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K3: Optimizing filter offsets for SSB TX and RX

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KM5Q

K3: Optimizing filter offsets for SSB TX and RX

Continued from: [CQ-Contest] SOME THOUGHTS ON USING THE K3 ON SSB

Reading these messages, I decided I should try adjusting the offset
for my 2.8 8-pole filter from the normal 0. I have been getting good
audio reports, but not "excellent".

Listening during adjustment, I found that as I reached -.20 some high
harshness was reduced. I thought that would be good, as I often find
myself cutting back the HI passband to get a similar effect. Then I
got on the Sunday Elecraft SSB Net. I couldn't get many opinions
because propagation was poor, but I had Phil NS7P give me his
opinion. He reported the least distortion around offset -.20, and
clearly an improvement over the 0 setting. So that's where I have it.
It's an easy test to make, since you can transmit with the CONFIG
window open.

Ever curious, I thought to play with my 2.1 filter offset (just for
receiving of course). I never liked listening to SSB with it because
the highs sounded harsh. As I turned it from the normal 0, down past -.
20, it started to sound better. I preferred around -.40 until I
checked it on a weak CW signal. It was making it weaker in comparison
with the other filters. So I compromised and set it at -.27. I'm happy
with that!

I think this is a good discovery! Maybe it's something the factory
should look into?

Windy KM5Q
K3 #764

Bill W4ZV wrote:
> After extensive experiments with tx audio settings in pursuit of
> "perfect
> audio" for my purposes - dxing on 80m - I came to the conclusion
> that for my
> voice with the HC-4, an offset of -0.07 with the 2.8 kHz filter was
> about
> right.
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Bill W4ZV

Re: K3: Optimizing filter offsets for SSB TX and RX

KM5Q wrote

Continued from: [CQ-Contest] SOME THOUGHTS ON USING THE K3 ON SSB

Reading these messages, I decided I should try adjusting the offset
for my 2.8 8-pole filter from the normal 0. I have been getting good
audio reports, but not "excellent".

<SNIP>

Bill W4ZV wrote:
> After extensive experiments with tx audio settings in pursuit of
> "perfect
> audio" for my purposes - dxing on 80m - I came to the conclusion
> that for my
> voice with the HC-4, an offset of -0.07 with the 2.8 kHz filter was
> about

I did NOT write that. That was a quote from G3UCK I was replying to regarding the fact that offsets up to 80 Hz in 8-pole CW filters are not uncommon. I've not done any testing on SSB or with the 2.8k 8-pole filter since I don't even have one (and haven't even been on SSB much). Check back with me in a couple of years when 10 meters opens again! :-)

73, Bill W4ZV

Joe Subich, W4TV-4

Re: K3: Optimizing filter offsets for SSB TX and RX

In reply to this post by KM5Q

If you crank in an offset with the 8 pole filters be sure
you test it with BOTH USB and LSB. An offset that enhances
low frequency response in USB will reduce the LF response in
LSB (enhance high frequency response) and vice versa.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of KM5Q
> Sent: Sunday, April 12, 2009 5:28 PM
> To: [hidden email]
> Subject: [Elecraft] K3: Optimizing filter offsets for SSB TX and RX
>
>
> Continued from: [CQ-Contest] SOME THOUGHTS ON USING THE K3 ON SSB
>
> Reading these messages, I decided I should try adjusting the offset
> for my 2.8 8-pole filter from the normal 0. I have been getting good
> audio reports, but not "excellent".
>
> Listening during adjustment, I found that as I reached -.20
> some high
> harshness was reduced. I thought that would be good, as I often find
> myself cutting back the HI passband to get a similar effect. Then I
> got on the Sunday Elecraft SSB Net. I couldn't get many opinions
> because propagation was poor, but I had Phil NS7P give me his
> opinion. He reported the least distortion around offset -.20, and
> clearly an improvement over the 0 setting. So that's where I
> have it.
> It's an easy test to make, since you can transmit with the CONFIG
> window open.
>
> Ever curious, I thought to play with my 2.1 filter offset (just for
> receiving of course). I never liked listening to SSB with it because
> the highs sounded harsh. As I turned it from the normal 0,
> down past -.
> 20, it started to sound better. I preferred around -.40 until I
> checked it on a weak CW signal. It was making it weaker in
> comparison
> with the other filters. So I compromised and set it at -.27.
> I'm happy
> with that!
>
> I think this is a good discovery! Maybe it's something the factory
> should look into?
>
> Windy KM5Q
> K3 #764
>
>
> Bill W4ZV wrote:
> > After extensive experiments with tx audio settings in pursuit of
> > "perfect
> > audio" for my purposes - dxing on 80m - I came to the conclusion
> > that for my
> > voice with the HC-4, an offset of -0.07 with the 2.8 kHz
> filter was
> > about
> > right.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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KM5Q

Re: K3: Optimizing filter offsets for SSB TX and RX

YOU ARE RIGHT, Joe !! I did my trials on USB. On LSB, I can tell by
listening and re-adjusting that you are quite correct. It's back to
zero for me.

:-|

I await further comments.
Windy

On Apr 12, 2009, at 5:10 PM, Joe Subich, W4TV wrote:

>
> If you crank in an offset with the 8 pole filters be sure
> you test it with BOTH USB and LSB. An offset that enhances
> low frequency response in USB will reduce the LF response in
> LSB (enhance high frequency response) and vice versa.
>
> 73,
>
> ... Joe, W4TV
>
>>

Joe Subich, W4TV-4

Re: K3: Optimizing filter offsets for SSB TX and RX

If I wanted to check for filter offsets in the 8 pole
filters, I think I would put them into the main RX
and run response curves (using the K3 Filter Utility
package) in both USB and LSB (or AFSK A NOR and REV).
Set the DSP bandwidth to 4.00 and the center frequency
to 1.50 (SSB) or 2.20 (AFSK A) to minimize the DSP
contribution to the response.

One set of data would need to be inverted and offset
to compare the two responses but one could overlay
the two curves and look for any asymmetry ... I would
check specifically to see if the -3 dB points were
spaced equally above/below the center frequency.

The skirts will not be symmetric in LSB/USB due to the
sharp cutoff near the carrier in USB/LSB (1500 - 1400
= 100 Hz). Any offset may be more apparent using the
AFSK A settings.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Windy Dankoff
> Sent: Sunday, April 12, 2009 10:28 PM
> To: [hidden email]
> Subject: Re: [Elecraft] K3: Optimizing filter offsets for SSB
> TX and RX
>
>
> YOU ARE RIGHT, Joe !! I did my trials on USB. On LSB, I can tell by
> listening and re-adjusting that you are quite correct. It's back to
> zero for me.
>
> :-|
>
> I await further comments.
> Windy
>
>
> On Apr 12, 2009, at 5:10 PM, Joe Subich, W4TV wrote:
>
> >
> > If you crank in an offset with the 8 pole filters be sure you test
> > it with BOTH USB and LSB. An offset that enhances low frequency
> > response in USB will reduce the LF response in
> LSB (enhance
> > high frequency response) and vice versa.
> >
> > 73,
> >
> > ... Joe, W4TV
> >
> >>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html