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Can someone please explain aerials

ianh64

Active Member
I thought that I has a grasp on how aerials worked and having been blessed with always having use of Crystal Palace transmitter, my theoretical knowledge fitted in with my practical experience.

However, interest in a property in Littlehampton, South Coast, Sussex has made me doubt my theoretical knowledge. http://www.avforums.com/forums/showthread.php?t=375122

Until recently, I had an interest with a 'property' in West Wittering (PO20 8NB). When we stayed there, we got no Five on analogue and on Freeview, nothing from Mux 2. Exactly as predicted here. Asking locally, and seeing comments on this forum, I was told that I needed a wideband aerial to pick up the missing Freeview channels.

What I would like to know is, why would a wideband aerial make any difference. I though that a wideband aerial had a broader range of frequencies that it would accept rather than boost the signal strength of existing distant channels. Surely what is really needed is a second aerial pointing at a transmitter within range of the missing channels.

Somehow, I think I am missing something here!

Would like to get my understanding sorted for Littlehampton transmissions which has a mismatch of channels from two transmitters.

Thanks
 
D

Deleted member 27989

Guest
I am by no means knowledge, but lets explain what happened to me...I live in a very much outer fringe of Crystal Palace with according to Freeview no reception...We used to have this old analogue system aerial which was just about able to get reception....For my computer use I needed to boost the signal a bit more as the computers are more sensitive...We got a big, I mean BIG wideband high gain arial installed at a longer mast....Previously it wasn't wide band and I only got the Crystal Palace signals...Now I am able (eventhough it is pointed at Crystal Palace) also to pickup signals by Sandy Heath...Now we don't want Sandy Heath, but for Channel 5 it doesn't matter at is not regional so we can pick and choose without having to have two arials installed.....

So in short it might be that by having a wideband version you can avoid having two arials installed....
 

Eye2007

Banned
Live out in Wittering, Littlehampton and you may as well live in the middle of Romney Marsh, away from civilisation and all things tv signal. The reception this way is highly poor. The only way to get a signal would be to build a crystal palace tower and set it to recieve only.

With a booster.
 

SamRadford

Well-known Member
ianh64 said:
Somehow, I think I am missing something here!
Decide which digital multiplexes you want to receive.
Determine which UHF channels they occupy (between 21 and 69).
Choose a high gain aerial group that includes that range of UHF channels and preferably no more.

It may be that no group aerial does exactly what you want so your choice will be a compromise.

For more info see http://www.the-cool-book-shop.co.uk/freeview_bible.htm
 

weedongle

Standard Member
The UHF band is split into 4 groups, A B C D.
The aerials are grouped accordingly A B/C & D. There is quite a dramatic fall off of signal if you use a group A aerial and try to receive group D signals. If you have ever seen an A and D aerial together physically the D aerial is considerably smaller, this is because it is designed to pick up the higher frequencies at the top end of the UHF band. A wideband aerial is designed to receive the signals for all the channels in the UHF band.
If where you are living say you have analogue on group A then the free view channels are likely to be spread over the other bands. Bearing in mind that analogue signals are more powerful than the digital you need the best reception you can get. Also bear in mind when the analogue signals are turned off the frequencies released will be used by other broadcasters, so the whole band will be used.
There is no way that a single group aerial is going to give you the quality of reception required in these circumstances unless you live on top of the transmitter or other freak condition.
If you want a quality set up then use a wideband aerial and satellite screened coax for the lead.
Remember crap in = crap out.
Best wishes for your set up.:)
 

LV426

Administrator
Staff member
http://www.dtg.org.uk/retailer/benchmarking.html

This page contains an "official" listing of approved aerial makes/models. The Triax UNIX 52 is among those listed. Somehow (and I can't prove this) I suspect those on sale at Wilkinsons do not appear on the same list.
 
A

Analogue

Guest
LV426 said:
http://www.dtg.org.uk/retailer/benchmarking.html

This page contains an "official" listing of approved aerial makes/models. The Triax UNIX 52 is among those listed. Somehow (and I can't prove this) I suspect those on sale at Wilkinsons do not appear on the same list.

