Technical Note

 

This information relates to the Bundaberg and Maryborough areas where residents have reported poor Digital TV signals and complete loss of some networks.

We make no representations of a commercial nature and offer our advice based on anecdotal evidence.

This page was written when Bundaberg received VHF AND UHF signals and although we don't use UHF any longer, we are leaving the information here for people in areas where they still get both VHF & UHF transmissions.

 

There is a RESOURCE area with links to Documents

“Combi” antenna installation

Bundaberg and Maryborough receive their TV signals from Mt Goonaneman, one of a few transmition towers with Dual Polarity.  Dual Polarity means that the signals are Vertical Polarisation for VHF and they are Horizontal Polarisation for UHF.  For this reason a combination antenna is seen on many homes.

Referred to as a “Combi", it has a larger antenna at the back with Vertical aluminium elements [pointing up and down] and a smaller ‘swordfish’ antenna out the front with Horizontal elements [pointing crossways].

What are my VHF Channels?

MT Goonaneman transmits on VHF for WIN, ABC, TEN , 7Network.

SBS was on UHF but has now changed to VHF as well.

It’s important to have a good ‘receiving antenna’ capable of receiving the full available signal so your TV can then pick out the different channels.

An Antenna with good sensitivity is said to have “gain” and you will see antennas advertised with “xxdB Gain” the higher the gain the better the antenna.

What’s wrong with some installations?

As you drive around town you may see the correct COMBI antennas but they’re not mounted correctly.  If the Antenna is bolted directly to the mast this is a poor installation which causes interference with the incoming VHF signal, resulting inpoor Digital TV reception.

The installation instructions for all new Antennas show the correct mounting method and clearly state that a Stand-off Bracket must be used if you're installing a Vertical antenna. [it's available as an optional extra].

Installers seem to ignore this one line in the instructions and never doubt themselves –but it is important for Digital TV.

Consider your coax & connections

If you have old coax it would be worth upgrading to a quad shielded coax which is less susceptible to interference.

Also take a look at the fittings on the ends of the coax – it’s time to get rid of those old “push-on” fittings and investigate the screw-on “F” connections.

Some installers use Compression Fittings on RG6 Quad Shield Coax Cable. In theory these fittings should work but many can be pulled apart with little or no force.

Crimp Fittings are the best as they are tight and keep the wires separated. Shrink-wrapping the fittings on the outside of your home will shield them from the weather and extend the life of the coax.

So to recap

You need to eliminate the chance of signal degredation inside your house... then place a Vertical Stand-off Bracket between your thick antenna mast and the Antenna.

These 2 things should improve the reception.

If installers don’t believe the packing/installation sheets refer them to the “Radio and Communications Handbook" where all this is repeated.

In our resource area we have a copy of Chapter 16 of the Handbook.

Refer to Pages 16.13  and 16.14 with the Heading  " Yagi Antenna Mounting Arrangements" and refer to  Figures.16.28 (a), (b), (c), (d)  which are Examples of Antenna Mounting.
The Smiley Faces denotes the Correct Mount.

 

CONSIDER - How far do you live from the Transmission Tower?

If you live more than 65-70km [as the crow flies] from your Transmission tower you need to rethink your Antenna design.

Maryborough is close to Mt Goonaneman so the Combi antennas work well there and provided they're installed correctly Maryborough should have good digital TV reception.
Bundaberg is further away and with many outlying regions so many homes will have to consider a different design.

A note about Hervey Bay; They now have their own Translator (Transmitter) which has all Networks on UHF Channels on Ghost Hill and don't have this Dual Polarity problem.

In the resources area there is a BundyBeaches report compiled by the ACMA in February 2012. It shows the varying signal strengths they recorded and this may assist people to determine if where they live is an area of High or Low signal.

There are areas just outside of Bundaberg which suffer a significant loss of signal strength and that means homes in that area will require larger, more sensitive Antennas. People living on the fringe of the signal will require either a 10 Element antenna or a Phased Array antenna.

In the resource area there is a document showing sample phased array antennas. This is a sample only and all Antenna manufacturers provide them. You should read sheets like these and then shop around for suitable antennas for Fringe areas… and most importantly avoid the Yagi and combi Yagi designs.

High trees are another hazard of Rural living and you should try for a clear signal between you and Mt Goonaneman. You might need a 16 Element Colinear antenna for VHF which has a wider angle for reception meaning it's not "directed" at the Mountain the way we direct a Yagi antenna. This Antenna sits broadside to the Mountain and compensate for the longer distance and the hills and trees blocking your signal.

Only you can decide:

If you’re close enough to Mt Goonaneman use a Combi 7 Element Antenna provided it has a 7 Element Vertical VHF Section and an 18 Element UHF section.

If you're in rural areas then you need something better, so consider a 16 Element Colinear for VHF and separate UHF antenna as pictured at the top in this page.

Why not just add a Mast Head Amplifier?

If an installer says you need a Masthead Amplifier ask yourself what it does!

It amplifies the signal that the Antenna has already received! It doesn’t help the antenna get the signal in the first place.

Only a better antenna design can do that.

Amplifiers don’t perform very well when it is raining or in poor weather conditions either, so put up the correct Antenna and in many cases there won’t be a need for a masthead amplifier.

Splitting you TV signal.

If a house has multiple TV sets, you are splitting and lowering the available signal in the house.

Considering buying an Indoor Distribution Amplifier to boost the signal and you can adjust the Gain control on this Indoor Amplifier to suit [a setting of about 10dB adequate].

 

Would you Do it Yourself?

Of course all this climbing ladders and roof installation should only be done by someone fit and capable who understands Work Health and Safety aspects of the job and can take the necessary precautions.

Don't forget to Note the direction your antenna is pointing. Take some bearings, note a tree or neighbours roof. Have some way of knowing the correct direction towards Mt Goonaneman when you put up your new antenna!

And to increase the life of you installation use Lanolin which repels moisture and sunlight. It comes in a pressure pack and is an excellent anti rust and anti oxidization application.

**Remember Safety First!**

**These jobs require getting onto your roof so all safety protocols should be followed**

 

 

Photo - incorrect installation

wrong1

These Antennas are mounted incorrectly!
The UHF Antenna is mounted in between the Vertical Elements of the VHF Antenna.

 

The Element Lengths and the Spacing between them are to a specific formula for best Performance and
placing a metal object in between them (the UHF Antenna) has degraded the whole installation.
There should be a gap of at least 450mm [a 1/4 Wavelength] between from the tip of one antenna to the next.

Both of these Antennas would suffer significant Loss of Signal, enough to cause Pixilation and
if the pixilation builds the TV will lose the signal completly and a "No Signal" message appears on the screen.

Note the Mast Head Amplifier - it will Amplify the Received Signal (with all the Interference)
It doesn't "pick out the good signal" to amplify - it amplifies everything!

 

 

 

ADDITIONAL RESOURCES

In the Documents area we have some reference material which may help readers come to grips with the scientific theory and answer some installation questions

1. A sample technical specifications sheet on Phased Arrays: The link is UHF/VHF Phased array .PDF Document

2. A guide published by the TV Networks: Tips on interference & guide to Wide Bay & Hervey Bay Channels

3. ACMA Signal Reports around Bundaberg Beaches: Compiled February 2012 BundyBeachesDVB.pdf

4. Radio Communications Handbook - Chapter 16: VHF UHF Antennas [File size 2.4mb]

5. A good Reference book: Understanding Digital TV [File size 3.6mb]

Understanding Digital TV is 73page reference, for those who like Technical info.
It covers Design and Characteristics of Digital Transmission with Graphs and explains also how the Digital Signal is measured