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87 posts

Master Geek
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Topic # 21219 19-Apr-2008 17:40 Send private message

Hi, just wondering if someone can give me some advice on the following aerial questions?

We're in  the Griffen Park area (Mt Roskill South/Lynfield North) which is surrounded by hills on the West & North (so hills between us and the transmitters). All our neighbours UHF aerials around us are on at least 2 metre masts pointing to Waiatarua. We currently have a combo aerial (VHF & UHF) that is 3 metres up and gets TV1 & TV2 well and TV3 marginally. Prime is "there" but unwatchable.

My questions are:

1) Our current aerial has a spec'd UHF gain of 8-14dB, dedicated UHF aerials I am looking at as a replacement for Freeview have a gain of 14-18dB. Obviously this is better, but practically will I see an improvement (RF being a black-art!)?

2) The two UHF aerials I am looking at are:
  a) http://www.freeviewshop.co.nz/freeview-very-high-gain-aerial-p-456.html
    &
  b) http://www.hillssignalmaster.co.nz/pages/HILLS_UHF.html  (SF91)
Does anyone have a recommendation?

3) For directing the aerial in the past I have used a TV tuned to Prime and much going-up-and-down-the-ladder, does anyone have a better suggestion? One idea I had was to buy a USB DVB-T tuner and use my laptop with s/w showing signal strength - anyone used this approach?

4) And finally I see on the Kordia site that Waiatarua is horizontally polarised, and that Skytower (a possible alternative for me) is vertically - to clarify this means I should physically mount the aerial flat or on its side (horiz' or vertical)?

Cheers

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722 posts

Ultimate Geek


  Reply # 124986 19-Apr-2008 20:23 Send private message

Let's see if I can help.

I live in Blockhouse Bay down a bit of a gully. Even with my VHF aerial mounted some 3 metres above the roofline,  I still get ghosting off a building in front of my house on normal TV. I have two aerials: one is a large element VHF model I bought from Hills some years ago. The other is a large element UHF model some 1-2 metres in length. This has given good UHF on stations like Prime in the past.

My only real recommendation is to find a UHF aerial that has a large number of elements for good reception. Unlike analogue TV, if the digital reception is suspect, you won't receive any signal: similar to a rainfade signal on Sky. I would try & get a guarantee from the aerial provide that you could exchange it if it doesn't work.

Be aware that combination aerials are a comprimise in receiving quality, ususally on the VHF side. A dedicated UHF aerial should have substantial reception gains over you're existing one; especially mounted on an extension pole.

As for how to install the aerial: it should always be mounted horizontally towards the strongest tramnsmitter.

I have just gotten Freeview working & I have NO ghosting or other artifacts on my reception. The first time ever. Best Of luck.

I will try & post a photo of my aerial as it was on the house when I moved in.

The other area to consider is the age of you're aerial cabling. Mine is old but yours may be compromising you're signal. One step at a time.




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3051 posts

Uber Geek
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  Reply # 124991 19-Apr-2008 20:49 Send private message

argo: We're in  the Griffen Park area (Mt Roskill South/Lynfield North) which is surrounded by hills on the West & North (so hills between us and the transmitters).

Yes, I know that road very well, always use it when driving from our Lynfield house into the city.  I don't think there is any possibility you will get a direct line-of-sight path to Waiatarua or Sky Tower from there, no matter how high your aerial mast is.

argo: 4) And finally I see on the Kordia site that Waiatarua is horizontally polarised, and that Skytower (a possible alternative for me) is vertically - to clarify this means I should physically mount the aerial flat or on its side (horiz' or vertical)?

If pointing at Waiatarua, your aerial should be "flat" i.e. Horizontally Polarised.

If pointing at Sky Tower, your aerial should be "on its side" i.e. Vertically Polarised.

If you want to try and receive TV3 on VHF from Sky Tower, and other channels from Waiatarua, you will need two separate aerials pointing/polarised in different directions, and a diplexer (aerial combiner).  Hills Signalmaster should be able to help you with that.

Being in such a low-lying area, I don't like your chances of getting a satisfactory DTT signal.  Basically, if you can't get a good clean analogue signal on Prime via UHF, you are unlikely to get a usable DTT signal according to what I have read.

Maybe Freeview via satellite is your best option, although if you are very close to the hill on your Northern side, there is a possibility you wouldn't get that either.



87 posts

Master Geek
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  Reply # 124997 19-Apr-2008 21:24 Send private message

Thanks for the replies guys Smile

grant-k, yep I know I don't have a hope of getting line-of-sight to the transmittters but I'm kind of hoping for a little bit of terrestrial signal wrap, at least enough to get a reasonable signal. From my old Civil Aviation days I remember enough to recall that the higher up the frequency spectrum, the more line-of-site the signal path needs to be, so UHF is not helping me there Frown

Any comments on this logic would be welcomed (calling all broadcasting engineers!!).

