[Elecraft] PSK31 on the K2

[Jim Brown]

On Mon, 6 Aug 2007 17:24:03 +0600, Igor Sokolov wrote:

>Has it
>something to do with VFO stability of phase shift in the filters - I do not
>know. But weak signals coming from my IC765 get easyly decoded by the
>program while if I use K2 the same program can decode only solid signals. 

I agree with others that it is probably a filter alignment issue. There are 
excellent resources in the Elecraft community to help you fix that. 

>I am not pleased with SSB performance of K2 either. 

First, you must remember that the K2 started out life as a QRP CW rig. As 
that, it's spectacularly good. The K2/100 is also a very good CW contesting 
rig, but for the excessive wideband phase noise that makes you very 
unpopular with your neighbors if you use it to drive an amp. 

I agree. The widest RX filter is the TX filter. It has very good magnitude 
and phase response, and it sounds great. But the "stagger-tuning" of the CW 
RX filters to provide narrower SSB RX produce a VERY bumpy audio response 
(both magnitude and phase) that only the programmer's mother could love. It 
sounds awful, and it degrades intelligibility. 

>Especially on TX. 

I agree with you, but there are some very good fixes that can improve it 
significantly. Many of them are written up on user websites, with links from 
the Elecraft webpage. The fundamental problem is that the K2 audio path is 
low on gain. The gain is also a bit lacking further on in the signal chain.

I developed a simple mod that helps a lot. On the SSB board, change R14 to 
2K, change C34 to 0.22 uF, and add 2.2 uF in series with R15. This provides 
6 dB additional gain for the mic, which allows you to hit the compressor 
harder and increase the average loudness. It also rolls off the low end a 
bit, which prevents "pops" from activating the compressor, making the 
compressor work better. 

>Having said that it is pretty good as CW contest rig and is almost on the
>par with my main radio.

Yep!  

Jim Brown K9YC