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Old 6-Feb-2021, 6:43 PM   #19
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,738
Originally Posted by videobruce View Post
Now, having said that, there is a fine line (almost literally) between just have tight a filter/trap is. Frequency and cost come into play. The 'math' is above my pay grade, but since I have 20+ years of tuning traps (as I call them), it's not just a 'art', but a major math problem. It's a classic case of "Robbing Peter to pay Paul" between attenuating an adjacent channel while trying to persevere the wanted channel. It really can't be done fully, it's all compromises.
At the present time, are you able to receive 17 that is adjacent a much stronger 16? That would seem impossible for a TV tuner to handle.

The receiver should meet or exceed the thresholds given in Table 5.2 for rejection of first adjacent-channel interference at the desired signal levels shown above the columns therein.
Wouldn't it be difficult to design a filter to attenuate 16 without doing damage to 17?

CR7-HT Series: Adjacent Friendly UHF Bandstop or Sharp Notch
CR7D-ch.# HT, CR7T-ch.# HT

Bandstop (CR7D-ch.# HT) “Adjacent Friendly” Rejection Filter

TV Bandstop available for ch.14 to 69, NTSC or ATSC

Highly Selective stopband with 20-45 dB attenuation can pass adjacent channel (3-4 dB loss at 1.5 MHz from stopband)

CR7D-HT contains 4 notches which can be combined for deep and wide notch or 4-6 MHz stopband. Example graph 2 shows video carrier notch, 1 Mhz wide. Example graph 3 shows 6 MHz stopband.

Ignoring cost, would that work, or is there still too much difference in strength between 16 and 17?

Is there a filter design that would work better?
Attached Images
File Type: jpg Tin Lee CR7D Bandstop Filter_1.jpg (126.1 KB, 1360 views)
File Type: jpg First Adjacent Channel Thresholds2.jpg (68.2 KB, 929 views)
If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 6-Feb-2021 at 9:51 PM.
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