Freeview UHF reception problems in Spreydon, Christchurch.

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Skolink

1081 posts

Uber Geek

#113406 16-Jan-2013 10:04

Hi, Just wondering if anyone else in Spreydon (or elsewhere in Christchurch) has had Freeview UHF reception problems since mid October 2012.

We have had Freeview UHF since TiVoHD first came (3 years ago?) and reception has been perfect. Suddenly in mid October 2012 we got reception problems. It was most evenings, and occasionally during the day. It affected all three muxes, but Mediaworks was the worst.

I found out that my workmate who lives 540m away (as crow flies) had exactly the same problem - perfect reception for years then suddenly mid October got breakup in the evenings.

I have been able to mostly eliminate the issue at our house by removing all the VHF elements from our combination areial. The last few days we have seen more breakup on the TVNZ mux (only on shows recorded in the evening).

I remembered I had a VHF attenuator which I gave to my workmate, and that seems to have solved his reception issues. He has a UHF medium gain antenna (straight elements, with corner reflector).

I have found out that my neighbour across the road has also had issues, and had Ascot TV come and fix the problem by fitting a filter (I haven't inspected it yet). She has a 'Gizmo' compact VHF/UHF antenna.

I believe the issue is something on the UHF band which has only been broadcasting (or emitting) since October. I can't think of anything that has changed locally, other than perhaps the Barrington Mall expansion. Could be refrigeration equipment.
The time of day is interesting, kind of implies it could be HAM radio.

We also have an analog TV recorder (TiVo Series 1). Before I removed the VHF elements from the aerial I recorded shows on the analog recorder at the same time as shows on the Freeview UHF recorder. Unfortunately I couldn't see any obvious interference on the analog shows, when there was breakup on the digital shows.

I have a complaint open with Radio Spectrum Management, and I am keen to hear from anyone else with a similar story to us.

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367 posts

Ultimate Geek

#745555 16-Jan-2013 10:56

I'm over in St Albans and since they reshuffled the frequencies have had those sorts of random problems. Mainly on TV One. Tivo would even loose signal all together at times. If I used the tuner in the tv it would be fine. Last time it happened I re-tuned the TV (I had never done this since the change as it was working fine) and my problem on the Tivo disappeared. Don't know why but it worked for me.

Skolink

1081 posts

Uber Geek

#745593 16-Jan-2013 11:29

I retuned both the TiVoHD and the TV (which is not normally connected to the aerial) in July 2012 when the restacking was done. There were no reception problems at all.

I should also mentioned that the TV exhibited the same picture breakup as the TiVoHD. My neighbour and workmate do not have TiVo (or any other DVB-T recording device).

jim.cox

224 posts

Master Geek

#745601 16-Jan-2013 11:38

Our place is just a bit too far under the hill to get Freeview on UHF - so cant comment there

But recently I have been experiencing break-up on some FM radio channels which are also broadcast from the Sugar Loaf transmitter

I wonder if something is amiss up the hill

=mjc=
.

nickb800

2719 posts

Uber Geek

Trusted

#745605 16-Jan-2013 11:41

It seems pretty clear from your experience that the Tivo (and many other tuners) doesn't like VHF signals, and this is backed up by other threads.

Sounds like tuning into frequencies closer to VHF (the lower UHF ones after restacking) is resulting in more VHF interference. If this is the case, this problem should be gone by April, when the analog switchoff is complete in Canterbury

Skolink

1081 posts

Uber Geek

#745615 16-Jan-2013 11:49

nickb800: Sounds like tuning into frequencies closer to VHF (the lower UHF ones after restacking) is resulting in more VHF interference. If this is the case, this problem should be gone by April, when the analog switchoff is complete in Canterbury

No, reception was perfect after the restacking (24 July) until mid October.

It is possible there have been changes made to other UHF transmissions in October. However the guy from RSM was not aware of any changes to Sugerloaf transmitters. It could be something on the nearby Marleys Hill (where the police radio equipment etc is).

Also, I contacted Mediaworks and they confirmed no changes were made to their transmission equipment in October.

Again I will point out that it generally only happens in the evening, but not every evening. It is also not weather dependant, it happens in clear weather, dry weather (eg dry norwester) and wet weather. If it were an analog TV signal causing the interference it would be more consistent.

Skolink

1081 posts

Uber Geek

#759279 11-Feb-2013 07:15

A week ago the guy from RSM came with his signal analyser. Surprisingly it seems the main issue is signal strength.

The TVWorks mux was approximately 44dBµV, which is apperently only just above the threshold for reception (the 'digital cliff'). The signals were stronger as the frequency increased, with TVNZ a bit stronger, then Kordia the strongest (around 49dBµV). Igloo had a very low signal strength (and is on a lower frequency then TVWorks).

Even though I have removed all the VHF elements from the aerial, the analog channels were still up around 60dBµV.

The other issue visiable on the equipment was the shape of the signal, it should look rectangular, but the upper side was sloping off. Igloo was a mess with a big notch in the middle. Apparently this can be caused by reflected signal.

It was a windy day, and the signal was fluctuating, which implied that the trees between the aerial and antenna are in fact causing significant signal loss.

I then bypassed the 6 way splitter in the roof, which should have given an 8-10dB increase in signal. Unfortuntately we still got picture breakup over the last week.

Next things to try wil be to shift the aerial to a different position along the roof. I'll also try lowering the aerial right down to roof level to eliminate refections off the roof.

So why was it fine for 2-3 years and now not? Perhaps the trees had a growth spurt, and during Oct 2012 were heavy with sap which aparently is a factor in how much they atenuate signals.
What about my workmate's reception - he says there are no trees between him and the hill?
And the neighbour across the road?

