[Elecraft] K2- setting the filters

[Don Wilhelm]

Jack,

The KSB2 will always use its own filter (OP1, OP2 or OP3 - they are all 
the same) to transmit.  The important thing is that the K2 will use the 
BFO settings associated with FL1 for transmitting.  So if you do not 
have the OP1 filter selected for SSB FL1, then the BFO frequencies will 
not be correct for the OP1 filter.

It is not unusual for the actual widths of the variable filter to vary 
substantially from those 'widths' shown on the K2 display.  That will 
depend on the exact crystals used in the filter, the varactor 
tolerances, and several other component tolerances.  It is always best 
to measure the actual filter width with Spectrogram - that is more true 
for the wide filters than the narrow CW filters - any discrepancy seems 
to disappear at filter widths of about 400 Hz, which is 'amazingly' the 
design center width of the variable filter.

You do not normally have to set FL2 to OP1.  The important filter is FL1 
because it is used for transmit.  FL1 can also be used for receive, but 
if the best transmitted signal quality results in a less than desirable 
receive signal with FL1, then the recourse is to set FL2 to OP1 and use 
that for receive.  BTW, I have almost never found that to be necessary 
in the many K2s that I have set up for SSB.

As a first trial, set FL1 to OP1, then using Spectrogram, adjust the 
BFOs for both LSB and USB so the passband is centered between markers 
placed at 300 and 2600 Hz.  Then try using FL1 for both transmit and 
receive.  If all is well, then set FL2 thru FL4 as you desire.  If the 
transmit signal needs adjustment, set the markers between 250 and 2550 
Hz and try again.  If your voice is quite unusually rich in low 
frequencies, you could go as low as markers between 200 and 2500 Hz.  
Should you have to go that low on the transmit filter, then you will 
likely have to set the FL2 filter to OP1 and adjust the BFOs for the 
most pleasant received signal.

Take a look at the K2 dial calibration article on my website 
http://w3fpr.qrpradio.com.  Part 3 of that article deals with the 
filter/BFO alignment and includes information about setting the SSB filters.

73,
Don W3FPR

Jack wrote:
> I have been operating my K2 as a CW only radio for a few months and 
> have now just added the KSB2 SSB board.
>
> When I only had CW, I set the filter widths and BFO settings as per 
> the defaults advised and was very happy with it. However, since 
> setting the default values suggested in the KSB2 book, I've discovered 
> a few unanswered issues.
>
> Q1, Do I have to set FL1 to OP1? I was under the impression I had to. 
> But a friend has set his FL1 to 2.4KHz. I know this is the filter that 
> is used to transmit. Is it OK to narrow it down? Is there any benefit?
>
> Q2, Why does the book also say FL2 should be set to OP1 on SSB? Is 
> this a typo?
>
> Q3, I have now set the filters using spectrogram. EVERYONE should do 
> this, it is so easy and makes a huge difference. And the program is 
> free! Do it !!!!
> I found that the default BFO values in the KSB2 book had CW and USB 
> pretty much perfect, but LSB was way off (3 or 400Hz). Retuning with 
> spectrogram has cured that and it sounds great on LSB now. Is it 
> normal to be so far off?
>
> Q4, The filter widths are actually much wider than that set on the K2 
> display. ie 2KHz filter is actually about 3KHz wide. To get the same 
> "sound" as my other HF rigs I am having to set the filter widths much 
> narrower than expected. ie set the display to 1.2KHz width to get an 
> actual 1.8KHz width trace on spectrogram. Is this normal? Can this be 
> adjusted? Am I worrying about nothing? :o)
>
> Overall i am very happy with the recievers performance. The K2 has 
> taken over as main radio, pushing japanese sets aside.
> But if anyone could advise on the above, that would aid my learing 
> process. Thats one of the reasons why i bought it :o)
>
>