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Filter alignment question

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info4mjs

Filter alignment question

Hi,

I was monitoring the K2's local oscillator frequency and I noticed that as I tune to WWV in the various modes, that the LO frequency is different at zero beat. I expected an offset (w/respect to SSB) in the CW mode but I expected the LO to be the same at zero beat whether I was in LSB or USB modes. It isn't so I am wondering if something is not aligned properly.

Any insight is appreciated.

Thanks

Mike, WA1SEO
K2 4778
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Don Wilhelm-3

RE: Filter alignment question

Mike,

Which oscillator are you referring to as "local Oscillator"? If you are
referring to the BFO, then it should be different from LSB to USB because
that is the way the sidebands are switched.

If you are referring to the VCO, then you must be retuning if that changes
between LSB and USB - if there is a need to re-tune to maintain zero beat,
then yes, a filter alignment is in order, and perhpas a dial calibration
also. Full, detailed instructions for setting the reference oscillator and
doing a dial calibration and filter alignment can be found on my website
http://w3fpr.qrpradio.com

73,
Don W3FPR

> -----Original Message-----
>
> I was monitoring the K2's local oscillator frequency and I
> noticed that as I tune to WWV in the various modes, that the LO
> frequency is different at zero beat. I expected an offset
> (w/respect to SSB) in the CW mode but I expected the LO to be the
> same at zero beat whether I was in LSB or USB modes. It isn't so
> I am wondering if something is not aligned properly.
>
> Any insight is appreciated.
>
> Thanks
>
> Mike, WA1SEO
> K2 4778
>

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Don Brown-4

Re: Filter alignment question

In reply to this post by info4mjs

Hi

Here is a way to check the alignment of the filters. Assuming a 600 Hz
sidetone tune to 4.000 MHz in CW normal mode You should hear the 4 MHz
internal oscillator as a 600 Hz tone, Switch to each filter and the tone
should not change frequency by more than a few hertz. Then switch to CW
reverse and go back through the filters. Again the 600 Hz tone should not
change. To check the SSB filters select LSB and tune to 4.00060. You should
hear the same 600 hertz tone then check each SSB filter and the tone should
not change. Now change to USB and tune to 3.99940 MHz and check for the 600
hertz tone on each filter. If you do not hear the correct tone on any of the
above tests then you need to recheck the filter alignment for that filter.
You may have it set on the wrong side of the filter slope or may need to
move it slightly. Use spectrogram to re-align the filters after first
setting them to the values listed in the manual so they are in the ballpark.
You should move each filters BFO frequency slightly even if it is correct so
the firmware will recalculate the sidetone offsets.

Don Brown
KD5NDB

----- Original Message -----
From: <[hidden email]>
To: <[hidden email]>
Sent: Monday, March 13, 2006 7:05 AM
Subject: [Elecraft] Filter alignment question

>
> Hi,
>
> I was monitoring the K2's local oscillator frequency and I noticed that as
> I tune to WWV in the various modes, that the LO frequency is different at
> zero beat. I expected an offset (w/respect to SSB) in the CW mode but I
> expected the LO to be the same at zero beat whether I was in LSB or USB
> modes. It isn't so I am wondering if something is not aligned properly.
>
> Any insight is appreciated.
>
> Thanks
>
> Mike, WA1SEO
> K2 4778
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

Michael Jensen

Filter alignment once again

Hi Guys

Can someone give and advice on my filter calibration on SSB, if I am on the
right track.

I have been looking through all the mail on filter calibration and have now
got it clear, that I will use FL1 only for TX and have focused on getting
the K2 to sound "good" (a very subjective thing I know). Then FL2-4 used for
RX.

FL1 are tuned by listening to the TX from K2 on my FT817 and changing the BF
until the sound are good. (all of this done due to reports I have received
telling that I sounded very sharp.. In audio that is J. )

FL2-4 have then been tuned based on TX from FT817 listening on K2 RX, to
make the sound ok. After that the result are checked with spectrogram using
the N-gen as input.

The result is found in a word in the following location:

http://aprs.the-jensen-dk.net/OZ1BZJK2filter.doc

No my concern are as I use PSK31 a lot, if I am going to be in trouble using
FL2-4 as RX filter, when FL1 are used. With the alignment I have tried here.

I seem to have a issue in LSB, where I can not set the BF any lower then
what it is now, but maybe ok as it sound ok.

This is my second filter calibration. The first was done only using
spectrogram for all filters.

Thanks in advance

OZ1BZJ

Michael

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Bill Coleman-2

Re: Filter alignment once again

On Mar 14, 2006, at 5:47 PM, Michael Jensen wrote:

> The result is found in a word in the following location:
>
> http://aprs.the-jensen-dk.net/OZ1BZJK2filter.doc

OK, here are some comments.

The first thing I notice is that the FL1 positions for LSB and USB
don't look right to me. The shape of the USB filter ought to be
exactly backwards of LSB, but yours looks the same, heavy on the low
frequencies and tapering off toward the highs. I wonder if your noise
generator has a bias toward low frequencies, or if there's some
frequency-limiting component in your measurement. Do you have the
KDSP2 installed? Did you disable it when you were taking your
measurements?

