[Elecraft] [K2] lack of sensitivity...?

[Geoffrey Mackenzie-Kennedy]

Hello Gil,

The ATU in your K1 could be making the difference.  It will or should 
transform the impedance presented by the 33.5 ft wire and 13 ft counterpoise 
to 50 ohms resistive, which is the source impedance which the K1's receiver 
likes to see.  The K2's receiver would also like to see a 50 ohm resistive 
source, but without an ATU it will see whatever source impedance is 
presented by the wire and counterpoise.

On 20m the wire and counterpoise would be seen by the K2's receiver as a 
fairly high impedance source, 2000 ohms or more resistive with some 
inductance in series.  On 40m, and depending on how you have the wire and 
counterpoise deployed and the effects of nearby objects, the receiver could 
be seeing a source whose resistive part is 20 ohms or less with some 
capacitance in series.  These are rough values simply to illustrate one 
possible reason why your K2 is deaf on 20m, and not quite as deaf on 40m.


If possible bypass the ATU in the KX1, and then make a comparison between 
your K1 and K2.  If your K1 becomes deaf as well, then buy an Elecraft ATU 
for your K2.  If buying an ATU is not an option, it is not difficult to 
homebrew a L Network for use as an ATU.  If you do decide to homebrew a L 
network, I suggest that the coil be solenoid wound rather than wound on a 
toroidal core.

73,

Geoff
LX2AO


On August 30, 2012 at 8:03 AM, "Gil G." <gil at keskydee.com> wrote:



> Hello,

> I knew this title would grab some attention ;-)

> Well, since my K1 worked so well, I decided to build a K2.
> It took me 30 hours over three days. Everything works, but…

> First, the receiver is pretty deaf on 20m. Not much static at all, faint 
> signals.
> I plugged in my K1 on the same wire, and what I could barely hear on 20m 
> on the K2 came in full blast on the K1.
> The preamp helps a little, but not much.
> On 40m, the score is closer, but still advantage to the K1 over the K2 
> with preamp on.
> I can use FL1 and FL2, but with 3, the signal is very attenuated, with 4 
> (200Hz), usually gone.
> The other bands, I haven't listened enough yet to make a diagnosis… I can 
> hear more static than on 20m.
> I have set the filters as indicated in the manual.

> The K1 has the ATU, would that make such a difference?
> I use a 35.5ft wire with 13ft counterpoise, directly out the BNC via a 
> binding post.

> By the way, I do get full output power on the K2 on all bands.
> I precisely peaked all bands on receive, then on transmit with my QRP 
> wattmeter.

> Any advise?

> Thanks!

> Gil.