View Full Version : Anyone know anything about TV / FM combiners/splitters/boosters ?

08-12-2004, 21:56:02
Well ?

This project has come to a hurdle.

The TV reception at my place hasn't been perfect since I moved in and so I've been going to install a decent system. The idea was to put something in the attic to plug the aerial into, and then it would be split and taken into about 6 other rooms on seperate cables.

No big rush, I decided to get the cable in first, then call in someone to sort out the roof/aerial bit at a later date.

I started in the main bedroom, and now have a box in the wall and a cable running through a pipe in the wall to the box. All nicely plastered over.

However these projects get modified as one goes along, and before getting to this stage it occurred to me that if I'm putting this distribution in, then why not run a 2nd cable to each outlet and have both TV and radio outputs available ?

So I bought a load of wall sockets with the TV / FM double coax outlets. And last night fed the cables through from the attic to the main bedroom.

I opened the first wall socket pack, and I discovered I've not read what I bought properly, and it seems both TV and FM are expected to be diplexed, since there is only ONE connection at the back !

Well it's no big deal to remove one of the cables, but this means I now realise I'm not as on top of this as I thought I was.


How or where does one combine the signals from the TV aerial I already have, and the FM aerial that I contemplate getting at some stage ?

Does the combiner have to be outside installed next to the aerials, thus necessitating a larger job for the professional later ? Or is it fairly normal to combine them somehow in the attic, by the splitter, allowing me to just ask that the aerials are fitted and the cable fed into the attic for connection ? (And probably checked to see that the signal is fine/max.)

Am I right in thinking the combining, however it is done, happens before, rather than after the splitter kit ?

Will any splitter kit cope with diplexed signals ?

How does one combine the signals anyway ?

Plus any other details.info anyone has would be gratefully accepted.


13-12-2004, 15:23:00
Not a thing, but I'll keep it bumped up.

13-12-2004, 16:12:53
Thanks for the thought.

I've concluded the folk here consider themselves knowledgeable about PC stuff, but less so on comms.

I've bought a cheap splitter/combiner from the local DIY store (Homebase) but it doesn't half look amateurish. since it isn't wall mounted or anything. Just destined to be jammed into the input of the splitter / booster unit.

I'm assuming that the splitter booster will cope so I can get the expert to run 2 cables in from the roof aerial to the combiner.

Meanwhile this is a slow process due to my lack of getting on with stuff on the evening, so plenty of time to find I've screwed it all up :)

13-12-2004, 22:16:16
How have your Google searches gone on this?

13-12-2004, 22:34:17
Not well. although I gave up on them just prior to posting the thread.

I may revisit it.

The Mad Monk
15-12-2004, 16:24:53
IIRC, all the signals are travelling through all the cables at the same time (much like they're all going through the same air at the same time), unless you have installed the filters to remove them, or if the rooftop antenna is unsuited to picking them up.

So combining them is not a problem, as they're already combined. Similarly, splitting sends the entire combined signals to, say the television and radio, and those devices just pick out what they need and dump the rest.

15-12-2004, 17:06:52
Assuming you are using a wideband antenna then what mad monk says it correct, all signals will be in that bit of coax.

If you are using a seperate TV/Radio antenna's then because they work at different frequencies a simple 2 into 1 Y connector will mix the signals and the opposite on the other end.

You may end up with increased noise levels on the frequencies you are after but if you put a decent head amp by both antenna then it won't prove a problem.

The reciever's will provide your selectivity between signals so actual filtering of signals isn't really necessary. We have a multi feed system in the barrack blocks at work and they come off two aerials into a wideband amp, which doesn't mix anything.

Cable's can give different losses to differing frequencies but again nothing i would really worry about.

So basically it will come down to the selectivity and sensitivity of your recievers, and the actual combining of the two signals wouldn't require a mixer and from my understanding of mixers they are used to produce a discrete frequency from summing of two other discrete frequencies (RF+IF=AF)

I believe the bands are sufficiently far apart that throwing them down the same coax won't be an issue (although i have sometimes observed ghosting on systems like this)

Suck it and see really, if you get horrendous noise on one or other of your systems, try removing or placing an amp in circuit (near to the head as possible) and also work on a 3db loss per connector (about the standard) so minimise connections as much as possible.

(reading my post i basically just agreed with everything mad monk said but reasoned it out to myself)


15-12-2004, 18:47:55
Thanks both. All input gratefully received.

