band III aerials

Galway

Anyone know where I can get a wideband 8, 10, 11 or 12 element VHF band 3 aerial? Preferable by mail order in Ireland. Or someone in the galway area. Dealers only seem to have those useless 3 or 4 element ones and want me to buy a VHF amp for €70!

thanks

byte

This is the only Irish site I could see selling VHF aerials. It has 7.5dB gain, though not sure if that's enough for you!

Other than that, I guess you try ordering direct from aerial suppliers. I suggest Anthony Tully Components though I don't have the phone number offhand at the moment.

Galway

thanks but thats a log periodic one and doesnt have enough gain - seems pricy too. If you come across that phone number Id be grateful.

Mike 1972

Dont have a spec on this one but
http://www.antiference.co.uk/outdoor.htm

LP7 Band III Aerial

Tuned to Band III VHF
Suitable for VHF TV in Ireland and Europe
Balanced performance accross Band
Compact and easy to assemble
Suitable for fringe DAB reception

And at the risk of stating the obvious dont use a booster with a crap aerial

You could also try some of the following links

http://www.televes.com
http://www.hirschmann.de
http://www.triax.dk
http://www.antiference.co.uk
http://www.maxview.ltd.uk
http://www.blake-aerials.co.uk
http://www.maplin.co.uk
http://www.cpc.co.uk
http://www.aerial-techniques.com
http://www.taylorbros.co.uk
http://www.diy.com/
http://www.anas.worldonline.es/ronsmith/main.htm

Galway

Thanks but I dont want a log periodic - not adequate gain really.

If you can find that phone number Id be grateful.

Thanks. It seems hard to get anything over the 4 element ones now which is ridiculous.

byte

Sorry, I forgot about it today, I will look tomorrow!

watty

Electrical Factors in Limerick have non-log Yagi.

But a higher gain Yagi can give less gain than a Logperiodic!

A Yagi, especailly the more elements you add gets narrower band to a single channel.

A Logperiodic does a whole band, with simlar gain on each channel


The ONLY wideband for Band III are Logperiodic.

The > 8 element yagi are by defintion NOT wideband

Galway

hey thanks I will be in Limerick over the weekend, Can you tell me the adddress and phone number of the place please.

Galway

Anyone know where I can get a wideband 8, 10, 11 or 12 element VHF band 3 aerial? Preferable by mail order in Ireland. Or someone in the galway area. Dealers only seem to have those useless 3 or 4 element ones and want me to buy a VHF amp for €70!

thanks

byte

PM on its way Galway

Also, try McGrath Components @ 094 31470. He's based in Mayo and may have what you're looking for.

watty

Electrical Factors are on Ballysimon Rd Crossagalla Ind Est.

Since they are really trade (but will take anyones money) they arn't open at weekends.

061-412403
Fax:061-417057

Ask for Bernedette and say Mike that buys lots of plastic boxes and aerial stuff recommended them.

I got a nice Band III yagi I cut up for something else there.
Also a very nice Televis VHF /UHF mast amp much cheaper than €70 (But I didn't buy the PSU as I have lots of those). Don't forget for a mast head amp you need a special PSU with aerial in/out at the bottom end of the feed cable.
But you knew that anyway.

Galway

Thanks I found that out last week - where they are and that they were closed on Sat! It is really close to where a friend of mine lives - he did not know and had to ask his mother's partner!

Do they stock all types of aerials? I need to improve my FM radio reception. Any advice? I have that circular aerial but are useless for gain so they say. Will the Televés vhf/uhf amp take a standard 12 v dc psu?

Mike 1972

For an article about FM aerials

Do a google search on "outdoor FM aerials why bother"

Most FM tuners and mini/midi systems have an input at the back for an FM aerial yet - despite the fact that few people would be content with an indoor aerial for TV reception - most people (even radio enthusiasts) seem content to either jam a piece of wire in the socket or use a cheap "rabbits ears" type aerial stuck down behind the tuner. Many (particularly National) broadcasters seem to encourage this practice by sticking large numbers of high power relays on all over the place ostensibly to fill in reception blackspots but in practice so that they can be heard even on cruddy insensitive radios.

Benefits of an outdoor aerial
The most obvious one is greater choice. You’ll be able to hear all those weaker stations (pirate and legal) and in many parts of the country some cross-border or cross-channel stations as well, with a lot less interference from computers etc or fading as you walk around the room. Plus, when there’s nothing worth listening to on your local station you’ll be able (in most places) to hear stations from neighbouring counties with reasonable reception

Other benefits
Another benefit of an outdoor aerial (particularly a directional multielement type) is freedom from multipath interference. Multipath affects higher audio frequencies and is particularly noticeable when listening in stereo. It manifests itself as a swishing noise and in severe cases causes increased distortion (something akin to what you hear when your radio isn’t tuned in to the station exactly). Often when people hear multipath effects they blame it on a lack of signal strength and look for another station but, in fact, multipath can cause noise, distortion and poor stereo separation on even the strongest stations. Ironically the more expensive your radio the more noticeable multipath interference becomes. What sounds fine on a cheap mono kitchen portable can be unlistenable on a stereo HiFi separate tuner (switching to mono can help but this rather defeats the purpose)

What causes multipath?

