Which aerial

[Aqua]

I'm going to replace our loft aerial for a chimney mounted outdoor aerial and would appreciate advice on a few points...

We recieve our signal from Bilsdale on the North York Moors direction from us to the transmitter is North - North East, having checked Wolfbane the antenna suggestion is 'amplified extra high gain'.

Having looked on Aerial Shack for such an aerial i've seen this http://www.aerialshack.com/blake-dmx10wb-wideband-very-high-gain-aerial-offer-price-p-266.html among others and i'm wondering if it is suitable or if another aerial would be better.

Also, we need a 4 way box in the loft to allow a fed to 4 different TV's, again looking at aerial shack i've seen this http://www.aerialshack.com/antiference-a240d-aerial-amplifier-signal-booster-p-477.html among others, again is it ok or is there a better option?

I fully understand there are many factors to this issue, however, having no experience of aerials i'm really looking for the best set up i can get, not bargin basement nor silly money, just good quality work a day kit.

Any advice will be appreciated, thanks

 

[ChrisFrost]

I don't think much of the aerial.

For a start, you can't have a wideband aerial that is also "very high gain". This is borne out by the gain figure of 12.5 dBi. (BTW, dBi is a very flattering way of measuring gain. Take dBi figures with a pinch of salt. Straight dB is a better measurement). Second, short aerials by their nature don't produce as much gain as a longer aerial with more elements.

If you want the highest gain possible then you need a grouped aerial (one tuned for the particular frequency band of the local transmitter) and it should be as long as possible. That usually means a Yagi type like this. There's a couple of things to watch out for though...

Yagis can suffer from interference as they pick up other transmitters as well as the signal you want. The competing signal(s) become noise, so some of the benefits of the extra gain are offset by this additional noise. Two steps forward, one step back. Also, the country is still in the middle of the digital switchover. Some signal groups are being shifted as part of that process.

The other thing is adding blanket gain with a distribution amp without some sort of gain control can cause similar reductions in signal to noise ratio too.

Maybe have a look at a different solution. Log Periodic aerials are wideband, medium gain, but very good at rejecting everything except the main transmitter signal. In other words they produce a cleaner signal (better signal to noise ratio). This is better than starting with a higher gain aerial that picks up a load of noise. Start off with something like this

Then add a variable gain masthead amplifier. This is a two-part device. A power supply with the gain control lives behind the TV or with the loft box. It feeds power up the same aerial cable that brings the signal back from the aerial, so there's no extra wires. The second part is the amplifier which, as the name suggests, attaches to the aerial mast. The closer any amplifier to the aerial then the cleaner the signal.

The purpose of a variable gain amp is to tune the gain level so that only the strongest signal is amplified. Again, this is about getting a clean signal.

After this, you can pipe the signal through any loftbox you want. This is the sort of thing.

To finish off, don't scrimp on the cable. Something like the Webro WF100 would protect that precious signal we've worked so hard to get clean.

 

[plugwash]

BTW, dBi is a very flattering way of measuring gain. Take dBi figures with a pinch of salt. Straight dB is a better measurement

There is no such thing as a straight dB measurement of antenna gain all measurements of antenna gain must be relative to some reference. dBi is relative to a perfect isotropic antenna. dBd (often reffered to as just dB) is relative to a half wave dipole. As long as you are comparing like with like or add in the appropriate offset if you aren't they are equally good measures.

 

[Aqua]

Firstly, thanks for the replies...

Having read but not really understood i have now come up with 2 options, this aerial http://www.aerialshack.com/antiference-rx20-wideband-digital-aerial-p-734.html and this 4 way amplifiyer http://www.aerialshack.com/wolsey-skypass-amplifier-booster-p-474.html

Or, this areial and fixing kit http://www.aerialshack.com/periodic-aerial-complete-fitting-p-1344.html with this 4 way masthead amplifiyer http://www.aerialshack.com/wolsey-wfav425-masthead-amplifier-p-473.html

Thoughts please (lol), if i can get the bits before the weekend i'd like to fit it all on Saturday, so of course, time is against me....

