Noise going up with reducing XTAL filter BW

Hello,

Can somebody explain to me why the "audio" noise
increase when i select a lower BW XTAL filter?
For example going from 1k8 to 400Hz.

As i use often BPSK31, the "blue" background
of my waterfall (without signal present) go
into the "yellow" color; (using Digipan with
"standard" waterfall colors).
I was expecting a "constant" level or a noise
reduction, but not an increase.

Is it a Filter gain setting to modify in my K3?

Mny tnx in advance!

73 QRO de Rudolf, HB9ARI

PS At 66 yo, it's not to late to learn something!


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[Julian, G4ILO]

hb9ari wrote

Is it a Filter gain setting to modify in my K3?

Yes, there is an FLx GN setting in the menu. Normally you need to increase it a dB or two for the narrow filters to compensate for the extra insertion loss.

Tim,

Thank you for info; i will look for
the current filter gain values and adjust
them if necessary.

73 QRO de Rudolf, HB9ARI

Tim Heasman wrote:

> Hi Rudolf,
>
> Just checked the gains on my 1 kHz and 400 Hz filters they are 3 and 8
> dB. I also checked the audio noise using the dBV display and the noise
> reduced each time I reduced the bandwidth from 2.8 kHz down to 200 Hz
> and lower.
>
> Use the K3 utility to check the gains.
>
>
> 73
>
> Tim
>
> gm4lmh
>
> ----- Original Message ----- From: "hb9ari" <[hidden email]>
> To: "elecraft" <[hidden email]>
> Sent: Monday, February 23, 2009 3:44 PM
> Subject: [Elecraft] Noise going up with reducing XTAL filter BW
>
>
>> Hello,
>>
>> Can somebody explain to me why the "audio" noise
>> increase when i select a lower BW XTAL filter?
>> For example going from 1k8 to 400Hz.
>>
>> As i use often BPSK31, the "blue" background
>> of my waterfall (without signal present) go
>> into the "yellow" color; (using Digipan with
>> "standard" waterfall colors).
>> I was expecting a "constant" level or a noise
>> reduction, but not an increase.
>>
>> Is it a Filter gain setting to modify in my K3?
>>
>> Mny tnx in advance!
>>
>> 73 QRO de Rudolf, HB9ARI
>>
>> PS At 66 yo, it's not to late to learn something!
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html 
>
>

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Julian,

Thank you for the quick replay!
May be the filter gain is too high
for low BW and i get an over compensation?

I will look at that this evening.

73 QRO de Rudolf, HB9ARI

Julian, G4ILO wrote:

>
> hb9ari wrote:
>  
>> Is it a Filter gain setting to modify in my K3?
>>
>>    
> Yes, there is an FLx GN setting in the menu. Normally you need to increase
> it a dB or two for the narrow filters to compensate for the extra insertion
> loss.
>
> -----
> Julian, G4ILO. K2 #392  K3 #222.
> http://www.g4ilo.com/ G4ILO's Shack   http://www.g4ilo.com/blog.html G4ILO's
> Blog    http://www.g4ilo.com/kcomm.html KComm for Elecraft K2 and K3
>  

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