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Author Topic: Kenwood TS-450s Notch Filter - huh?  (Read 1502 times)
W7EJT
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Posts: 132




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« on: November 11, 2012, 12:51:31 PM »

OK, I've been off the air (HF) for over thirty years, and just getting back into this excellent hobby. I don't claim to be an expert on Notch Filtering - maybe one of you fellas can fill me in here.

I'm reading my Kenwood TS-450s "Instruction Manual" (Operators Manual) and do not understand the following from page 49:

"The NOTCH function is used to reduce or eliminate heterodyne, or CW type signals. The NOTCH filter will not be effective against SSB, AM or FM type signals..."


So, the filter is not good for SSB, AM FM and CW - gee, that doesn't leave anything Huh

Surely this is an error in the manual...

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AC5UP
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Posts: 3822




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« Reply #1 on: November 11, 2012, 01:18:47 PM »

No error at all......... An audio notch filter is a frequency selective attenuator with a steep bandpass characteristic. It can reduce or eliminate a heterodyne whistle as well as a CW note since both are single frequency (tone) signals.

The filter cannot eliminate an SSB, AM or FM signal as the audio is too wide for a filter so narrow. It can knock a hole in it, and you can select the frequency attenuated, but otherwise the notch filter is best suited for a single tone you want rid of. I have a TS-690s which is the HF+6 version of the TS-450s and the notch filter works as advertised.

Easiest test is to tune in a relatively stable (little QSB) CW signal then turn on the notch filter and adjust the frequency. At some point the CW tone all but disappears. When you have two CW signals very near each other you can filter one out and that's the purpose of the filter..........
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WB6BYU
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Posts: 13014




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« Reply #2 on: November 11, 2012, 01:45:38 PM »

The notch IS effective against a CW signal or hetrodyne on a single frequency.
Most commonly it would be used if, for example, there was a constant carrier signal
that was interfering with an SSB signal:  the carrier can be notched out without
too much impact on the other frequencies of the SSB signal.

I use the notch to narrow up the filter passband on CW, and also on SSB in weak
signal conditions to notch out the center of the passband that doesn't contribute
to the intelligibility of the voice signal.
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W7EJT
Member

Posts: 132




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« Reply #3 on: November 11, 2012, 02:24:24 PM »

allrightythen! Now I get it. Will use it for CW.

thx!
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NR4C
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Posts: 306




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« Reply #4 on: November 14, 2012, 06:13:22 AM »

The NOTCH is very useful for SSB and digital modes as well.  Don't take it lightly.  Often I am trying to work a DX station, and someone thinks that the frequency is a good one to use for tuning up his amp.  The NOTCH filter will almost if not completely eliminate the 'tuner-upper' and allow me to hear the DX station I'm trying to work.

...bill  nr4c
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