Which High Gain Antenna To Use Within A Uhf Sfn?

[Theres Always Radio]

The objective of any installation is to get the most reliable highest quality signal for the customer. When this objective occurs within an SFN, the choice of antenna becomes more important since the process avoiding the unwanted transmitters results in better quality signals, the best way to do this is with a higher gain antenna.

Ideally the highest gain antenna (within reason) should be installed within an SFN and this more capable antenna is used not for it's gain but rather for its increased directivity.

Then the next choice is to use a yagi or phased array and does it really make that much difference? In my case on the Gold Coast it may. Here in this SFN we have two transmitting horizontally, Tamborine and Springbrook and one vertically Currumbin, just to make the choice more interesting.

The standard 4 bay phased array when set up horizontally polarised it has horizontal directivity as broad as a barn door but its vertical directivity is quite narrow. When its set vertically polarised it's horizontal directivity is now quite narrow and its vertical directivity quite broad. The Yagi on the other hand is the reverse, when set up horizontally polarised it has excellent horizontal directivity and broad vertical directivity, alternately when vertically polarised it has broad horizontal directivity and good vertical directivity.

In the case where Currumbin is the desired transmitter, a vertically polarised phased array will better reject signals coming in from the side than a vertically polarised Yagi. If Tamborine is the desired transmitter then a horizontally polarised yagi will better reject Springbrook and Currumbin and the same applies where Springbrook is the transmitter of choice.

If this is accepted, this means that the best antenna in an SFN where all transmitters are horizontally polarised is the yagi and for an all vertically polarised services in an SFN, the 4 bay phased array is the one to choose.

For those within an SFN, I think it would be interesting to know if you are coming to similar conclusions to myself or have some other ways of achieving good results. Looking forward to hearing your experiences in this area.

Cheers

James

[wahroonga farm]

Good work as always James.

A crude picture is worth a thousand words.

Note: A 4 dipole hoizontally polarised phased array typically has a useful vertical arperture of 25deg and a horizontal arperture of 45 deg.

Whilst I don't have access to an SFN, your observations are supported both by my practical experience and basic antenna theory.

The cones demonstrate the antennas radiation patterns (approximated) 3db points, in three dimensions.

But remember gain is still gain and a 4 di-pole phased array max's out at 13dB. And gain is good

[alanh]

James,

Thanks for comfirming what I have written in Antenna Design Basics + Amplification, Terms and comparison of types

AlanH

[Theres Always Radio]

AlanH

I would appreciate you not making any inference that I may be confirming anything you have ever copied and pasted into your posts please.

James

[dig2all]

ouch!

[damntv]

Very interesting

[alanh]

James,

None of the information in my antenna posts is copied and pasted. It is original work.

I past links rather than paste the work of others, so they can get credit for their work, and they can tell their story.

AlanH

[Theres Always Radio]

Reply withdrawn.

[wahroonga farm]

Back to the topic (minus Alan's ego), it is very odd to me, that with the exception of the phased array (Wisi E006), our beloved antenna manufacturers provide very limited if any beam specifications, and certainly none for the opposite polarity.

So it's very difficult to apply science to the problem ..... just more antenna waving from many inept installers.

Here's wot happens with antenna stacking. Graphics courtesy of Laceys.com.au. Stacking follows the same principles of a phased array.