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Merlarts

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A few days ago somebody was asking who it might be who's been experimenting
with shielding on the KSB2 board. I was that guy I suspect, because nobody
else I've observed on this net seems to be as annoyed as I about the bad
skirts, high ripple, bad ultimate selectivity, etc. when the K2 is used with the
KSB2.

This is an unbelievably competent radio; no matter whether it's measured
against $10,000 machines, $600.00 machines, or whatever.
BUT------------------------

The performance of its filter, and the way that it performs when installed
in the radio, is DISMAL!!!!!!!!

On sideband, tight skirts (the electronic kind, gentlemen!) are terribly
important, maybe more so than on CW. There is nothing neater than listening to
a weak SSB signal through an IF system that has a 1.2:1 shape factor. That
complete absence of interference on the sides is marvelous to hear. I'd be
surprised if the KSB2 manages 2:1. Just tune through loud broadcast signals on
forty meters sometime; listen to the audio "images" the other side of zero
beat even on moderately strong signals. If this radio were a piece of junk
that might be acceptable. On a radio that is truly world class in every other
respect it's absolutely unacceptable.

Take a look at something like a TR-4C; the way the sideband switch is
oriented so that the input side of the filters cannot "see" the output is typical
of the care that used to be taken with filter installation. Similar with
Collins S line receivers: those not so wonderful mechanical filters are,
nevertheless mounted in such a way as to utilize every drop of filtering that's
available. That was fifty or so years ago! How far have we come?

I have had good success on the KSB2 with shielding the input and output
toroids in little tine cans. Yeah, I know, toroids are self shielding; but even
the small wires that go into the board act as little antennas. I've also
tried putting a small shield on the bottom of the board, separating the input
from the output. It works, as well. All of these things work, but I'm more
than a little disappointed that apparently no concern was given to filter
isolation when the design was originally created.

How about somebody designing a filter? I've contacted Inrad; they already
have a CW filter for the K2, but the K2's CW performance isn't as much of a
problem as it's sideband performance. Inrad doesn't just doesn't seem to be
interested in coming up with a sideband filter.

Is anybody else as annoyed as I am about this stuff?

Merlin

W3ICT

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Ron D'Eau Claire-2

Tight Skirts...

Merlin, W3ICT wrote:

...nobody else I've observed on this net seems to be as annoyed as I about
the bad
skirts, high ripple, bad ultimate selectivity, etc. when the K2 is used
with the
KSB2. ...On sideband, tight skirts (the electronic kind, gentlemen!) are
terribly
important, maybe more so than on CW. There is nothing neater than
listening to
a weak SSB signal through an IF system that has a 1.2:1 shape factor.

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

My SSB operating is only casual but I can say with half a century of
operating behind me that I absolutely LOATHE steep-sided filters on CW. They
produce a lot of "trash" in the bandpass caused by the way they modulate
signals on edge of the bandpass. Of course, signals varying at all in
frequency, including noise, are amplitude-modulated by the filter slope,
with causes further sidebands, etc.

A lot of work has been done by both engineers and mathematicians working out
the best shape to minimize these effects, but this ol' operator simply likes
listening to a big chunk of the band at one time and letting my grey-filter
between the ears do the work for me.

I use OPT1 a lot for CW, and switch to the narrower filters mostly when I
need the improved S/N ratio the narrower bandpass provides to dig for a weak
signal. From many QSO's and posts on this reflector and others, I know that
I am not alone in that preference.

Even so, I bet if you came up with ways to make the improvements you'd like
to see, I bet lots of operators who love tight skirts would appreciate your
efforts.

One thing about Elecraft is that they encourage experimenting and improving.
A number of the "improvements" that have been made to the K2 over the years
have been the direct result of someone like you sitting down and saying
"What if...."

Ron AC7AC

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N8LP

Re: Tight Skirts...

Sounds like the age old debate in the hifi world about the "sweet" sound
of tube amplifiers vs. the "hard" sound of clearly superior modern solid
state amps.

Preferences aside about slopes and shape factors... I'd like to have
MUCH better ultimate rejection... and a true rf clipper would be a nice
addition, especially when using QRP.

