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|uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.|
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at800 filter for channel 60
I had a play with one of the at800 channel 60 filters today. It had been
installed by AN Other and Co and the white nylon cable ties had snapped.
We've seen a lot of these filters fixed with white ties and wonder if
the ties are supplied with the filters.
The filter appears to have six notch filters in series. It is possible
to tune each stage by bending the lugs in and out. There might be
further tuning adjustment inside but I didn't look. The six notch
filters can be adjusted by bending the lugs to provide a spread across
the relevant frequencies. Through loss is remarkably small at about 2dB.
This filter was on a communal system situated very near to the Crosspool
tx but completely screened from it. Hence reception was from Belmont.
The complaint was that there was no reception of ch60.
'As found 01' shows the response 'as found'. No wonder there was no ch60
reception. I wondered if someone had re-tuned the filter to improve
rejection of the unwanted frequencies and had inadvertently lost ch60.
The other possibility was that the filter has been affected by damp,
although it seemed dry inside.
'As found 02' is the same but with the limits of ch59 marked.
'Re-tune 01' shows my best attempt to re-tune the filter (by bending the
lugs) to pass ch60. Not satisfactory, obviously.
'Re-tune 02' shows the result when I re-tuned to improve rejection of
the unwanted frequencies, accepting the loss of chs 59 and 60 ch60.
'Re-tune 03' is a wider view of the same thing.