As explained, the wall fitting with the output sockets unexpectedly has the one position at the back for connecting the cable (I did pull out the 2nd one I'd fed through). It immediately goes to a board, the other side of which I can't view, so I expect it does filtering anyway, whether needed or not.

As far as receivers are concerned, just got the TV for the bedroom, which is a standard Daewoo PAL TV. Any radio is to be added at a later date.

Likewise, on the roof are merely the normal (UHF ?) TV aerials that were there when I bought the place (and which don't seem quite good enough for the digital Freeview signals as I get occasional freezing). Any FM aerial is likely to be added when I get a guy in to reroute the cables.

(If I had a ladder here I'd do it myself but I'm not going out and buying one for one job. No idea where I'd keep it anyway.)

The addition of the FM was just a whim when I decided that as I was putting TV cable into the wall, why not do both while I was at it.

OK another question. Good old analogue TV and radio is all very well, but any idea how these items (splitter/combiner/booster) is likely to cope with digital signals ? Digital radio is going on apace, as is Digital TV, for which I already use the Freeview boxes. Is digital signals likely to screw the filters ?

Hoping I didn't make a bigger error with these wall outlets than I first thought.

15-12-2004, 20:17:38
You won't have any problems with digital signals mate, they sit in the same baseband as far as im aware (or your standard aerial wouldn't work) and aren't upset by grounded shields.

Unlike cable and sat there is no driver voltage in the core so you won't have any problems with amplifiers or splitters either.

I don't know what your loft access is like mate, but i would consider fitting a new higher gain yagi for your tv and an omni FM aerial for the radio, not too up on the DAB radio situation to be totally honest, but i think the digital system will use the same antenna, you can get all these bits at a reasonable price from farnell(cpc) and fit them yourself, if you have loft space then sticking the aerial in there will protect it from the elements and high winds.

What region are you in mate, do you know what your transmitter site is?

15-12-2004, 22:06:29
I'm in Hatfield Garden Village, in Herts. Unsure where the nearest transmitter is. Perhaps I'll do a Net search later this evening.

Loft access isn't a problem. I've not got around to fitting a loft ladder yet, but I have a step ladder that serves just fine. Are you suggesting that you don't get much attenuation through the roof tiles ? I always imagined it was likely to be a problem or else everyone would put it there.

Looking around on neighbouring rooves I see a few have the same size aerial as myself, but the majority has slightly longer aerials. I think the reason for the occasional periods of digital 'stuttering' is probably down to that.

I'll check out Farnell, see what I can find. Thanks.

15-12-2004, 22:52:50
DTT transmitters within "local" range

Crystal Palace 25 miles 163
Hemel Hempstead 9 miles 248
Sandy Heath 25 miles 358

BBC/ITC 1-4 transmitters within "local" range

Hemel Hempstead 9 miles 248
Crystal Palace 25 miles 163
Sandy Heath 25 miles 358
Hertford 7 miles 69


16-12-2004, 14:25:30
Right looking at the information you have stuck up there, i would head for the hemel transmitter, the FM AE should you buy one is omni directional so it won't care where its pointed.

The roof will actually attenuate the signal minimally, and at 9 miles i don't see you having a problem, how many directors are you running on your current ae (the bars infront of the half wave dipole (the square bit the cable comes off)

I would probably go for a 12 element (directional) aerial which will give you a higher gain but will be more critically aligned. And it won't suffer being in the loft space.

I would offer to come and sort it out for you, i am on leave for a week following friday, assuming i can get a leave pass for AH and DIY duties it would be a simple enough task between us.

16-12-2004, 20:42:07
Directors eh ? Well it's too dark to check right now (and I never did work out whether one counted the slightly different "loop" element at the back) but from memory the existing aerials on my roof have about 8 to 10, I think.

From what I recall, neighbours have either that many, or more commonly about 12 to 16. I can count them tomorrow if that's important but can only rely on my limited memory at the moment.

I was assuming I'd be better off going for highest gain, and attenuating it if I find I've overdone it. At least I'm a little cheesed off with the existing problems, which, of course is why I'm gradually changing stuff.

I already have an 8 one I brought from my last place where I was trying to use it as an indoor aerial (with limited success). But interestingly, in the loft, the last owners seem to have left a 16 long one. No cable connected to it though. I assumed there must be something wrong with it. Maybe I should take a closer look, if I knew what I was looking for.

Also I have no omni-directional one at present. I take it that these can easily be got locally though.

That's an offer I didn't expect ! Might be tempted to take you up on that How far away are you ? I take it fairly close then ?

