[Elecraft] Calibrating K2 Xtal Filters

Sun Apr 11 16:26:04 2004

I have K2 S/N 1289 and nowhere in the documentation that came with it is =
any
mention of Spectrogram. The procedure for setting up the filters is =
somewhat
like Bill has described.=20

As I recall, the use of spectrogram was first promulgated right here on =
the
Elecraft reflector just about the time I built my K2.=20

Inquisitive and interested Hams who knew about Spectrogram experimented =
and
showed everyone how to use it.=20

I have built and "aligned" dozens of crystal filters over the years, =
most of
them of my own design. I had always laboriously measured the bandpass by
sweeping it with a signal and measuring the signal level at intervals. =
One
of the projects on my "to do" list was to automate that process, but I
hadn't ever gotten around to it. So when spectrogram was mentioned I =
jumped
on it. And I've enjoyed using it.=20

What you've done, Bill, is to approach the alignment a bit differently =
than
most. From reading your posts, you are doing it more like Wayne and Eric
originally expected it to be done! I agree, if you are trying to set the
bandpass EXACTLY centered on the signal, Spectroram probably isn't the =
most
accurate way. I found that centering it as close as I can see on =
Spectrogram
isn't always what I want.=20

I have noticed using spectrogram is that the bandpass is NOT exactly
symmetrical. (That's true of my experience will all of my homebrew =
"ladder
filters".) So, using Spectrogram, I set the marker on the peak in the
bandpass that is closest to the center on the narrower bandwidths. After
all, the only reason I have any bandwidth to the filter beyond the =
minimum
needed to pass the keying waveform of the CW signal is so that I can =
hear
what's going on around me. Personally, I don't like the sound of a =
narrow
filter and only use it when I'm forced to do so by QRM/QRN. So I don't =
care
if my bandpass extends a few hundred Hz off to one side of the signal =
more
than the other.=20

On my K2, those ripples in the bandpass, even on CW, can be 3 dB or =
more, so
I suspect that you'd see a noticeable change if level if you happen to =
have
the dip of one filter bandwidth right at the mathematical center and the
peak of another at the same point.=20

So, if after you're done you find one filter bandwidth setting seems to =
have
more insertion loss than another, you might try shifting that one off to =
the
side a bit and see if that doesn't level the responses better - assuming
that you're okay with one setting not be exactly centered.

Also, in the widest bandwidth, you don't want the bandwidth centered on =
the
signal. You want it extending away from zero beat, mostly. Otherwise, =
you'll
lose single-signal reception because the passband will cross over the =
"zero
beat" point. But I suspect you are completely aware of that.

Ron AC7AC

-----Original Message-----
From: [email protected] =
[mailto:[email protected]]
On Behalf Of Bill Tippett
Sent: Sunday, April 11, 2004 12:25 PM
To: [email protected]
Subject: Re: [Elecraft] Calibrating K2 Xtal Filters

Hi Vic,

At 01:08 PM 4/11/04, Vic Rosenthal wrote:

 >I can do all of the CW filters with Spectrogram in about ONE minute!

	I doubt that was the very first time you used Spectrogram.  I
thought about time I needed to search for the right webpages, download =
N0SS'
documentation, download and install Spectrogram on my computer, hook up =
my
soundcard to the K2 and carefully read through all 7 pages of the
documentation (CW only) before even getting to the calibration routine
itself and decided I could be finished long before that using only the =
K2,
XG1 and my head.  I also now know how to do this accurately in the field
without a computer.

	I'm sure Spectrogram is worth the investment in time to learn if you
need to recalibrate filters frequently, but it is NOT the only way to=20
calibrate
them accurately.  BTW, if I were going to use a computer display to do =
this,
I would probably use K6STI's DSP Blaster instead since I'm already =
familiar
with it.  It has both waterfall and spectrum displays which can be used =
just
like Spectrogram to display audio output vs frequency...plus it is a =
very
versatile DSP program which is my primary use.

					73,  Bill  W4ZV

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