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ageorge

626 posts

Ultimate Geek


#115157 15-Mar-2013 17:00
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Hi our locality is Waihi Beach where I have historically installed Satellite DVB-S dish instead of UHF as its a patchy/fringe area for Te Aroha or Kopukairua/Tauranga, and not recommended for terrestrial TV reception.
The difference between DVB-T and DVB-S picture is huge. Once you have seen good terrestrial TV its likely like me, you wont be happy with Satellite. So my problem, bad Terrestrial signal area, how to fix?

I have a satellite meter, but no UHF meter, so the option I took was to initially set a Phased Array to horizontal polarisation for Te Aroha, on a wandering coax with extension pole which I move around the house outside. At one point all DVB-T 23 channels were received in great quality which indicated that the mounting apex on roof (much higher and clearer position) should improve it more. I also had the addition of a masthead amp to help cable length dropout.
TIP While analog is still available, this medium is the best to align the aerial for best signal; tune to Maori or Prime which are analog UHF (analog ending 2013). EG set your TV to scan for Analog and use one channel for your aerial alignment.

This Phased Array is quote 'Suitable for tree lined areas and undulating terrain Channels (21-69)'
Using a 1.5m extension aluminium boom & couple of U clamps, I mounted it to the old Satellite dish roof mount.
The Te Aroha picture was abysmal. I thought it might be a lead problem then eventually traced to o/c balun.
Unlike vhf which is a transformer balun, Phased Array uhf has inductive capacitive balun appearing as o/c to a meter, WHICH IS CORRECT!
There was no fault in wiring so I changed the aerial to vertical polarisation and pointed it at Kopukairua.
TV scanned 13 channels which indicated signal levels still patchy. I then installed a Masthead amp and this brought in all 23 channels, but still a little patchy on anything but 1/2/3. Then fitted a much longer pole giving a 2m height increase and the signal deteriorated!

Being pedantic, I purchased a 92 element yagi.  This Yagi aerial had claimed slightly better gain and different performance than the phased array. I removed and replaced the Phased Array by this aerial at the top of the mast. It was by default in horizontal polarization so pointed it at Te Aroha (with masthead amp). No channels at all. Changed polarity to vertical and pointed Tauranga, got 11 channels but nil on 1,2,3. Even tried feeding both aerials to the masthead amp but it was worse than single phased array system which I am now back to using. Comment - the Yagi balun had low impedance output.


We have power lines running across the road in an already fringe area. 100m away another phased array gets perfect reception on Te Aroha all channels so I guess I may be back to Satellite unless I can borrow a UHF meter to double-check the whole roof of this residence.

Summary
In my opinion, Phased array is a superior aerial than the best Yagi in our location. Also, the Yagi is cumbersome and much greater wind resistance than the tidy Phased Array. Aerial prices very similar around $60-$90 with masthead amp around $70-$90




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chris48
10 posts

Wannabe Geek


  #805698 26-Apr-2013 07:58
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Hi

I have similar issues working from waiatarua at Ruakaka about 120 km from the transmitter. A few points that might help..
1. When you are receiving UHF by diffraction, which is probably your case, the signal can be very localised. A quarter wave can make all the difference. Try your earlier location again. Higher is not always better. I have found best signal points as low as a metre from the ground.
2. Commercial aerials are optimised for gain at the top end of the band. Freeview HD is at the low to mid channels. This can make a few dB difference, enough to fall over the precipice. Try making your own, or search for one optimised for band 4 only.
3. Because of point 1, a phased array is often better as it has more resilience to the variation over short distances vertically.
4. It is important to have a very low noise preamplifier. Many are poor in that respect. Check the specs and get one with a nf less than 2db. If necessary, source from the UK. This is the most important part of your setup.
5. Expect variations. Wind churn across ridges between you and the transmitter can drop the signal several dB.
6. Try a stb instead of your inbuilt tuner. Some have much better receivers.

Good luck

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