[Elecraft] K2 a little deaf?

[w2bvh]

Thanks Don,

As you say, I also would expect the signal from the 8640B to be clearly 
audible at -140 dBm on the K2.

I took your advice checked the filter bandwidths. I used the old noise 
source I built when I originally built the K2 ( Tom Hammond design?) 
along with the filter measurement instructions from your web site, and 
the Spectrogram 5.17 program.  No changes were needed. The filters are 
centered on 550 Hz. So that is not causing the MDS problem. It was well 
worth doing to eliminate that as a possible cause.

The reply on the Elecraft reflector from KN5L was helpful for me to make 
more MDS measurements and help me validate the ones I made originally. I 
used the instructions that come with the XG3 manual to set up the K2 and 
calculate the MDS. I used the 8640B as the signal source.  The results 
of those measurements are:

_XFil BW Hz)                    MDS (dBm)
_400                                  -125
700                                  -123
1500                                -121.5

So these results are actually a couple of dB WORSE (at the same 
bandwidth)  than the ones I originally got (e.g. the ones from my 
original email to the reflector a couple of days ago).

Any additional advice you may have would be greatly appreciated. I don't 
know if you have fixed this type of problem before, but if you have, 
maybe I should be mailing it off to you to fix it?

I did a qrp-qrp qso with an F5  last night on 40M, but it was pulling 
teeth to copy him. Another 1 1/2 s-units (or so) of signal would have 
been very welcome!

Please let me know either way.

73 & happy 4th,
--Lenny W2BVH

ps - as for bringing the siggen to the K2  or vice versa, the siggen had 
to be upstairs in the shack for antenna measurements (can't bring the 
antenna connection down to the basement ;-).  MDS measurement was an 
afterthought -- which I'm glad I did.

__


On 7/1/2018 11:55 PM, Don Wilhelm wrote:
> Lenny,
>
> Are your IF filters aligned so a 550Hz signal is within the passband.
> With the K2, simply setting STP for 550 Hz will not do it, you must do 
> CAL FIL to make 550Hz appear well within the receive passband.
>
> A properly tuned K2 will typically have a good response to a -140dBm 
> signal from the HP8640B.
>
> It is easier to take the K2 to the signal generator than to lug that 
> heavy signal generator to the hamshack!
>
> 73,
> Don W3FPR
>
> On 7/1/2018 4:35 PM, w2bvh wrote:
>> I dragged my HP8640B out of the "lab" (basement) to the second floor 
>> shack to do some antenna testing about a week ago. Before dragging 
>> this 50 lb instrument back down two flights of stairs I decided to do 
>> a quick MDS measurement on my K2 and got some results I'm a little 
>> concerned about.
>>
>> Yesterday I did an informal test. K2 set for cw, 1.5 KHz bandwidth, 
>> 14.05 MHz, AGC on, preamp off. Attached siggen, tuned the K2 to 550 
>> Hz tone and cranked down the siggen amplitude until the signal and 
>> noise were about equal, "by ear". Siggen output was -130 dBm. This 
>> was enough to cause me to look further.
>>
>