As its name suggests multipath is caused by signals reaching your aerial by more than one path. The main path directly from the stations transmitter to your aerial and one or more secondary paths through the signal bouncing off objects such as hills, buildings, trees, vehicles, cranes etc (and with an indoor aerial internal walls, metalwork and even people). Multipath signals are often almost as strong as the main signal but arrive at your aerial slightly later than the main signal. While this in itself doesn’t cause any problem, timing and phase differences can result in some frequency components of the FM signal being strengthened (pre-emphasised) and others weakened (de-emphasised). The resultant non-linearity causes increased noise and distortion which affects the higher audio frequencies including stereo and (where applicable) SCA subcarriers particularly badly

How does an outdoor aerial help reduce multipath effects?
1) By being outdoors the aerial is not going to be affected by reflected signals from objects inside your house.
2) As it will (usually) be mounted fairly high up, reflections from nearby objects on the ground (e.g. vehicles) won't reach the aerial or, if they do, will be arriving at an angle off the main lobe and will therefore be attenuated somewhat.
3) By having a clearer, less obstructed line of sight to the transmitter, the main signal should now be stronger than the reflected signals and so the signal should not be as badly affected by multipath.
4) Many outdoor aerials are of the directional (multielement) type and by virtue of their enhanced sensitivity in the direction of the wanted station, multipath signals from other directions won't affect reception as much, although even a non-directional (omnidirectional) dipole will have some benefits over an indoor aerial
Even a small reduction (3-5dB) in multipath signal results in bringing major benefits to audio quality due to a phenomenon in FM tuners known as "capture effect" whereby signals that are weaker than the wanted signal are (almost) completely ignored by the receiver

Polarisation Horizontal or Vertical?
A topic which still causes lot of confusion when discussing aerials is polarisation - whether aerials should be mounted horizontally or vertically.
In the early days (1950s) of FM radio it was found that when the signal was transmitted with horizontal polarisation it seemed to be much less severely affected by vehicle ignition interference. Those were the days when there were very few portable, or in-car, receivers so nobody ever bothered dealing with the problem of ignition interference at source.
However by the 1970s, with transistors having almost completely replaced valves and radios appearing in cars, vehicle manufacturers started paying attention to the problem of engine interference (no point having a car radio if all you can hear is the noise off the spark plugs) and most radio listening was now being done on portable radios with small telescopic aerials which 'pointed up the way' (i.e. vertically).
Suddenly Horizontal polarisation didn’t make much sense anymore and broadcasters started reverting to either mixed (Horizontal and Vertical), or pure vertically, polarised signals. Nevertheless, old habits die hard and many aerial installers and even manufacturers still insist that FM aerials should be mounted horizontally (the fact that most TV transmitters use horizontal polorisation adds to the confusion).
In a very small number of cases (where a station one wants to hear is using mixed polorisation and there is interference from one using vertical polorisation) it makes sense to use a horizontally mounted aerial but, 99% of the time, aerials should be mounted vertically.

Cables
Two factors have to be taken into account when choosing coaxial cable - namely loss (attenuation) and screening.
Many of the cheap cables sold in hardware shops have very poor screening. This means that signal leaks out and they can also pick up lots of electrical noise and computer interference. Worst of all in this regard is that cheap white flexible stuff that you see cheap flyleads and extension leads made from. At VHF frequencies loss (measured in dB per metre) usually isn't too much of a problem unless you're diplexing UHF TV signals into the same downlead (which is perfectly acceptable provided the cable is in good condition and good quality diplexers are used at each end) or using a very long run of cable (which you should try and avoid if possible).

Other cable hints
Try and avoid kinks and sharp bends in cables.
If you are running lengths of cable outdoors put clips or fasteners (although not TOO tight) on at regular intervals. If a cable is allowed to flop around loose in the wind eventually water will get in and destroy it
Try and minimise splits and joins on cables but, where this is unavoidable, always use good quality connectors and accessories (especially on outdoor sections of cable) and (although it might seem to be stating the obvious) any fittings devices connections made outdoors must be weatherproof
Never allow water to seep into coaxial cable. Even the smallest amount of water will make its way through the whole length of the cable causing corrosion and massive signal leakage.

So what type of aerial should I use

First off, avoid those "halo" circular type aerials (left). They're horizontally polorised and, while they're still better than an indoor aerial, a vertical dipole (right) will give better results for less money.

