interferance on bbc2 analogue

[moosegoose]

hi ive noticed some interference on bbc 2 some static and general snowy. at times saturation. we have a signal strength of 70 dbvu and cn 42. so there no prob there. there is no ghosting or co channel interferance. last night i manually tuned the tv to c 55 on uhf spectrum which is bbc2 on tacolnston transmitter in norfolk. and then fine tuned down to c 54 where i found another bbc2 at 39dbvu cn 13. i have checked all the uk transmitters and only found two in london 120 miles away on a vertical pol. is there a way to determin where the signal is coming from. as there are no reginal variations on bbc2. and the teletext wont work.any ideas many thanks in advance.

 

[Analoguesat]

Atmospheric pressure is very high at the moment to ducting could be carrying the signals a very long way.

The only BBC2 services I can find on C54 are Cane Hill near Croydon and Forest Row near Tunbridge Wells.


Cane Hill has: BBC1 - 61 / BBC2 - 54 / ITV - 58 / C4 - 68

Forest Row has: BBC1 - 48 / BBC2 - 54 / ITV - 62 / C4 - 66

so see if you can see any of the others.

 

[PaulR]

If there's no ghostly picture showing then it's probably interference from a digital signal. This gives the symptom exactly as you describe - what looks like a loss in signal on your normal analogue channel.

 

[moosegoose]

ok checked the uhf analogue and i found the norwich central transmitter which is at the bottom end of the band. also found a extra bbc1 on channel 51 which isright next door to c5 on 52. i checked it out when the local news came on and it was bbc east. and i see there is one on the sudbury transmitter which broadcast our local channels. none of the channels u listed were present just bbc2 on c54. i will have to check the digital on sudbry to see if there any conflicts. many thanks

 

[rolfw]

You have given no details of the system, whether it is communal, or a private residence, whether this is a meter reading straight from the aerial, or the signal on a system linked through a video.

 

[satelliteman]

It's most likely Co-Channel Interference seen all over the country many times around this time of the year. We have had Crystal Palace with over 60dBuV in the Midlands before now

Lots of other things can cause the same symptoms of course.

 

[moosegoose]

hi it is a private residential. Not strait from the aerial IT go through a maxiview 1 in 4 out distribution amp. but not being looped through anything video freeview sky ect. U are probably right about the co channel interferance. I might try a more directional aerial and attenuating the signal a bit. and may be replace the trusty maxiview distribution amp. cheers any way.

 

[satelliteman]

My suggestion would be to also change over the distribution amplifier to one with a mid-stage gain control. Try to avoid amplifiers with front end attenuators on fixed gain amps as they will crush the C/N as you turn the att level.

A more directional aerial will help of course, X type etc.

If the signals off air are to high then attenuate them prior to the amplifier and then you can control the levels with the amplifier.

Remember the window of operation for Analogue terrestrial signals at the outlet are 60dBuV - 80dBuV and 45dBuV - 70dBuV for DVB-T

SM