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K3 receiver desensing on CW during contest

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Jim Brown-10

Tutorial about Filters and AGC

On Mon, 23 Feb 2009 13:57:32 -0500, Steve Ellington wrote:

>Is this correct?
>If a cw signal falls within the DSP passband it should and will pump the
>AGC. If a CW signal falls outside the DSP passband it should not pump the
>DSP's AGC. The problem here is defining what the DSP's passband it. If a
>signal is just outside the audio range of the DSP (can't be heard) then I
>would consider it "outside the DSP passband" and it should not pump the AGC
>however this is never the case. I see moderate signals just slightly outside
>the audio passband that pump the AGC. This is partly what is confusing us.
>Signals that we can't hear pumping the AGC worry us. What we hear coming
>from the speaker doesn't match how the AGC is responding. If my WIDTH is set
>for 100hz and a signal is at 110hz, I won't hear him but my S-meter responds
>to him as well as my AGC "desenses" (reduces gain).
>All of this has nothing to do with the roofing filter.

There are several HUGE gaps of understanding in this question, so I'm going
to attempt to respond to this tutorially.

First, the shape of the skirts. You seem to be viewing the response of a
filter as if it were square -- that is, no skirts. When you build a filter
for a bandwidth of 100 Hz, 100 Hz is the width between the -3dB points on the
filter's response. Depending on the design of the filter (how many poles and
how they are aligned), the response may be -20 dB at a 200 Hz width, -40 dB
at 400 Hz width, and so on. The filter's cutoff may be sharper or narrower,
depending on the design. To get a feel for how filters work, go to the Inrad
website and poke around until you find graphs of the response of some of
their filters. Inrad makes high quality after-market IF and roofing filters
for a lot of ham receivers, including the roofing filters used in the K3.

Second, the -3dB points of a 100 Hz filter are 50 Hz above and below the
center of the filter. Third, let's say that the signal you're trying to copy
is 50 uV and the interfering signal is 5 mV. That's 40 dB difference. To make
those signals equal in level in your earphones, the filter must be 40 dB down
at the frequency of the interfering signal. Many of the stronger signals on
the band may be 60-100 dB stronger than the weak signals we're trying to
copy. If one of them is within the passband of the roofing filter or the IF,
the skirts of both filters come into play.

A fourth issue is that the all the filters in a system act in cascade -- that
is, the total response is the sum of the responses of each filter. Let's say
you have a 400 Hz roofing filter installed and you set the DSP IF to 400 Hz.
The roofer may be -3dB at 200 Hz off frequency, the DSP is -3dB at 200 Hz off
frequency, so the cascaded response is -6dB at 200 Hz off frequency. At 400
Hz, if each filter had the same shape (unlikely) and was -20dB, the two in
cascade would be -40 dB. In general, 8-pole filters have steeper skirts (that
is, their response cuts off more sharply as you move off center) than 5-pole
filters, so a 5-pole 200 Hz filter might have the same response 200 Hz off
frequency as an 8-pole 400 Hz filter.

All of these filter shape and cascading concepts apply whether the filter
uses crystals or DSP. From "outside the hardware box," the primary
differences between them are their degrees of adjustability, how much signal
it takes to make them non-linear, and what they do when they overload. One
major reason for using a roofing filter is to protect the DSP filter from
being overloaded by strong signals. The other major reason is the cascading
it provides.

Now, let's look at the AGC. I haven't taken the time to study design details
of the K3's AGC, but from what Wayne and Lyle have posted here, I think I
understand that there are two AGC functions, one in hardware and one in
software, that sense signal levels at different points in the signal flow and
control gain at different points in the signal flow. The AGC in hardware is
not adjustable directly, but we CAN (and MUST) prevent it from pumping by not
overdriving it. The AGC in software (that is, the last IF) is VERY adjustable
from the CONFIG menu.

Another way of looking at the problem is to understand that the AGC turns
down the system gain if the signal at the output of the IF is too high. If we
let the AGC do it, the AGC will pump on a strong signal that gets through the
filter skirts. But we can prevent most, if not all, of that pumping by
turning down the RF gain with the controls on the front panel of the radio --
that is, turning off the preamp and turning on the attenuator and turning
down the RF gain controls. That's how W4ZV operates his radio, and it's how I
operate mine. We're both quite happy with how our radios are working.

73,

Jim Brown K9YC

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N8LP

Re: K3 receiver desensing on CW during contest

In reply to this post by Alan Bloom

Not today... but give it a couple years. There is a lot of R&D being
poured into this by a number of competing chip manufacturers. Even if
the next batch of designs falls a little short, an all digital design
with BDR close to the best conventional designs would probably enjoy a
very substantial market.

