Interference from 4G

[Shez]

I had a flyer through my door a few weeks back warning of possible interference from new 4G services to my Freeview reception. My aerial points to Birmingham so I've never been able to pick up Leicester services well; I've not noticed any significant issues so far though.

 

The flyer offered to send out a free filter to fix any problems. Presumably that just low-passes at ~700MHz. It did make me wonder about radio mics in ch.70 however. Has anyone experienced any issues yet?

[pete10uk]

I also received a flyer and a couple of Days later a filter turned up even though I hadn't requested one, I don't seem to be having any issues with freeview.

 

The filter is a channel 59 filter and has branding on it "at 800"

 

Not sure if all areas are the same but I'm in sheffield.

[daifuse]

I had a flyer through my door a few weeks back warning of possible interference from new 4G services to my Freeview reception. My aerial points to Birmingham so I've never been able to pick up Leicester services well; I've not noticed any significant issues so far though.

 

The flyer offered to send out a free filter to fix any problems. Presumably that just low-passes at ~700MHz. It did make me wonder about radio mics in ch.70 however. Has anyone experienced any issues yet?

 

Called in my friendly aerial man a while ago, thought there must be something amiss with the aerial/feeder on the roof. It seems that local freeview reception on BBC channels in particular has been intermittently affected (pixellation, freezing) by in-band interference from somewhere - either 4G or something else - investigations on-going. Many others around here are also affected.

[dbuckley]

Bit of a farce really. There is some mob set up to manage interference problems and hand out filters, of which they have bought a shed load, and the threatened problems have not materialised....

[pete10uk]

The whole frequency management seems to be a bit of a farce. A bit like buying back loads of radio mic equipment from licence abiding companies and then selling it back to the general public for a knocked down price.

 

It really does make you wonder who is the brains behind these ideas.

[cedd]

Not had problems with Channel 70, but I've had trouble with channel 38. Our local repeater has a multiplex on channel 39 and it causes no end of trouble. Before I had the benefit of a spectrum analyser I was pulling my hair out (those who know me will realise I haven't got much to lose!) at why I was getting poor RF performance. Drop outs, splats and generally misbehaviour. It was only in 2 venues and I eventually put it down to the structure of the buildings (RSJ's in the walls next to my aerial positions maybe). Then I did a couple of city centre venues in much bigger theatres and just didn't have a problem.

 

It was only then that we discovered we had some pretty hefty transmissions right above out radio mics.

 

Here's a poor photo of the spectrum analyser screen. Initially it looks like the interference is cutting in to the top of channel 38 (614MHz) but a check with a better spectrum analyser reveals that it's actually safely within channel 39.

http://i513.photobucket.com/albums/t335/ceddison/Yeadon%20Interference/42276E57-0E36-47AD-B1B4-15CF60957C24-18962-00001E7410EFC860_zps6d0817eb.jpg

This is taken right outside the theatre, so the spikes on the left are actually our radio mics. The square section in the middle is the offending tv mast, and the spike on the right is from a different TV mast (Emley Moor) and was something I included in the span as a known reference whilst interference hunting (I originally thought my interference was another signal from the same mast, so in theory if it had been, the RF levels of both would have tracked pretty closely).

 

Not much you can do about it. Get your aerials nearer and make sure that the signal your radio mic receivers see significantly more of is your mics. Channel specific, directional aerials and where possible remove as much gain as you can from the system (aerial amps etc. - they amplify noise a well as wanted signals).

Somebody out there really needs to make some very tight radio mic channel specific filters. They'd have to be active to get a tight enough slope, or very large barrels! Even then I think channel 38 and 39 are a bit close for it to work. I tried cutting a quarter wave stub filter but it just isn't tight enough.

[peza2010]

Im in leicester and have had Lots of issues with freeview for the past fortnight. normally I dont have any issues whatsoever but atm I cant watch tv. hopefully this is the issue however I didnt get a flyer.

[dosxuk]

Im in leicester and have had Lots of issues with freeview for the past fortnight. normally I dont have any issues whatsoever but atm I cant watch tv. hopefully this is the issue however I didnt get a flyer.

