DVB-T Comparison Phased Array VS Yagi in fringe area reception

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ageorge

419 posts

Ultimate Geek

#115157 15-Mar-2013 17:00

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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255 posts

Ultimate Geek

#782394 15-Mar-2013 17:15

Thanks for your comments.

I too am in a fringe area and use a 92 element yagi like the one showing in the photo.

I do not have a balun installed. Should I and what type, or is the balun incorporated in the aerial?

Obsequious hypocrite

ageorge

419 posts

Ultimate Geek

#782395 15-Mar-2013 17:20

I would expect your aerial will include a balun which has a F-type Female outlet. EG using F-male you plug coax directly in.

Yagis work well for many, in fact there are more yagis up here at Waihi Beach than Phased Arrays. But they are much more directional and prone to object interference than my preferred Phased Array.

Note the purchase of a UHF masthead amp will be a big help if your cable is longer than 5 metres.

bfginger

1116 posts

Uber Geek

#782554 16-Mar-2013 00:05

If a standard aerial isn't enough you could look at getting something much more sensitive like a parabolic UHF
http://www.rocketroberts.com/cm4251/cm4251.htm

This is the only one I can find sold locally. There isn't much demand for real fringe reception aerials in NZ as most people would just use satellite.
http://www.paceelectronics.co.nz/products.php?product=Engel-an6111-parabolic-uhf-antenna-active-%2835db%29
http://www.dtvs.co.nz/index.php?main_page=product_info&cPath=3&products_id=85

Skolink

1081 posts

Uber Geek

#782576 16-Mar-2013 08:14

Thanks for the informative post. Could it be that when using the masthead amp with the Yagi it is being overloaded by the analog UHF signals, hence no reception?

Deev8

481 posts

Ultimate Geek

#782639 16-Mar-2013 12:23

You might be interested in the British website http://www.aerialsandtv.com/aerials.html
It has a lot of good information on selecting the appropriate aerials and installing them to get the best signal. There is some transmitter-specific information on the site which doesn't help us, but most of the information is basic stuff that applies everywhere.

Skolink

1081 posts

Uber Geek

#782687 16-Mar-2013 14:24

Deev8: You might be interested in the British website http://www.aerialsandtv.com/aerials.html
It has a lot of good information on selecting the appropriate aerials and installing them to get the best signal. There is some transmitter-specific information on the site which doesn't help us, but most of the information is basic stuff that applies everywhere.

What a fantastic website! It has made me realise that removing all the VHF elements from my aerial is not the same as a UHF yagi, as someone had already suggested.

Every TV aerial I have ever seen for sale in New Zealand is wideband, does anyone know where a Group B antenna can be purchased?

mm1352000

1148 posts

Uber Geek

Trusted

#782707 16-Mar-2013 15:46

Skolink: ...does anyone know where a Group B antenna can be purchased?

Just a thought: considering that the spectrum allocated for DTV use is currently 502...694 MHz I would have thought a combined group A + B would be the best choice (if you can get one). At present Freeview in your location is 562..602 MHz, but World TV and Igloo are down at 530..554 MHz depending on transmitter. So the mid A range may be just as useful/necessary.

Skolink

1081 posts

Uber Geek

#782712 16-Mar-2013 16:07

mm1352000:
Skolink: ...does anyone know where a Group B antenna can be purchased?

Just a thought: considering that the spectrum allocated for DTV use is currently 502...694 MHz I would have thought a combined group A + B would be the best choice (if you can get one). At present Freeview in your location is 562..602 MHz, but World TV and Igloo are down at 530..554 MHz depending on transmitter. So the mid A range may be just as useful/necessary.

You are quite right, Group A, or perhaps Group K would be much more appropriate than Group B

Apsattv

1680 posts

Uber Geek

Subscriber

#782713 16-Mar-2013 16:13

It looks like you have at least half a meter of cable from the phased array antenna down the mast to the masthead amp. Try mounting the masthead much closer. It looks like it could bolt on the back side of the antenna and cut the cable length down to a few inches.

Apsattv

1680 posts

Uber Geek

Subscriber

#782715 16-Mar-2013 16:17

another thing if you mount the yagi vertically you really need to use a stand off side arm otherwise you have the mount pole interfearing.

B1GGLZ

1960 posts

Uber Geek

#782721 16-Mar-2013 17:15

Apsattv: another thing if you mount the yagi vertically you really need to use a stand off side arm otherwise you have the mount pole interfearing.

I don't think so.
With UHF antennae the mount pole is normally behind the reflector and doesn't interfere with the elements.

Apsattv

1680 posts

Uber Geek

Subscriber

#782725 16-Mar-2013 17:35

With small UHF antennas yes the Ubolt is usually clamped on the end. But with a 91 element mounted vertically, you can see in the image the mounting pole clearly is in line with the antenna elements. They are not usually mounted like that as it will effect the antenna performance

B1GGLZ

1960 posts

Uber Geek

#782768 16-Mar-2013 20:17

Apsattv: With small UHF antennas yes the Ubolt is usually clamped on the end. But with a 91 element mounted vertically, you can see in the image the mounting pole clearly is in line with the antenna elements. They are not usually mounted like that as it will effect the antenna performance

Sorry, misread your post and thought you were referring to the phased array.
You are quite correct. The larger yagis when in vertical polarisation should be on a stand-off mount.

illicit

553 posts

Ultimate Geek

#783385 18-Mar-2013 12:28

The 91 Yagi has a stand off built in.... its in the pic above.

ageorge

419 posts

Ultimate Geek

#783405 18-Mar-2013 13:06

Since we have finally received rain - yeh! its been a test of the aerial over the extreme distance to Tauranga from here. There has been sometimes significant rain fade but it still comes back to needing just a bit more gain would sort it.
I notice that there is another version of the phased array sold in NZ which has a couple of directors in front of each array. This could give an added amount of gain I dont know, but anyone considering buying one of this type of aerial that model may be worth purchasing. Matchmaster distribute both makes.

Im still hoping to get a loan of a decent signal strength meter which will enable me to find the best spot on our roof which is not always the apex I have found in the past.

Yes, the 91 EL does come with standoff. The stacked picture above was a last desperate attempt at combining the output of both aerials to improve the signal. As earlier mentioned, the Yagi was tried unsuccessfully in both horizontal and vertical polarization and mounted correctly. Note that the yagi is cumbersome compared to the tidy phased array.

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