73,
Larry N8LP

Alan Bloom wrote:

> On Mon, 2009-02-23 at 18:40, N8LP wrote:
> ...
>
>> I think the days of receivers with xtal filters are numbered. High speed
>> ADCs capable of 140dB dynamic range without xtal filtering are on the
>> horizon. A 20-bit ADC with enough processing gain would do it.
>>
>
> I don't think you'll find a 20-bit ADC with a high enough sample rate to
> digitize the 3-30 MHz HF band (i.e. >65-70 MHz or so). At least not at
> a reasonable cost.
>
> I believe the best suitable, reasonable-cost ADCs available these days
> are able to achieve a 500-Hz blocking dynamic range in the low 120's dB,
> maybe 15-20 dB worse than the K3. That's significantly better than the
> previous generation of ADCs could achieve, and no doubt someday we'll
> get even better parts that are good enough to challenge the traditional
> superhet/crystal filter architecture. But I don't believe we're close
> to that level of performance today.
>
> Another issue, of course, is spurious responses. I'm pretty sure that
> current ADCs don't have good enough spurious-free dynamic range to
> challenge a state-of-the-art receiver like the K3.
>
> Al N1AL
>
>
>
>

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P.B. Christensen

Re: Tutorial about Filters and AGC

In reply to this post by Jim Brown-10

> Now, let's look at the AGC. I haven't taken the time to study design
> details
> of the K3's AGC, but from what Wayne and Lyle have posted here, I think I
> understand that there are two AGC functions,..."

And that, I believe is the root issue on the matter.

(1) What is the passband of the hardware AGC, and what is its dependency
(i.e., filter selection); and
(2) What is the passband of the DSP AGC, and what is its dependency (i.e.,
filter selection).

Looking at the K3 block diagram, it appears the DSP is fed back to the IF
amp -- meaning that the hardware and software form a loop and hardware and
DSP AGC are not independent (although a portion of the DSP could still be
independent and not shown on the diagram)

Concerning DSP in either the hardware AGC loop and/or the DSP AGC loop, is
the passband of either loop variable as a function of the DSP bandwidth
setting? Or, is the DSP AGC passband fixed, irrespective of the DSP filter
setting?

My apologies if this has been covered in prior messages, but I have not yet
been able to extract the answers to these questions. Tnx!

Paul, W9AC

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Alan Bloom

Re: K3 receiver desensing on CW during contest

In reply to this post by N8LP

I agree this is something amateur equipment manufacturers like Elecraft
should be keeping their eye on. If Analog Devices or someone came out
with an under-$100 ADC with performance close to the K3, then you could
save a lot of money and complexity by going to a directly-sampled RF
front end architecture.

But a lot of brilliant engineers have been working for many years trying
to optimize ADC design. I just really have my doubts that they are
going to make a 15-20 dB breakthrough any time soon.

Al N1AL

On Tue, 2009-02-24 at 09:55, Larry Phipps wrote:

> Not today... but give it a couple years. There is a lot of R&D being
> poured into this by a number of competing chip manufacturers. Even if
> the next batch of designs falls a little short, an all digital design
> with BDR close to the best conventional designs would probably enjoy a
> very substantial market.
>
> 73,
> Larry N8LP
>
>
>
> Alan Bloom wrote:
> > On Mon, 2009-02-23 at 18:40, N8LP wrote:
> > ...
> >
> >> I think the days of receivers with xtal filters are numbered. High speed
> >> ADCs capable of 140dB dynamic range without xtal filtering are on the
> >> horizon. A 20-bit ADC with enough processing gain would do it.
> >>
> >
> > I don't think you'll find a 20-bit ADC with a high enough sample rate to
> > digitize the 3-30 MHz HF band (i.e. >65-70 MHz or so). At least not at
> > a reasonable cost.
> >
> > I believe the best suitable, reasonable-cost ADCs available these days
> > are able to achieve a 500-Hz blocking dynamic range in the low 120's dB,
> > maybe 15-20 dB worse than the K3. That's significantly better than the
> > previous generation of ADCs could achieve, and no doubt someday we'll
> > get even better parts that are good enough to challenge the traditional
> > superhet/crystal filter architecture. But I don't believe we're close
> > to that level of performance today.
> >
> > Another issue, of course, is spurious responses. I'm pretty sure that
> > current ADCs don't have good enough spurious-free dynamic range to
> > challenge a state-of-the-art receiver like the K3.
> >
> > Al N1AL
> >
> >
> >
> >

N8LP

Re: K3 receiver desensing on CW during contest

You may be right, Al. I think the improvements may be incremental, and distributed among various aspects of the design, not just the ADC. For instance, ultra-low jitter clock sources, faster FPGAs with improved IP cores, etc. I think most hams would be thrilled with an improvement to 130dB BDR, along with getting rid of phase distortion, ringing and other anomalies in the xtal filters and other analog components. Unless you live near a shortwave broadcast station, or have a high power ham nearby on the same band, you're not likely to need 130dB BDR anyway. Even in those cases, having 200dB BDR probably wouldn't help unless there is a LOT of improvement in transmitter spurious emissions, distortion and phase noise.