I do not accept that this list is in any way "official". This list is now some 2 years out of date and covers only a small selection of the aerials available on the market. The range of Aerials offered by Wilkinsons are I believe made by Maxview one of whose lower gain (Cat 3) aerials figures in this list. As far as I am concerned there can be nothing special about a "digital" aerial and the parameters concerning an aerials performance apply equally to an aerial for analogue or digital transmissions. The only difference with the choice of aerial for DTT is that because of the signal strength and spacing of the Multiplex channels (and their relationship to the analogue channels) a wideband higher gain design is often required. Following the link you gave however I came across this http://www.dtg.org.uk/publications/books/r_book2.pdf which explains a lot about all aspects of dtt transmission/reception and made very interesting reading. So thanks for this pointer.
 

SamRadford

Well-known Member
skygnome said:
the blake dmx10a is supposed to be better and cheaper than the televes dat 45
That's like saying that a Honda CBR1000RR racing bike is better than a Ford Galaxy car. You aren't comparing like with like.

The DMX10A is a group A aerial and the DAT45 is a wideband aerial. (Note the correct spelling of "aerial" BTW).

A DMX10A might be fine for Crystal Palace but you could be in for a disappointment if you point it at, say, Winter Hill.
 

LV426

Administrator
Staff member
Analogue said:
..there can be nothing special about a "digital" aerial and the parameters concerning an aerials performance apply equally to an aerial for analogue or digital transmissions. The only difference with the choice of aerial for DTT is that because of the signal strength and spacing of the Multiplex channels (and their relationship to the analogue channels) a wideband higher gain design is often required.....
Yes, thanks. I am fully aware of how DVB-T is transmitted and the nature of UHF frequencies vs. aerial groupings. I'm equally aware that aerials, of whatever grouping, come in as wide a range of "quality" standards as, say, TV sets.

Now, it's my personal experience that, in the general sense (i.e. not in relation to TV aerials) the products on sale at Wilkinsons fall generally towards the lower end of the "quality" range. This is especially true of own-brand stuff. In my limited experience.
 

Mike Campbell

Standard Member
What a funny old business this aerial game is!
Well a benchmarked aerial is tested for its capability to reject unwanted signals as much as receiving wanted ones but doesnt measure build quality which should be taken into consideration if mounted externally, beware of some diy packs.The main criteria is locating the bundle of metal to pick up all the signals across the chosen transmitter range equally. I may spend 1/2 an hour on a roof armed with a spectrum analyser just testing to get all the muxes in with no drop out or slope. Its all about location.
 

weedongle

Standard Member
Mike Campbell said:
What a funny old business this aerial game is!
Well a benchmarked aerial is tested for its capability to reject unwanted signals as much as receiving wanted ones but doesnt measure build quality which should be taken into consideration if mounted externally, beware of some diy packs.The main criteria is locating the bundle of metal to pick up all the signals across the chosen transmitter range equally. I may spend 1/2 an hour on a roof armed with a spectrum analyser just testing to get all the muxes in with no drop out or slope. Its all about location.

I couldn't agree more, sometimes moving the aerial 6 feet or less from it's original location can make a marked difference.
 

SamRadford

Well-known Member
You mention a "spectrum analyser". That's a bit outside my price range. Do you think a relatively cheaper aerial meter would suffice? This is the cheapest I can find:

http://www.satcure.co.uk/accs/page6.htm#digiair

I only need it for myself and a couple of neighbours so I don't want to spend a fortune.
 

Chris Muriel

Distinguished Member
I'm pretty sure you already know the answer and are just acting as devil's advocate here, Sam.
A proper spec an. should be used by all professional installers , preferably one that gives a BER (Bit Error Rate) reading too .
Failing that there are halfway house meters that do at least give BER on a simpler mono LCD display (not a real screen).
The one you linked will help where budgetary constraints rule out the purchase of a proper analyser - but keep an eye out on Ebay etc., purchasing with care as features vary enormously. I got a job lot of 5 Felec analysers and sold 3 of them virtually at cost to techie friends ; my profit was just enough to cover the cost of the 2 I kept and my mates were pleased at 25 quid per analyser.
It helped that I knew exactly what I was purchasing though and the guys I sold the other 3 to were also RF and electronics conversant .

Chris Muriel, Manchester
 

Voiceedit

Active Member
To get back to the original question, according to the transmission area map of the Rowridge Freeview transmitters, the Littlehampton area should receive all Freeview muxes from Rowridge and should not require any need to receive from Whitehawk Hill. Therefore a Group A aerial is all that is required in the first instance in order to experiment. As this is the same group of aerial as for analogue reception from Rowridge it should be easy to test this out. Adjustment of the aerial's height and overall position may be necessary. You need to receive all Freeview muxes from the same transmitter - for Littlehampton area Whitehawk Hill is in a totally different direction from Rowridge!
 

