1.8Ghz Wireless - Anyone usingT this frequency?

[jpinewoods]

I am looking at adding some Senheisser G3 systems to our hire stock and wondered whether purchasing some in the 1.8Ghz band would be an interesting alternative to standard Channel 38. It should be possible to run up to 12 additional channels here and according to my latest Ofcom licence the requirement for a separate licence for each location has been lifted, making it a true viable alternative to Channel 38.

 

Has anyone had any experience in using 1.8Ghz and can share any issues?

[david.elsbury]

Isn't that frequency shared with DECT cordless phones?

[jpinewoods]

Isn't that frequency shared with DECT cordless phones?

 

I think DECT is 1.9Ghz in the UK.

[laolu]

Yes - right - and... cordless phones are mostly used at home and in offices, while wireless mics are mainly used on stage etc. Also their number is probably decreasing, since everybody and their uncles have cell phones nowadays. A bigger problem seems to me the 2.4 GHz band, which is much more congested with wireless mics, IEMs, WiFi and so on. If I had to buy, I' d go with the 1.8 GHz. No matter which band we use, a scan beforehand for a free channel seems to be inevitable. Edited August 3, 2015 by laolu

[paulears]

Scanning is a pointless and hit and miss method, I never use it. All it does is show you a channel is vacant NOW. It wrecks your intermod performance and makes multi channel operation unreliable. If you have one channel, then scanning plonks you somewhere with no thought as to why. For the scan to be useful, you need loads of channels in operation, so it finds a gap - which may well be one to help somebody else with intermod, not a real clear channel. Scanning is a blunt tool and as far as I'm concerned, pointless and potentially dangerous.

[Shez]

I presume Paul is a referring to the kind of scan that some radio mic systems can do in order to automatically allocate frequencies, which I agree isn't a good idea.

To my mind however, a scan would mean using an RF scanner to see what traffic is about before manually picking frequencies - it still only shows the situation "now" but involves some intelligence in selecting frequencies.

[paulears]

The only really meaningful tool is a spectrum analyser - which are not that dear any longer. Scanners only really work with strong signals on the centre frequency - not the low level spurious stuff that causes the problems.

[Shez]

My bad - must use the correct terminology. I use the RF Explorer - seemed to be the best and most economical option when I bought it. Nice bit of kit.

[mackerr]

My bad - must use the correct terminology. I use the RF Explorer - seemed to be the best and most economical option when I bought it. Nice bit of kit.

 

I think as far as this discussion, the difference between a scanner and a spectrum analyzer is the speed of the scan. Scanning with the actual mic receiver takes 5-10 seconds, scanning wideband with a TTi can take as much as 10 seconds, same with RF Explorer. Scanning with a R&S FSH8 takes a small fraction of a second allowing it to display intermittent signals that would be missed by the others. We still call the TTI, RF Explorer, and the R&S spectrum analyzers although with as much as a 10s scan time the lower priced devices are not really "real time".

 

Scanning (analyzing) to know what the local RF conditions are is critical to creating a successful band plan, but the other half of creating the plan is determining a relatively intermodulation free frequency allocation. It is impossible to achieve zero intermodulation, but we want it to be of a low enough level and far enough away from the frequencies of our wireless mics, comms and IEMs to not cause interference or desensitize the input of the receivers. These calculations are fairly easy with the software we have available today. Shure Wireless Workbench 6, and Sennheiser Wireless System Manager are both free, and both Windows and MacOS compatible, Professional Wireless Systems IAS is fairly expensive, but is widely used on events with very high wireless device counts. I have coordinated events with close to 200 frequencies between mics, comms, and IEMs with IAS.

 

Intermod software can't do the whole job without knowing the local RF landscape, and knowing the local RF landscape doesn't give you an intermod free frequency set. It takes both, and then testing your system buy turning off one transmitter at a time and checking the receivers for stray RF to assure that your plan is working.

 

Mac

[OddSocks]

What would worry me about the GHz ranges is the complete line of sight that they have.

 

I recently went back to rc car racing and got a nice new 2.4Ghz control and was shocked at how easy it was for the car to loose the connection.

[Shez]

It's really not that much of an issue. I regularly run half a dozen L6 mics on 2.4GHz without any troubles, under several layers of clothes and with the receivers at FoH, even in the presence of WiFi base stations. The range isn't quite as far as G3s on CH.38 but still perfectly usable. Not all such mics are made equal though.

[Simon Lyall]

The concern about any RF is going to be twofold: Is there any congestion, and what's it's dispersion. Higher frequencies are not going to penetrate masses as far (like bodies, walls etc) and as such are a bit more 'line of sight'... and that must be considered. In terms of congestion: are the other RF sources predictable? Will it work in rehearsal, but when you fill the room with audience with 2.4GHz wifi (the number of people constantly running their phone as a hotspot always surprises me). What uses 1.8GHz? Dect phones, (less common) but also increasingly I've noticed micro-controller type systems that use them for short range comms...

 

About 5 years or so, at a PLASA I was chatting to someone from Sennheiser about wireless microphones. I was asking about whether they thought they were ever going to go down the digital route (as an Electronic Engineering student at the time, I was learning about the technology that made it possible). I was musing on the possibility of more channels in a given bandwidth, better coping with noisey RF situations etc. I was shot down and laughed at by the man... and told in no uncertain terms that Sennheiser would never go digital, and always be analogue, as digital would never give a good enough audio quality.

 

Funny that.

[laolu]

Maybe we should enlighten the major producers of wireless mics about the pointless and dangerous feature they install into their products? Haha, only joking. :P

BTW, the scanning with a spectrum analyser (Rhode & Schwarz, Tektronix etc. or the really handy RF explorer) also just shows the actual RF traffic (the "NOW"), which, doesn't help any, when the show is running (unless you're really quick in changing frequencies).

Audio Technica brought out a system, I think 2 years ago it was, that seems to do just that: The "System 10". It continuously scans a given frequency range and automatically switches to another channel on both receiver and transmitter, if there is any interference. According to the specs, it does that without any audible delay or artifacts. Agreed, it is a simple setup for smaller events, maybe not exactly for the big stage, but the idea is attractive. Also works in 2.4 GHz and - if the distance isn't too big - even works with a wall between.

 

Norbert

[henny]

I keep meaning to buy a cheep usb SDR off ebay to use as a spectrum analyzer

 

https://www.youtube.com/watch?v=51JC6pbcpaE

[paulears]

I wouldn't bother. They have loads of spurious emissions that mask many of the frequencies you want to listen to, so as an analyser tool, I'd imagine much of what you would see would be internally generated? I bought one and was pretty disappointed. The rf preamp is as wide as a barn door and appears to have very little filtering.