The highest signals I have seen here, during Field Day when there were several stations operating within a few miles of me, were <120dB above the noise floor. Of course, it's very important not to use any more front end gain than necessary for the band/conditions.

73,
Larry N8LP

Alan Bloom wrote

I agree this is something amateur equipment manufacturers like Elecraft
should be keeping their eye on. If Analog Devices or someone came out
with an under-$100 ADC with performance close to the K3, then you could
save a lot of money and complexity by going to a directly-sampled RF
front end architecture.

But a lot of brilliant engineers have been working for many years trying
to optimize ADC design. I just really have my doubts that they are
going to make a 15-20 dB breakthrough any time soon.

Al N1AL

On Tue, 2009-02-24 at 09:55, Larry Phipps wrote:
> Not today... but give it a couple years. There is a lot of R&D being
> poured into this by a number of competing chip manufacturers. Even if
> the next batch of designs falls a little short, an all digital design
> with BDR close to the best conventional designs would probably enjoy a
> very substantial market.
>
> 73,
> Larry N8LP
>
>
>
> Alan Bloom wrote:
> > On Mon, 2009-02-23 at 18:40, N8LP wrote:
> > ...
> >
> >> I think the days of receivers with xtal filters are numbered. High speed
> >> ADCs capable of 140dB dynamic range without xtal filtering are on the
> >> horizon. A 20-bit ADC with enough processing gain would do it.
> >>
> >
> > I don't think you'll find a 20-bit ADC with a high enough sample rate to
> > digitize the 3-30 MHz HF band (i.e. >65-70 MHz or so). At least not at
> > a reasonable cost.
> >
> > I believe the best suitable, reasonable-cost ADCs available these days
> > are able to achieve a 500-Hz blocking dynamic range in the low 120's dB,
> > maybe 15-20 dB worse than the K3. That's significantly better than the
> > previous generation of ADCs could achieve, and no doubt someday we'll
> > get even better parts that are good enough to challenge the traditional
> > superhet/crystal filter architecture. But I don't believe we're close
> > to that level of performance today.
> >
> > Another issue, of course, is spurious responses. I'm pretty sure that
> > current ADCs don't have good enough spurious-free dynamic range to
> > challenge a state-of-the-art receiver like the K3.
> >
> > Al N1AL
> >
> >
> >
> >

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Eric Scace K3NA

Re: K3 receiver desensing on CW during contest

At the W1KM contesting site, we routinely see signals of +5 dBm or
louder on/near 40m from SWBC stations (using a single Yagi). We also
have two modest-power local AM stations (1 to 5 kW, a few miles away)
just below 1500 kHz that show up even a bit stronger than that on our
160m antennas.

Without taking into consideration signals from our own multi-multi
transmitters, a receiver is already faced with >>130 dB range between
weak signals on 160m in mid-afternoon arriving from Europe and these
other signal sources.

WD3Q, a contester in Washington DC, has much stronger AM BC stations to
deal with, including a 50 kW station on 1500 kHz.

Wide-open receiver front ends attached to an A/D converter are not yet
viable for these locations.

-- Eric K3NA

on 09 Feb 24 20:44 N8LP said the following:

> You may be right, Al. I think the improvements may be incremental, and
> distributed among various aspects of the design, not just the ADC. For
> instance, ultra-low jitter clock sources, faster FPGAs with improved IP
> cores, etc. I think most hams would be thrilled with an improvement to 130dB
> BDR, along with getting rid of phase distortion, ringing and other anomalies
> in the xtal filters and other analog components. Unless you live near a
> shortwave broadcast station, or have a high power ham nearby on the same
> band, you're not likely to need 130dB BDR anyway. Even in those cases,
> having 200dB BDR probably wouldn't help unless there is a LOT of improvement
> in transmitter spurious emissions, distortion and phase noise.
>
> The highest signals I have seen here, during Field Day when there were
> several stations operating within a few miles of me, were <120dB above the
> noise floor. Of course, it's very important not to use any more front end
> gain than necessary for the band/conditions.
>
> 73,
> Larry N8LP
>
>

Alan Bloom

Re: K3 receiver desensing on CW during contest

Hopefully this discussion is not too far off-topic. But
state-of-the-art receiver design certainly does seem related to the K3.
:=)

On Tue, 2009-02-24 at 19:50, Eric Scace K3NA wrote:
> At the W1KM contesting site, we routinely see signals of +5 dBm or
> louder on/near 40m from SWBC stations (using a single Yagi). We also
> have two modest-power local AM stations (1 to 5 kW, a few miles away)
> just below 1500 kHz that show up even a bit stronger than that on our
> 160m antennas.

