EnglishPaul

I have a leaky roof at the moment, and the roofer has had to get some scaffold up, so it would seem an ideal time to improve on my aerials.
I was just wondering if anyone knew the goods and bads of aerial installation. I am looking to put up FM, DAB and DVB-D (or uhf), and probably also a motorised satellite. I am also quite open to the idea of improving MW and LW, but I have a weird idea that I may need a licence to put in the right size aerial!
Interested in all aspects: cables to use, boosters and attenuators, mountings, aerials, positioning, distribution.

Thanks for any help you can give me.

DonaldG

It is my understanding that as long as the dish is no bigger than 1 metre in diameter, you do not need planning permission.


It depends on the sort of budget you have...

With respect to the other stuff, I recommend that your TV aerial be replaced with one that will service the Digital Freeview service. If the coax feeder of the original aerial has been up for 10 - 15 years, it may be worth replacing with good quality low-loss stuff because that outer plastic sheath will degrade with UV over time & water can/will seep in and give much signal loss.

Unless you live under the transmitter mast, you probably won't need any attenuators.

It will cost more, but specify 'thick wall' aluminium mast (2") if you can. This will be good for motorised dish fittings & fixed digital TV...I don't know of any stainless steel mast fittings in the UK so specify Galvanised Steel mountings.

It is possible to DIY... but a motorised dish is a bit more complex - may be worth getting an aerial fitter in who has the proper alignment meters.

The digital TV aerial is usually quite easy. The reception capture width is quite wide and if you are off by a few degrees, it may not be a problem if you are in a strong area. What I have done in the past is look at the neighbours aerials and point mine in the same direction - it's worked each time with no problem. The dish is alignment IS critical. That is why I suggest a specialist.

With respect to distribution, I bring the coax for the DTV into the loft (about 15 feet of coax run) and into a 4 way distribution amp in said loft that then feeds around the house. My Sat dish feeds directly into the receiver in one room (about 35 - 40 foot run)

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EnglishPaul

Hi Donald. Thought you may have something to say on the topic after seeing a picture of all the aerials on your house.
Thanks for the info. I see satellite as a challenge, and I expect it to be really difficult; I have very little expectation as to what I will end up with. Its like radio ham for sat but without the need to learn morse code! I'll put it up and see what's out there.
I have heard roumers that sat is tipped to be the HD freeview medium of choice, so I'll be ahead of the curve I hope.

One question that has occurred to me is wheter there is any spacing needed between FM and UHF aerials? I wouldn't want them interfering.
I live on a hill and can see the repeater transmitter, so I will not get a particularly hi gain UHF aerial, and will use omnidirectional radio receivers.

I had wondered if it is better to run separate cables, or to use a loftbox multiplexing amp.You have already implied that I don't need a mast head (external) amp prior to a loft box.

Still none the wiser about AM radio. But that is more just a point of interest, as it is well nigh obsolete for all but hams, hospitals and community projects.

I am going to get new cable all round as I am a believer that the war is usually won or lost on the cable.

DonaldG

Spacing between uhf (TV) & vhf (FM broadcast): This should not cause a real problem for you as neither is going to be used for transmission of RF power.

I have no experience of using a multiplexing amp. So no comment either way, other than to say an amplifier is an amplifier and as such will increase the signal voltage to the feeders

Remember, the signal voltage captured by aerial is incredibly small, way down in the microvolt region. All feeders (coax or transmission lines) will have a loss factor that will attenuate the signal. In weak signal areas, reducing this loss is the order of the day. However in good to strong signal areas it is not at all critical.

Without going into the specific figures, mainly because different types of coax have different loss figures, but the main things that will influence the quality of perceived signal reception are:
* Signal level in your area
* Efficiency of the Aerial (measures in Gain when compared to a quarter wave dipole)
* Polarity of a directional aerial (vertical or horizontal) Get this wrong could result in a 28 db cross polarisation loss - That is a massive loss of 1/256th!
* Angle off zero degrees from the transmitter heading. (Directional aerials)
* Quality of coax/feeder (Loss in db per 100 feet)
* Length of coax/feeder (Every 3 db of loss = a halving of the signal voltage)
* Signal to Noise (s:n) ratio of the 'front end' of the receiving equipment is the measure of it's sensitivity.

