Occasional picture interference - on 2 installations

[jeallen01]

We seem to have been concentrating somewhat on the possibility of there being "something new in the local environment", but here's another thought: What if the EMI suppression on an existing unit has failed?

The mate that had had boiler interference later said to me that there had been a "bang" from his amp (and so he switched it off!). When I opened it up, I found that a contact suppression capacitor across the internal mains switch contacts had simply melted (and smoked a bit!) - so I simply snipped the capacitor leads and removed it, and the amp worked fine after that ( and without any reports of a new source of interference in the house!) .

 

[Captain Jack]

Grmblwd: *takes the entire boiler apart*
Wife: What are you doing?!
Grmblwd: Trying to fix the telly!

 

[Grmblwd]

I have checked the cables for continuity and all of them are OK.
I did wonder if the Humax boxes were at fault, but seems unlikely they would have a fault at the same time.
My neighbour had a heat pump installed about 18 months ago and that is about 60 meters away, with large stone walls between us. He also has an old tractor but that has never given any interference. I remember the television having a dotted line across the screen and crackling years ago when an old car that wasn't suppressed went past the house in the UK. (maybe 60 years ago.)
Birds do rest on the arm of the dish, but I rush out to see if they are there and of course they are not.
As suggested it may be an airborne thing I'll have to put up with.

 

[Satspot]

Possibly the most logical thing to do is get your hands on an alternative receiver, a loan possibly and connect it up and see if you experience similar behaviour. That would help to rule out/in problems with the Humax boxes. After that, as already suggested do a fresh run of cable from the LNB to one of the Humax receivers.

 

[Grmblwd]

Thanks for all the suggestions, I don't have access to an alternative receiver, but will ask around.
Thanks again.

 

[jeallen01]

.... I remember the television having a dotted line across the screen and crackling years ago when an old car that wasn't suppressed went past the house in the UK. (maybe 60 years ago.)
'''

About 40 yrs ago, I had a couple of Amstrad 5000 tuner amps (bought very cheaply from the local Currys!) and every time a local taxi cab drove past, I got the taxi radio breaking through very clearly on one of those (presumed to be via the 10.7MHz IF) - never bothered to try to fix the problem, or had similar problems with any other audio equipment.

OTOH, also had a problem with intermittent cracking on the audio equipment that I tracked down to a fridge thermostat - dealt with that by fitting mains transient-suppression components to the power input to the whole audio system.

Was working for HP (UK) at the time and we had a "problem" with a particular range of (I think) frequency generators where the internal power supply crowbar protection ccts tripped permanently the first time any such unit was plugged in on a particular MoD site. That site turned out to have a particularly high single-phase mains voltage, which regularly ran higher that the level to which the US design division had tested it, and that, + the regular high transients, tripped the crowbars. I had carefully chosen varistors fitted to the input circuits of all the units, and we never had similar problems again (and the US division learnt a hard lesson about the need for wider mains voltage-range design & testing!) .

 

[Channel Hopper]

We seem to have been concentrating somewhat on the possibility of there being "something new in the local environment", but here's another thought: What if the EMI suppression on an existing unit has failed?

The mate that had had boiler interference later said to me that there had been a "bang" from his amp (and so he switched it off!). When I opened it up, I found that a contact suppression capacitor across the internal mains switch contacts had simply melted (and smoked a bit!) - so I simply snipped the capacitor leads and removed it, and the amp worked fine after that ( and without any reports of a new source of interference in the house!) .

Yes, works well with many white goods, though the manufacturer's claim it increases RF interference.

There may be a reason to reduce 'i' , or inductive surge on a motor device, but I've not found anything substantial yet with the two Watt meters here through the whole cycle of dish washers or washing machines.

 

[jeallen01]

Yes, works well with many white goods, though the manufacturer's claim it increases RF interference.

There may be a reason to reduce 'i' , or inductive surge on a motor device, but I've not found anything substantial yet with the two Watt meters here through the whole cycle of dish washers or washing machines.

Incoming spikes and, probably inductive surges (which would be relatively a lot slower) from small domestic appliance motors, are very fast (a few uS or mS) and so you'd need a metering device that reacts much faster than a typical wattmeter to "see" them!

Typically (having done quite a bit of this when running kit through CE marking EM immunity certification tests!) you use a specialised hi-spec radio receiver (from the likes of Rhode & Schwarz, etc.) together with a specialised matching network between the mains source (also to a specific set of impedance/frequency characteristics) and the EUT, with the feed to the receiver tapped off from that network. The results are either recorded within the receiver or fed to an external recorder, whilst at the same time very carefully monitoring/recording the performance of the unit against a set of acceptable performance characteristics as defined by the manufacturer to determine the effects, if any, of the incoming interference spikes or surges.

The incoming spikes and surges differ considerably and are generated by different types of (very expensive!) waveform generators to internationally standardised and repeatable waveforms/timimgs.

All of the above are intended to allow realistic and repeatable assessments and comparisons of measurements made in differing test labs around the World!

By comparison, a typical "wattmeter" is designed to average (or read the RMS value of) the current & voltage (and thus power) passing through its measuring circuits to give a realistic reading of the power consumption of the EUT in a "typical" operating environment - and if it didn't have some sort of averaging/RMS function then you wouldn't be able to get useful results because the needle or display would typically be "flying all over the place"!

I think that should help to explain that the measurements made by, and perceptable effects noted by, a typical "wattmeter" in a "typical" operating environment are not really comparable (nor are they intended to be!) with the results obtained under controlled test laboratory conditions - and that's certainly very true for immunity testing because it often identifies performance effects/defects that are not perceptable to the "human brain" (&/or a "wattmeter").

As a result, dedicated immunity testing can identify potential performance shortfalls/glitches that cannot be identified, or even observed, using a "wattmeter", but nevertheless can/will affect the performance of kit (especially sensitive electronic kit like sat receivers) in day-to-day service. It can also help to determine if a domestic appliance is susceptible to incoming spikes/surges - after all, you wouldn't want your washing machine to run your woolens through a long high temp "cotton" programme when you'd set it to a short low temp "woolens" programme because an incoming spike/surge had caused the microprocessor to "glitch", would you???