Larry N8LP

Ron D'Eau Claire wrote:

>Merlin, W3ICT wrote:
>
>...nobody else I've observed on this net seems to be as annoyed as I about
>the bad
>skirts, high ripple, bad ultimate selectivity, etc. when the K2 is used
>with the
>KSB2. ...On sideband, tight skirts (the electronic kind, gentlemen!) are
>terribly
>important, maybe more so than on CW. There is nothing neater than
>listening to
>a weak SSB signal through an IF system that has a 1.2:1 shape factor.
>
>--------------
>
>My SSB operating is only casual but I can say with half a century of
>operating behind me that I absolutely LOATHE steep-sided filters on CW. They
>produce a lot of "trash" in the bandpass caused by the way they modulate
>signals on edge of the bandpass. Of course, signals varying at all in
>frequency, including noise, are amplitude-modulated by the filter slope,
>with causes further sidebands, etc.
>
>A lot of work has been done by both engineers and mathematicians working out
>the best shape to minimize these effects, but this ol' operator simply likes
>listening to a big chunk of the band at one time and letting my grey-filter
>between the ears do the work for me.
>
>I use OPT1 a lot for CW, and switch to the narrower filters mostly when I
>need the improved S/N ratio the narrower bandpass provides to dig for a weak
>signal. From many QSO's and posts on this reflector and others, I know that
>I am not alone in that preference.
>
>Even so, I bet if you came up with ways to make the improvements you'd like
>to see, I bet lots of operators who love tight skirts would appreciate your
>efforts.
>
>One thing about Elecraft is that they encourage experimenting and improving.
>A number of the "improvements" that have been made to the K2 over the years
>have been the direct result of someone like you sitting down and saying
>"What if...."
>
>Ron AC7AC
>
>
>_______________________________________________
>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
>
>
>
>

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Eric Swartz - WA6HHQ

Re: Tight Skirts...

Administrator

We designed the KDSP2 to improve ultimate SSB filter ultimate rejection
in the K2.

The KDSP2, with its brick wall SSB filter settings, when cascaded after
the KSB2 filter, totally eliminates any residual leakage from strong
signals outside the passband. It also tightens the net filter shape
factor. The ultimate rejection is 60-75 dB on the xtal filter, which
means a strong residual off freq. signal will not activate the K2's AGC,
allowing the DSP to do its job without signal degradation.

This is how I run my K2 and I hear no difference with strong off
frequency signal blow-by between it and the other $3K+ rigs we have in
the lab. :-)

73, Eric WA6HHQ

Larry Phipps wrote:
> Sounds like the age old debate in the hifi world about the "sweet" sound
> of tube amplifiers vs. the "hard" sound of clearly superior modern solid
> state amps.
>
> Preferences aside about slopes and shape factors... I'd like to have
> MUCH better ultimate rejection... and a true rf clipper would be a nice
> addition, especially when using QRP.
>
> Larry N8LP

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N8LP

Re: Tight Skirts...

OK Eric... I just picked up my radio used, and I haven't checked the
alignment yet... this was just an impression I had. I'll put it on the
bench and make some measurements before commenting further.

Larry N8LP

Eric Swartz - WA6HHQ, Elecraft wrote:

> We designed the KDSP2 to improve ultimate SSB filter ultimate
> rejection in the K2.
>
> The KDSP2, with its brick wall SSB filter settings, when cascaded
> after the KSB2 filter, totally eliminates any residual leakage from
> strong signals outside the passband. It also tightens the net filter
> shape factor. The ultimate rejection is 60-75 dB on the xtal filter,
> which means a strong residual off freq. signal will not activate the
> K2's AGC, allowing the DSP to do its job without signal degradation.
>
> This is how I run my K2 and I hear no difference with strong off
> frequency signal blow-by between it and the other $3K+ rigs we have in
> the lab. :-)
>
> 73, Eric WA6HHQ
>
>
> Larry Phipps wrote:
>
>> Sounds like the age old debate in the hifi world about the "sweet"
>> sound of tube amplifiers vs. the "hard" sound of clearly superior
>> modern solid state amps.
>>
>> Preferences aside about slopes and shape factors... I'd like to have
>> MUCH better ultimate rejection... and a true rf clipper would be a
>> nice addition, especially when using QRP.
>>
>> Larry N8LP
>
>
>
>

N8LP

Re: Tight Skirts...