I'm hoping that as my gain-compromised multi-band aerial does manage to get some UHF reception (Prime) then a better setup will get me there - oh well! We can definitely go DVB-S as Sky is fine at our house, but want who wants SD if there is a chance of getting HD!!

Maybe I'm best to get a professional in who can measure my chances of success? If anyone can recommend a Prime (UHF) aerial installer that knows their stuff that may be the best way forward??

Again thanks all, ideas/discussion welcome!

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Uber Geek
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  Reply # 125005 19-Apr-2008 22:08 Send private message

argo: From my old Civil Aviation days I remember enough to recall that the higher up the frequency spectrum, the more line-of-site the signal path needs to be, so UHF is not helping me there Frown

Any comments on this logic would be welcomed (calling all broadcasting engineers!!).

Well, I'm an engineer, and I used to work for broadcasting (many moons ago) so I can definitely help you here Smile
Cyril7 has more up-to-date knowledge than I do, but this is quite an easy question.

Lower frequencies definitely suffer less attenuation from "Scatter Effect" than higher frequencies do.  For an extreme example of this, compare Medium Wave AM radio broadcast signals with FM radio and TV.  AM radio hugs the earth using a variety of propagation mechanisms, whereas FM radio is much stronger if you have a direct line-of-sight path to the transmitter.

FM and VHF signals however, will "bend" to a reasonable degree using Scatter Effect and other Diffraction modes of propagation e.g. over the brow of a hill.  This is what gives you quite watchable signals on TV1 and TV2, whereas Prime being on UHF suffers much greater attenuation from the Scatter Effect and it effectively makes the signal unwatchable for you.

argo: I'm hoping that as my gain-compromised multi-band aerial does manage to get some UHF reception (Prime) then a better setup will get me there - oh well!

My concern would be that even allowing for the extra 4-6dB of gain which would be provided by a new aerial, you will still not have a strong enough UHF signal to give you usable DTT reception.  Cyril7 may be able to confirm or refute this.

argo: Maybe I'm best to get a professional in who can measure my chances of success?

That would definitely be a good idea.  If I was in Auckland, and had a signal meter, I would offer to help you out myself.

Maybe someone else here could help Argo out?

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  Reply # 125330 21-Apr-2008 15:01 Send private message

I've just moved into a new house in Rothesay Bay and hoping for DTT reception.  I haven't tried the current UHF aerial yet but hoping Prime reception is OK.  If not, I'll be in the same boat so will probably rather get a pro in to have a look at our stuff.  I'm assuming I need a view of the Pinehill transmitter.  Does anyone know exactly where it is?  I might try getting up on my roof and having a look.  We're down a bit of a hill, but I'm hoping it will still be OK.

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Uber Geek
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  Reply # 125333 21-Apr-2008 15:08 Send private message

bazzer: I'm assuming I need a view of the Pinehill transmitter.  Does anyone know exactly where it is?

Yep, right here on this map:

http://www.kordiasolutions.com/files/Image/high-sites/full-size/Auckland.jpg

2841 posts

Uber Geek
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  Reply # 125349 21-Apr-2008 15:47 Send private message

Anything closer (by that I mean the map, something more detailed)?  From that map, it looks something like the corner of Rosedale Rd and East Coast Rd.  Does anybody know?  That's very close to my place (just over 1 Km) so hopefully it will be good.

24 posts

Geek


  Reply # 125492 22-Apr-2008 09:30 Send private message

Hi All,

I have just moved into a new place in Ellerslie. The house doesn't have a aerial at all. I do have a Sky dish connected to my PVR which is running a Hauppauge HVR3000.

The current issue is that we can only record/watch one channel. I'm thinking of adding another card to watch DVB-T in the future, but the PVR will need an upgrade to handle H.264.

At this stage I think the best thing to do is get an UHF aerial that will do both. Plug it directly into the TV for the moment and worry about DVB-T later. At least that will get the misses of my back :)

Can anyone suggest a aerial that will fulfil my needs?? Is the coax different for DVB or will the RG6 do both??

Thanks in advance.



Paul




146 posts

Master Geek
+1 received by user: 4


  Reply # 125504 22-Apr-2008 10:28 Send private message

We got freeview HD working with perfect reciption at the Hamilton V8s - inside a steal warehouse with a set of $30 rabbit ears. Didnt even align them just pluged them in and hit tune.

We could barily get TV3/Prime on the standard in-tv tuner. I was flabbergasted.

We had a full HD 60" samsung plasma - the Freeview HD channel was amazing!

