UHF Aerials

Main kinds of aerial for UHF.

  1. Small whip. Really vertically polarised and supplied with USB sticks etc. Very poor. Telescopic on handheld TV.
  2. Dipole. usually horizontal but can be used vertical. Marginally
    better than whip. Often inside a plastic box with an amplifier. Can be
    implemented as a plate rather than rod.
  3. Yagi. A Dipole with a Reflector and one to 19 directors. 16 to 19
    directors or a boom length of wavelength x 2.5 is useful maximum size.
    After that stacking is better. For more than four stacked dipoles a dish
    may be better.
  4. Log periodic. Looks like a yagi. But all the elements are dipoles.
    poorer gain and wider band for same boom size as Yagi (but less ghosting
    sometimes).
  5. Array of dipoles on a reflector. Sometimes called Grid or Bowtie
    aerial. Common to have 4 bows or dipoles but poorer dual element are
    available. In theory an 8 element is possible.
  6. Dish and dipole. Dish needs to double in diameter when you halve
    the frequency, so a UHF dish equivalent to MMDS would be 2600/600 = 4
    times diameter or 16 times wind load/ area!
There is no such aerial as a DTT or Digital Aerial.
Aerials are Aerials.
The only defining features are things like gain and band or group.

Outdoor and Attic UHF Aerials

Outdoor aerials can be in the attic or outdoors.

Really all that counts (in order) in comparing UHF aerials

  1. Length of aerial overall. Longer is better. (unless it's a grid array).
  2. Size of rear reflector. Bigger is better
  3. How many "directors" there are. they can be flat strips, rods -- pairs of >  and  <    or  X  shapes.

The Reflector at rear, driven element (dipole, the bit coax connects to)
and directors is the number of Elements. Not the entire number of
spikes or rods as some manufacturers dishonestly count.

They must be chosen for correct group.

Channels 21-37 35-53 48-68 35 -68 39-68 21-68
Aerial Group A B C/D E K W
Cap Colour

Red

Yellow

Green

Brown

Grey

Black

Yagi not recommended for Group W (Wideband). Use a Grid.

Since about 2012 there is a new Wide band aerial that reduces gain above 790MHz (LTE 800 Band). It's not a substitute for an LTE rejection filter which will be needed on many Mast Amps.

Receiving Divis after ASO

Most wide band  aerials work better above the middle of channel range than below it, so after ASO (Analogue Switch Off, 24th October 2012 in N.I. and Ireland) a Group A or Group B is better than K or W for channels below 50. Group B are usable at channels 54 to 60 (limit of digital) and at Channel 53 a Group B is superior to a Group C/D, but C/D, E, K and W are usually poorer than B for 35 to 50. Perhaps someone will make a Group C or B/C aerial.  High gain and Wide Band at same time is impossible on a Yagi.


grids

Wide Band Grid or Bow Tie aerial (shown Horizontal)

A Grid/Bowtie does 7.5dBd (cheap) to 12dBd (best) gain.

Yagi Aerials

SR13WB

Blake SR13  Yagi (Horizontal, may also be used vertical)

I compared Blake 18 element (i.e. Reflector, driven element and 16 directors) with the BIG DX aerials, the Fragile Hershman, Kathrein and Unix 100 etc (Not 100 Elements, closer to 21) The fact is that a pair of 18 Element was more robust, fraction of price and within 1dB of same gain when using quality combiner.

I tested SR18A, B and C/D group aerials.
[url]http://www.blake-uk.com/page/aerial_range/aerial_sr[/url]
WB is 12.5dB
A  is 13dB and of course the C/D is higher gain due to higher frequency is 14.8dB

A Blake 10 element group aerial will be about SAME gain as that so called 48 element wideband that would be wrecked in 1st blow or bird landing.

There has been almost no advance in yagi design since late 1970s. The "modern" and "Digital" style ones are cosmetic marketing and dishonest counting of "elements".

Basically for any well designed Yagi, the "boom length" is the important parameter anyway and at about 2.5 times wavelength any increase has very little increase in performance. Doubling the number of smaller identical aerials however gives about +3dB

So two 14dB aerials = 17dB  (realistic limit for any yagi and 1dB to 2dB more than most)
Four 14dB aerials = 19dB (2dB to 3dB more than any yagi).