The second thing is that the FL1 positions for LSB and USB don't have
(about) the same base frequency. The "knee" of the USB curve is
around 800 Hz, but the same point in the LSB curve is about 600 Hz.
If you listen to LSB and then press CW REV to go to USB, you'd
probably notice a large change in the background noise. This is
because your sidebands don't have sufficient frequency symmetry. (It
is possible to get the LSB and USB background noise to sound ALMOST
exactly the same when properly adjusted. There's a slight shift in
"color" because of asymmetry in the bandpass fiilter)

The third thing is that both LSB and USB seem to be adjusted a bit
high -- the bandpass is a bit far from the carrier. You're going to
lose a lot of low-frequency energy in your voice -- which may be OK
if you are a very high-pitched voice. The bandpass should start to
rise around 300 Hz, with the "knee" about 500 Hz. Your FL2 settings
seems closer to being correct, and are a lot more symmetrical (see
the first two points)

The last thing I'll talk about is the other filter settings for LSB
and USB. I have 1.8 and 1.6 kHz widths programmed in to FL2 and 3 on
my K2, but frankly, I never use them. I don't like the way the
variable-bandwidth filter sounds at these wide settings, because of
it's wild asymmetry. (In fact, I have FL1 programmed for 1.0 kHz in
CW, which makes tuning the band a pretty quiet experience, even in a
contest. 1.0 kHz is about as wide as the variable-bandwidth filter
gets while staying symmetrical) Instead, I use the filtering
capability of the KDSP2 to clean up the sides of the crystal filter.

I also do RTTY and PSK31, but I've programmed the RTTY mode filters
for this mode. I don't recommend using a low frequency for either
PSK31 or RTTY, as you have programmed FL4 to pass 850 Hz. The reason
is that if your AFSK source has any harmonic energy, they'll pass
through the sideband filter and cause adjacent-frequency QRM.

Classic RTTY uses tones of 2125 and 2295 Hz. The "low tones" are 1275
and 1445 Hz. The second harmonic of 1275 is 2550 Hz, which may be
outside the K2 bandpass, depending on your filter.

The K2 makes it tough to use the classic RTTY high tones because of
limited BFO range. You may not be able to get the BFO to shift far
enough for both sidebands. (And as the BFO range increases, the BFO
step accuracy decreases) Even if you get LSB set up correctly, the K2
actually uses the USB settings on 21 MHz and above, due to the
inversion at the first mixer.

I ended up using 1500 Hz as the center frequency for RTTY (I use
tones of 1415 and 1585 Hz). This also made it easy to program the
KDSP2 for RTTY as well. I still had to modify the K2 BFO to get
sufficient range.

Hope this helps

Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901

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Ron D'Eau Claire-2

RE: Filter alignment once again

Bill, AA4LR wrote:

The shape of the USB filter ought to be
exactly backwards of LSB, but yours looks the same, heavy on the low
frequencies and tapering off toward the highs. I wonder if your noise
generator has a bias toward low frequencies, or if there's some
frequency-limiting component in your measurement. Do you have the
KDSP2 installed? Did you disable it when you were taking your
measurements?

----------------------------------

Taking audio from the "phones" jack can produce a rolloff much like that as
well, caused by the electrolytics in the circuit. The auxiliary speaker jack
is a better choice.

Ron AC7AC

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Tom Hammond-3

RE: Filter alignment once again

In reply to this post by Michael Jensen

Folks:

If the shapes of the LSB and USB filters are NOT opposite of each
other, the implication is that BOTH are on the SAME SIDEBAND, rather
than being on OPPOSITE sidebands. This can be confirmed by comparing
either the DAC counts or the FREQUENCIES of the BFO. If both sets of
values (DAC _or_ FREQ) are on the SAME side of the filter center
frequency, then they're both on the same sideband, though possibly
not on the same exact frequency.

73,

Tom Hammond N0SS
_________________________

Bill, AA4LR wrote:

The shape of the USB filter ought to be
exactly backwards of LSB, but yours looks the same, heavy on the low
frequencies and tapering off toward the highs. I wonder if your noise
generator has a bias toward low frequencies, or if there's some
frequency-limiting component in your measurement. Do you have the
KDSP2 installed? Did you disable it when you were taking your
measurements?

----------------------------------

Taking audio from the "phones" jack can produce a rolloff much like that as
well, caused by the electrolytics in the circuit. The auxiliary speaker jack
is a better choice.

Ron AC7AC

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Bill Coleman-2

Re: Filter alignment once again

On Apr 17, 2006, at 11:31 PM, Tom Hammond wrote:

> If the shapes of the LSB and USB filters are NOT opposite of each
> other, the implication is that BOTH are on the SAME SIDEBAND,
> rather than being on OPPOSITE sidebands.

This occurred to me, but since the BFO frequencies he listed seemed
right, this didn't seem possible. That's why I thought there was some
sort of other high-frequency attenuation going one. Ron hit it on the
head - the caps across the headphone jack cause this rolloff.

> This can be confirmed by comparing either the DAC counts or the
> FREQUENCIES of the BFO. If both sets of values (DAC _or_ FREQ) are
> on the SAME side of the filter center frequency, then they're both
> on the same sideband, though possibly not on the same exact frequency.

Yup. Made that mistake once myself.

Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901

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