+5 dBm is S9+78 dB. Definitely pinning the S-meter!

> Without taking into consideration signals from our own multi-multi
> transmitters, a receiver is already faced with >>130 dB range between
> weak signals on 160m in mid-afternoon arriving from Europe and these
> other signal sources.
>
> WD3Q, a contester in Washington DC, has much stronger AM BC stations to
> deal with, including a 50 kW station on 1500 kHz.
>
> Wide-open receiver front ends attached to an A/D converter are not yet
> viable for these locations.

Even with direct sampling of the RF signal with an ADC you would still
want bandpass filters in the front end. For best performance, each one
should be just wide enough to cover a ham band, as they are in the K3.

> -- Eric K3NA
>
> on 09 Feb 24 20:44 N8LP said the following:
> > You may be right, Al. I think the improvements may be incremental, and
> > distributed among various aspects of the design, not just the ADC. For
> > instance, ultra-low jitter clock sources, faster FPGAs with improved IP
> > cores, etc. I think most hams would be thrilled with an improvement to 130dB
> > BDR, along with getting rid of phase distortion, ringing and other anomalies
> > in the xtal filters and other analog components. Unless you live near a
> > shortwave broadcast station, or have a high power ham nearby on the same
> > band, you're not likely to need 130dB BDR anyway. Even in those cases,
> > having 200dB BDR probably wouldn't help unless there is a LOT of improvement
> > in transmitter spurious emissions, distortion and phase noise.
> >
> > The highest signals I have seen here, during Field Day when there were
> > several stations operating within a few miles of me, were <120dB above the
> > noise floor. Of course, it's very important not to use any more front end
> > gain than necessary for the band/conditions.

Thermal noise in a 500 Hz bandwidth is about -147 dBm. Assuming band
noise on a quiet band is, let's say, 12 dB above that, the noise floor
is -135 dBm. If Eric is seeing +5 dBm interference, that implies you
need 140 dB of blocking dynamic range. Admittedly that does seem pretty
close to a worst-case situation.

> >
> > 73,
> > Larry N8LP

Al N1AL

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Bill VanAlstyne W5WVO

Re: K3 receiver desensing on CW during contest

In reply to this post by N8LP

N8LP wrote:
>...Unless you live near a shortwave broadcast station, or
> have a high power ham nearby on the same band, you're not likely to
> need 130dB BDR anyway. Even in those cases, having 200dB BDR
> probably wouldn't help unless there is a LOT of improvement in
> transmitter spurious emissions, distortion and phase noise.

This point is brought home all the time here in Albuquerque, where we have to
deal with the radiation from ten or more TV/FM analog transmitters
line-of-sight on top of Sandia Crest. While all these transmitters except
Channel 2 have fundamentals well above 54 MHz (I run a DCI bandpass filter to
keep it out of my preamp), the accumulated grunge from the transmitters'
perfectly legal low-level spurious emissions and passive mixes are enough to
render 6 meters unusable for weak-signal work in the direction of the
mountaintop. Since the spurious gunk is actually radiated on hundreds of
different frequencies within the 6-meter band -- not to mention the broad-band
noise coming from the same mountaintop -- there is little filtering can do
about it. Hopefully this will be alleviated to some degree when the last of
the analog TV transmitters finally relocate to UHF digital come June (yes,
they all elected to stay on the air past February 17th), but at least until
then, there is little I can do about it except deploy longer and sharper yagis
to minimize the unusable arc of the "dead zone". Ergo, BDR isn't everything.
It is still unfortunately necessary to take into account who your RF neighbors
are. They may be operating perfectly legally on frequencies well outside your
own area of interest, and still pollute the band with spurious RF that the FCC
says is within acceptable limits for their class of operation.

