@Lucid - reporting the results of my experiments in the order in which I did them .... I recently wrote:
I find that rather confusing, and difficult to interpret/understand. As above, the fact that I had to reduce the capacitance when I moved back up to ch68 seems to suggest that the interfering signal was fairly close in frequency to the channel being used. However, if that were the case then (a) as noted above, why apparently very similar amounts of interference with both channels? and (b) in the case of ch68, why did, say, 10-20dB from the attenuator have more beneficial effect than ~40dB from the filter? and (c) in the case of ch48, why did the filter have any effect (actually a marked effect, albeit not as much as my capacitor)? I'm still thinking, but the perception of different pair of eyes, and a new brain,' would be very welcome!
Do you think there is still something to be gained by trying the attenuator (or, indeed, my capacitor) downstream of the Sky box?
Kind Regards, John
Reverting to ch68 made no discernible difference to what the filter achieved - i.e. the picture quality with it was still clearly inferior to what I had been seeing with my in-line capacitor. However, in order to restore the ('near perfect', to my eyes) picture I had previously been seeing with the capacitor, I had to appreciably reduce its capacitance - to the extent of almost completely 'unmeshing' its plates. That seems to suggest that the 'interfering' signal was close to the RF channel being used (but with both ch48 and ch68, which seems odd).... I was about to write a note to confess that I may not have given the filter a fair trial. Looking at the spec of the (Labgear) filter, I see that it's cut-off frequency is about 700 MHz, so that it is meant to 'pass' up to ch48 and 'reject' everything from ch50 upwards. However, although I had intended to change back to ch68 before I tried the filter, I forgot to do that - so what I recently reported with the filter was whilst still using ch48. Hence, once 'er indoors has stopped watching Sky, I'll change it back to c68 and see how the filter then performs.
I've so far only tried it before (upstream of) the Sky box. The instructions which came with it are 'long lost' but with the adjuster fully clockwise it doesn't seem to do anything noticeable, so I presume that is the "0dB" end of the attenuation range. With it adjusted to anywhere between the anti-clockwise end and the middle of its travel (so maybe 10dB-20dB if the adjuster is anything like linear in relation to dB), the result is similar to the ('near-perfect') picture I see with the (reduced value) capacitor.What would be interesting is taking the 4G filter out of the equation, and then comparing the capacitor to a standard wideband signal attenuator. In fact, I'd go one step further and get hold of a 0-20dB variable attenuator .... Try this before and after the Sky box adds its signal.
I find that rather confusing, and difficult to interpret/understand. As above, the fact that I had to reduce the capacitance when I moved back up to ch68 seems to suggest that the interfering signal was fairly close in frequency to the channel being used. However, if that were the case then (a) as noted above, why apparently very similar amounts of interference with both channels? and (b) in the case of ch68, why did, say, 10-20dB from the attenuator have more beneficial effect than ~40dB from the filter? and (c) in the case of ch48, why did the filter have any effect (actually a marked effect, albeit not as much as my capacitor)? I'm still thinking, but the perception of different pair of eyes, and a new brain,' would be very welcome!
Do you think there is still something to be gained by trying the attenuator (or, indeed, my capacitor) downstream of the Sky box?
Kind Regards, John