Radio Equipment

[Dave_NA]

We are looking at purchasing some radio equipment but we are not sure which frequency to use. UHF or VHF.

 

We work indoor and outdoor venues, and I am aware that VHF is better for outdoor use, however when working at places like the NEC I am led to believe that UHF would be better.

 

What frequency range would people suggest to get the best out of both but only using one set.

 

Cheers

[Nicktaylor]

Just out of interest, why do you say VHF is better outside. This is news to me!

[Tomo]

It's not really a case of "better", more like "less bad"

 

When running radio inside a metal box (which is what most venues come down to), the higher the frequency the better* as you'll get fewer and smaller "dead spots".

 

Outside of the metal box, it makes very little difference so the cheaper VHF equipment could be more cost-effective.

 

Which is why the house robots (on a UHF band) on Robot Wars had almost no radio problems, but the competitors (on 40MHz) often did.

 

(*Up to a point - many parts of the GHz bands are absorbed by components of the atmosphere which limits the range to around 10m)

[Dave_NA]

We are looking at purchasing some radio equipment but we are not sure which frequency to use. UHF or VHF.

 

We work indoor and outdoor venues, and I am aware that VHF is better for outdoor use, however when working at places like the NEC I am led to believe that UHF would be better.

 

What frequency range would people suggest to get the best out of both but only using one set.

 

Cheers

I was always led to believe that VHF is better outside as it would give you a better range. Forgive me if I am wrong, but that is why I am posting on here to get the facts.

[Tomo]

Signal power is the greatest determinant of range.

Both VHF and UHF are essentially line-of-sight, and will give almost identical ranges at the kind of power you'll find in a normal radio beltpack.

 

You'll only see significant differences in range when you are transmitting at tens of watts of radiated power - basically, TV antenna and amateur radio, where VHF does have a longer range.

[Ellis]

The biggest advantage of UHF over VHF is channel availability. This used to be out-weighed by the additional cost of UHF electronics, but that has been negated by developments driven by the mobile phone industry.

 

This is partly due to the propagation losses at higher frequencies and partly because more people want VHF because it is better for longer range communications, low-band being better than high-band (Amateur Radio and the police have the allocations between these). Since the signals travel further, fewer people can share a given frequency by geographical separation. (i.e. more users & less slots)

 

As the frequency increases, a given frequency can be shared by more people by geographical separation.

 

To illustrate this, a radio amateur using a frequency in the 1.8-2Mhz amateur band may well be heard all over the globe, so only one user can use that frequency. A signal from mobile telephone cell on 1700/1800 Mhz will only travel a few miles, so operators can use the same frequencies on many cells across the country.

 

A good example of geographical sharing breaking down is when the Azores High extends over the UK in October in some years terrestrial television suffers from co-channel interference due to a phenomenon called "Tropospheric Tunnelling".

 

HTH

 

Ellis

G7SAI

[paulears]

Woah guys.

 

Let's not get into propagation issues. Radio transmission on HF bands has a whole different set of issues surrounding it. Please don't open that one up!

 

In real terms if we consider radio microphones, then the critical issues are freedom for co-channel interference - other users mostly. You hear great tales about taxis, police and the fire brigade, but these are largely chinese whispers stuff - rare in my experience. With radio microphones we're talking about low power devices, with aerial systems jammed up against a hot sweaty bag of water (as in us!) Receiver aerials are usually stuck in places where they too perform badly. VHF systems have a longer wavelength meaning that efficient aerials are physically larger. In practice, we use more compact versions that don't work so well. Some transmitter packs use a dangly 1/4 wavelength aerial - about 40cms would be great, but thats a bit too long, so they get cut down a bit. This loses some efficiency - not as much energy gets away from the person wearing it. On top of this the cable often gets shoved into pockets or just gets squashed up, making it even worse. VHF kit can have a helical aerial - a longer length wound on a spiral. Electrically great, but perfomance suffers again. Look at the receive aerial. normally just a short rod type - these things need either another element going the other way, or a large ground plane to be efficient. So sticking one out of a tiny box doesn't make for an efficient aerial either. So we've got VHF - low power with both aerial systems compromised. Moving to UHF, then the 1/4 wavelength aerial is just a short piece of wire about 8-9 cm long. The receive aerials can be the short rod type, or better efficiency dipoles, but still compact in size. For dodgy venues, directional aerials with effective gain can be used. Add the fact that the UHF band is much larger, has more channels available with the correct licence means less chance of unwanted stuff getting in the way of good reception. Problems can always arise, but the benefits of UHF have relegated VHF to poor cousin now that the cost of electronics has dropped.

 

 

So UHF has more brownie points - BUT VHF has still got fans. UHF does have a few drawbacks, it tends to get attenuated more easily for one, but the benefits gained by better aerial system design and stable electronics make it a winner for most of us.

[soundo26]

just a word of warning..........the current frequencies will soon be changing in the period 2007-2012, so be aware of buying now. search for JFMG for info