Bill W5WVO

> The highest signals I have seen here, during Field Day when there were
> several stations operating within a few miles of me, were <120dB
> above the noise floor. Of course, it's very important not to use any
> more front end gain than necessary for the band/conditions.
>
> 73,
> Larry N8LP
>
>
>
>
>
>
>
>
>
>
> Alan Bloom wrote:
>>
>> I agree this is something amateur equipment manufacturers like
>> Elecraft should be keeping their eye on. If Analog Devices or
>> someone came out with an under-$100 ADC with performance close to
>> the K3, then you could save a lot of money and complexity by going
>> to a directly-sampled RF front end architecture.
>>
>> But a lot of brilliant engineers have been working for many years
>> trying to optimize ADC design. I just really have my doubts that
>> they are going to make a 15-20 dB breakthrough any time soon.
>>
>> Al N1AL
>>
>>
>> On Tue, 2009-02-24 at 09:55, Larry Phipps wrote:
>>> Not today... but give it a couple years. There is a lot of R&D being
>>> poured into this by a number of competing chip manufacturers. Even
>>> if the next batch of designs falls a little short, an all digital
>>> design with BDR close to the best conventional designs would
>>> probably enjoy a very substantial market.
>>>
>>> 73,
>>> Larry N8LP
>>>
>>>
>>>
>>> Alan Bloom wrote:
>>>> On Mon, 2009-02-23 at 18:40, N8LP wrote:
>>>> ...
>>>>
>>>>> I think the days of receivers with xtal filters are numbered.
>>>>> High speed ADCs capable of 140dB dynamic range without xtal
>>>>> filtering are on the horizon. A 20-bit ADC with enough processing
>>>>> gain would do it.
>>>>>
>>>>
>>>> I don't think you'll find a 20-bit ADC with a high enough sample
>>>> rate to digitize the 3-30 MHz HF band (i.e. >65-70 MHz or so). At
>>>> least not at a reasonable cost.
>>>>
>>>> I believe the best suitable, reasonable-cost ADCs available these
>>>> days are able to achieve a 500-Hz blocking dynamic range in the
>>>> low 120's dB, maybe 15-20 dB worse than the K3. That's
>>>> significantly better than the previous generation of ADCs could
>>>> achieve, and no doubt someday we'll get even better parts that are
>>>> good enough to challenge the traditional superhet/crystal filter
>>>> architecture. But I don't believe we're close to that level of
>>>> performance today.
>>>>
>>>> Another issue, of course, is spurious responses. I'm pretty sure
>>>> that current ADCs don't have good enough spurious-free dynamic
>>>> range to challenge a state-of-the-art receiver like the K3.
>>>>
>>>> Al N1AL
>>>>
>>>>
>>>>
>>>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
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n7ws

Re: K3 receiver desensing on CW during contest

In reply to this post by Mike K2MK

--- On Wed, 2/25/09, Bill W5WVO <[hidden email]> wrote:

This point is brought home all the time here in Albuquerque, where we have to
deal with the radiation from ten or more TV/FM analog transmitters
line-of-sight on top of Sandia Crest. While all these transmitters except
Channel 2 have fundamentals well above 54 MHz (I run a DCI bandpass filter to
keep it out of my preamp), the accumulated grunge from the transmitters'
perfectly legal low-level spurious emissions and passive mixes are enough to
render 6 meters unusable for weak-signal work in the direction of the
mountaintop. Since the spurious gunk is actually radiated on hundreds of
different frequencies within the 6-meter band -- not to mention the broad-band
noise coming from the same mountaintop -- there is little filtering can do
about it. Hopefully this will be alleviated to some degree when the last of
the analog TV transmitters finally relocate to UHF digital come June ...

[snip]

I don't know how to break it to you but you're still going to have channels 7 and 13 after the transition. The alleged purpose of this transition was to free up spectrum that could be auctioned off. But a lot of broadcasters are going to wind up right back where they always were. Pity, as an over the air TV watcher, I was looking forward to needing only a UHF antenna, but noooo, I will still have to have a high band VHF antenna for local channel 9.

Wes N7WS

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Gary Smith

Re: K3 receiver desensing on CW during contest

In reply to this post by Alan Bloom

Although my contesting this past weekend was severely interrupted by
a non-K3 related hardware failure, over the course of the contest I
did use the K3 throughout all day and night segments on various
bands.

I did not call CQ except for a very little bit and the majority was
S&P on all bands except 10M which was for me, dead. There were the
usual high powered stations crammed in tightly on all bands except
for 15 where there were some spaces between CQs.

I really put the K3 to the test with this one and made good use of
the filtering and, considering the desensing thread have this
observation to make: I noticed no desensing with the K3 in the
presence of strong signals.

I found that I was able to get rid of all but the most "dead on" of
signals and those within those 50 Hz were not going to go away.
Adjacent clicky signals were for the 99% of the time totally removed
and for that "1%" of the time the clicks remained, I was able to pull
in the faintest signals.