Oh gee, I'd have to tidy up the bachelor pad ! :eek:

16-12-2004, 21:38:33
We live in bracknell mate, i used to live in the dark north and we had a 12 element antenna in our loft space, during the days of on-digital i was able to recieve all channels without any problems even though the provider assured me it wouldn't be available in my area. Assuming the connections to the 1/2 wave can still be made then a 12 will do you well enough.

TV aerials tend to have one reflector, and any number of directors, you don't count the square thingy that the cable runs off as that is actually the element which does the receiving.

I'll try and explain this simply, the dipole alone would have a perfectly spherical beam pattern (think doughnut) in that it would recieve signals within a given range equally, by placing the reflector on the back the energy which would be expended behind the array is pushed into the forward plane increasing the apparent aerial gain, (it would look like a fat sausage) as you include directors you tighten this beam pattern until you can have a pencil beam which has extensive range and good gain, basically more directors means narrower beam means better range - but at the cost of alignment tolerance.

In real world terms you can't have too much gain from a recieve antenna as it is a passive device, so 16 will give you the best reception possible but will provide a headache with alignment.

The only thing you need to align an aerial are a portable set and a compass.

As for the FM antenna these tend to be a bit more choosy about location i have found, as they are susceptible to noise interference on a larger scale than tv.

Bracknell isn't far away, not when i have to commute 200 bloody miles every weekend. A mere strollette.

17-12-2004, 22:46:34
Ah Bracknell, Berks. I take it. Yeah I've been through it on occasion.

Uh... well I know where you're at with the 200 miles per weekend. Coincidentally I do much the same, but nevertheless we're still looking at about 90 miles round trip. I think I'd feel a bit guilty getting you to run round that far just to give me a hand with a loft aerial. (There's not enough time during one lunch hour to get in sufficient pints as a thank you :)) So, no offence, but I think I'll pass on the offer.

But if you are ever in the area and want to meet up for a pint, let me know. I don't ever seem to find the time for the "official" Counterglow meets. So it'd be a shame to chuck away an opportunity.

But back to the task in hand. Both youself, and others, have assured me that the kit bought should be fine, so that's a relief, And I've now enough info for it to not seem such a daunting task any more. I mean, how difficult can it be ?

Now you've put the idea of trying an aerial in the loft, and I've discovered one hanging there anyway, There's a plan. And it doesn't need me phoning a local aerial installer.

(However, the aerial in the loft is clearly not pointing in the right direction at the moment, unless Hemel Hempstead is hiding in the front garden :). So it does need refixing.)

I'm unsure what clamps I can get to hold it on the rafters/joists, pointing in the right direction, but when I find out where to buy the FM aerial, the same place must have the relevant clamps too. (I'm thinking it would take Farnell a while to get an order to me at this time of year anyway. And it isn't likely I'll go buy it this weekend since I'm way behind with Xmas gift buying.)

By the way, I did check out the aerials in the local area. There are a few odd ones, but about 2/3 to 3/4 are 16 directors, with about 1/4 to 1/3 having just 8. I presently seem to have 2 of the shorter variety which may be part of the problem.

Your comment on the FM aerial surprised me. If it is trying to capture signals from all directions, then I'd have thought it would be less critical where it's sited. What do you reckon is up with that then ? Are reflections causing the problem ?

18-12-2004, 10:37:29
90 miles wouldn't be a problem mate, but it's your call.

Farnell (cpc) will do next day delivery and this is still in effect, up until about the 22nd i think, that's usually the day they stop saying next day, they use a courier rather than royal mail and if you spend over 30 it's free.

I'll have a quick scan at the online catalogue and point out some bits.

Remember the doughnut/sausage/pencil scenario, the FM antenna is the doughnut end of the spectrum, it's doesn't care where it's pointed but being omnidirectional it's gain is considerably less than a yagi array which is what makes it more prone to noise and interference. As far as putting it in the loft, it's a case of suck it and see, i could go into the maths of wavelength difference between the Radio and TV signals and work out propogation characteristics, which would probably give me an idea as to wether the roof would upset it, but for the time and brain work involved it would be quicker to try it on in the loft if that doesn't work, then clamp it too an outside wall.

If you have a compass it will make it alot easier to re-align the loft antenna and when you are connecting the co-ax to it, hopefully the junction box should be marked if not then core goes to 1/2 wave shield goes to ground, the shield is as important as the core for signal quality. When you are moving the antenna, try to find a spot which will give you somewhere close and convenient to place the splitter/amp as the devices are really a waste of time if they aren't placed within a couple of feet of the head.

