Hi,
I hope the ferrite filter suggestion works although I have a suspicion it might not. If the interference is being picked up by the TV aerial then putting a ferrite around a screened TV downlead my not be terribly effective. However fitting a band pass filter in series with the lead may be more successful. I found the following on another forum (
http://www.digitalspy.co.uk/forums/showthread.php?p=3900193) do take note of the marginal signal strength comments though:-
" I have the same interference problem as you do, and I have improved this greatly for little money or effort. I have a Nokia 221T freeview box in a poor signal area (<33% of maximum of the Nokia signal strength meter). I used to get brief screen freezes and sound dropouts and popping when a light switch was used, my boiler ignited (it is a modern one with no pilot light so it self ignites using a spark), if a car or moped went by, fridge door opening etc etc...
Now I get only occasional pixellation and the odd sound dropout but no screen freezes and sound popping is rare (which is nice as it is annoying).
How did I do this 'magic'? I simply fitted an inline RF coax passive bandpass filter. You lose some signal level (about 5% of the signal meter scale which might be a problem if you are in a marginal signal area), but happily interference is only a small issue for me nowadays. Light switches, fridges etc are no problem at all, and only some vehicles and my shredder can cause interference but it is much less frequent and severe than before. It has transformed my viewing experience. My shredder is still bad (but improved) but that is to be expected.
I got it from www.cpc.co.uk, the part number is "APFILTER" (Mikerobe:
http://cpc.farnell.com/_/filter/high-pass-interference-filter/dp/APFILTER?Ntt=APFILTER)
and it costs £3.055 plus vat and postage(Mikerobe: they have gone up a bit since).
Obviously, I can't guarantee it will help anyone, but it really has helped me greatly. You just plug it inline with your aerial cable at the point where you connect the aerial lead into your freeview box.
I am also about to replace my cheapo loft aerial with a "DX8W" aerial from Antiference (about £26 from CPC, small acceptance angle, large forward gain, large front to back ratio, has a PCB balun and is only about 1m long so it will fit in my loft or won't blow about that much on your roof (which could give me signal dropouts as I am in a weak signal area with a small acceptance angle aerial).
I am also replacing my coax with the "100" type (mine is DS100 but I think it is the same as CT100). This is the 'double insulated' type which means it has a braided screen (like the cheapo stuff has), but it also has a solid foil which should give much better screening. I believe that the braid gives less than 85% coverage (I've also read it is nearer 65%), so I am hopeful that the superior screening area (100%!) will remove the rest of the interference(!). There is less attenuation in this cable also (compared to 'low loss coax'), but I don't see that as a great factor since my cable run is only about 10m (although I am in a weak signal area so you never know...!).
I have read elsewhere that people have tried pointing their aerial a little upwards, and I can well believe that that can help for some people."I also found this rather useful PDF about selecting spark plugs for Vespa and Lambretta scooters which might help explain the issue some. Apologies for the tinyurl but I couldnt find a better link from google
http://tinyurl.com/yzw2ho6I Quote a portion here:-
"To make matters worse, many of the spark plugs being sold today have been designed for modern and not vintage engines and are fitted with an internal resistor that actually reduces the voltage to the spark plug and so reduces the spark size. The main purpose of this resistor is to reduce RFI (Radio Frequency Interference) and so protect modern vehicles electronic devices, such as engine management systems, inbuilt mobile car phones, GPS systems, TV’s etc, which your typical vintage scooter is probably not and never will equipped with."So that may in part explain the lack of RFI from modern vehicles and greater prevalence on older ones. The others, I suspect, being:- the use of Electronic ignition systems rather than points based systems and the fitting of suppressor caps and suppressor capacitors to ignition coils, alternators and any other electric motors (
http://www.indiacar.com/infobank/car_radio.htm). I suspect points may well make more interference across a broad spectrum of frequencies. I am sure everyone at some time has suffered crackles and buzzes on their radios when things like the contacts on the relays on their central heating boiler start to get old and warn.
I am not sure what remedial measures one might be able to take on a vintage bike. For the reasons stated in the Scooter document I dont suppose suppressor caps are feasible and neither would be the appropriate plugs. Let alone the aesthetics of fitting non standard caps. I am not sure what the situation would be with suppression capacitors. I will try and find out more from someone I know who knows more about this than I.
Mike 8-{>