I know I must have P.O.ed more than a few people as I would scroll up
the band and work a strong station and within 1Khz, work two others
that were faint but clearly identifiable. Some of those faint ones, I
had to call them for them to know I was hearing them. Thing is,as I'd
tune up with fine tuning, I kept hearing station overlaying another
and I had to be QRMing most of these other stations including the
ones I just worked and the ones I would be working next.

If the K3 has a liability, to me, it is not in any way related to
desensing in the presence of strong signals. My old Omni V was a fine
CW Rx but was nowhere as good as the K3 and I can say the same for my
Corsair II which will be my backup rig for life.

The K3 is stellar.

Gary
KA1J

Any spelling ewrrors are the result of my laptop's keyboard...

:)
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Jim-168

Re: K3 receiver desensing on CW during contest

Agree, The K3 is stellar.

Never any desensing in the presence of strong signals observed with my K3.

I have found nothing that compares.

73 de KE4WY Jim

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Gary Smith
Sent: Wednesday, February 25, 2009 9:41 AM
To: [hidden email]
Subject: Re: [Elecraft] K3 receiver desensing on CW during contest

Although my contesting this past weekend was severely interrupted by
a non-K3 related hardware failure, over the course of the contest I
did use the K3 throughout all day and night segments on various
bands.

I did not call CQ except for a very little bit and the majority was
S&P on all bands except 10M which was for me, dead. There were the
usual high powered stations crammed in tightly on all bands except
for 15 where there were some spaces between CQs.

I really put the K3 to the test with this one and made good use of
the filtering and, considering the desensing thread have this
observation to make: I noticed no desensing with the K3 in the
presence of strong signals.

I found that I was able to get rid of all but the most "dead on" of
signals and those within those 50 Hz were not going to go away.
Adjacent clicky signals were for the 99% of the time totally removed
and for that "1%" of the time the clicks remained, I was able to pull
in the faintest signals.

I know I must have P.O.ed more than a few people as I would scroll up
the band and work a strong station and within 1Khz, work two others
that were faint but clearly identifiable. Some of those faint ones, I
had to call them for them to know I was hearing them. Thing is,as I'd
tune up with fine tuning, I kept hearing station overlaying another
and I had to be QRMing most of these other stations including the
ones I just worked and the ones I would be working next.

If the K3 has a liability, to me, it is not in any way related to
desensing in the presence of strong signals. My old Omni V was a fine
CW Rx but was nowhere as good as the K3 and I can say the same for my
Corsair II which will be my backup rig for life.

The K3 is stellar.

Gary
KA1J

Any spelling ewrrors are the result of my laptop's keyboard...

:)
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alsopb

Re: K3 receiver desensing on CW during contest

Jim,

Ditto here. #1129. AGC slope= 13, AGC THR =8. AGC set to fast. Never
touched the RF gain control.

I was totally amazed to be able copy weak ones under strong ones within
the passband.
Experienced none of the mushing reported here.

However, when I first got the K3, I did manage to set the K3 AGC
characteristics so that noise and all signals appeared to be at the same
audio level. This made it difficult to separate signals. The rig
sounded "flat".

73 de Brian/K3KO

Jim wrote:

>Agree, The K3 is stellar.
>
>Never any desensing in the presence of strong signals observed with my K3.
>
>I have found nothing that compares.
>
>73 de KE4WY Jim
>
>
>

Bill W4ZV

Re: K3 receiver desensing on CW during contest

In reply to this post by Jim-168

KE4WY:
Never any desensing in the presence of strong signals observed with my K3.

KA1J:
I noticed no desensing with the K3 in the presence of strong signals.

I agree. 160 is the ultimate test for dynamic range (and desense or BDR) for any rig. Operating SOSB/160 I never experienced *any* desense this weekend in breaking the current USA record by >25%.

If anyone experiences true desense (and some don't understand what that means), they don't have their K3 set up correctly. The simple way to do this on any band is to find the *minimum* gain combination which will result in hearing band noise when the antenna is connected (versus disconnected). On 160m, this usually means ATT ON and RF Gain backed off to 12-2 o'clock. For a Beverage only (not diversity), more gain may be necessary (i.e. ATT OFF but no PRE). For diversity, I like to balance the signal from my vertical TX array (about +5 dBi gain) with my Beverages (about -13 dBi gain following a splitter). In that case I use PRE for the Beverage side, but even on my Beverage port I never heard *any* desense this entire weekend.

You can make the K3 desense by running with PRE ON and maximum RF Gain, but that's simply operator error and not the fault of the K3.

