DECT Phone causing interference to satellite TV reception.

[Robbo]

This thread wasn't about getting a fuzzy picture, and no-one said that a DECT phone would cause a fuzzy picture. So whether its fuzzy or not, is not relevant.

Hysteresis in digital circuitry will generally prevent a digital bit being neither a 0 or a 1 anyway.

[TheCoder]

Originally Posted by Robbo

This thread wasn't about getting a fuzzy picture, and no-one said that a DECT phone would cause a fuzzy picture. So whether its fuzzy or not, is not relevant.

Hysteresis in digital circuitry will generally prevent a digital bit being neither a 0 or a 1 anyway.

To be fair you didn't really mention the type of interference one way or the other but being a signal interference problem I assumed the most likely affect to be analogue in nature as, for the reasons i've explained, purely digital interference is unlikely.

Yes, your initial example could occur (1892Mhz) but what would the result be of mixing two fundamentally different modulation methods and basic bit rates ?

The answer is probably not a lot. It should be simplicity with even simple digital signal processing techniques (of which both box and phone will have) to recover both signals fully intact

I suppose its possible you could worsen a situation where reception is marginal in the first place. If the digital signal is already producing lots of errors then it may just push the recovery system beyond its ability to recover and you end up with those little green squares.......

Originally Posted by pedro2000uk

are you a programmer .. ?

Of a sort, I design embedded systems including satellite receivers (although not recently - mainly in the analog days).

[Robbo]

With the interference on the IF, (which it is), two different modulation schemes are not mixed. The DVB carrier is on a particular frequency, the interfering carrier (DECT) is on or very near the same frequency, but within the bandwidth of the front end circuitry.

It is fundamental that in order for a system to work, the modulated carrier received must have sufficient SNR and low enough BER for the information to be received clearly. With another signal being received at the same time of sufficient amplitude relative to the wanted signal, it just isn't going to happen.

There really isn't an argument on this. And can easily be proven by practical means, try it. (Eg with a DVB-T from an aerial, a combiner, and the output of an old VHS recorder with the channel set to the same as the DVB-T carrier). With an adjustable attenuator on one of the inputs, whilst monitoring using a spectrum analyser,(and a DVB-T receiver) you would be able to see the point at which the DVB-T transmission fails.

No systems are immune from this, except those that are specifically designed to withstand narrowband interference such as spread spectrum techniques like those used in some 3G/4G mobile phone networks.

EDIT, no need to prove it, its already been done, with the jamming of satellite uplinks or downlinks.

http://www.techwatch.co.uk/2010/03/2...llite-jamming/

[pedro2000uk]

Originally Posted by TheCoder

.............

Of a sort, I design embedded systems including satellite receivers (although not recently - mainly in the analog days).

I was ... and I had the same point of view as you -- then we started to notice sonething ... better HD or not... not low detail blockies or unresolved blocks but lower res or safter versus sharper etc... ... & I had to get the the bottom of it...

way too busy atm .. (footy manana.. etc.. )

great subject! ... but .. just figure out how you would save £s by programming naughty shortcuts in processing .. but still stick HD on it......

[gary44uk]

came across this forum while searching for this problem.
i have this issue also. thought would just add to it.
always had this issue since having sky years ago.
had numerous boxes and phones with same effect.
i do have a long run from dish at front of house which runs just about right around the house (3 bed semi) about 18m run.
recently changed to a freesat system.
so old coax has been replaced (thought this would had been main cause as was old coax put in 7 years ago by sky) with twin WF100. got panny TV and panny hdd recorder. so good quality equipment (cost enough!)
1.phone only cuts out the channels with a lower signal.
2. its the TV / recorder that it effects and is not being picked up through the coax run. after a lot of trial and error, if u stand in front of tv, its ok. so u block the signal from phone. if coax was at fault this would not effect it.
3. got a twin tuner so used twin WF100. one coax feed gives a slighlty stronger signal and is not effected even through the runs are same lenght same route? (tried swiching lnb feeds and other things to come to conclusion that it is the coax only)

just something got to live with as seems no real solution except select right coax feed or switch off phone) (unless keep replacing coax till get a run with better signal)

[Robbo]

OK, I had forgotton about this thread, but did come across it occurring a few weeks ago. Problem was exhibited when tuning to Tiny Pop which is on one of the transponders that is affected.

I replaced both cables coming from dish with wf100 with no wall plates etc, and problem was cured. Originally customer had wf65 cable fed to wall plates in property. Signal quality was high, but picture on screen was heavily pixelated.

[pedro2000uk]

Originally Posted by gary44uk

........

i have this issue also. thought would just add to it.
always had this issue since having sky years ago.
had numerous boxes and phones with same effect.

Which channels

What brand of DECT phone is it & makes you have had in the past that have done it.

Where's the dish & where does it aim in relation to the DECT phone and what is in it's view (BT overhead telephone lines &/or a street pole with lots of them all coming together, a mobile phone mast, a substation, trees, aerial/s, street lamps, a factory,any building with aerials on it or machinery in it etc...

Noise issues are quite a big science - one answer is if the dish is either badly aligned, has a poor LNB or LNB/dish match, is aiming past the dect phone &/or is being compromised in other or related ways that can exaggerate DECT phone interference issues.