A Really Dumb Question about UHF Aerials

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juliant

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Topic # 22462 29-May-2008 04:16

I found what looks to be an old Sky UHF aerial in the garage, so thought I'd use it to see what my reception was like on Prime. It was missing the balun so trotted down to Mastertade and bought RG6 cable and one of those Hills indoor/outdoor coax to ribbon terminal baluns (Product L4465 at Dick Smiths). Now I wasnt 100% sure if this is what I needed, but noticed the VHF aerials they had for sale all had these same baluns loose as part of the pack with the aerial. (No UHF in stock to compare)

What I wasnt sure about, is where the ribbon terminals actually connect to the aerial (This is the dumb question part). So all I tried was inserting the spade type terminals under the two bolts that connected the aerial to the mast.

Unfortunately the picture quality was not great so leaves me undecided whether I could get Freeview HD. Now it could be that the very old aerial is knackered, or that I was missing an important fitting of some sort that the ribbon terminals need to be connected to?? Even though the aerial is a bit old and rusty I suspect it would still do the job.

So short of buying a new UHF aerial on the off-chance it works, is there some other type of Balun I should be trying (maybe a coax to coax rather than ribbon terminal? Is there such a thing. I couldnt see anything else on Hills website that really helped.

I also managed to snap off one of the spade connectors in the process of changing the aerial direction (the bolts were very rusty).

On a side note - RG6 at Mastertrade $1 a metre v $2.89 at DSE and the Balun was $5 v $10

tonyhughes

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Reply # 134045 29-May-2008 07:34

Not an aerial expert at all, but steer clear of ribbon if you have anything less than perfect reception!

If you want Freeview HD, then I assume you have spent (or are willing to spend) $300+ on an STB and $1500+ on an HD television - my suggestion is get a new, professionally installed UHF antenna.

Tell the business you engage that its for Freeview HD only, and then if it doesn't work, you are covered under the CGA for them to get it working, or refund it.

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argo

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Reply # 134063 29-May-2008 09:19

Sounds like you have quite an old aerial there! So the ribbon you mention is a short piece from the aerial terminals to the BALUN (the Balanced part of BALUN) box? And then you then used coax to your receiver? You say you "inserting the spade type terminals under the two bolts that connected the aerial to the mast", by "mast" do you mean the mast that is attached to the roof (or bargeboard), or the horizontal member that the elements attach to? Probably all a mute point if everything is rusted up anyway as this sort of 'invalidates' the whole experiment

As TH says, you could get professionals in. Maybe the first step should be to ask for a site-survey and they will then tell you exactly what your situation is, this will cost a few dollars though. I have personally talked to Hills SignalMaster about this service but in the end took a more personal approach as described here: http://www.geekzone.co.nz/forums.asp?ForumId=83&TopicId=22349 .

Also (and I assume you were looking at Prime as a test for FreeviewHD) have you looked at the Kordia DTT map to see if there is transmitter closer? In my case all the my neighborhoods UHF aerials are pointed to Waitairua ("through" a hill), but with the Skytower becoming a DTT transmitter, I now only need to swing my aerial 90degrees to get line-of-site reception!

So your options:
a) First look at the Kordia map to see your likelihood of DTT reception (free!)
b) Get a site-survey done or as TH says an installer to provide an aerial (~200 or 300 bucks?)
b) Buy/borrow a UHF aerial and do what I did in the thread linked above (assumes you have PC/laptop - NOVA-T-Stick=$90, aerial=$90, coax test cable=$30)

If you buy an aerial, be aware that they all (or should be) using a PCB Balun with a F-Connector actually built into the aerial. A much nicer impedance-matching/cabling solution!!

Hope this helps!

juliant

55 posts

Master Geek

Reply # 134073 29-May-2008 10:22

Yes it is an old aerial and a bit rusty.
I guess what I was trying to say is that the aerial has no terminals. So the ribbon I referred to was on the balun I purhcased ie coax at one end and 2 ribbons at the other with spade connectors. I gather this is because aerials used to be 300ohm so you need a balin to convert to 75ohm for coaxal?
So the problem was i didnt have anywhere to attach the spade connectors so just connected them where the aerial screws onto the mast (barge pole?). This is the mast attached to the roof
I really dont think I need a professional installation.- I'll go for your option 3 - a new UHF aerial (do the DSE ones have the PCB coax terminal as recommended?) and see how the reception is. If its no good I'll return the aerial. And yes it is to test the prime signal to determine suitability for Freeview DVB-T.

argo

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Reply # 134176 29-May-2008 14:55

Yep, sounds like a new aerial would be the go. Don't forget that a crappy coax will nullify your efforts, though if I read your post correclty you have already bought a new coax run from Mastertrade.

