Re:K2 compared to others rigs

[Dave-Boat Guy]

Hi Phil,

A bare-bones K2 is a fine radio, although there are
still a couple of unresolved issues, like the tuning
clunks you hear on crowded bands, due to the
synthesizer.  I'm still puzzled why it hasn't been
addressed.  If you can ignore that, then it performs
very well even without the convenience features found
in most other radios (PBT, IF SHIFT, variable notch
filters) and buttons and knobs to control them.  That
being said, it's hard to avoid talking about the cost
of a fully featured K2.  When you begin to add in the
costs of the 160m, 60m, DSP, SSB, 100W, and noise
blanker options, you rapidly approach the 2K mark.
Add in the cost of Jack Smith's panoramic display
(which requires you to use a separate computer to take
advantage of the neat features or have another box on
the desk) that isn't integrated into the radio and
you're in the price range of an ICOM Pro3...and that
doesn't take into account the time involved in
assembling the equipment.  If you need/want large
buttons, add another $125 and visit Mike Stricker's
page (home.att.net/~info4mjs).  So now you have almost
$3000 into your radio.  

The new Ten-Tec Omni 7 looks like it may be
interesting.  How about a used Ten Tec Omni 6+?  You
could do a Yaesu with an INRAD filter option or even
an older ICOM 765 or 775DSP with INRAD filter option.

But if you want a good basic radio that you want to
know all the ins and outs about, the K2 is still fine.

Dave


 
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[Darrell Bellerive-2]

I agree that the synthesizer "tuning clunks" every 5 kHz in the presence of
strong signals needs to be addressed.

I know that Elecraft found that muting the receiver to eliminate these
noises was worse than the noises, but there must be a solution to at least
lessen these "tuning clunks."

On March 24, 2007 03:25 am, Dave-Boat Guy wrote:
> A bare-bones K2 is a fine radio, although there are
> still a couple of unresolved issues, like the tuning
> clunks you hear on crowded bands, due to the
> synthesizer.  I'm still puzzled why it hasn't been
> addressed.  
--
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
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[Geoffrey Mackenzie-Kennedy-2]

This might be a tough nut to crack in terms of the surgery required. From a
quick thus limited investigation into this "clunk" problem in my K2  I am
reasonably certain that the lack of shielding to protect the VCO and
Reference, together with the lack of suitable interface filtering , is
responsible. I don't think that the BFO is directly involved but I could
well be wrong. In my K2 the "clunks" appear, as you say, in the presence of
strong signals, and are found on every band that I have been able to check
so far, 40m is perhaps the worst case. What appears to happen is that the
strong incoming signals leak into the VCO / Reference area, and when their
composite level exceeds some value, which is frequency and leakage
dependent, attempt to take over control of the VCO which results in
"clunks". The frequency separation between "clunks" is not always 5kHz but
does seem to be related to the frequencies of the incoming signals which are
attempting to take over. I must stress that I have not had the opportunity
yet to undertake an in depth investigation, but I am very aware of the
leakage between the front end and the VCO / Reference from earlier work with
my K2. "Clunks" should not be confused with "Clicks" whose cause(s) are
quite different!

Here the received individual carrier levels of the BC stations above 7100
kHz can approach -10dbm / -5dbm with an antenna looking East, and there are
many of them. It is not uncommon for my K2's LO system to lock onto one of
these carriers, and only let go after the receiver has been retuned about 1
kHz.

73,
Geoff
GM4ESD


Darrell Bellerive <[hidden email]> wrote:

>I agree that the synthesizer "tuning clunks" every 5 kHz in the presence of
> strong signals needs to be addressed.
>
> I know that Elecraft found that muting the receiver to eliminate these
> noises was worse than the noises, but there must be a solution to at least
> lessen these "tuning clunks."
>
> On March 24, 2007 03:25 am, Dave-Boat Guy wrote:
>> A bare-bones K2 is a fine radio, although there are
>> still a couple of unresolved issues, like the tuning
>> clunks you hear on crowded bands, due to the
>> synthesizer.  I'm still puzzled why it hasn't been
>> addressed.

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[Darrell Bellerive-2]

First of all let's be sure we are all on the same page. Please define
"Clunks" vs. "Clicks".

While it would be best to find a total cure for the problem, anything that
reduces the severity or frequency of them would be most welcome.

