K3 Signal blocking inside of the crystal filter BW

[Dave Anderson, K4SV]

Hi All,

I recently purchased a brand new K3 and after a factory tuneup, it is a very nice radio.

I discovered a situation using it that I would like to mitigate.

When trying to work a station simplex in a pileup I experienced receiver blocking.  While trying to listen to the DX station others were calling so I narrowed the passband down to 200hz.  I was unable to copy the weaker station very well because the louder stations were retarding the AGC.  This blocking is common to AF DSP radios like a IC746 but I would have not expected it to occur on the K3.  I have owned a IC7800 for 5 years and even though the lab tests show it to be not as good as the K3 I have never experienced blocking inside of the selected passband like I have seen on my K3.

I found if the DSP is set the same as the 400Hz crystal filter ,I have 8 pole, the blocking does not occur.  But larger signals inside of the crystal filter BW makes copy hard.

Is there a way to fix this?  Perhaps a setup value change or something.  I purchased this radio to take on DXpeditions.  At this point I not sure if I could reduce the BW using the DSP inside of the 400Hz filter without problems.

Thanks in advance,
 
Dave Anderson, K4SV
Tryon, NC
 828 777-5088
 
www.K4SV.com
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[Dave Hachadorian]

I'm sure the Elecraft crew will respond to your post, but
here are my recommendations. Load the latest beta firmware
and try the settings below, in my order of preference. In
all cases, the most important setting is to keep the RF Gain
turned down as low as possible, allowing you to just barely
hear the weakest signals clearly. A 200 Hz filter may help a
little, but not much if you are dealing with a pileup of
closely-spaced signals.

1.
AGC=OFF
AF LIM=nor 030
Headphones plugged into speaker jack (to avoid tripping the
K3's ugly AF limiter)
AF gain at about 10 o'clock (or whatever it takes to protect
your ears on the loudest signals)

2. (uses new AGC HLD and AGC DCY=soft functions)
AGC=SLOW
AGC DCY=SOFT
AGC HLD=0.2
AGC PLS=NOR
AGC SLP=0
AGC THR=008
AGC-F=200
AGC-S=20

3. (uses new AGC DCY=SOFT function)
Same as 2 above, except AGC=FAST

Dave Hachadorian, K6LL
Yuma, AZ



----- Original Message -----
From: "Dave Anderson, K4SV" <[hidden email]>
To: <[hidden email]>
Sent: Friday, March 27, 2009 3:43 PM
Subject: [Elecraft] K3 Signal blocking inside of the crystal
filter BW



Hi All,

I recently purchased a brand new K3 and after a factory
tuneup, it is a very nice radio.

I discovered a situation using it that I would like to
mitigate.

When trying to work a station simplex in a pileup I
experienced receiver blocking. While trying to listen to the
DX station others were calling so I narrowed the passband
down to 200hz. I was unable to copy the weaker station very
well because the louder stations were retarding the AGC.
This blocking is common to AF DSP radios like a IC746 but I
would have not expected it to occur on the K3. I have owned
a IC7800 for 5 years and even though the lab tests show it
to be not as good as the K3 I have never experienced
blocking inside of the selected passband like I have seen on
my K3.

I found if the DSP is set the same as the 400Hz crystal
filter ,I have 8 pole, the blocking does not occur. But
larger signals inside of the crystal filter BW makes copy
hard.

Is there a way to fix this? Perhaps a setup value change or
something. I purchased this radio to take on DXpeditions. At
this point I not sure if I could reduce the BW using the DSP
inside of the 400Hz filter without problems.

Thanks in advance,

Dave Anderson, K4SV
Tryon, NC
828 777-5088

www.K4SV.com
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http://www.qsl.net/donate.html 

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[KK7P]

Hello Dave!

> When trying to work a station simplex in a pileup I experienced receiver blocking.  While trying to listen to the DX station others were calling so I narrowed the passband down to 200hz.  I was unable to copy the weaker station very well because the louder stations were retarding the AGC...
>
> I found if the DSP is set the same as the 400Hz crystal filter, I have 8 pole, the blocking does not occur.

The basic design of the K3 is to make use of the 1st IF crystal filter
to narrow the in-band bandwidth to be consistent with the modulation
method in use.  This is why the K3 can accommodate such a wide range of
roofing filters and with so many bandwidth options.

The great numbers the K3 has in terms of narrow-spaced dynamic range
(see for example < URL:http://www.sherweng.com/table.html > are due to
the use of narrow roofing filters.

To maximize the in-band dynamic range, the sensitivity floor of the
radio should be set to just below the current band/antenna noise floor.
  On most bands, the ATTN can be used, adding about 10 dB to the level
before which the hardware AGC activates.  Most bands do not require the
use of the PREamplifier, getting another potential gain of 10 dB or so.

73,

Lyle KK7P

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[Dave Anderson, K4SV]

Thanks to all who replied, I will give some of the suggestions a try.

Best 73
 
Dave Anderson, K4SV
Tryon, NC
 828 777-5088
 
www.K4SV.com
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