Hills are a manufacturer/wholesaler only and sell via DSE and Electrical outlets. If you buy from DSE you will quite probably be buying a Hills aerial.

To let you know there are a number of suppliers of UHF aerials, for instance www.freeviewshop.co.nz sell a range as does others. Here's a discussion on this subject: http://www.dtvforum.co.nz/forum/showthread.php?t=413 (the topic does end up turning into a bit of spec debate!).

I have had good advice from Cyril7 on this subject when I thought I didn't have line of site to a tx. To read go here: http://www.geekzone.co.nz/forums.asp?ForumId=83&TopicId=21219 .

Good luck, hope it goes well!

cyril7

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Reply # 134189 29-May-2008 15:46

Juliant, the balun should attach to the ends of the dipole on the antenna, and yes the balun should have a bit of ribbon that goes to the antenna, a folded dipole has a nominal 300ohms impedance, and the balun infact transforms from 300ohm balanced to 75ohms unbalanced. That said a dipole once no longer on its own and part of a yagi array has a somewhat different impedance than 300ohms, however for reception purposes this is often not a big issue.

It sounds to me like you were attaching to the wrong part of the antenna, ie not the dipole ends but infact the mount. Purphaps a photo would help.

I actually think you should buy a new antenna with a ferriteless PCB balun and suited to your location, however like you I think its worth getting an old antenna working to see your chances then proceed from there.

Cyril

juliant

55 posts

Master Geek

Reply # 134706 1-Jun-2008 04:48

Purchased a new UHF aerial from DTV in Tawa (I'm in Tawa so its handy), and worked like a charm. I bought a Hauppauge Nova T USB stick ($101) and installed that and Media Portal - couple of gltiches initially installing but got it all working. As its an older PC with AGP slot (7600Gt) I knew TV3 would be out of the question, but its working well on all the other channels. TV3 is definitely a no go - locks everything up if I choose that channel. Given thats the only channel with HD content aside from the test channel one could argue its a pointless exercise. But it lets me have a bit of a play and now I'll wait and see what the Freeview HD PVRs cost when they come out and decide then whether to upgrade the PC or go with a PVR. (DTV indicated they may have something available in a month or so)
I think I'll go with a PVR unless they end up being very expensive - just easier and tidier than having a PC in the lounge. (I assume they'll come with twin tuners?)
BTW I'm very happy with my Sony 50" LCD Rear Projection TV that I purchased a few months back - largely on the recommendations Cyril and others had made about them :-)

cyril7

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Reply # 134708 1-Jun-2008 07:39

Hi, glad you got it sorted, you do realise that in Tawa depending on where you are you have a choice of two Tx sites. If you are in the north of Tawa (linden end) then you should have clear site (or near) of KauKau to the south on Horizontal, however if you are to the south you may not be able to see KauKau at all but you can use Baxters Knob, this is directly above WhitfordBrown drive near the police college and on Vpol.

Baxters knob shares the same frequencies as Fitzherbert (Hutt Valley) and Ngarara (Kapiti) which are different to KauKau.

Cyril

juliant

55 posts

Master Geek

Reply # 134758 1-Jun-2008 15:10

Thanks -re Baxters Knob - no wasnt aware until guy at DTV mentioned it, but as I am in about the middle of Tawa (Hampton Hill) I pointed to Kau Kau although its not line of sight, and in tuning, the strength and quality were close to 100% (maybe those Engel aerials are good).
Hi-def test channel looks fantastic, but just now watching some sport on One, I was very impressed with how good the standard def is. Just have to wait for a PVR to come available - the PC I realised is not quite handling it too well- its not obviously jerky but then you realise it is not as fluid as it should be and gets slightly tiring on the eyes after a time.