UHF DTT Antenna, wiring and coverage

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mcraenz

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#21886 10-May-2008 00:43

I'm in Auckland, Mt Wellington. Right where the "t" for Mt Wellington is on this coverage map.
http://freeviewnz.tv/images/auckland.pdf

I've got a UHF antenna but I'm getting artefacts on DVB-T. The house has a hill on the side the antenna is pointing towards (Waiatarua). i.e if was to look down the length of the antenna I would see houses up on the hill.

I looked at the antenna today; it's pretty rusty especially the mesh guard at the back. The contacts were pretty corroded, so I cleaned them up. There was also a masthead amp which I've taken out while trouble shooting. I'm still getting problems with reception even though the signal is reported by my PCI card as 100% quality.

The cable comes down off the roof and up under the floor behind the TV then there is a run of about 3 meters in parallel with network, DVI, satellite cables etc (no mains), the cables are all bound with that spiral cable tidy stuff. The cable then goes in to a splitter 1 side goes to PC1 with a DVB-T card the other side goes to PC2 with a analog capture card.

Now for the questions:

1.Since my antenna is about 20 years old and rusty and basically falling apart, I'm going to replace it. Given my location what is my best bet? should I go with a high gain 91 element jobby to combat the fact that I've got the hill "in the way"?

2.Am I better off without the masthead amp? It was in the house when I moved in, It's one with a power feeder at the TV end, I've always used it with analog (Prime); the picture is pretty good.

3.Can running all these cables parallel bound together cause interference?

4.Could the splitter with the 2 PCs be causing a problem. (I will try without the splitter, I just need to change some plugs.)

It seems that most of the time the picture is perfect, sometimes it will be perfect for 1/2 an hour at a time then there will be some disruption; it seems quite random, but it's by no means constant disruption.

Any help would be much appreciated. :D

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Nirodha

80 posts

Master Geek

#129799 10-May-2008 01:50

I'd probably start looking at graphics card drivers (or other potential pc configuration issues) before I went through the time, effort and expense of replacing an antenna system that was already giving me a 100% quality digital signal - seriously.

richms

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#129802 10-May-2008 02:26

Record it and then try playing it back several times in various software/codec combinations and see if the pixelation happens in the same place. Unfortunately there doesnt seem to be any software to give long term quality readings of the reception of each mux when I looked a couple of months back, just instantaneous values that really dont show a hell of a lot.

If the cable is 20 years old I would suspect that, water gets in and can cause bad things to happen, and the splitter really should be one with F connectors on it, not the old beige box crappers that installers used to use. Belling-lee plugs are evil as well. Especially the wire on types. Even a screw on F plug into a F to belling-lee adapter is much better then anything with a little screw to hold the pin on the center wire.

Richard rich.ms

mcraenz

1140 posts

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#129826 10-May-2008 10:44

Yeah I don't really trust the signal stats reported by the BDA drivers. I haven't ruled out a software problem but since the antenna is so old and crusty I think I should replace it so I've got a good starting point.

Which of these would suit best? Also what cable should I be using? The current cable seems to have very little braiding.

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richms

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#129840 10-May-2008 12:16

mcraenz:

Which of these would suit best? Also what cable should I be using? The current cable seems to have very little braiding.

None of those - go to an antenna supplier - http://clayworth.co.nz/ - aweful site but if you call they are helpful and have ok prices - also sell on trademe as antronic1 - I have bought a few things from them.

Cable should be at least RG6 dual shield, some say to use quad shield but thats mainly an issue with cable rather then FTA, since they have concerns about signal egress from it.

Richard rich.ms

kevthesparky

79 posts

Master Geek

#130004 11-May-2008 11:25

Hi if your antenna is 20 yrs old then I would assume your cable is likewise is it RG59?? if so get rid of it I would reccomend Quadshield RG6, Dual shield is good but quad is better as it has better ingress qualities (less chance for interferance). The cable may have to be replaced because if your contacts have been corroded then there has been moisture/water presant at a point where water can trace down through the cable (like water in a straw) and that can give you all sorts of problems. How old is the masthead amp that may be giving you problems. Unfornatually it's going to be a process of elimination and that can take time.

mcraenz

1140 posts

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#130487 13-May-2008 09:15

I've just been looking around the neighborhood and most people seem to have a big 91 element UHF antennas so I think I better get one; my current is antenna is only 43ele.

Looking at the map the Remuera transmitter is much close to me but my current antenna and my neighbours all seem to be pointing at Waiatarua. I guess Waiatarua is much more powerful?

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geekiegeek

2513 posts

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#130723 13-May-2008 21:39

I was having this same issue and it went away after a rebuild - but I have now worked out it wasnt the rebuild that fixed it. The breakup was caused by interference from a Western Digital MyBook USB HDD that I had plugged in. I found this out purely by chance when I plugged it in yesterday to transfer some files - breakups started straight away - unplug the drive breakup goes away.

I also read a post somewhere of a guy who tracked his breakups to a cordless phone causing the interference.

You may want to try switching off everything in your house and unplugging any external devices to see if it is just something interferring with the signal.

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Spyware

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#130743 13-May-2008 23:23

Remuera power is only 9 dBW or 8W which is very very low compared to 52 dBW - 150 kW of Waiatarua.

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mcraenz

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#130768 14-May-2008 07:55

@geekiegeek: Good advice. I tried last night to eliminate all sources of noise bar the PC and the LCD screen, turned off all wireless/network switches, laptops, removed all all usb devices except mouse. But still getting the problem.

The picture mainly beaks up when changing channel. so I started to think well maybe it's not a signal problem maybe it is a software problem But that problem has got worse since I removed the mast head amp. Before I removed the masthead amp I got breakup occasionally when changing channels but now I get it every time.

I have a new theory: When you change channel the TV card graph is rebuilt and the card is re-tuned so could the break up be caused by card taking too long and having trouble getting a lock on the signal because of a poor quality / week signal? I don't really know how DVB-T works.

@spyware: Yeah I guess that's why all my neighbors are pointed at Waiatarua.

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geekiegeek

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#130783 14-May-2008 09:04

Mine does still have a small amount of breakup when changing channel so you could be on to something there. I usually have breakup in the first few seconds of recordings as well.