K3 AGC behaviour, in particular for pulse noise

[Arie Kleingeld PA3A]

All,
 
I would like to share the following experience on the AGC settings of
the K3.
 
 
Situation at my QTH:
There is an electric fence nearby my home that gives a pulse type of
noise.
The K3 handled that pretty well with the AGC PLS setting to ON.
Switching the AGC PLS to OFF gave me a lot of trouble because the AGC
was reacting to it. So the AGC PLS thing did its job. I was happy.
 
 
PROBLEM:
Recently I noticed that I could hear the pulses again very well. The K3
S-meter reacted (from S7 local noise peaking to S9+20 on the spike). AGC
was immediately back to normal, probably because of the AGC PLS
algorithm. Switching OFF the AGC PLS immediately made the AGC work also.
Defenitely wrong thing to do.

When I compared this to the reception of my FT1000MP, no pulses were
heard and nothing was seen at the MP's S-meter. So the pulsed noise
certainly attacked the performance of the DSP... and succeeded.
The only way to fight this, was to switch on the NB. DSP NB set to 1-1
did the job immediately. But still.... what changed during the past
weeks that made the pulse noise into a trouble again?
 
 
ANSWER:
NO, it was NOT the new FW !! Rolling back to an older version did not
cure the problem.
BUT it was the setting of AGC HLD. I had changed that a while ago  from
zero to 20 or so. (I have had good results with hanging AGC in another
TRX so why not give it a try).  Checking this setting out, I saw a
direct relation between the setting of AGC HOLD and the performance of
the RX regarding the pulse noise. Setting the AGC HLD to ZERO solved the
problem.
 
 
EPILOG:
We have been talking about the AGC behaviour a lot. So maybe this e-mail
will help some of you.
I'm learning more of the K3 ways of DSP every day .
 
 
 
73
Arie PA3A
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[Geoffrey Downs-2]

Thanks for sharing this with us Arie. For the past few years I, too, have
suffered from pulses that sound like electric fences (especially on 80m).
AGC PLS at "nor" reduces them like magic from S9+10 down to the noise level.
In fact until your posting on the reflector I had forgotten about them. I
have not used AGC HLD so was not aware of its effect but, having just tried
it, I confirm what you say. In my circumstances it is definitely best for it
to be set at 000.

My K3 (Ser No 266) replaced an FT1000MP Field which, unlike yours, was
affected by the pulses and the only way to get rid of them was to use the
noise blanker, a cure with side effects that were often worse than the
problem.

73 to all

Geoff
G3UCK


----- Original Message -----
From: "Arie Kleingeld PA3A" <[hidden email]>
To: <[hidden email]>; <[hidden email]>
Sent: Saturday, September 27, 2008 1:59 PM
Subject: [Elecraft] K3 AGC behaviour, in particular for pulse noise


> All,
>
> I would like to share the following experience on the AGC settings of
> the K3.

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