Darrell  VA7TO

On March 25, 2007 03:16 am, Geoffrey Mackenzie-Kennedy wrote:

> This might be a tough nut to crack in terms of the surgery required. From
> a quick thus limited investigation into this "clunk" problem in my K2  I
> am reasonably certain that the lack of shielding to protect the VCO and
> Reference, together with the lack of suitable interface filtering , is
> responsible. I don't think that the BFO is directly involved but I could
> well be wrong. In my K2 the "clunks" appear, as you say, in the presence
> of strong signals, and are found on every band that I have been able to
> check so far, 40m is perhaps the worst case. What appears to happen is
> that the strong incoming signals leak into the VCO / Reference area, and
> when their composite level exceeds some value, which is frequency and
> leakage dependent, attempt to take over control of the VCO which results
> in "clunks". The frequency separation between "clunks" is not always 5kHz
> but does seem to be related to the frequencies of the incoming signals
> which are attempting to take over. I must stress that I have not had the
> opportunity yet to undertake an in depth investigation, but I am very
> aware of the leakage between the front end and the VCO / Reference from
> earlier work with my K2. "Clunks" should not be confused with "Clicks"
> whose cause(s) are quite different!
>
> Here the received individual carrier levels of the BC stations above 7100
> kHz can approach -10dbm / -5dbm with an antenna looking East, and there
> are many of them. It is not uncommon for my K2's LO system to lock onto
> one of these carriers, and only let go after the receiver has been
> retuned about 1 kHz.
>
> 73,
> Geoff
> GM4ESD
>
> Darrell Bellerive <[hidden email]> wrote:
> >I agree that the synthesizer "tuning clunks" every 5 kHz in the presence
> > of strong signals needs to be addressed.
> >
> > I know that Elecraft found that muting the receiver to eliminate these
> > noises was worse than the noises, but there must be a solution to at
> > least lessen these "tuning clunks."
> >
> > On March 24, 2007 03:25 am, Dave-Boat Guy wrote:
> >> A bare-bones K2 is a fine radio, although there are
> >> still a couple of unresolved issues, like the tuning
> >> clunks you hear on crowded bands, due to the
> >> synthesizer.  I'm still puzzled why it hasn't been
> >> addressed.
>

--
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
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[wayne burdick]

The K2 is a careful balance between high performance, small size, low
current drain, and low cost, while at the same time using through-hole
parts to make it easy to build. As the principle designer of the rig, I
can tell you that this required a number of design tricks to
accomplish.

The "clunks" are a side-effect of one of these design choices. A little
background will help explain this. I'll also briefly describe what
could be done about it.

An all-band, downconversion superhet transceiver needs a wide tuning
range, and we accomplished this using a single-VCO synthesizer with
just three inexpensive relays to select capacitor ranges. (I still have
the spreadsheet that I sweated over for a couple of weeks, trying to
optimize the topology in order to cover all the ham bands.) To get fine
steps for the phase-locked loop, another trick was required: we used a
D-to-A converter driving varactor tuning diodes on the crystal
reference oscillator. The alternatives (such as a DDS reference or a
dual-loop design) didn't meet our signal purity, cost, current, or
other criteria.

The crystal oscillator (technically a temperature-compensated VCXO)
tunes a small range to preserve stability. This requires that we change
the PLL divider values every 5 kHz as you tune the VFO. All this is
done for you by the firmware, which includes an autocalibration
procedure involving a lot of even trickier firmware. K2 owners know it
as the "CAL PLL" menu entry. I know it as the thing that kept me up
until 4 AM on a couple of occasions, trying to get the critical part of
the algorithm to fit in available code space!

When you cross a 5-kHz boundary (which may actually occur at odd
frequencies, not even 5-kHz boundaries), the VCO is forced to "slew"
some distance in frequency as the PLL re-locks. We achieved an
excellent lock time with our synth design, but no matter how fast you
do this the synth can, for a few milliseconds, stray into territory
where there may be a strong signal -- say, up the band 10 or 15 kHz.

We experimented with muting the receiver at these boundaries, but that
creates a very annoying effect as you tune. So, based on hundreds of
hours of operation by field testers, we elected not to do the muting,
and live with the occasional boundary artifact.

It might be possible to remove the artifact using DSP. For example, if
the DSP knew that an artifact was imminent, it could briefly invoke a
shaped limiter in the audio channel. Under normal circumstances you
wouldn't notice the effect of this at all while tuning, even with
strong signals nearby. There are some edge conditions that would
require optimization of the DSP code (AGC interactions, etc.), but it
might be a good solution.

