[1000mp] IF-notch in the MP is good

Sun, 3 Mar 2002 07:53:46 -0700

Bill and group,

Just to fill in the blanks in Bill's message as far as my own situation is
concerned...

(I'm the guy who said I thought the notch was way too wide, and not deep
enough)

I have the Inrad mod, with the IF gain set to 10.
I usually have my RF gain at about the 12:30 or 1:00 position, well off from
max gain.
My filters are:
    Stock 2400 Hz. 8M IF
    Stock 500 Hz. 8M IF
    Inrad 400 Hz 455K IF
    Inrad 250 Hz 8M IF
    Inrad 250 Hz. 455K IF
I never operate SSB (well, 99.44% CW).

When operating CW, if I am using the 2.4K filter, and if there is a
heterodyne quite a ways above my signal (maybe 1KHz. or 1.5 KHz.), the notch
can do some good to get rid of it.  But if this is the case, I just turn on
one of the narrower IF filters.

For closer things, it does as much damage to the desired signal as it does
to the offending one.  For any of the narrower CW filters, the notch
bandwidth seems to be about as wide as my IF passband, so it doesn't help
any.  I get a lot more mileage out of using the SHIFT and WIDTH controls,
which are quite effective.  And they also have the beneficial effect of
keeping the bad guy out of the AGC that Bill mentions.

Just my experience.  Your mileage may vary.  Has anyone ever measured the
width and depth of the notch with a spec an?

73,
Tom / W7GT

----- Original Message -----
From: "WD8ARZ" <[email protected]>
To: <[email protected]>
Sent: Saturday, March 02, 2002 5:31 PM
Subject: [1000mp] IF-notch in the MP is good

> Actually I frequently use my Notch Filter with and with out the auto dsp
> heterodyne killer. The IF Notch filter in my MP is much better than many
> other rigs I have used over the years.
>
> Keep in mind that the better the filters you use in your radio, the better
> the effect of the notch filter. Also the Inrad mod (and turning down the
> internal i.f. gain to rebalance the gain) helps the notch filter and noise
> blanker do a better job too. If your menu 9-1 Rcv i.f. gain is cranked up
> beyond its proper setting (8-10 with inrad mod, 10-12 with out), the i.f.
> filter, noise blanker, and other features just will not perform as well,
or
> even as intended.
>
> The I.F. Notch Filter also does something that the internal and external
Dsp
> filters can not do. It reduces the offending carrier (and parts of the
> passband) from a strong signal near a weak signal and allows the agc to
> recover so you can now copy the weak signal with out the strong signal
> dominating the agc performance. You will be able to hear this difference
and
> see the results on the S meter.
>
> Remember your sliding a deep null across the intermediate filter stage and
> not the audio stage, thus improving the rest of the system features
ability
> to do their job, including the dsp filters in the last i.f., detector
> stages, and of course at the audio level.
>
> I would not underestimate appropriate usage of the i.f. notch filter in
the
> mp.
>
> Best of the weekend to one and all.
>
> 73 from Bill - WD8ARZ
> [email protected]
>
>
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