As for doing it yourself, nowadays i wouldn't advise using an aerial installer to anyone, i've seen the kind of job they can do, and they aren't roof builders so sometimes are a little unsympathetic to your roof, last thing anyone needs is a leak or tiles replacing.

24-01-2005, 22:11:59
Was going to sort the TV aerial out tonight (still not got the FM one). But I'm easily put off, like the umpteenth time having to go down and up the steps again for something I don't have with me.

Maybe finish it tomorrow. This week anyway.

But the interesting thing is, having checked using the compass, despite being further away, all the roof aerials around here seem to point to Crystal Palace. (Of course the chart I found didn't indicate signal strength, which I guess may be a factor.)

What's rather amusing is that the aerial I'm using, the one left by a previous owner, was presumably never used, since I had to remove the fitting from a rafter that had no horizontal or vertical side, the rafter being at the angle of the roof. There's no way they properly could use the aerial as it was since there was no way to set the aerial horizontal, screwed in where it was ! They seem to have got it wrong first of all, then left it in disgust.

25-01-2005, 04:14:31
How long have you been there before you tried to do something about it?

25-01-2005, 08:37:40
I've been here just over a year now, although it's not the only task on the go, nor on the list.

The fact is that the aerials on the roof are almost adequate. They bring in the analogue signal, but the digital is occasionally getting the freeze picture or the pixelation problem. More so of late for some reason.

So with a (almost) working system, it not a high priority, just something I want to fix when I get around to it. I probably decided I must do something sometime, about 9 months ago.

27-01-2005, 22:20:40
Sad to say this doesn't seem to be going as well as it could.

Made an effort this week to get the aerial up and working to the socket in the main bedroom. It was connected to the rafter earlier this week and tonight I moved the cables and portable TV up to check it out.

Well I know I was using a long coax, and I'm unsure what problems if any that gives, but I was unwilling to chop it just for a test lead. Anyway turns out that despite being further away, Crystal Palace is a much better signal than Hemel. But even so the picture is just adequate, not that sharp. And that was analogue not digital as I left the freeview box below.

And any little movement away from the ideal and the white flecks appear. Even putting the booster in circuit seemed to make no difference (do they EVER make any difference or are they just a con ?)

And this was the 16 element aerial that some earlier owner left. It looks perfectly ok to me.

I could go order a major gain digital aerial, but I'm wondering if it is all just not a goer, and I need to forget the loft aerial and get an expert to put one on the chimney.

(Oh and just to make the day complete I've discovered one of the water pipes to/from the cold water tank is leaking, but not leaking enough to be clear which one of the five it is :( Arhhh houses !)

27-01-2005, 23:54:14
Have you thought about the joys that Sky might bring?

28-01-2005, 00:27:38
Not for as moment. Enough day-to-day bills already. Never really understood the desire to encourage a pay-for-view system when there is a equally awful ad pay system in place.

29-01-2005, 16:22:50
If you can get power into the loft space gary the booster needs to be as close to the head as possible, otherwise it just amplifies signal noise in the cable as well as the signal itself. Boosters do work but the budget ones tend to give a 3 to 6db gain, and they are very wideband which makes them suffer from noise.

Have you tried polarising the aerial in the opposite plane, in the horizontal plane your beampattern is very height discrimatory but easier to align on the horizontal, try turning it 90 degrees on its end axis and repoint see if you get any improvement, what cable are you using just out of interest, there are 50 and 75 ohm types available for standard TV its usually 50 but for sat and digital in general 75 is recommended.

29-01-2005, 16:28:24
I just had a look at the transmitter details and it's vertically polarised, so if you have your antenna with the yagi's horizontal you will need to rotate it. Although it would be worth turning it once you have it aligned horizontally as you have got the shoot as accurate as possible, if that makes sense.

29-01-2005, 16:36:30
But according to the bbc it's horizontally polarised, and throwing out a megawatt.
You could try the sandy heath one as well although that will pic up anglia region tv, its putting out the same power and from what you said earlier is at the same range.


29-01-2005, 20:17:35
Cheers. I may try turning it when I get back then. During the week. But the Ali bar is now fixed so it's vertical, so it's going to be a pain to try to get it turned. I'd have to go back and look, but maybe I can just put the clamp on differently, or something. Have to say that fixing the bar in at one end only doesn't make for a very stable construction, still I guess no one's likely to knock it in there.