 

Unlikely. The offending 4G transmissions haven't started up yet, apart from in a few trial areas (and I don't think Leicester was one of them).

[paulears]

For years, living on the east coast, UHF radio propagation used to go berserk in the summer months, with a phenomena called troposheric ducting wiping out our old TV channels and replacing them with Dutch ones. The previous summers haven't been very hot, so it's only been an occasional issue - but now a few locals are complaining that they keep losing the pictures - and I'm wondering if it's this rather than 4G that's the issue here. The North Sea with it's damp, humid air makes these ducts quite easy to form given the correct combination of temperature and humidity - and very often it the land breaks it up and the dutch stuff that entered the duct, kind of hops out, with signal strengths that make them seem very local.

[peza2010]

Strange as my network operator for my mobile also text me telling me signal would be poor for a while with 4g. pressumably unrelated in that case.

[dosxuk]

Strange as my network operator for my mobile also text me telling me signal would be poor for a while with 4g. pressumably unrelated in that case.

 

That would suggest you have a contract with EE - their 4G transmissions are running, but on a different band, up in the 2-3GHz range.

[peza2010]

Strange as my network operator for my mobile also text me telling me signal would be poor for a while with 4g. pressumably unrelated in that case.

 

That would suggest you have a contract with EE - their 4G transmissions are running, but on a different band, up in the 2-3GHz range.

 

im actually with three. who certainly are not rolling out 4g yet as far as im aware. it has to be said that despite the warning text I havent noticed any problems.

[richardash1981]

For years, living on the east coast, UHF radio propagation used to go berserk in the summer months, with a phenomena called troposheric ducting wiping out our old TV channels and replacing them with Dutch ones. The previous summers haven't been very hot, so it's only been an occasional issue - but now a few locals are complaining that they keep losing the pictures - and I'm wondering if it's this rather than 4G that's the issue here.

Certainly had a lot of ducting a couple of weeks back - other UHF band users were reporting significant problems with this across eastern England. So at the moment could well be ducting issues, although I'm sure that 4G will make itself felt in due course (given the transmitter powers they are using in urban areas). Thank goodness for S3500 systems!

[audiomik]

ran a couple of 'basic tests' last evening to assess the potential for Co-Channel interference to Ch-70 Radio Mics from within the former Ch-69 allocation, now to be rolled out for 4G Mobile phones.

 

Wasn't able to assess signals from Mobile Base Stations as they aren't enabled here yet, but using a suitable RF Signal Generator set to a Frequency towards the top of the former Ch-69 allocation, Co-Channel Interference from this source occurred well before an attenuated signal from the Radio Mic transmitter was 'lost' by the Receiver.

 

Monitoring kit used included

An HP141T+8554B+85542B Spectrum Analyser, with an Anritsu MH648A wideband amplifier, (to monitor the signal applied to the antenna socket of the Mic RX)

HP 83310A Modulation Domain Analyser, (to monitor the RF output of the Mic TX)

HP 8657B RF Generator, (to provide the 'Interfering' signal)

Variously: Attenuators, signal combiner, etc

None of this kit is currently in calibration so absolute measurements aren't really valid, but had an indication of relative signal levels etc.

The setup combined both the Mic TX and RF Generator outputs (attenuated) into the Mic RX and provided indications of what was happening.

 

Didn't have time to set up a Distortion test for the Audio signal between the Mic-Tx and Rx which may degrade earlier than loss of the 'wanted' signal.

 

Agreed with owner of the Radio-Mic kit not to declare it's type until a response has been received from the manufacturer

 

Conclusion must be that the likelihood of Mobile Handset Interference could be the greater issue than Base Stations perhaps?

 

hope this adds to the discussions in this thread

Mik

[paulears]

The base stations aren't in this band - so the mobile handsets will indeed be the snag. Sennheiser predicted this quite a while ago. Probably worse case is when the nearest base station is not that local, because the outputs will ramp up, and the filtering in them is the first thing to go as production gears up and there's a need to cut costs. Not going to be nice!