[Elecraft] Lousy Tx audio reports using K2

[Don Wilhelm]

Eddy,

Since you mentioned a lack of highs, I doubt that the low-frequency 
response mod will help much, but you certainly can try.

What is more important is the place the low frequency corner of the FL1 
passband close to 300 Hz.  If you do that, when you tune an SSB signal 
so it sounds right in your K2, you will transmit on his frequency 
(because you tuned his voice to fall into the 300 to 2800 kHz range 
where it sounds best to most ears).  If you OP1 filter is set 100 Hz 
high or low, then you can still receive by skewing the frequency (you 
really will not know you are doing that, but it happens that way), but 
then when you transmit, you do not sound right to the person on the 
receiving end.

When I set up a K2 that is in here for repair, I listen not only to the 
received signal, but I listen to a transmitted signal on another 
receiver.  I have found that the 300 Hz filter corner (-3 to 6 dB point) 
is the one most important factor in making transmit and receive line up 
properly.

73,
Don W3FPR

k6sdw wrote:
> Good stuff Don!
>
> I'm concerning doing the G3RXQ mod to the KSB2 and see if that helps with
> the low-freq response.
>
> 73.......
>
>
>
> Don Wilhelm wrote:
>   
>> Eddy,
>>
>> It is important where you set the audio passband.  Normally, there is no 
>> lack of high frequency response with the 2.6kHz bandpass.
>>
>> Using Spectrogram to set the SSB filters, I normally recommend that you 
>> set markers at 300 Hz and the filter width plus 200 Hz - or in your 
>> case, 2800 Hz.  Center the FL1 (OP1) passband between those markers and 
>> try it out.  With most voices and microphones, those settings are 
>> correct, and wil work quite well for receive as well.  For FL2, I use 
>> the variable filter and set it 300 Hz less than FL1 - it is important to 
>> measure the actual width with Spectrogram since at wide setting the 
>> numbers shown by the K2 are usually incorrect.  Set the low frequency 
>> corner of all the SSB filter passbands at 300 Hz to maintain 
>> intelligibility as the filters are narrowed.
>>
>> If you are 'netting' with other hams at a specific frequency, you should 
>> check your dial calibration - if you are not tuned to the actual 
>> frequency of the other hams (because your dial calibration is off), it 
>> could be that your audio is OK, but you are placing your transmit 
>> frequency a bit high or low.  The K2 Dial Calibration article on my 
>> website http://w3fpr.qrpradio.com can give you the procedure for 
>> obtaining good dial calibration.
>>
>> If filter alignment as I have outlined does not solve your problem, you 
>> may have a microphone that is lacking in response at the higher audio 
>> frequencies, but the MH2 usually has a bit of boost for the highs - you 
>> might want to see if one of the locals near you has an MH2 that you can 
>> compare with.
>>
>> 73,
>> Don W3FPR
>>     
>