[Elecraft] [K3] Loss of Gain below 550Hz filter width - firmware problem?

[David Ferrington, M0XDF]

You may remember I have a problem with my K3 whereby dropping the  
filter width below 550Hz means I loose almost all AF gain.

I have just had a little time to look into it.
I was running the latest Beta software (1.96) which I see is now  
production.
I've now loaded the latest production code, but the problem is still  
there.

On a whim, I loaded 1.58 which I had hanging around from previous  
tests and everything works just great - right the way down to 50Hz  
filter width.

I then tried standard production f/w v 1.96 again and the problem was  
gone, but that was before it had loaded the DSP code (I didn't realise  
it hadn't competed the load) and once the DSP loaded, the problem is  
back.
I then tried v1.88 and the problem is still there.
I worked backwards through versions I have (I may not have them all)  
until I got to version 1.66 which still had the problem, but 1.58 does  
not. So this looks like a problem with DSP1 code from somewhere after  
v1.48 of DSP onwards.
I have now restored to the latest version.
I noticed the gain on the 1.58 code is considerably higher than on the  
latest code anyway.
The IIr trick doesn't make a difference to this.

I understand other people don't have this problem, so what is it that  
makes my K3 unique?

I have the following filters:
slot 1 - empty awaiting KFL3B-FM; FL1 BW = 0, FL1 FRQ = 0, FL1 GN = 0,  
FL1 ON = NO
slot 2: KFL3A-6K;     FL2 BW = 6.00, FL2 FRQ = 0, FL2 GN = 4db, FL2 ON  
= YES
slot 3 - KFL3A-2.8K; FL3 BW = 2.80, FL3 FRQ = 0, FL3 GN = 4db, FL3 ON  
= YES
slot 4 - KFL3A-1.8K; FL4 BW = 1.80, FL4 FRQ = 0, FL4 GN = 4db, FL4 ON  
= YES
slot 5 - KFL3A-400;  FL5 BW = 0.40, FL5 FRQ = 0, FL5 GN = 4db, FL5 ON  
= YES

With the following options:
KAT3, KPA3, KBPF3, KXV3, KTCx03-01

No mods yet.

You'll note this problem occurs below 550Hz, but that I have the 400Hz  
filter installed and it does switch filters at the correct point.

So suggestions anyone?
73 de M0XDF, K3 #174
-- 
Ok, so what's the speed of Dark?