KX3 Notch Filter (Was Noise Blanker Comments)

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KX3 Notch Filter (Was Noise Blanker Comments)

Elecraft mailing list
       Wayne,
      While on the subject of DSP filtering,  I have always felt that my notch filter on the KX3 wasn't as useful as it could be since it drops the volume so much compared to my other radio. Are others noticing this too? Any suggestions?  73 Mike KF6KXG
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Re: KX3 Notch Filter (Was Noise Blanker Comments)

GM4JJJ
My only complaint with the notch filter is that on SSB it is only automatic, and cannot be manually tuned like on CW. I find that I can get an annoying weak heterodyne that is too weak for the auto notch to find, and if I could tune the notch manually I would be able to notch it out.

73 from David GM4JJJ

> On 11 Dec 2015, at 21:32, Mike Lichtman via Elecraft <[hidden email]> wrote:
>
>       Wayne,
>          While on the subject of DSP filtering,  I have always felt that my notch filter on the KX3 wasn't as useful as it could be since it drops the volume so much compared to my other radio. Are others noticing this too? Any suggestions?  73 Mike KF6KXG
> ______________________________________________________________
>
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Re: KX3 Notch Filter (Was Noise Blanker Comments)

Don Wilhelm-4
David,

Manual notch is available in all modes.  The auto-notch is available
only for voice modes.
Tap NOTCH once will select auto, tap it a 2nd time to change to manual.
See page 27 of the manual.

73,
Don W3FPR

On 12/11/2015 5:12 PM, David Anderson wrote:
> My only complaint with the notch filter is that on SSB it is only automatic, and cannot be manually tuned like on CW. I find that I can get an annoying weak heterodyne that is too weak for the auto notch to find, and if I could tune the notch manually I would be able to notch it out.
>
>

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Re: KX3 Notch Filter (Was Noise Blanker Comments)

GM4JJJ
Don,

Not on my KX3...

I think you may be referring to another model.

73 from David GM4JJJ

> On 11 Dec 2015, at 22:57, Don Wilhelm <[hidden email]> wrote:
>
> David,
>
> Manual notch is available in all modes.  The auto-notch is available only for voice modes.
> Tap NOTCH once will select auto, tap it a 2nd time to change to manual.
> See page 27 of the manual.
>
> 73,
> Don W3FPR
>
>> On 12/11/2015 5:12 PM, David Anderson wrote:
>> My only complaint with the notch filter is that on SSB it is only automatic, and cannot be manually tuned like on CW. I find that I can get an annoying weak heterodyne that is too weak for the auto notch to find, and if I could tune the notch manually I would be able to notch it out.
>
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Re: KX3 Notch Filter (Was Noise Blanker Comments)

Don Wilhelm-4
Sorry, I was thinking of the K3 - I only glanced at the subject line.

73,
Don W3FPR

On 12/12/2015 4:37 AM, David Anderson wrote:
> Don,
>
> Not on my KX3...
>
> I think you may be referring to another model.
>
> 73 from David GM4JJJ
>
>

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Re: KX3 Notch Filter (Was Noise Blanker Comments)

GM4JJJ
No problem Don.

I did go and check my KX3 as you had raised my hopes that this had been updated and I hadn't noticed!

73 from David GM4JJJ

> On 12 Dec 2015, at 12:31, Don Wilhelm <[hidden email]> wrote:
>
> Sorry, I was thinking of the K3 - I only glanced at the subject line.
>
> 73,
> Don W3FPR
>
>> On 12/12/2015 4:37 AM, David Anderson wrote:
>> Don,
>>
>> Not on my KX3...
>>
>> I think you may be referring to another model.
>>
>> 73 from David GM4JJJ
>
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Re: KX3 Notch Filter (Was Noise Blanker Comments)

WD4SDC
In reply to this post by GM4JJJ
GM4JJJ wrote
 I find that I can get an annoying weak heterodyne that is too weak for the auto notch to find, and if I could tune the notch manually I would be able to notch it out.
I was thinking perhaps for the weak heterodyne issue, you could use the RX EQ feature.  It is a broad brush, but it does have +/- 16dB of range in 8 bands.  I tried that and found something rather interesting.  The RX EQ is applied *before* the AGC!  I never knew that - maybe I'm the only one.  Makes sense since the IF is 0Hz - why waste AGC on energy I don't want.  Kudos to the Elecraft engineers that thought that though the extra step!

The auto-notch feature is great for intermittent tuneups or other (multiple) CW signals in the SSB passband, but it is applied after the AGC. That works well if interferer is equal to or less than the level of the SOI (signal of interest), but for the case where the interferer is much stronger than the SOI, the AGC is dominated by the RFI and can make the SOI difficult to copy.  At least the tone is not blasting away in my ear;)  But it does present a problem.  

There is a work-around.  Use CW mode to receive the SSB signal, and harness the power of the manual notch.  If in a QSO, use split mode to operate SSB on transmit and CW mode on receive with the filters widened and pitch offset removed to receive the SSB signal. Don't forget to turn off split when your done! =:O.

I put the KX3 on the bench and measured the CW notch depth using the built-in dBV meter.  I measured more than 60dB!  If I adjusted the VFO about +10Hz, it was over 90dB!!!  How accurate is 90dB?? Well, call it +/-10dB and you still get 80dB min!  That is a *considerable* RFI countermeasure.  And the best part?  It is before the AGC!!!  

As an experiment, I tuned to 7255KHz where ECARS is active and used a siggen to create a CW RFI in the middle of the passband at S9+20dB.  The auto-notch completely removed the tone, but I could not copy the net - S meter still at S9+20dB.  Switch to CW mode and adjust for SSB receive.  I could completely remove the CW RFI with the manual notch - gone! And the AGC was now totally operating on the signals - noise level was S2, signals were as low as S3. I suppose technically the AGC was noise driven at S2, but that is the point - no RFI. Note: for LSB use CW, for USB, use CWR.

This is a really cool thing.  I have, on occasion, had the problem of the "antenna matching enthusiast" coming up in the middle of a QSO, and making things challenging...for several minutes.  I guess they are going for that last decimal point - and have no need for RX mode:\.  Using CW mode and the CW notch in this situation makes it very easy to apply rule #1: Don't acknowledge the presence of the interferer - because they are no longer there!  This is especially useful if the RFI is not an "antenna matching enthusiast", and does have RX mode :(.

Happy Holidays!

73,
Steve
WD4SDC