K3 Filter Gain question.

[John Ronan]

Hi,

#2184 was recently fitted with a sub receiver (very nice). It occured  
to me that I never sat down to figure out how best to set the gain  
figures for the filters. I have
Main:
KFL3B-FM
KFL3A-6K
KFL3A-2.7K (-77)
KFL3A-500 (-73)

Sub:
KFL3A-2.7K (-76)
KFL3A-500 (-75)

The handbook suggests 1-2db for 500Hz, and I've seen posts warning  
against using excessive gain. Any suggestions?

Also, using diversity receive on the same antenna, the signal seems  
to 'move' slightly more than once per second between my headphones.  
I assume this is a feature of diversity and the different signal  
paths through the radio, as I've never had a radio with diversity  
receive before.

Regards
de John
EI7IG

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[Bill W4ZV]

John Ronan wrote

#2184 was recently fitted with a sub receiver (very nice). It occured  
to me that I never sat down to figure out how best to set the gain  
figures for the filters. I have
Main:
KFL3B-FM
KFL3A-6K
KFL3A-2.7K (-77)
KFL3A-500 (-73)

Sub:
KFL3A-2.7K (-76)
KFL3A-500 (-75)

The handbook suggests 1-2db for 500Hz, and I've seen posts warning  
against using excessive gain. Any suggestions?

Also, using diversity receive on the same antenna, the signal seems  
to 'move' slightly more than once per second between my headphones.  
I assume this is a feature of diversity and the different signal  
paths through the radio, as I've never had a radio with diversity  
receive before.

Regarding gain, although the actual insertion loss for 500 Hz filters is more than 1-2 dB, but I would follow Elecraft's recommendation.  I previously set mine to the actual loss (5-6 dB) but have since backed off to 0 dB after reading some comments by Lyle and Wayne (which cautioned about other problems induced by gain being too high).

Regarding the warbling sound you're hearing in diversity, it's because your filters are set to different offsets.  In your case you should set both 500s to -0.74 and both 2.7ks to the same (either -0.76 or -0.77).

73,  Bill

[Bill W4ZV]

Bill W4ZV wrote

Regarding gain, although the actual insertion loss for 500 Hz filters is more than 1-2 dB, but I would follow Elecraft's recommendation.  I previously set mine to the actual loss (5-6 dB) but have since backed off to 0 dB after reading some comments by Lyle and Wayne (which cautioned about other problems induced by gain being too high).

W7TEA asked:

"Bill, don't remember comments by Lyle and Wayne on the reflector.  Would you share please?"

Here's one...

http://mailman.qth.net/pipermail/elecraft/2009-June/111676.html

73,  Bill

[John Ronan]

Thanks Bill,

On 9 Aug 2009, at 13:10, Bill W4ZV wrote:

>
> Regarding gain, although the actual insertion loss for 500 Hz  
> filters is
> more than 1-2 dB, but I would follow Elecraft's recommendation.  I
> previously set mine to the actual loss (5-6 dB) but have since  
> backed off to
> 0 dB after reading some comments by Lyle and Wayne (which cautioned  
> about
> other problems induced by gain being too high).
>

Yeah, that was the post I recevied.

> Regarding the warbling sound you're hearing in diversity, it's  
> because your
> filters are set to different offsets.  In your case you should set  
> both 500s
> to -0.74 and both 2.7ks to the same (either -0.76 or -0.77).


Ok, I assume though that this will make the (moved) filters slightly  
asymmetric then in the passband.  Also I found this post from Wayne  
that says it's ok :)
http://www.mail-archive.com/elecraft@.../msg71951.html

Thanks
John



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[Bill W4ZV]

John Ronan wrote

> Regarding the warbling sound you're hearing in diversity, it's  
> because your
> filters are set to different offsets.  In your case you should set  
> both 500s
> to -0.74 and both 2.7ks to the same (either -0.76 or -0.77).

Ok, I assume though that this will make the (moved) filters slightly  
asymmetric then in the passband.  Also I found this post from Wayne  
that says it's ok :)
http://www.mail-archive.com/[e-mail]/msg71951.html

You'll never notice the difference in shifting your 500s by + and - 10 Hz (i.e. both to -0.74) since 10 Hz is only 2% of total bandwidth.  However both offsets should be identical to avoid the warbling sound you're hearing in diversity.  Of course the 2.7k is even less sensitive to a 10 Hz shift since it's a much wider BW.

Thanks for locating that post by Wayne (which W7TEA had asked about).

73,  Bill