SamRadford

Well-known Member
Chris Muriel said:
I'm pretty sure you already know the answer and are just acting as devil's advocate here, Sam.
No, it was a serious question. I fail to see the benefit in using a spectrum analyser if all you are trying to achieve is to aim the aerial directly at the transmitter. In fact, to be honest, the compass bearing itself should be sufficient, surely? Why use a meter at all?

After all, the aerial alignment isn't as critical as that of a satellite dish and you won't find any Sky installers toting a spectrum analyser around!
 

weedongle

Standard Member
SamRadford said:
No, it was a serious question. I fail to see the benefit in using a spectrum analyser if all you are trying to achieve is to aim the aerial directly at the transmitter. In fact, to be honest, the compass bearing itself should be sufficient, surely? Why use a meter at all?

After all, the aerial alignment isn't as critical as that of a satellite dish and you won't find any Sky installers toting a spectrum analyser around!

Do you know what a spectrum analyser is and what it shows you? I believe that if you did you would not make the above statement. However you are quite right that most aerial installers don't use one (mores the pity). The digital transmissions use less power and cover a broader spectrum than the old analogue channels. Usually you can get away with using a compass bearing or looking where every body else pointed their aerials but in difficult locations/circumstances it may be the only way to ensure complete coverage of ALL the available channels.
There is more to a good installation than pointing the aerial in the general direction of the transmitter.
When sky was installed in my home a signal strength box with spectrum analyser was used by the installer to achieve perfect alignment.
It may be that other installers don't have or use one and maybe I was fortunate.
 

ianh64

Active Member
Voiceedit said:
To get back to the original question, according to the transmission area map of the Rowridge Freeview transmitters, the Littlehampton area should receive all Freeview muxes from Rowridge and should not require any need to receive from Whitehawk Hill. Therefore a Group A aerial is all that is required in the first instance in order to experiment. As this is the same group of aerial as for analogue reception from Rowridge it should be easy to test this out. Adjustment of the aerial's height and overall position may be necessary. You need to receive all Freeview muxes from the same transmitter - for Littlehampton area Whitehawk Hill is in a totally different direction from Rowridge!
Thanks. Yesterday I finally could put the theory in to practice. Connected an old Freeview box and got many more channels than I expected - I don't think that I got everything but will check what is missing next time I am there.

Why the descrepancy with the dtt.org.uk channel list? ie I get C5 and CBEEBIES which sre not isted on the Rowridge list. Its a communal aerial probably sited up high. Is it because it because its probably a well setup aerial. Signal strength is 70% with no apparent errors which is on a par/ if not better than I get at home from Crystal Palace.
 
D

Deleted member 27989

Guest
SamRadford said:
I fail to see the benefit in using a spectrum analyser if all you are trying to achieve is to aim the aerial directly at the transmitter. In fact, to be honest, the compass bearing itself should be sufficient, surely? Why use a meter at all?
If pointing it in the right direction is all you are trying to achieve you may have a point...But having a good installation is about a lot more than having an antenna in the right direction.....How are you suppose to pickup interference with a compass? How are you supposed to isolate where in your installation it is happening for example....Pointing the antenna in the right direction is only the beginning of perfect signal bliss...
 

SamRadford

Well-known Member
Yes, I'm familiar with the spectrum analyser. But I don't see how it helps. Once the aerial is aligned on the transmitter, what are you going to "adjust" if the S.A. indicates a problem? (And what sort of problem do you get?)

I can only imagine that you might be referring to side- or rear pickup from another transmitter. But, if you'd done your homework, you'd already have chosen the most appropriate aerial to minimise interference.
 
D

Deleted member 27989

Guest
SamRadford said:
Yes, I'm familiar with the spectrum analyser. But I don't see how it helps. Once the aerial is aligned on the transmitter, what are you going to "adjust" if the S.A. indicates a problem? (And what sort of problem do you get?)

I can only imagine that you might be referring to side- or rear pickup from another transmitter. But, if you'd done your homework, you'd already have chosen the most appropriate aerial to minimise interference.
And what if it is not the antenna but the cabling in your property....And then how do you propose to isolate which strand it is? Oh and the aerial interference doesn't just come from other transmitters, there's loads of other possibilities...To name one those stupid little motorbikes....Or choosing the right aerial and then not installing it correctly....
 

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