In reply to this post by Eric Swartz - WA6HHQ

You may have just sold me on a KDSP2 down the road Eric. I just ran some
tests on my "new used" K2 (#568), and to cut to the chase... I measured
ultimate rejection out 5 kHz as 80dB with the KSB2 OP1 filter in, better
than you indicated. But with FL2, which is set for 1.8 kHz, I measured
115dB. Is this a result of the KSB2 being outboard?

Larry N8LP

Eric Swartz - WA6HHQ, Elecraft wrote:

Eric Swartz - WA6HHQ

Re: Tight Skirts...

Administrator

Hi Larry,

OP1 is the KSB2's SSB fixed b/w filter, which has been optimized for
minimum ripple at one SSB b/w. In SSB it is always used for transmit,
but it or any of the CW filter bandwidths can be used for receive. Looks
like you are using one of the CW settings at 1800 Hz..

Any of the variable CW filter settings (1800 Hz etc.) use the varactor
tuned CW filter on the motherboard. This variable CW filter is really
optimized for user settings below 700 Hz. (You can chose what b/w to use
in each of the four filter memories for each mode..) Wider CW filter
settings will have more ripple and poorer out of filter rejection. We
allowed the variable CW filter to be set wider to facilitate quickly
tuning the band in CW mode and for simple SSB reception in K2s that do
not have the SSB adapter. We recommend using the OP1 filter for most SSB
reception.

One interesting side note: The SSB OP1 filter can be used with different
BFO settings in each of the four SSB filter memory settings, creating
low and high cut settings. See the filter calibration section of the K2
and KSB2 manuals for information on setting up the filters.

73, Eric WA6HHQ
-------------

Larry Phipps wrote:

>
> You may have just sold me on a KDSP2 down the road Eric. I just ran some
> tests on my "new used" K2 (#568), and to cut to the chase... I measured
> ultimate rejection out 5 kHz as 80dB with the KSB2 OP1 filter in, better
> than you indicated. But with FL2, which is set for 1.8 kHz, I measured
> 115dB. Is this a result of the KSB2 being outboard?
>
> Larry N8LP
>
>
>
> Eric Swartz - WA6HHQ, Elecraft wrote:
>
>> We designed the KDSP2 to improve ultimate SSB filter ultimate
>> rejection in the K2.
>>
>> The KDSP2, with its brick wall SSB filter settings, when cascaded
>> after the KSB2 filter, totally eliminates any residual leakage from
>> strong signals outside the passband.

Eric Swartz - WA6HHQ

Re: Tight Skirts...

Administrator

In reply to this post by N8LP

Oops! - I missed one point in your email. Yes, the above board mounting
of the KSB2 reduces ultimate rejection due to its longer ground return
paths. But as you noted, with 80 dB of ultimate rejection, following it
with the KDSP2 kills any residual blow by.

A number of the $3K and above DSP rigs on the market today take a
similar approach to the K2. They use a simple moderate rejection crystal
filter followed by the brick wall DSP to gain ultimate filter rejection.
The crystal filter does the heavy lifting to keep off frequency signals
from pumping the AGC and the DSP cleans up any weak residual blow by
that gets past the crystal filter.

73, Eric

Larry Phipps wrote:

Geoffrey Mackenzie-Kennedy-2

Re: Tight Skirts...

In reply to this post by Ron D'Eau Claire-2

After having fingers burnt while designing very 'srtrong' receivers, may I
add comment.

IF filters with very tight skirts do allow the recovery of very good SSB
audio or CW. To do this the filter must NOT have sharp corners at the top of
its 'response', the corners should be a little rounded. i.e. the response at
the top, often the top 6db, should "approach Gaussian". My understanding of
this is that the Group Delay through a filter with SHARP corners varies
greatly especially at the corner frequencies, resulting in "raspy" SSB or as
you put it, trash on CW. After the slight rounding at the top, the skirts
can drop at a rate of knots. Cohn style Ladder filters are poor when Group
Delay is considered. Other types of Ladder filter at mid HF using 14
crystals can yield SSB bandwidths, <0.2db ripple, symmetry, 6/60db shape
factors of 1.2 or sometimes a bit less, and stopband attenuation of 100db.
How the filter is built and terminated are very important considerations,
and for my part I prefer ladder filters with an even number of crystals for
reasons of "mesh tuning".

