Phone the BBC Engineering Department for the bearing and for general advice.

If this is too much, you could always go the whole hog and get D.A.B.

Nemo

[Mark Carver]

Be aware that that only transmits BBC stations and Classic FM, most of London's local stations, in addition to 'filler' services of R1-4 and Classic are transmitted from either Croydon or Crystal Palace. The latter national services from CP are vertical polarization only, the locals (and Wrotham) are mixed polz.

No good for serious quality listening I afraid, but it will get you extra stations not available on FM.

[tony sayer]

In article , nemo writes

Not quite. Wrotham transmits Mixed polarisation but you might find it simpler to mount your aerial horizontally. If your in parts of South London, Crystal palace may give you better results.

Not if your talking about hi-fi reception;(....

[Dave Plowman (News)]

Absolutely. The BBC national stations from Wrotham are terrible in this part of S London due to the hills in the way. Driving down Trinity Road where it crosses Wandsworth Common in a traffic jam where it inches forward results in near total cancellation of an R4 signal at times due to extreme multipath. My current car uses diversity reception - it has two aerials and selects the best one - but is still not perfect. The 'fill in' transmitter at CP cures this problem totally.

John Birt when DG of the BBC used to live just off this road in the 'Toastrack'. There was no external FM aerial on his house, but a standard UHF TV one. After a Feedback discussion on general FM reception problems I wrote to them saying that either he never listened to BBC FM radio, had cloth ears, or had a line feed. I have an 8 element yagi for FM on my house and still had problems with Wrotham. A short time later we got a fill in transmitter. ;-)