K2 10m sensitivity

[Alastair Couper]

I have just received a new old K2 here. It has most of the important mods,  
AtoB upgrade, and is working as well as it can, as best I am able to  
determine. The alignment is fine, and it puts out OK on all bands. I have  
not been able to find any posts about the sensitivity on 15m-12m-10m being  
not so great. On 40m-80m-160m it is what I would expect. 20m it's just OK  
with wider filters, but there is plenty of internal noise with the  
narrower filters.

I don't have a microvolt source to get a precise reading. But with a 5 el  
yagi on 10m, band noise completely covers internal noise on my Yaesu. On  
the K2, I can hear the band noise, but the internal noise is rather more  
than I like. Even strong signals don't move the S meter much, and that is  
after I have tweaked the settings, and adjusted the AGC threshold.

I know audio filtering will help with this. I also did the mod to increase  
the gain of the RF preamp. I wonder if anyone else sees the 10m  
sensitivity as a problem? Is there perhaps a wider bandwidth transistor to  
use in place of the 2n5109?

NH7O
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Don Wilhelm-4]

  The 10 meter sensitivity of the K2 is normally quite good.
I would suggest checking the tuning of the bandpass filters.
When tuning the bandpass filters, remember that they are shared by 2
bands, and you must tune the inductors first, and after that, tune the
capacitors.  Do 10 meters first, then 12 meters -- do 15 meters first
and after than do 17 meters.

Set the K2 power to 2 watts, connect a dummy load and adjust the proper
bandpass filter element for a peak in the power output.  If the power
increases dramatically, exit tune and then re-enter to drop the starting
power back down to the 2 watt level.

After adjusting the bandpass filters to a peak during a transmit (or
tune), they are properly tuned for receive too.

You will need to buy or borrow a calibrated signal generator to make any
definitive measurements of the sensitivity.  It is difficult to make a
judgement based on antenna noise alone without some instrumentation.  
The Elecraft XG3 is a great tool to do exactly that - it has controlled
output levels and can be used to make MDS measurements, and you can use
it to properly set your S-meter.

73,
Don W3FPR

On 6/6/2011 3:36 AM, Alastair Couper wrote:

> I have just received a new old K2 here. It has most of the important mods,
> AtoB upgrade, and is working as well as it can, as best I am able to
> determine. The alignment is fine, and it puts out OK on all bands. I have
> not been able to find any posts about the sensitivity on 15m-12m-10m being
> not so great. On 40m-80m-160m it is what I would expect. 20m it's just OK
> with wider filters, but there is plenty of internal noise with the
> narrower filters.
>
> I don't have a microvolt source to get a precise reading. But with a 5 el
> yagi on 10m, band noise completely covers internal noise on my Yaesu. On
> the K2, I can hear the band noise, but the internal noise is rather more
> than I like. Even strong signals don't move the S meter much, and that is
> after I have tweaked the settings, and adjusted the AGC threshold.
>
> I know audio filtering will help with this. I also did the mod to increase
> the gain of the RF preamp. I wonder if anyone else sees the 10m
> sensitivity as a problem? Is there perhaps a wider bandwidth transistor to
> use in place of the 2n5109?
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html