73, Bill

N8LP

Re: K3 receiver desensing on CW during contest

In reply to this post by Eric Scace K3NA

Those are impressive numbers, Eric. +5dBm would only be about 120dB above the background noise level on 40m here on a typical night, though. I am located in a relatively quiet area, but on the edge of suburban/rural. Of course, I don't have a Yagi currently, and I'm not on the East Coast or in Europe ;-) My comments were aimed at typical ham stations, not multi-multi contest stations. Even the best conventional receivers need help in that environment with external filters, tuned stubs, etc.

I wasn't saying the front end should be wide open ;-) I would assume there would be bandpass filters for each band, and both high pass and low pass filters ahead of the ADC. I guess my point was that it seems like a reasonable compromise for most users to have 130dB BDR for all signals, as opposed to 140dB for signals outside the roofing filter, but only mid 90dB range for signals inside the roofing filter. I would like to see the variable BW xtal filters released, as that would improve the situation.

It's all about compromises, and the K3 is as good as it gets in that regard, but so is the QS1R, which represents the state of the art in direct sampling DDC designs available to hams. Of course, I'm only talking receiver RF performance here, not the issue of knobs, buttons, QSK keying, etc. ;-) I would like to see how a QS1R with proper front end filters would perform in your environment. As an inveterate experimenter, I will be playing with the next generation of ADCs when they arrive.

73,
Larry N8LP

Eric Scace K3NA wrote

At the W1KM contesting site, we routinely see signals of +5 dBm or
louder on/near 40m from SWBC stations (using a single Yagi). We also
have two modest-power local AM stations (1 to 5 kW, a few miles away)
just below 1500 kHz that show up even a bit stronger than that on our
160m antennas.

Without taking into consideration signals from our own multi-multi
transmitters, a receiver is already faced with >>130 dB range between
weak signals on 160m in mid-afternoon arriving from Europe and these
other signal sources.

WD3Q, a contester in Washington DC, has much stronger AM BC stations to
deal with, including a 50 kW station on 1500 kHz.

Wide-open receiver front ends attached to an A/D converter are not yet
viable for these locations.

-- Eric K3NA

on 09 Feb 24 20:44 N8LP said the following:
> You may be right, Al. I think the improvements may be incremental, and
> distributed among various aspects of the design, not just the ADC. For
> instance, ultra-low jitter clock sources, faster FPGAs with improved IP
> cores, etc. I think most hams would be thrilled with an improvement to 130dB
> BDR, along with getting rid of phase distortion, ringing and other anomalies
> in the xtal filters and other analog components. Unless you live near a
> shortwave broadcast station, or have a high power ham nearby on the same
> band, you're not likely to need 130dB BDR anyway. Even in those cases,
> having 200dB BDR probably wouldn't help unless there is a LOT of improvement
> in transmitter spurious emissions, distortion and phase noise.
>
> The highest signals I have seen here, during Field Day when there were
> several stations operating within a few miles of me, were <120dB above the
> noise floor. Of course, it's very important not to use any more front end
> gain than necessary for the band/conditions.
>
> 73,
> Larry N8LP
>
>
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Barry N1EU

Re: K3 receiver desensing on CW during contest

In reply to this post by alsopb

alsopb wrote

Ditto here. #1129. AGC slope= 13, AGC THR =8. AGC set to fast. Never
touched the RF gain control.

I was totally amazed to be able copy weak ones under strong ones within
the passband.
Experienced none of the mushing reported here.

The "mushing" requires 10-15+ not-very-strong signals calling at once - i.e., a serious pileup. I experienced it many times on 40M/20M in ARRLDX and CQWW cw contests.

The "mushing" has nothing to do with desensing and I don't think anybody ever implied that it did. Several threads have gotten intermingled here.

73,
Barry N1EU

RussG

Re: KX-1 what do you use for an antenna when you're in a place with no trees to throw the vertical up?

In reply to this post by Bill VanAlstyne W5WVO

I have a camping trip planned and will likely be in a few places where
there are no trees where I will easily get a vertical wire up. What
does everyone else do when the surroundings are not ideal for a wire in
a tree? I have seen other antennas referenced such as the buddystick
and the PAC-12.

Thanks

Russ Garrett
Kd7mpk

mail.bullivant.com made the following annotations
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Stephen Prior

Re: KX-1 what do you use for an antenna when you're in a place with no trees to throw the vertical up?

Russ

I camp with my KX-1 (and the family!) in Europe every summer. I have tried
the buddipole, buddistick and the MP-1, but there is one antenna I've tried
which surpasses them all, in my experience and opinion.

