[Elecraft] K3 Rx IMD

[Ramiro Aceves]

Hello all

As David suggested we continue the discussion on the list. I have done 
some new poor man tests, using a local AM carrier on Medium Wave at 917 
KHz. For generating the other tone, I am using the same home made DDS 
generator as before. At this lower frequencies the signal generated by 
the DDS is much more cleaner.  The antenna is a 6.5m long dipole on the 
balcony and an open wire feeder as in the earlier tests, but using only 
one half of the dipole by just directly connecting one open wire end to 
the K3 antenna connector. The reasons of doing that is that my T match 
tunner does not work below 1.8 MHz. This eliminates the posibility of 
IMD products produced on the tuner toroids. It does not remove, just in 
case, other no-linearities found everywhere as suggested by (sorry for 
my poor english, I hope you understand me).

10 Hz spacing, ACG-F:

http://ea1abz.ure.es/acg-F.png


Now with AGC-S, notice the strong reduction of IMD:

http://ea1abz.ure.es/agc-S.png



Now see the AGS-S to AGC-S-soft transition on the middle of the capture:

http://ea1abz.ure.es/agc-S_vs_agc-soft.png



Now see the IMD at 100Hz spacing, AGC-F to AGC-S transition at the 
middle of the screen:

http://ea1abz.ure.es/100Hz.png


Sorry for the poor noise floor, is the Madrid band noise received by the 
antenna. Hi.

I see that the IMD problem is worse with small carrier distances. At 100 
Hz spacing they are much more weaker and not problematic.


73, Ramiro.

EA4NZ