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Uber Geek
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  Reply # 125506 22-Apr-2008 10:35 Send private message

Argo, Band IV/V is more line of site than VHF you are correct, however with the power levels you can expect in most of auckland and DVB-T tollerance to multipath you may find you can get reasonable reception where analog was dodgy. That said without actually doing site tests we are all guessing.

When you have a diffused path (ie not line of site and partially obstructed) it is advisable to use a broadside array as opposed to a yagi, these deal with this situation much better, Hills have a selection of both yagis and broadside arrays (hunter phased array in link). Ideally it is receommended that you use an antenna with a non ferrite balun (ie PCB phased line is better) and has a F connector directly on the balun rather than saddle and clamp.

Paul RG6 is suitable for both satellite and DTT, although it is often recommended but not imperitive that Quad shield is used for DTT as opposed to duobond as normally used for satellite due to its superiour interference immunity, I would not get to excited about this detail.

Cyril



87 posts

Master Geek
+1 received by user: 1


  Reply # 125727 22-Apr-2008 23:31 Send private message

Thanks for this very useful info cyril7.

Regarding: "When you have a diffused path (ie not line of site and partially obstructed) it is advisable to use a broadside array as opposed to a yagi, these deal with this situation much better, Hills have a selection of both yagis and broadside arrays (hunter phased array in link)."

Would you mind elaborating? Are you saying that because with DTT we can actually take advantage of reflections (which previously in analogue would have caused ghosting) it is better to have a broadside array rather than a more (?) directional Yagi?

I note on the Hills website that their best Yagi has a fwd gain of 13-18db, whilst their Hunter has 7-11dB gain, hence my question (gain is better with the Yagi). I write this on the assumption a Hunter Array is less directional than the Yagi (I can find very little layman's info on broadside arrays) and is therefore able to receive multiple signal paths.

Thanks again.

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Uber Geek
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  Reply # 125741 23-Apr-2008 05:46 Send private message

When an obstruction (hill) prevents line of site reception, the signal is going to physically move at the capture point as a net result of the main obstruction and other objects nearby, essentailly a layering effect occurs as you are in effect dealing with a freznel zone situation that is dynamic so the layering peaks and troughs move, so you need an antenna with a larger capture area which may mean less gain. A broadside array has a larger capture area so can maintain a better end result.

You can get higher gain broadside arrays with four dipoles or more, here is an example of a guy well north of Auckland.

From what you describe you are not in a good location, its possible that you may end up with dodgy broken reception, but you may also be lucky, without doing a site survey and seeing for myself I cannot tell. From what you say a broadside array on a 2-3meter mast may get you acceptable reception.

COFDM can deal with fading signals and nearby reflection that would have resulted in unwatchable analog reception. So not so much that it can take advantage of ghosting, more its more tolerable in the final displayed outcome.

Cyril

Ben

317 posts

Ultimate Geek

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  Reply # 126793 28-Apr-2008 14:02 Send private message

grant_k:
If pointing at Waiatarua, your aerial should be "flat" i.e. Horizontally Polarised.

If pointing at Sky Tower, your aerial should be "on its side" i.e. Vertically Polarised.


This is interesting, because I've just replaced my aerial (went to move the old one and it was all corroded around the mount and inside the balun box).  The old aerial was horizontal and pointing at Waiatarua, and we had rain fade on DVB-T during heavy rain.

With my wife downstairs alternating between Prime and the "manual scan" page on the Zinwel box, I alternated between pointing at the Sky Tower, and Waiatarua, in both polarisations.  I could actually see the black band on the Sky Tower from my roof, but I couldn't see the Waitakere hills (behind houses and trees).  Using this aerial: http://www.dse.co.nz/cgi-bin/dse.storefront/48152e8f06fb2aae273fc0a87f3b06b6/Product/View/L4713

The results was that reception was best with the antenna "vertical" and pointing at Waiatarua.  Totally counter-intuitive to what I expected.  This was with a completely new run of cable and new aerial.  Prime is now massively more clear than it was with the old aerial, with a bit of ghosting.  Freeview signal/quality are always both above 80% on both channels.

Could it be that the Sky Tower is tuned to broadcast more heavily north and west?  So us being on the west side of the Sky Tower are better off picking the signal from Waiatarua?

The only other possibility I can think of is that the signal strength is too high!?  Talking 10km direct line of sight to the Sky Tower with a 43 element aerial.

Ben

317 posts

Ultimate Geek

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  Reply # 126795 28-Apr-2008 14:04 Send private message

One more thing: I can actually lock on to the Sky Tower channels with the aerial pointed at Waiatarua.  Signal quality and strength are "ok" but not fantastic.  More evidence that perhaps the signal is too strong with the aerial pointed directly at the tower?

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