I have a DK9SQ 10 metre long 'fishing pole'. I connect a 12m or so length
of wire to the top, allowing it to hang down vertically. I normally bungee
the pole to a tent or car door handle, whatever is available. I use a
variable length counterpoise (teflon wire on a reel) which I just measure
out roughly a quarter wavelength for the band of interest along the ground
and then use the autotuner in the KX-1. I'm not interested so much in 80m,
but it covers 40, 30 and 20m just fine and I get far more qsos than I did
before with the admittedly neater, yet significantly more expensive
alternatives. There may be other poles of this length, but I can thoroughly
recommend the DK9SQ 'mast' and I'm pretty sure I've seen it advertised your
side of the pond.

Hope that's food for thought.

73 Stephen G4SJP (about to book the sea crossing for the next trip to
mainland Europe :-))

On 25/02/2009 21:04, "Garrett, Russ" <[hidden email]> wrote:

>
> I have a camping trip planned and will likely be in a few places where
> there are no trees where I will easily get a vertical wire up. What
> does everyone else do when the surroundings are not ideal for a wire in
> a tree? I have seen other antennas referenced such as the buddystick
> and the PAC-12.
>
> Thanks
>
> Russ Garrett
> Kd7mpk
>
>
> mail.bullivant.com made the following annotations
> ---------------------------------------------------------------------
> Please be advised that, unless expressly stated otherwise, any U.S. federal
> tax advice contained in this e-mail, including attachments, is not intended to
> be used by any person for the purpose of avoiding any penalties that may be
> imposed by the Internal Revenue Service.
> *********************************************************
> This e-mail is for the sole use of the intended recipient(s) and contains
> information belonging to Bullivant Houser Bailey, which is confidential and/or
> legally privileged. If you are not the intended recipient, you are hereby
> notified that any disclosure, copying, distribution or taking of any action in
> reliance on the contents of this e-mail information is strictly prohibited.
> If you have received this e-mail in error, please immediately notify the
> sender by reply e-mail and destroy all copies of the original message.
>
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>
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AC7AC

Re: KX-1 what do you use for an antenna when you're in a place with no trees to throw the vertical up?

CONTENTS DELETED

The author has deleted this message.

Stephen Prior

Re: KX-1 what do you use for an antenna when you're in a place with no trees to throw the vertical up?

Hi Ron

Well, as you imply, it's no surprise. Size does matter, and as has often
been said, you cannot defeat the laws of physics! Which, as a teacher of
the subject gives me some pleasure!

73 Stephen G4SJP

On 25/02/2009 22:24, "Ron D'Eau Claire" <[hidden email]> wrote:

>
> You've shown again that when it comes to an antenna, size does matter.
> Especially when the physical length is less than 1/2 wavelength, every
> little bit of additional length helps a lot!
>
> It's pretty easy to achieve resonance with a short antenna using loading
> coils but until we have room-temperature superconductors cheap enough to use
> for a Ham antenna, short, loaded antennas will always be very inefficient.
> That doesn't' mean they won't "get out" or even work DX under the right
> conditions, but they'll still be a distant second to anything larger.
>
> Ron AC7AC
>

Bob Cunnings NW8L

Re: KX-1 what do you use for an antenna when you're in a place with no trees to throw the vertical up?

In reply to this post by RussG

Out here I often operate in the desert, with no trees at all for
antennas or shade! I use a 32 foot telescoping fiberglass pole
(sometimes 2) from The Mast Company to get wire in the air nice and
high, either as horizontal doublets, vees, or slopers.

http://www.tmastco.com/main/page_products_telescopic_poles.html

Bob NW8L

On Wed, Feb 25, 2009 at 2:04 PM, Garrett, Russ
<[hidden email]> wrote:

> I have a camping trip planned and will likely be in a few places where
> there are no trees where I will easily get a vertical wire up. What
> does everyone else do when the surroundings are not ideal for a wire in
> a tree? I have seen other antennas referenced such as the buddystick
> and the PAC-12.
>
> Thanks
>
> Russ Garrett
> Kd7mpk
>
>
> mail.bullivant.com made the following annotations
> ---------------------------------------------------------------------
> Please be advised that, unless expressly stated otherwise, any U.S. federal tax advice contained in this e-mail, including attachments, is not intended to be used by any person for the purpose of avoiding any penalties that may be imposed by the Internal Revenue Service.
> *********************************************************
> This e-mail is for the sole use of the intended recipient(s) and contains information belonging to Bullivant Houser Bailey, which is confidential and/or legally privileged. If you are not the intended recipient, you are hereby notified that any disclosure, copying, distribution or taking of any action in reliance on the contents of this e-mail information is strictly prohibited.
> If you have received this e-mail in error, please immediately notify the sender by reply e-mail and destroy all copies of the original message.
>
> ---------------------------------------------------------------------
>
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