A (Vertically polarised) dipole aerial (Antiference "Radio Rod")
TV aerials (especially UHF types) tend to perform poorly at FM frequencies. VHF TV aerials are a little better but what you really want is an aerial designed for FM (VHF band 2) radio For most people a single element vertical dipole (such as the antiference "radio rod") is an ideal choice being cheap (about £15,) easy to install (well within the capability of most DIY'ers who have access to a ladder), and are omnidirectional (will pick up stations equally well from all directions). Those wanting something a little better might go for a 2 (H or X type) or 3 element yagi which will offer a little more gain and multipath rejection for one's favourite stations while still retaining the ability to receive signals from other directions pretty well.
In weak signal areas, where all the stations you want to hear are coming from approximately the same direction, you might want to stretch to a larger aerial of between 4 and 9 elements. If you are interested in stations from several directions and have plenty of money you can invest in a device called a rotator although finding someone who can install such an aerial system can be difficult). But if you are seeking the ultimate (and have unlimited financial reserves and plenty of space and tolerant neighbours ) you can go for a massive 18-32 element system.

Does it HAVE to go on the roof?
Ideally, it should but in practice, if roof access is a problem you can mount it high on an outside wall (you can get special brackets for this) or in an attic.

Is it a good idea to use an aerial preamplifier ("booster")?
If you live anywhere within 15 miles of a transmitter (and if you live in a large city you probably do) the answer is probably no. What usually happens is that strong signals overload the booster and, either by themselves or mixed with other signals, appear on strange frequencies all over the FM band interfering with weaker stations - which rather defeats the purpose. Also, if you’re using a booster to make up for a poor aerial, you’re probably just amplifying signals that are riddled with multipath distortion in the first place. The foregoing also applies to those "amplified indoor aerials" one sees in shops as well.

byte

Can you provide a link to the source, please?

From google, I thought it was http://www.radiowaves.fm/technical/OutdoorAerials.shtml but all i get is a 404 error.

Mike 1972

It was hosted on radiowaves but not anymore

Google have a cache of it do a search on "outdoor fm artials why bother"

byte

Ah i see it now! I was looking for an image of the radio rod, though but to no avail.

Mike 1972

http://www.maplin.co.uk/images/catalog/pictures-all/ModuleImages/873i0.jpg

gives a picture of a radio rod (Its just an outdoor vertically polorised FM dipole)

http://www.maplin.co.uk/products/module.asp?CartID=030614184025852&moduleno=873&modulecode=

watty

The almost circular / halo aerials are for UK horizontal or slant polarisation. VHF Radio here is mostly vertical so they won't work.

I think EF do VHF Radio aerials too.

So do homebase (but overpriced and just a dipole).

byte

Originally posted by watty
The almost circular / halo aerials are for UK horizontal or slant polarisation. VHF Radio here is mostly vertical so they won't work.

Well, I was considering something to improve my reception of BBC Radio (from Brougher, I think), so I'd imagine that one of those halo's (like Antiference Allrounder) would be suitable for this!

lawhec

A "Halo" aerial is only of use if you live in an area where all the stations you want broadcast have a strong horizontal polarisation ERP. In the UK this isn't much of a problem. But some halo aerials even have a "loss" of signal rather than no gain (0db) at all.

In the Republic, the only RTÉ transmitters that use mixed polarisation are at Kippure, Three Rock and at Holywell Hill. There were plans for Clermot Carn to be mixed polarity but these were quietly dropped. The only independents that use mixed polarisation (so I'm told) are Wired FM in Limerick and Red FM Cork.

For Brougher Mountain, a halo might be suitable for the BBC Services only, but if you want to pick up Downtown and Q101 as well, you would be better off with a vertical dipole as DTR and Q use the full allocated power for their vertical transmitting plane (5kW), but only use low power on their horizontal transmitting plane (3.2kW for DTR, 1.5 kW for Q)

watty

Yes I agree, a regular dipole at right angles to transmitter direction for horizontal or a 1/4wave or 5/8ths wave vertical will work better than a halo as the halo does have negative gain being omnidirectional.

There are omni aerials with gain, because they "squash" the vertical giving a "doughnut" omni response rather than the near "sphere" of a halo. These are usually "colinear arrays" and are expensive. The higher the gain of a "colinear" type omni, the less reception toward the sky and ground (doughnut squashed to discus shape) it has. They only work for vertical polarisation.


The only virtues of a halo is that for a Slant(mixed) or horizontal polarisation you don't need to know which direction the transmitter is and will thus work on a minibus etc.

But of course a whip or 1/4wave or 5/8ths wave, or vertically orintateded dipole also work in all directions with Slant (mixed) or Vertical polarisation with more gain than a Halo.

This is why since VHF-FM became common for portable in late 70s vertical polarisation is more popular. Some of the old UK Tx sites date back to 1950s and thus used horizontal as over longer distances to fixed receivers with external aerials it was believed to be better (than recieving on a whip with vertical).