The other approach would be to make the reference oscillator for the
PLL tune over a much wider range. This would eliminate the need to
switch the PLL dividers so often, and it's the solution found in both
much more expensive radios and radios with much lower performance -- in
both cases, different design tradeoffs are possible. You can either
throw a lot of components at it, or you can live with awful DDS spurs.

Note that you could emulate the DSP solution using a carefully-designed
analog AF limiter (ahead of the LM380), triggered by the SPI bus chip
select to the PLL IC.

The rest is left as an exercise for the reader  :)

73,
Wayne
N6KR


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[Geoffrey Mackenzie-Kennedy-2]

Wayne,

Thank you for your comments, all understood. I know about 4 am sessions,
been there <g>.  Due to time restraints I have yet to examine in detail the
cause(s) of  my K2's PLL (i.e. the Reference plus VCO) behaviour in the
presence of strong incoming signals, but from spectral analysis it does
appear that situations do arise when strong incoming signals (and products?)
gang up to upset legitimate lock.
The extreme case that I have observed with the K2 occurs when tuning through
a strong 40m BC station whose carrier level is in the region of -10dbm, and
other BC stations are within the same band at similar carrier levels.
Behaviour is normal while the target BC station enters the IF passband up to
the point where the carrier is at zero beat with the BFO. Continuing to tune
the receiver away from the BC signal does not change the signal's position
in the IF passband until the displayed frequency is roughly 1 kHz away from
the BC station's carrier frequency, at which point the receiver lets go and
returns to normal operation. If the BC carrier is modulated at a very high
level the 'let go' point can be more than 1 kHz away from the carrier
frequency. If I stop tuning the receiver away from the BC station at some
point between the carrier frequency and the 'let go' frequency, the BC
carrier remains at or within 100 - 200 Hz of zero beat with the BFO, further
observation required.  Reduce signal levels and there is no problem.

It does remind me of the not uncommon problem where a PLL can be upset by
intruding external sources, descibed to me many years ago as the 'Monkey in
Kitchen' problem.

My apology for this brief response, I am leaving for Luxembourg shortly.

73,
Geoff
GM4ESD


----- Original Message -----
From: "wayne burdick" <[hidden email]>
To: "Elecraft Reflector" <[hidden email]>
Sent: Wednesday, March 28, 2007 4:19 AM
Subject: [Elecraft] Tuning clunks: technical explanation


> The K2 is a careful balance between high performance, small size, low
> current drain, and low cost, while at the same time using through-hole
> parts to make it easy to build. As the principle designer of the rig, I
> can tell you that this required a number of design tricks to accomplish.
>
> The "clunks" are a side-effect of one of these design choices. A little
> background will help explain this. I'll also briefly describe what could
> be done about it.

<snip>


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[Geoffrey Mackenzie-Kennedy-2]

Good idea. As I understand it 'Clicks' = clicks heard every 5 kHz or
thereabouts even if the antenna is discoinnected, generated inside the K2.
'Clunks' = strange behaviour noticed or sounds heard while tuning when
*very* strong signals are being received in or close to the band in use.
'Clunks' disappear as signal levels decrease.

This nomenclature is a disaster :-)

Geoff
GM4ESD


Darrell Bellerive" <[hidden email]> wrote:

> First of all let's be sure we are all on the same page. Please define
> "Clunks" vs. "Clicks".
>
> While it would be best to find a total cure for the problem, anything that
> reduces the severity or frequency of them would be most welcome.
>
> Darrell  VA7TO


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[Bill Coleman-2]

On Mar 24, 2007, at 1:14 PM, Darrell Bellerive wrote:

> I agree that the synthesizer "tuning clunks" every 5 kHz in the  
> presence of
> strong signals needs to be addressed.

Agreed. It would be really nice to eliminate these. When I'm tuning  
the bands and I encounter one of these clunks, I often tune back to  
see what the signal was that I missed. I've noticed that the rig will  
often clunk one way, but not the other.

Another related issue is the appearance of phantom signals while  
keying CW under QSK. This is especially apparent during contests.  
You'll hear someone sending something, so you'll stop sending -- and  
the signal disappears. Kinda defeats the purpose of all that big  
dynamic range....

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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