K3: APF effectiveness

[Ralph Parker]

>...perhaps less gain and a little wider BW
>or give the user the tools to do it ourselves.

I was thinking exactly that myself last night on 160m - no problem with the
bandwidth, but I'd gladly give up a db or two of APF gain to reduce the
ringing.
Because of the ringing, I can hear signals that aren't even there!

Ralph, VE7XF

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[Barry N1EU]

What you're describing ("hear signals that aren't even there") sounds to me like the APF is working just as intended.  You're hearing faint ringing at your sidetone frequency when no signal is present.  When a signal is present and tuned in, it will have precisely that same tone but will pop further out of the noise than that "phantom" signal.  It just demands a little practice and patience along with fine tuning.

If someone wants a lower Q APF with less gain, they should try a dsp width of 50hz without APF.

73, Barry N1EU

Ralph Parker wrote

>...perhaps less gain and a little wider BW
>or give the user the tools to do it ourselves.

I was thinking exactly that myself last night on 160m - no problem with the
bandwidth, but I'd gladly give up a db or two of APF gain to reduce the
ringing.
Because of the ringing, I can hear signals that aren't even there!

[Don Wilhelm-4]

  Ralph,

You have heard that to reduce the ringing, increase the DSP bandwidth.  
The 50 Hz filter width has a bit of ringing by itself, so add the APF
and the situation becomes more pronounced.

You can't have your cake and eat it too.  The bit of ringing will bring
out weak signals just like the old Q-Multiplier used to do (and it
caused "ringing").  The APF was not intended to be used full-time, turn
it on only when it will help -- besides, it is too sharp for "tuning
around".

73,
Don W3FPR

On 1/25/2011 7:40 PM, Ralph Parker wrote:

>> ...perhaps less gain and a little wider BW
>> or give the user the tools to do it ourselves.
> I was thinking exactly that myself last night on 160m - no problem with the
> bandwidth, but I'd gladly give up a db or two of APF gain to reduce the
> ringing.
> Because of the ringing, I can hear signals that aren't even there!
>
> Ralph, VE7XF
>
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[Pete Smith N4ZR]

Heck, I can hear thiose phantoms with the radio off (tinnitus).  
Fortunately it subsides in the presence of other noise - just like with
the APF, which works FB for me on the low bands.

73, Pete N4ZR

The World Contest Station Database, updated daily at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000



On 1/25/2011 7:55 PM, Barry N1EU wrote:

> What you're describing ("hear signals that aren't even there") sounds to me
> like the APF is working just as intended.  You're hearing faint ringing at
> your sidetone frequency when no signal is present.  When a signal is present
> and tuned in, it will have precisely that same tone but will pop further out
> of the noise than that "phantom" signal.  It just demands a little practice
> and patience along with fine tuning.
>
> If someone wants a lower Q APF with less gain, they should try a dsp width
> of 50hz without APF.
>
> 73, Barry N1EU
>
>
> Ralph Parker wrote:
>>> ...perhaps less gain and a little wider BW
>>> or give the user the tools to do it ourselves.
>> I was thinking exactly that myself last night on 160m - no problem with
>> the
>> bandwidth, but I'd gladly give up a db or two of APF gain to reduce the
>> ringing.
>> Because of the ringing, I can hear signals that aren't even there!
>>

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[Robby.VY2SS]

That was me!

-Robby
VY2SS

[Jim Sheldon]

Hey Ralph & Robby,
After all the contest activity on 160 yesterday, after I shut down I had trouble getting to sleep because I was hearing all those phantom CW calls for several hours before it subsided.  

Seriously I was able to hear stations right on the noise that I would never have been able to pull out with the IC-7000 I used to have.  Robby, I distinctly remember working you last night and you had a nice clean signal (ref your other post on audio distortion).  It must have been just on receive.  I didn't notice that problem here and there were many-many S9+20 and bigger signals showing on the P3 and I had the span set to 6KHz (3-C+3).

Another plus for the K3/P3, was able to find those weak stations in between the +20 guys and work them thanks to the super selectivity of the K3.  400 Hz 8 pole filter is sufficient to keep out the adjacent frequency strong signals even from an Alpha 9500 running 1K+ less than 5 blocks from me.  Never even knew he was in the contest until I rolled across him.  Centered up, he bloomed the P3's trace up pretty wide, but I could still copy S3 to S5 signals within 1KHz either side of him without any IMD problems.  Couldn't see the weaker signals on the P3 due to his overload, but had no trouble working them.

Jim - W0EB
Park City, KS

>
> That was me!
>
> -Robby
> VY2SS
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