wireless microphone

[pantoman]

please can someone please explain the diffrences, ( apart from the obvious ) strengths & weaknesses of UHF V VHF wireless systems

thanks

[djdave]

Hi

 

Just a quick suggestion. You will get more luck if you put the post in the sound section

[cedd]

UHF "scatters" far more easily, it will go through walls, round doors and generally find its way to your receiver easier. VHF is good for line-of-sight and indeed, actually has better range than UHF when used in the right circumstances. (In my day job a 5W transmitter in UHF will communicate with a ground vehicle half a mile away on the other side of the airfield, a 5W VHF set will talk to an aircraft 60 miles away. Obviously a little higher end stuff than we're talking about here, but the waves behave in exactly the same way.

[paulears]

Moderation: As Dave said - you plonked this in lighting, so I've moved it here.

 

I'm not sure which differences you already know - you mention the 'obvious' ones?

 

VHF can be good - just as good as UHF. The trouble was that cheaper systems used to be VHF only, so these channels were congested - quite badly sometimes. You could squeeze in 4/5 channels into the standard slots, with odds and ends available in other slots, if you had the right licence. The expensive systems were UHF with plenty more space. As technology marched on, UHF became as easy to produce and purchase, so everyone goes there now, and the band is busier - but still in the regions, fine.

 

What other things? Well, aerials are smaller, and intermod problems are a bit less troublesome. Feeder loss is a bit higher. I'm sure somebody else will hink of something I've forgoten.

[StevieR]

VHF systems tend to be fixed frequency whereas UHF systems are synthesised and therefore allow the frequency to be changed as required.

[soundo26]

VHF tends to be more unreliable, picks up minicabs' transmissions and as far as I know, the VHF frequencies will be defunct with the DDR switchover when it happens! (not to say that most UHF channels will be too with the way things are going!!).

[Shez]

as far as I know, the VHF frequencies will be defunct with the DDR switchover when it happens!

 

I was under the impression that only the TV channels (i.e. 21 - 69) were affected by the DDR; I don't recall reading anything about the VHF band.

[bruce]

VHF isn't as sexy, is a bit "old fashioned", and tends to be immediately dismissed by people who don't fully understand. After all, the U in UHF stands for Ultra, which is far better than Very, isn't it. :unsure:

 

In practice, a well-designed VHF system will give excellent results, and can often be a good "get-out-of-jail-free" card when you're running short of frequencies.

 

I use both, and would chose my 20-year-old Micron VHF units in preference to most budget UHF units any day.

[paulears]

There is some very odd information here. Some is based on fact, but presented oddly.

The comparison between ground vehicles and aircraft is a good one. I spoke to a bloke in the space shuttle using just a small 1W radio - perfect reception. Aircraft using UHF or VHF is almost line-of-sight, so the comparison with the ground vehicle introduces path loss that gets muddied as we're comparing bands. transmitters for VHF have poor antenna matching - helicals are often used on VHF to offer a reasonable electronic match, but their capture area is lower, so efficiency is poor. UHF systems can if required have more directional aerials with gain - quite handy. You can use 3 or 4 element yagis at VHF but they are big beasts.

 

Synthesised VHF receivers have been around for ages now. Crystal controlled, fixed frequency equipment is quite rare now. VHF systems operate around the same area as PMR - such as minicabs. The Taxi transmit frequency being in the band below the basic VHF channels down at 175MHz. However, taxi transmissions are narrow band FM, not wide band and I have never had PMR breakthrough, even when somebody in the crew operates a transmitter right next to the racks. It's not impossible, but in my experience not really an issue, although the story is told very often.

 

As for DDR - doesn't really impact on VHF at all.

 

UHF, Watt for Watt is more easily absorbed than VHF, but once the poorer antenna efficiency is taken into account, the differences are not really obvious. One of my racks (not quite sure why) has 4 VHF and 4 UHF Trantec receivers in it. (4 x 3500, 4 x 4000) and as the packs look very similar too, some have VHF and some have UHF. As the rack sits on stage in the corner, and is semi-permanently connected, I have no idea which is which - the desk often seems to be labeled 1,2,3,4 and so on - the patching often skewed, so I pfl, hear audio and use it - I'm not bothered (or able to tell) which one is which band.

[Bobbsy]

Ditto to what paulears and Bruce have said. My 20 year old Audio Ltd. RMS 2000 VHF radio mics were still going strong when I sold them prior to moving down under and, despite being non-diversity, gave far few reception problems than UHF. As has been said, UHF is more prone to absorbtion, particularly by...er...overweight actresses. I've also never had a whisper of problems of interference from PMR users. The one tech issue I ever had was when a director presented me with her own VHF system that seemed to killed everything else...a quick check indicated that it seemed to be transmitting on everything from about 174 MHz up to over 200 MHz! Needless to say, this one was binned!

 

The only real drawback is the relatively small number of frequencies available. You're lucky to get more than 3 channels in on the licence free area and it can become pricey to licence the other available frequencies (and even with these there aren't THAT many available).

 

As for the future, I haven't seen any proposals one way or another for the VHF PMSE bandwidth. However, the paranoia in me says that, if all of Channel 69 is given over to licence free, some bright spark might decide to try and take away the VHF bandwidth. It's in an area close to aviation and military frequencies so I daresay there could be a market for it. I hasten to add, this is all speculation on my part and NOT based on any documents I've found.

 

Bob

[cedd]

VHF will also go much further down a length of cable! UHF is very lossy.

 

To be honest, just for the time being, whilst I need and would like some more wireless kit, I'm really holding back until the waters clear a little and we see what's going to happen for sure with the digital switchover. 2013 is not far away. If I buy kit now, it will only be 5 years old when it (potentially) becomes redundant. Certainly to be spending a large amount of money on a racked, multi-reciever system could be folly unless over 5 years you can hire and use it enough for it to make its momey back. If not, let a hire company make the changeover for you and use their kit. Theirs almost certainly will be used enough. Long term plans for the individual might not be cost effective.

 

BUT, This isn't a thread about digital switchover, we have some very in-depth threads on that elsewhere, however, it is an issue to be taken into account in this case I feel.

[soundo26]

Apologies for the earlier misunderstanding, SOME VHF frequencies are being cleared for DAB, here is a section from JFMG's website.......

 

5/10/2006 VHF (209 – 217 MHz) - the story so far.

 

 

 

Since our last news item on VHF spectrum Ofcom has updated the Spectrum Information Sheet which provides further details on the frequencies affected by the implementation of further Digital Audio Broadcasting (DAB) in the UK.

 

We are now able to clarify exactly which frequencies will cease to be available to PMSE after 31 December 2007. Our diagram, available here, illustrates that only frequencies between 211 – 217 MHz will need to vacate the band.

 

We are currently working with Ofcom to determine a channel plan that will provide alternative VHF spectrum for displaced radio microphone users. Further information will be provided as soon as it becomes available.

 

That article was dated October 2006 and may be out of date by now, things keep changing and it's hard to keep up!!!!