K3 Received Signal Drops When Roofing Filter Switched In

[engineercm]

Gents,

I wasn't sure how to even search for a question similar to mine, so if this a duplicate, please forgive me.
Have a K3 with the 400 Hz 8-pole filter.  With the band conditions being so poor, I've been experimenting with different settings of DSP on weak signals.  I've also been experimenting with NR on weak signals.  

Tonight I as listening to D4D on 17m CW.  Using NR with a wide setting for DSP, I could copy him fine. When I turned OFF the NR and readjusted DSP to 400 Hz (where the filter kicks in), the noise level dramatically dropped as did the signal.  In fact, I could copy him better at 450 Hz when the roofing filter is not switched in.  It's almost like there is some insertion loss in the filter.  Is that what I'm hearing?  I would expect a step-function change in noise between 450 hz (no roofing filter) and 400 hz (roofing filter) but not the signal.  

I'm using headphones and the Rx Eq is set up to per p.127 of KE7X manual with 6db boost at 400 hz and 800 Hz.  

73,

Clark/WU4B

[Don Wilhelm-4]

Clark,

You can adjust the gain of the 400 Hz filter in the filter menu.  If I
recall somewhere between 3 and 6 dB is recommended for the 400 Hz filter.

73,
Don W3FPR

On 10/20/2015 9:20 PM, engineercm wrote:
> Gents,
>
> I wasn't sure how to even search for a question similar to mine, so if this
> a duplicate, please forgive me.
> Have a K3 with the 400 Hz 8-pole filter.  With the band conditions being so
> poor, I've been experimenting with different settings of DSP on weak
> signals.  I've also been experimenting with NR on weak signals.
>
>

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[engineercm]

Thanks to all that pointed me to the filter gain settings accessible with the Utility.  It was set at 2 db which is the recommended value in the K3 manual.  Now that I know where the parameter is, I'll experiment more with weak signals.  The manual does not suggest going above 2 db claiming DSP operation would be impaired in some way.  

I've also concluded that the sharp drop in noise when the filter kicks in is to be expected.  I found the same instantaneous drop in noise with the 200 Hz filter is engaged.  Not at all annoying; I was just trying to understand this marvelous radio.

I'm primarily a CW op and will leave the Rx Eq set at +2db around the sidetone frequencies and all others -10 or better.  That seems to suit my ears and my current operating skill.  

73 de Clark WU4B

[Vic Rosenthal]

I used the dBV function to match the filter gains so that there would be
no difference when switching filters. In my case I found it necessary to
set the 400 Hz filter gain to +5 dB. You can do it by ear, but either
way you need a steady signal. I used my little Elecraft XG1 to generate
a steady 1 uv signal.

Note that if you have the subreceiver, filter gains may need to be
different. The easiest way to set them is with the K3 utility.

Regarding the RX EQ, I don't use it at all on CW, because at narrow
bandwidths the pitches that you hear are determined by the width and
shift. If you like to listen to CW with 2 kHz bandwidth, then it might
be useful, but I don't.

You absolutely should NOT set the RX EQ to boost any frequencies on CW.
Just cut the ones you don't want. This is because the RX EQ is turned
off at bandwidths < 150 Hz. As a result, if you are boosting 400 Hz by 2
dB, then when you go to a narrow bandwidth the boost disappears --
exactly what you don't want!

73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/

On 22 Oct 2015 03:13, engineercm wrote:

> Thanks to all that pointed me to the filter gain settings accessible with the
> Utility.  It was set at 2 db which is the recommended value in the K3
> manual.  Now that I know where the parameter is, I'll experiment more with
> weak signals.  The manual does not suggest going above 2 db claiming DSP
> operation would be impaired in some way.
>
> I've also concluded that the sharp drop in noise when the filter kicks in is
> to be expected.  I found the same instantaneous drop in noise with the 200
> Hz filter is engaged.  Not at all annoying; I was just trying to understand
> this marvelous radio.
>
> I'm primarily a CW op and will leave the Rx Eq set at +2db around the
> sidetone frequencies and all others -10 or better.  That seems to suit my
> ears and my current operating skill.
>
> 73 de Clark WU4B
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K3-Received-Signal-Drops-When-Roofing-Filter-Switched-In-tp7609366p7609423.html
> Sent from the Elecraft mailing list archive at Nabble.com.
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> Please help support this email list: http://www.qsl.net/donate.html
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>

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