The 'front end' of the receiving equipment, for the sake of this conversation can be defined as the FIRST active amplifying device. This could be inside the TV/Radio/Video Recorder etc OR it may be inside the multiplex amplifier or aerial line amplifier.

In general terms, your situation is ideal for reception. (On a hill and can see the TV repeater)
The front end sensitivity should not cause any concern at all. The only consideration will be the quality and length of the feeder from the aerial to the first amplifier device. If you have a short run from the aerial into the loft and into a distribution/multiplexer amplifier, you will probably experience minimum signal losses. I can't remember the actual average figures but a decent amplifier will increase the signal voltage by many times, certainly enough to feed a good level of signal in most household setups.

You are absolutely right about the cable (coax) being the primary thing to look at. Replacing the coax around the house, may or may not be necessary. It depends on the original quality of coax, how old it is and the quality of the installation engineer’s workmanship!

One thing I would pay attention to though is each wall socket. Coax is made from copper wire. Copper tarnishes. The electrical connection inside the wall socket relies on a mechanical integrity of a screw/nut & bolt. Check that there is no excessive tarnishing and that the screw/nut& bold are tight. (CAUTION: if there is a line amplifier in use, make sure it is disconnected before checking the sockets. There may be a small 'drive' voltage of about 9 - 12V and accidently shorting it out could 'blow' the amplifier power supply)

The other thing that bugs me is that most, if not all ‘Belling Lee’ type TV coax plugs are put together in a solderless method. IE: the centre conductor is slightly bent and inserted into the hollow centre pin, relying on the bent wire to rub against the centre pin to make contact and transfer the signal voltage to the TV equipment! Personally, I always solder the centre pin, but this can be tricky as the heat can/will melt the plastic insert but it can be done!

Coming back to a satellite dish setup, Google ‘Satellite Dish Installation” or something similar. You may find lots of useful info that may help to decide if you can do the install of a motorised system yourself. There are Sat forums outh there that are ‘almost’ as helpful as TSF.

Just a side note about AM medium wave (and shortwave reception). Over the years I have used some weird aerials that actually worked very well: In New Zealand, I connected a length of hook up wire to the top strand of a sheep fence that went for miles! It made a fantastic aerial. On another occasion, in a hotel, I used the metal bed frame as a makeshift aerial. During the Falklands conflict, I made an emergency aerial by tying a nut onto the end of some hookup wire, threw it into a tree and pushed the other end into the output pin of a 150 watt single sideband transmitter and was in contact with Port Stanley on days 1 – 3 of the invasion (That is another story!).

If you have a central heating system in the house, you can try using that as an efficient aerial but be aware it is a DC ground and could be a problem if you try to connect a line amplifier! That said, the connection to a central heating system in all probability will not be a ground to an AC signal. It is very much a ‘suck it and see’ exercise!

I have even used a TV with a short length of hookup wire stuffed into to the socket of the TV in a good signal area!

Final anecdote: Last year, I ended up in hospital for several weeks. The ward had a TV but the picture was virtually unwatchable with ‘snow’. I discovered that there was no aerial on the coax. I found some metalized plastic wrapping from the coffee cup machine which I cut up into two lengths that I guessed was about the right length. I ‘borrowed’ some surgical tape from a nurse. Using a couple of matches and the tape, I jammed the metallised plastic into the coax connector and taped the improvised aerial to the window. Perfect reception on all channels!

These anecdotes show that although there are specific formulae, theory and science about aerial systems, the book can be thrown away a lot of the time! Don’t spend too much time and money for a small improvement when you already appear to be is a strong signal area. In a strong signal area improvements to the signal level that was already more than enough will not be seen/heard.

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