I was looking at the high gain digital aerials on the Net this morning. They're not 'that' expensive, and the web site I was using for info was recommending high gain plus booster for my co-ordinates. And that was for an outside aerial presumably.

I can see why the vast majority of folk point to Crystal Palace. You'd have thought the nearest was best but that wasn't my experience. Didn't try Sandy Heath though, figured that if it was a good option I'd see more local aerials pointing that way. But I may check to see what it can provide.

Power will be going into the loft, eventually, it's just a case of deciding which upper floor socket is the best bet for adding a radial to. The act of putting cable into the wall messes up the decor. I tried to minimise it with this TV socket in the bedroom but despite my best efforts the wallpaper didn't just flap back into place. :( Seems one has to accept a redecoration is on the cards for every room I add TV sockets to.

Thanks for the advice.

31-01-2005, 17:45:39
:confused: http://www.wrightsaerials.tv/photography/cross%20polarised%20reflector.jpg I'd just be interested to know, HOW ?

20-02-2005, 11:29:10
Just to bore you all again.

I decided that, since this was going into the attic, and as the 16 element aerial didn't work, I needed the biggest gain UHF aerial I could get, so I bought a DAT 75. I also got an additional amp (MRD ?) for it too.

Given the lack of reception in the loft I opted not to go for an omnidirectional FM radio aerial, looked around for a directional one instead in the hope it would be better. Got confused when I realised one can get separate FM and DAB aerials, so thought "sod it" and got one of each. Just over 130 the lot inc p&p.

How it isn't obvious that the FM and DAB aerials are not the same size I don't know. They looked the same size in the photos. The DAB aerial was as expected, the FM one about 4 times the size ! Put together it is about 6'6" x 5' ! WTF !

Anyway, I constructed the DAT 75, it's a bit of a beast too, ending up about 6' long when done. Hauled it up into the attic Saturday morning, connected the portable. RECEPTION NO DAMN DIFFERENT TO THE OTHER AERIAL !

I can not believe it. I even shortened the co-ax test lead in case that was the problem. Now I know next to nothing about aerials, but I was surprised that there didn't seem to be a metal connection between the main frame of the aerial and the box one joins the co-ax to. Is this normal ? I assumed that fitting the box to the aerial would make a connection, but it looks as if all contact is via the plastic.

In any case this is a disaster. An FM aerial that's going to be a pain to install in the attic, and from the experience of the UHF aerial, not a lot of point in doing so anyway.

Having looked around the local area again, there are a very few (2 or 3) that actually use a tall pole to connect their aerial to. Now wondering if the attic is simply not a goer, or whether there is something else wrong. To be honest mounting these monster aerials outside looks a major overkill to me. I'd be concerned about the fittings in a storm.

23-02-2005, 23:38:01
Gary i think you have greater issue's here than simple aerial gain problems, you may be sitting in a dead spot for some reason, and i know you wont want to hear this but i just opened an account with a company called grandata in wembley who have high gain aerials for poor/weak reception areas along with 12dB head amps with a noise gain of not greater than 4dB.

The plastic box is supposed to be floating (not connected, as you only want to connect the coax to either end of the dipole.

24-02-2005, 00:11:28
Cheers. Been over to digitalspy forums and I'm sort of convinced that's the case.

They had some interesting links there, in their sticky FAQ thread. One can create a graph of your own TV aerial to the transmitter of your choice, and spot if you get a good line of sight. Turns out that to CP it's rather questionable, but not to HH, which makes the fact that the signal was better to CP rather surprising.

I'm taking a few days break from it, but I've concluded that this area isn't brilliant for reception, which probably accounts for some of the aerials around here mounted on poles to take them a few feet higher (although that graph I referred to above suggests a few feet shouldn't make a lot of difference. Well 75 of them maybe :)).

I think I have a limited number of options now. First off, although I will retry the loft again, I think it'll need to go on the roof, and that means either I do it myself, or I get an expert in.

Well I'm not going up there this weather anyway, and even if I leave it until late spring I'm going to need to buy ladders, so I'm not looking forward to that.

And how the hell does one adjust a TV aerial on the roof when the TV is inside ? Ha !

Then there's the fact that as an outside aerial it probably didn't need the gain and thus need to be so big & heavy. It's going to be a risk in windy/stormy weather up there.

I think it makes no sense to try to install the 5 foot square (?!?) FM aerial up there as well, so I may just put up the smaller DAB one.

Meanwhile the sound interference on Freeview is gradually getting worse, for some unknown reason, and drives me around the bend :( Well that's life I guess.