[Elecraft] Dramatic improvement in K3 RX sensitivity below 500 kHz -- looking for testers

[Wayne Burdick]

That excellent sensitivity will allow the use of lossy antennas like small loops, etc. I was tuning around listening to beacons from 200-300 kHz, and the difference with the mods is very apparent. 

Wayne
N6KR

----
http://www.elecraft.com

> On Apr 29, 2015, at 10:53 PM, Barry LaZar <k3ndm at comcast.net> wrote:
> 
> Wayne,
>    I don't think I'd get too spun up over sensitivity of better than -95 DBM below the AM BC band. You are going to run in to a practical limit set by atmospheric and man made noise. If you assume a -147 dbm for a perfect receiver in a 500 Hz BW, used because the math is easier, and then subtract 60 db for expected value of noise on 80 meters, you should find that the K3 sensitivity greatly exceeds what could practically be used. I did not look at the noise figure for the K3 as I assume it is much, much better than the expected value of what the antenna will see. And, the environmental noise gets worse as you decrease frequency. I guess what I'm trying to convey is the idea that  you already have a superb design. So, will you have done anything to the radio's characteristics in the higher regions of the spectrum to achieve better MF and down performance?
> 
> 73,
> Barry
> K3NDM
> 
>> On 4/29/2015 11:55 PM, Wayne Burdick wrote:
>>> On Apr 29, 2015, at 8:30 PM, drewko <drewko1 at verizon.net> wrote:
>>> 
>>> IIRC, original statement for the new board was -120 dBm at 475 KHz.
>> That was conservative.
>> 
>> 
>>> Now saying -133 with the mods.
>> At least on my lab K3.
>> 
>> 
>>> Maybe broadcast band DXers would find it useful on the lower half of the AM band?
>> 
>> Could be. On my K3, with the mods, the MDS at 1.0 MHz is now -136 dBm, preamp on (400 Hz BW).
>> 
>> Just keep in mind that in the lower frequency ranges, you'll want to use RX ANT IN or XVTR IN to avoid the loss of the high-pass filter in the T/R switch.
>> 
>> Wayne
>> N6KR
>> 
>> 
>> 
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