My opinion is the  SR10, SR13 or SR18 are the ones to buy. If you are "fringe" or want UK DX reception then use 2x or 4x of the SR18 of correct group stacked at correct spacing.

The "Contract" model Blake is cost reduced version, hence small reflector and poorer interference rejection. 

A grid only does 7.5dBd (cheap rubish model) to 12dBd (best model, peak gain) gain.

A smallest 7 Element Contract Yagi maybe 7dBd to 8dBd Gain

SR series 13 Element yagi about 10dBd to 11dBd

SR series 18 Element about 12.5dBd to 15dBd depending on model and Channel.
http://www.blake-uk.com/sr.aspx
This is the most robust and "proper" yagi. The spiky ones are "Fashion"
http://www.blake-uk.com/dmx.aspx
(Argos, Maplin, B&Q etc less sturdy X styles equivalent would be about 64 to 75 element.

A "100 Element" Yagi is usually really 21 to 25 elements and about 15dBd
JBX21     S&C     A-B-CD-W     104 "eleements"     14.5-15 dBd (21 bays)
Much less robust (Unix100, Triax, Kathrien DX aerials)  http://www.blake-uk.com/jbx.aspx

Having 4 yagis is same principle as 4 x bowties on a Grid (dipoles).

Each time you double the number of aerials, the gain is +3dB more.
Now the coupling to match pair to coax loses signal, but it attenuates the noise too, so a low noise mast amp just after the coupler is best.

The SR series are not "fashionable" but they are best Yagi money buys. Very robust and best gain for you money.

Basic reception

A grid/Bowtie does 7.5dBd (cheap) to 10.8dBd (best) gain.

Blake SR10 = 9dBd to 11dBd depending on Channel

Medium gain
SR13 . 11dBd to 13dBd approx (varies according to channel)

High gain
SR18  12.5dBd to 15dBd depending on channel

DX
2 x SR18 coupled = 15dB to 18dBd equivalent (assuming very low noise mast amp to cancel loss of combiner).

4 x SR18 coupled = 18dBd to 21dBd  equivalent (assuming very low noise mast amp to cancel loss of 3 combiners, combine pairs, then combine combiner).

The Group W or Wide band Yagi are really only nearly wideband at the smallest lowest gain size (poor on Group A). It's not possible to design a wide band medium or high gain yagi. That's what Log periodic is for http://www.blake-uk.com/dml.aspx (note misprint of gain on bottom aerial, it's 6.5dBd probably, not 22dBd)

The Wideband yagi have rapidly dropping gain below Group B (worst at lowest Group A channel) and slowly drooping gain above Group B. They are really "broader" Group B/C aerials so always are poorer than Group Aerial. For High Gain or DX you need a Grouped Aerial (A, B or C/D). If you need more than one group and more than low gain you then need grouped Preamp, helical filters for group/Channels and combiners, especially if you need weak Group A channels.

Stacking /Arrays/Coupled Aerials.

Use two way F-connector splitters for each pair. All coax same length.

http://www.directivesystems.com/STACKING.htm

http://www.iw5edi.com/ham-radio/?stacked-yagi-antennas,90

http://www.i1wqrlinkradio.com/ccarray/click.php?id=26

Combine pairs with a F-Connector splitter as a combiner using equal length cable. Multiples of 1/4 wave reduce impedance mismatch. Take into account velocity factor (i.e. length need is shorter as speed in coax is 80%)

If you need more gain combine two pairs

I've seen up to 32!

Each time you want 3dB more you have to double the number of aerials.

Subtract losses of combiners. 

These are  splitters used as combiner. Cheap ones are about 1dB to 1.5dB (subtract 3dB from splitter quoted loss as 3dB is inherent in splitting signal). Only really expensive ones are 0.5dB loss
(Cheap spiltters http://www.blake-uk.com/page/amplifiers_distribution/proception_protaps )

Indoor UHF Aerials

indoor indoor2 indoor3

Typical Indoor aerials suitable for UHF Analogue or Saorview (Digital Television)

May also be used in loft/attic via extension cable and optional amplifier

(Leftmost model need holder cut to swivel to vertical. A two rod reflector version does swivel fully. Right-most model is wide band).

DIY Aerial for strong signals

See Saortv.info Installing TV aerial


Further Reading

TV Aerial Information with gain curves   and more gain information