Aerial - sans VHF elements

view from far end of roof

Goosey

2832 posts

Uber Geek

Subscriber

#759318 11-Feb-2013 09:16

Is the mall in the same path of your LOS to the Loaf?
Quite a rather large steel roof there now?
Also back in October I can recall the wastewater repairs/ upgrades around sparks road commenced.... those huge pumps/generators and they are still working their way through your area (but then that would mean everyone would be complaining).

Sharesies

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Goosey

2832 posts

Uber Geek

Subscriber

#759319 11-Feb-2013 09:17

Off Topic... this is my 500th Post !

Skolink

1081 posts

Uber Geek

#759407 11-Feb-2013 12:12

Gooseybhai: Quite a rather large steel roof there now?

Good point! The extension is exactly in the path. The signal analyser indicated the main reflection was 15m away, but as the RSM guy said it could be another building further away (but it would have to be huge I said). Hmm...

Gooseybhai: Also back in October I can recall the wastewater repairs/ upgrades around sparks road commenced.... those huge pumps/generators and they are still working their way through your area (but then that would mean everyone would be complaining).

None of that work going on in our area (yet).

B1GGLZ

1961 posts

Uber Geek

#759437 11-Feb-2013 12:51

Had you thought about trying a UHF only antenna.
The one in the pictures doesn't look very suitable.
If it was a composite VHF/UHF with the VHF elements removed it may not be suitable as still got the combiner network in circuit.
New UHF and new co-ax may work wonders.
However I have similar line of site to you here in Auckland with full signal strength and I've noticed several times over the summer we've had pixellation and dropouts early evening. One program recorded on the PC was totally unwatchable. I suspect sometimes it's at the transmission end and not the receiving end.

Skolink

1081 posts

Uber Geek

#759517 11-Feb-2013 14:20

The VHF was combined with the UHF signal externally by means of straps/bars from a VHF element to the dipole. The connector box contains only a balun circuit. I'm wondering if I should also have removed the reflector element behind the dipole.

Prior to modifying the antenna, I did try a new UHF aerial, but it was an awful one from Jaycar so not a good comparison.

The cable is only 5 years old, Sky approved RG6 twinsheild.

Hopefully someone like Matchmaster (formally Lincrad) in Christchurch, or Tennatron in Motueka will make a narrow band antenna for Freeview|UHF which should solve a lot of problems.

B1GGLZ

1961 posts

Uber Geek

#759535 11-Feb-2013 14:42

Skolink: The connector box contains only a balun circuit. I'm wondering if I should also have removed the reflector element behind the dipole.

Prior to modifying the antenna, I did try a new UHF aerial, but it was an awful one from Jaycar so not a good comparison.

The cable is only 5 years old, Sky approved RG6 twinsheild.

OK.
I'd remove the reflector dipole too as it will affect the UHF.

That's the antenna I have (from Jaycar) and it works perfectly. Been up in the Auckland salty air for 5 years now.

Your co-ax should be fine.

Maybe this one from Freeview Shop may be better.
http://www.freeviewshop.co.nz/medium-phased-array-aerial-for-freeview-hd.html

Skolink

1081 posts

Uber Geek

#759610 11-Feb-2013 16:16

B1GGLZ:
Skolink: Prior to modifying the antenna, I did try a new UHF aerial, but it was an awful one from Jaycar so not a good comparison.

That's the antenna I have (from Jaycar) and it works perfectly. Been up in the Auckland salty air for 5 years now.

How did you assemble the thing? Of the 4 staff in the shop, noone know how to assemble it properly. The coax clashes with the reflector grid bracket. Also the dipole sites well below the director elements, rather than inline as one might expect. The F-Type connector broke off one the first one I tried. The second one had worse results than the combination VHF/UHF antenna (which I have now modified).

B1GGLZ:
Maybe this one from Freeview Shop may be better.
http://www.freeviewshop.co.nz/medium-phased-array-aerial-for-freeview-hd.html

While it might solve refelction problems, the gain is too low. Perhaps the Large Phased Array would be suitable though.

B1GGLZ

1961 posts

Uber Geek

#759632 11-Feb-2013 17:06

Yeah. Just had a close look at the Jaycar picture vs my antenna. That was the first one I had and was a pig to assemble. I broke the balun circuit board and had to fix it. The elements just click into place on the boom though they are rather a tight fit.
I think I fed the co-ax throught the mesh reflector. Most of these types don't have the main element very much in line with the other elements. Doesn't seem to matter much. Replaced it when the rust and corrosion took over.
My current one is very similar and came I think from Bunnings and was much better to assemble and had a much better folded dipole main element.

You don't need much gain where you are as you can virtually see the transmitter.
The phased arrays are better for obstacles and reflections as they have a wider capture pattern.
Either one would be worth a try.

Spyware

3762 posts

Uber Geek

Lifetime subscriber

#759668 11-Feb-2013 17:54

You'll probably find that your issue is resolved simply by shifting your current antenna. An antenna installer has a meter of course so is the best person to do a site survey and advise. Otherwise its all just guess work.

Spark Max Fibre using Mikrotik CCR1009-8G-1S-1S+, CRS125-24G-1S, Unifi UAP, U6-Pro, UAP-AC-M-Pro, Apple TV 4K (2022), Apple TV 4K (2017), iPad Air 1st gen, iPad Air 4th gen, iPhone 13, SkyNZ3151 (the white box). If it doesn't move then it's data cabled.

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