 

[ChrisFrost]

The Log Periodic would be my first choice. I don't now if the mounting kit is right for you though. It sounds like it won't give you any height. Are the aerials on the other houses mounted up on poles?

Do you need Sky IR pass through in the distribution amp?



Here's your shopping list:

Log Period aerial

Masthead variable gain amp

5ft or 6ft pole

Chimney stack bracket & lashing kit

Webro WF100 cable

Distribution amp with*/without* Sky IR pass (* as required)

F plugs and coax plugs as required

Self amalgamating tape

 

[Aqua]

Thanks, i've not got sky so no need for IR Pass (whatever that is) and yes the other houses around here have aerial poles, so here's my updated list,

http://www.aerialshack.com/antiference-lp28f-wideband-periodic-aerial-p-269.html

http://www.aerialshack.com/wolsey-wfav25-variable-25db-masthead-amplifier-p-472.html

http://www.aerialshack.com/foot-aluminium-aerial-mast-inch-diameter-p-274.html

http://www.aerialshack.com/stack-strap-chimney-mounting-p-692.html

http://www.aerialshack.com/wolsey-skypass-amplifier-booster-p-474.html

http://www.aerialshack.com/webro-wf100-double-screened-coax-cable-metre-white-p-1267.html x 10 metres

http://www.aerialshack.com/rg58-connector-twist-pack-p-1302.html pack of 10

http://www.aerialshack.com/standard-male-coax-connector-p-439.html x 5

Total cost £101.79 free p&p....

I'm not wanting to be tight here, but is there any savings to make on the above list, ie equally suitable equipment but cheaper than the above items?

 

[ChrisFrost]

That's pretty cheap for what you need. I had a look at the wholesale prices for what I'd use in the same circumstances. There's not a lot of profit in the job when you factor in the free postage. I suppose it depends on what service they're using if it is being give free - Will the stuff arrive in time for this weekend?

My kit would be slightly different in a couple of ways, but would cost about the same to supply.

I'd choose a Masthead amp where the gain was adjustable from a control near the TV rather than on the roof. The reason being that you aren't going to have a the sort of spectrum analyser meter that an installer would use to see the signal level, so you'll have to rely on the TV picture and it's hard to make those adjustments when the screen is in the living room and the control is on the roof. I'd also buy the right sized F connectors. The RG58 ones won't fit on standard WF100.

 

[Aqua]

Thanks, the postage is free over £50, next day delivery.

Re the mast head amp being adjustable from near the TV, how does that work re upto 4 different TV's? and could you link to that type of unit please.

Is it possible to have an all in one mast head amp mounted in the loft with 4 outlets to seperate TV's? so as not too have two different units.

Also, i didn't know there were different types of F connectors, i'll check again lol.

Cheers

 

[Aqua]

Thanks for your help Chris, i've now spoken to the guy at Aerial Shack and although the list has changed slightly due to the area we are in, exact distance from mast etc i will be making the order later today for delivery on Friday....will report back after installation and testing....hopefully with good news..thanks again

 

[Donkmeister]

I'd choose a Masthead amp

Chris, I've posted in here before re. aerial issues and as someone who is clued up on aerial and AV issues I hope you can enlighten me. Anyone else feel free to add their two pennyworth...

Is it just me or is an amplifier assumed as a necessary part of any installation now? Isn't it sufficient to choose an aerial that is of the correct design and size?

I've always been of the mind (possibly incorrectly) that a passive antenna, correctly sized and tuned for the intended use, is superior to an antenna that is insufficient on its own but has an amp bolted on. This allows the (higher quality) amplifier in the tuner circuit to do its job with a cleaner signal plus it negates the power use and inherent unreliability of an additional amplifier stage.

I am not an RF engineer but have an appreciation of RF systems. I have always assumed that SNR is king.

Am I wrong? Or are there practical reasons why an amplifier is required?

