[Elecraft] K3 receiver desensing on CW during contest

[Steve Ellington]

I think what they are seeing is this: Strong signals that fall slightly 
outside the DSP's audio passband are still pumping the S-meter and the AGC 
is desensing the receiver. The DSP is acting more like and audio filter than 
an IF DSP. In other words, the DSP's audio bandpass is very steep but it's 
IF bandpass is broad. This is with the 200Hz roofing filter installed but we 
are dealing with this 50Hz issue. To illustrate, tune in an S-9 carrier 
using the 50Hz filter. Tune off his signal 60Hz. The audio is gone but the S 
meter still reads S-9 telling me that the slopes for audio and IF are 
different.
Also, at 50Hz BW the Passband tuning is indeed useless since it tunes in 
50Hz increments. Can that be reduced?
Steve Ellington
N4LQ at carolina.rr.com
----- Original Message ----- 
From: "wayne burdick" <n6kr at elecraft.com>
To: "K2MK" <k2mk at comcast.net>
Cc: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Sunday, February 22, 2009 9:27 PM
Subject: Re: [Elecraft] K3 receiver desensing on CW during contest


> Mike,
>
> The K3 is virtually desense-proof, with a BDR of ~140 dB. But to take
> advantage of this, you need a narrow crystal filter -- the closer to
> the DSP bandwidth the better. This is exactly the situation that we had
> in mind when we designed the 200-Hz 5-pole filter. For CW pileups, you
> can't beat it.
>
> What crystal filter were you using at the time?
>
> Of course if the transmitting stations are "wide" due to key clicks,
> there may be situations where no amount of filtering can help (for any
> receiver). The DSP noise blanker and NR may be useful sometimes -- you
> might give this a try.
>
> Wayne
> N6KR
>
> On Feb 22, 2009, at 4:45 PM, K2MK wrote:
>
>> I had a great time with my K3 during the ARRL DX contest. I do S&P and
>> I was
>> trolling around with my filter width at 50Hz. Absolutely outstanding.
>> The
>> auto spot is equally outstanding.
>>
>> At 50Hz width it was quite clear that many stations call off frequency.
>> Using RIT, I could see that it was typical for them to be 70Hz or more
>> away
>> from the DX station but I could not hear them in my 50Hz passband. The
>> real
>> problem was when one of them was S9 or greater. They completely swamped
>> weaker DX stations.
>
> ---
>
> http://www.elecraft.com
>
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