[Elecraft] K2 #6593 Transmit Performance

[Don Wilhelm]

Merlin,

Since you suspect some common connection, you might try removing all 
common connections by running the K2 on a battery for a test.  A 12 volt 
automotive type battery is usually easily available even if you have to 
take the K2 to the vehicle.  Make the battery connections tight when 
using that method.
If you are working with a QRP K2, you can use a gel cell if you have one.
If you are working with a K2/100, remove the KPA100 and test with only 
the QRP K2.

73,
Don W3FPR

m0trx wrote:
> Don,
>
> Thanks for your reply. I shall try to use spectrogram to get a comparison of
> the spurious emissions on 40m and 10m. The fact that the level of the
> spurious signals relative to the carrier is different on two different
> receivers would indicate to me that the problem may not be with the K2's
> output at all. I have known similar problems in the past with different
> transceivers when trying to monitor signals locally in order to determine
> the quality of the signal.
>
> Merlin Cooper
> M0TRX
>
>
>
>
>
> Don Wilhelm-4 wrote:
>   
>> Merlin,
>>
>> Please define "noisy" so we can have a better understanding of what is 
>> happening.
>> If you have a selective receiver available you can scan the spectrum on 
>> each side of the signal for about 1 kHz and gain the same information as 
>> with a narrow band spectrum analyzer.  Another method is to use a DC 
>> receiver and look at the audio output of that DC receiver with 
>> Spectrogram to view up to 6 kHz of the spectrum at the signal frequency.
>> Are you certain it is not your receiver's response with a short antenna 
>> attached?
>> Although the source could be anywhere in the transmit chain (or even 
>> outside the K2 as you hinted (power supply maybe?) - there are 3 main 
>> areas I would look first, BFO, VCO and transmit mixer.
>>
>> 73,
>> Don W3FPR
>>
>> m0trx wrote:
>>     
>>> Dear All,
>>>
>>> I recently finished building K2 #6593 and have been thoroughly impressed
>>> with the performance of the receiver. However, having done some initial
>>> tests on transmit into a dummy load, whilst monitoring the signal on
>>> another
>>> receiver, I have noticed that the the signal starts to sound noisy as the
>>> frequency is increased (i.e. 40m sounds clean but 10m sounds far from
>>> clean). I do not currently have access to a spectrum analyser in order to
>>> check this quantitatively.
>>>
>>> The K2 is located far from my linear power supply (at least 3-4 feet) so
>>> I
>>> doubt this is due to modulation of the VCO from the 50Hz supply. If this
>>> were the case then the problem would be prevalent on all bands anyway. I
>>> wonder whether anyone could shed some light on the likely cause of this.
>>> I
>>> am beginning to wonder whether the frequency components I am hearing are
>>> actually on the transmitted signal or as a result of some mains coupling.
>>> The reason I think this is because the level of said frequency components
>>> relative to the carrier is higher on one receiver than on another (both
>>> in
>>> same room, aerial etc).
>>>
>>> Any commnets would be most welcome.
>>>
>>> Regards,
>>>
>>> Merlin Cooper
>>> M0TRX
>>>   
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