[Elecraft] K3 receiver desensing on CW during contest

[N8LP]

Those are impressive numbers, Eric. +5dBm would only be about 120dB above the
background noise level on 40m here on a typical night, though. I am located
in a relatively quiet area, but on the edge of suburban/rural. Of course, I
don't have a Yagi currently, and I'm not on the East Coast or in Europe ;-)
My comments were aimed at typical ham stations, not multi-multi contest
stations. Even the best conventional receivers need help in that environment
with external filters, tuned stubs, etc.

I wasn't saying the front end should be wide open ;-) I would assume there
would be bandpass filters for each band, and both high pass and low pass
filters ahead of the ADC. I guess my point was that it seems like a
reasonable compromise for most users to have 130dB BDR for all signals, as
opposed to 140dB for signals outside the roofing filter, but only mid 90dB
range for signals inside the roofing filter. I would like to see the
variable BW xtal filters released, as that would improve the situation.

It's all about compromises, and the K3 is as good as it gets in that regard,
but so is the QS1R, which represents the state of the art in direct sampling
DDC designs available to hams. Of course, I'm only talking receiver RF
performance here, not the issue of knobs, buttons, QSK keying, etc. ;-) I
would like to see how a QS1R with proper front end filters would perform in
your environment. As an inveterate experimenter, I will be playing with the
next generation of ADCs when they arrive.

73,
Larry N8LP




Eric Scace K3NA wrote:
> 
> At the W1KM contesting site, we routinely see signals of +5 dBm or 
> louder on/near 40m from SWBC stations (using a single Yagi).  We also 
> have two modest-power local AM stations (1 to 5 kW, a few miles away) 
> just below 1500 kHz that show up even a bit stronger than that on our 
> 160m antennas.
> 
> Without taking into consideration signals from our own multi-multi 
> transmitters, a receiver is already faced with >>130 dB range between 
> weak signals on 160m in mid-afternoon arriving from Europe and these 
> other signal sources.
> 
> WD3Q, a contester in Washington DC, has much stronger AM BC stations to 
> deal with, including a 50 kW station on 1500 kHz.
> 
> Wide-open receiver front ends attached to an A/D converter are not yet 
> viable for these locations.
> 
> -- Eric K3NA
> 
> on 09 Feb 24 20:44 N8LP said the following:
>> You may be right, Al. I think the improvements may be incremental, and
>> distributed among various aspects of the design, not just the ADC. For
>> instance, ultra-low jitter clock sources, faster FPGAs with improved IP
>> cores, etc. I think most hams would be thrilled with an improvement to
>> 130dB
>> BDR, along with getting rid of phase distortion, ringing and other
>> anomalies
>> in the xtal filters and other analog components. Unless you live near a
>> shortwave broadcast station, or have a high power ham nearby on the same
>> band, you're not likely to need 130dB BDR anyway. Even in those cases,
>> having 200dB BDR probably wouldn't help unless there is a LOT of
>> improvement
>> in transmitter spurious emissions, distortion and phase noise. 
>>
>> The highest signals I have seen here, during Field Day when there were
>> several stations operating within a few miles of me, were <120dB above
>> the
>> noise floor. Of course, it's very important not to use any more front end
>> gain than necessary for the band/conditions.
>>
>> 73,
>> Larry N8LP
>>   
>>
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