 

[Monkeh]

One reason for an amplifier is splitting the signal. I'd love to see you stick an aerial on the roof of your house big enough to feed eight rooms by itself!

 

[Donkmeister]

One reason for an amplifier is splitting the signal. I'd love to see you stick an aerial on the roof of your house big enough to feed eight rooms by itself!

I actually could... I have clear line-of-sight to the rather powerful Sandy Heath transmitter (I am, as I type, admiring the aircraft warning lights on it from 2-3 miles distance) Many here have to install attenuators to avoid saturating their receivers.

Realising most aerials aren't in such an advantageous position, what size aerial would typically be required to feed eight tuners? Assuming decent PF100 cable, a decent splitter, f-connectors apart from the b-l on the back of the telly etc. And not a house deep in a valley situated 100 miles from the nearest transmitter!

Having seen a good many cheap TV aerials in less-than-perfect orientation, far from the transmitter, with cheap cable, random splices and multiple belling-lee connectors between aerial and TV, but still picking up a good analogue picture, I wonder if a few dB loss from a signal splitter in a well-installed system would be any worse!

 

[ChrisFrost]

I'd choose a Masthead amp

Chris, I've posted in here before re. aerial issues and as someone who is clued up on aerial and AV issues I hope you can enlighten me. Anyone else feel free to add their two pennyworth...

Is it just me or is an amplifier assumed as a necessary part of any installation now? Isn't it sufficient to choose an aerial that is of the correct design and size?

I've always been of the mind (possibly incorrectly) that a passive antenna, correctly sized and tuned for the intended use, is superior to an antenna that is insufficient on its own but has an amp bolted on. This allows the (higher quality) amplifier in the tuner circuit to do its job with a cleaner signal plus it negates the power use and inherent unreliability of an additional amplifier stage.

I am not an RF engineer but have an appreciation of RF systems. I have always assumed that SNR is king.

Am I wrong? Or are there practical reasons why an amplifier is required?

If you have a decent signal and good line of sight then a mast amp might well be superfluous. I'm currently running on an unamplified wideband log periodic - a lower gain aerial - pointing at Holme Moss. I tried a little signal attenuation experiment using the cheapest Freeview box I could find. On the strongest channels I found that I could attenuate by 36-40dB and still get a perfectly watchable signal. The weaker channels pixelated at around 20dB attenuation.

If I changed to a wideband Yagi which would be higher gain but less discriminatory I could probably expect to pick up a little interference from say Moel-y-Parc. Using a variable masthead amp I'd probably be able to adjust the gain so as to exclude the lower power transmitter. The result would be a cleaner signal using the amp as a selective filter that just running the aerial on its own.

The other thing to consider is the digital switchover. The highest gain aerials will be those tuned to a specific channel group. But as the digital switchover is rolling out over the country there have been stories of people losing channels as the transmitter bands have been altered (more info here). A wideband aerial won't have this problem, but nor will it differentiate between transmitters as discussed in the previous paragraph.

We have to be quite general with advice on forum sites. Signal predictors and transmitter information can give us a best guess at what might work, but until one does a site survey then it's impossible to be sure.

 

[Aqua]

Well the aerial is up and the masthead amp is working, so too is the 4 way split box and everything's working fine....thanks Chris for your advice i apprecite it.....all the best

 

[Aqua]

Hi Ronat42,
Great and interesting story and just shows how the old gear can still work well today.
Before starting the change to a new aerial etc, the loft aerial we had was only really any good for 1 tv, as soon as we put a signal to another they were both rubbish, but then again we got 10 years of tv out of that aerial (it was working long before we bought the house) however, just today i said to 'her indoors' how great it is to watch a crystal clear picture downstairs while the kids both watch something different upstairs.....
The whole new aerial thing has worked perfectly and i have to say i've enjoyed checking here for advice, sorting the order with Aerial Shack and doing the installation myself (i've no problem with working on the roof luckily)
Once again, thanks to everyone who has posted here and thanks to DIYnot.com