Megalithia home

Student Options

It was a surprise to me to see the number of students on the DTT tech forum of digital spy. TV is obviously important to some of you.

To be honest, you are taking a rocky road going for DTT. Many students seem to use the PC for their TV display too, using a tuner card or outboard DTT tuner like the Nebula TV device or equivalent, sensibly reducing the amount of gear they have to take up and down from uni each term. The problem with DTT is that you have to get enough signal strength or you have picture freezes that drive you nuts. As a student you generally can't put up outside aerials, so you and use indoor aerials. You might be on the wrong side of the hall of residence block as well.

You are generally limited to what you can get in your room, unless you are out in digs and rent a house with others. Even then there are limits on what you can do if you don't want to weaken your already slim chances of prising your deposit out of the claws of the landlord when you move out.

So you'll tend to be using a particularly inadequate aerial system. DTT is an option if you can see the transmitter from your window. Otherwise at least test out with borrowed kit or see what results other people get before going down that road.  

stay analogue for an easy time

If you have an analogue service available in your area, you'll be able to work with a far poorer signal. Analogue will still give you a usable result with 10% of the specified minimum signal level. DTT won't.  So if you want minimum pain, use analogue. Sure, you'll get noise and ghosting, but you will still be able to follow the programme in a way you can't with DTT dropping in and out. Experimental verification is here

don't use a set-top aerial  - and specially not an amplified one!

Students seem more susceptible than more to the advertising siren song of 'perfect reception with this amplified high-gain set-top antenna.'[1] Avoid set top aerials if possible, and avoid amplified set-top aerials at all costs. If you have a set-top aerial and want an amplified one, stick a booster after your set-top aerial .It won't improve your signal unless your TV is really old (or you are using a PC card), since this is one of the incorrect uses of booster amplifiers, but you'll be able to sell it on the notice board to next year and there are correct applications of boosters you might have in future - like before a PC card.

So what should you use? Get a 'standard 2' grade CAI benchmarked aerial and 3m of CT100 cable  and mount the aerial on something (shelves above the desk are usually near the window in halls) just behind the window and aim it out through the window. The glass doesn't attenuate DTT frequencies that much so there's no need to open the window..

Your hall cleaner will hate you and you may look a bit of a geek, but it's handy small enough to be derigged and slung on the wardrobe when you're not using it if that is an issue. The performance will be so much better than any kind of set-top aerial. and your outlay will be about the same. Even if you use a cheap Maxview 10 element from B +Q and reuse some cheap and nasty brown 'low loss' cable you'll be better off.

No guarantee of good DTT reception - just a promise of better reception than with a set-top aerial.

Students should also note that the key component of the Poor Man's DTT tester is a popular PC solution for students, and even if you aren't using a Nebula card you may be able to borrow one for a day, so you can measure 

Using a PC card in a computer? Consider using a booster

What! Have I gone mad - I have a whole page dedicated to why you really shouldn't have the booster in the same room as the TV and that boosters don't solve bad reception and here I tell you to use a booster before your PC card?

The reason this makes sense is that the PC generates an awful lot of RF noise, much in the same band as the signal you are trying to receive. Some of that will inevitably find its way into your PC card tuner, and as a result these can be the equivalent of a 20-year old telly with noisy input stages. You are therefore using the booster for the original correct use of booster amplifiers. The PC card is a rare example of a noisy modern TV, because of the environment the card must work in. I first observed this with a Hauppauge analogue WinTV card, which gave patterning on the picture if I connected the 70dBuV (exact middle of spec) feed, a level which gave a great picture on my TV free of any patterning. Running the card hot at 80dBuV (maximum spec) improved things and pushing this to 90dBuV eliminated the interference. Pushing that even higher started to give the usual patterning you'd expect from overload. The performance of PC cards varies, so you might want to borrow a booster first. If your PC/PC card combination is good, sticking a booster in front may give you worse results by making you more susceptible to impulse interference - a 15dB booster means you have 15dB less immunity to out-of-band signals overloading your receiver. For a DTT receiver, these out-of-band signals might well be the analogue signals from the same transmitter site.

For the noise reason, you might prefer a USB2 external tuner over an internal one. USB1 analogue tuners suck because the analogue video needs to be compressed to send to the PC, which trashes quality - particularly noticeable with noisy signals that don't compress well! (USB1 DTT tuners are okay since the off-air signal for one channel is up to 5Mbps can fit in the USB1 bandwidth of 12Mbps). Getting the tuner out of the PC helps a bit, though the booster trick might still be worth considering.

This recommendation is one of the reasons I advocate getting a booster instead of an amplified set-top aerial.  Students are the only people likely to be watching TV using PC cards and a set-top aerial - most other users will come off at least a  loft aerial, and if the quality sucks they'll go and use their main TV. Which shouldn't have a booster is the same room!

Selecting and siting your TV aerial

Why DTT is different from an analogue install


back to electronics index

electronics home

  1. Run, do not walk, from anybody trying to sell you a UHF TV aerial with anything that looks like a parabolic dish on it. To be effective the diameter of the dish needs to be at least one wavelength, which is 0.5m at 600Mhz for the middle of the UHF TV band. That is one BIG set-top aerial. Any dish at UHF TV frequencies is marketing frippery, not engineering.

M E g A L i T h i A
Text and photographs RM 2005 unless otherwise credited