[Elecraft] K3 Receiver Noise Level -- Evaluation and Adjustment

[Joe Subich, W4TV]

I had this same exchange with Eric earlier today ... 

1) the LPF board will be available "shortly."  It is in stock 
   and will added (along with instructions) to the web page 
   soon (I read that as the next day or two). 

2) The DSP upgrade now being shipped is "Rev D" which is "Rev C" 
   (the low frequency enhancement) plus the LPF board (the ADC 
   spurious elimination filter). 

I did not get price information on the LPF board but was assured 
it will be up with the rest of the information. 

73, 

   ... Joe, W4TV 
  



> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of K4IA at aol.com
> Sent: Friday, December 18, 2009 5:11 PM
> To: n6kr at elecraft.com; elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 Receiver Noise Level -- Evaluation 
> and Adjustment
> 
> 
> Wayne
> 
> Is the low pass filter module available separate from the 
> entire DSP  Rev C 
> board replacement?  If so, what does it cost and how 
> complicated is  it to 
> install?
>  
> Buck
> k4ia 
> K3 #101
>  
>  
> In a message dated 12/18/2009 10:12:29 A.M. Eastern Standard Time,  
> n6kr at elecraft.com writes:
> 
> The K3  has a lot of overall gain. This is necessary to provide  
> sufficient  speaker output in operating locations with high ambient  
> noise  levels.
> 
> But you can adjust the amount of gain, and shape it, to meet  
> your needs.
> 
> If you feel that the noise level of your K3's receiver is  
> excessive,  
> please try the following:
> 
> 1. Turn off the preamp.  In many cases it is not needed (especially  
> below 20 m), because the  receiver is still very sensitive working  
> directly into the  mixer.
> 
> 2. If overall AF gain is higher than needed for your headphones  or  
> speaker, set CONFIG:AF GAIN to LOW. This makes the K3's audio 
>  output  
> level (and overall gain) very similar to a K2.
> 
> 3. Use  the factory defaults for AGC. These were carefully chosen to  
> adjust  gain in the presence of significant band noise.
> 
> 4. Use narrow filter  bandwidths when listening to narrow-band modes  
> (CW or DATA). Noise  output is proportional to bandwidth, and 
> in narrow- 
> band modes, reducing  WIDTH can dramatically reduce the 
> signal-to-noise  
> ratio. I strongly  recommend installing at least one narrow crystal  
> filter (500 Hz or  lower) if you use CW or DATA modes. The 
> K3's entire  
> receiver  philosophy is built around the use of roofing filters that  
> are  matched to the operating mode.
> 
> 5. Use noise reduction. NR is  specifically designed to 
> reduce wideband  
> stochastic (white) noise. I  suggest using the lowest setting 
> (F1-1) to  
> obtain a modest  noise-reduction benefit with minimum impact 
> on signal   
> characteristics.
> 
> 6. If you're sensitive to high-pitched noise,  consider 
> installing (or  
> having us install) the new DSP low-pass  filter (LPF) module. 
> (Contact  
> k3support for details.) This filter  rolls off everything at 
> about 4.5  
> kHz, including some low-level AF  sampling artifacts from 10-14 kHz  
> that some operators with excellent  ears can hear. The LPF module,  
> which is easy to install, can improve  the overall listening  
> experience. It has already been phased into  production.
> 
> 7. If you still feel that noise level is too high, try  doing an MDS  
> (minimum-discernable signal) test to see if the  receiver is meeting  
> spec. You can use your own signal generator or  an Elecraft 
> XG1 or XG2,  
> in conjunction with the K3's built-in  true-RMS AF voltmeter (see  
> alternate VFO B display modes in the  owner's  manual).
> 
> 73,
> Wayne
> N6KR
>