SSB and CW bandwidth filters can also be built at low VHF, but the CW ones
difficult for mass production.

How much filter stopband attenuation is useful at a given offset is
determined in the greater part by how much noise is produced by the LO
driving the mixer ahead of the filter and post mixer amplifier (if the type
of mixer requires the isolation). Reciprocal mixing is one bugbear. To take
advantage of 100db stopband attenuation the LO must be quiet.

The effect of noise/signals on the skirts is tied to the linearity of the
filter, and Ron, here we could spend hours!!

The filter between the ears is super, it also tracks!

73,
Geoff.
GM4ESD

............................................................................
................
Merlin, W3ICT wrote:

...nobody else I've observed on this net seems to be as annoyed as I about
the bad
skirts, high ripple, bad ultimate selectivity, etc. when the K2 is used
with the
KSB2. ...On sideband, tight skirts (the electronic kind, gentlemen!) are
terribly
important, maybe more so than on CW. There is nothing neater than
listening to
a weak SSB signal through an IF system that has a 1.2:1 shape factor.

--------------
On March 04, 2005, Ron AC7AC wrote:

My SSB operating is only casual but I can say with half a century of
operating behind me that I absolutely LOATHE steep-sided filters on CW. They
produce a lot of "trash" in the bandpass caused by the way they modulate
signals on edge of the bandpass. Of course, signals varying at all in
frequency, including noise, are amplitude-modulated by the filter slope,
with causes further sidebands, etc.

A lot of work has been done by both engineers and mathematicians working out
the best shape to minimize these effects, but this ol' operator simply likes
listening to a big chunk of the band at one time and letting my grey-filter
between the ears do the work for me.

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Ron D'Eau Claire-2

RE: Tight Skirts...

In reply to this post by Eric Swartz - WA6HHQ

Eric wrote:
The SSB OP1 filter can be used with different
BFO settings in each of the four SSB filter memory settings, creating
low and high cut settings.

I installed the mod kit to widen my OPT1 filter and I'm really pleased with
it. Listening to AM stations, the K2 sounds as good as most any
"communications" receiver I've ever had and, with an external speaker, as
good as most AM radios I have.

I have programmed in several different BFO frequencies to allow me to shift
that passband around a bit - sort of pre-programmed "passband tuning" - that
is very handy to provide the best response when listening to various rigs
and voices. I'm strictly a "casual" SSB operator so I'm concentrating on the
quality of the audio, not in digging in the mud for the weak ones. I'll
leave that for CW <G>

You can call me an "easy listening" SSB operator.

Ron AC7AC

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Bill Coleman-2

Re: (no subject)

In reply to this post by Merlarts

On Mar 3, 2005, at 7:38 PM, [hidden email] wrote:

> The performance of its filter, and the way that it performs when
> installed
> in the radio, is DISMAL!!!!!!!!
>
> On sideband, tight skirts (the electronic kind, gentlemen!) are
> terribly
> important, maybe more so than on CW. There is nothing neater than
> listening to
> a weak SSB signal through an IF system that has a 1.2:1 shape factor.
> That
> complete absence of interference on the sides is marvelous to hear.
> I'd be
> surprised if the KSB2 manages 2:1. Just tune through loud broadcast
> signals on
> forty meters sometime; listen to the audio "images" the other side of
> zero
> beat even on moderately strong signals.

Of course, every K2 is subject to variability in its construction and
alignment. While I'll agree the filter in the KSB2 isn't perfect, I am
not experiencing this kind of performance. I do not hear images in my
KSB2, even with the strongest 40m signals.

I would suggest something is amiss either with your BFO alignment or
with the construction of your KSB2.

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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Bill Coleman-2

Re: Tight Skirts...

In reply to this post by Eric Swartz - WA6HHQ

On Mar 4, 2005, at 1:20 AM, Eric Swartz WA6HHQ - Elecraft wrote:

> OP1 is the KSB2's SSB fixed b/w filter, which has been optimized for
> minimum ripple at one SSB b/w. In SSB it is always used for transmit,
> but it or any of the CW filter bandwidths can be used for receive.

Here's an interesting question -- what are OP2-5 for? I spent a while
studying the schematic trying to figure out if these selections also
activated some other I/O lines in the KSB2 controller. None that I
could find.

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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