Fellow listers,
I'd like to add some clarity to the audio chirp problem mentioned by
Barry. As some of you may or may not know, I took over for Don Wilhelm,
W3FPR when he retired in February of 2019. I am a third party service
provider through my company W8FGU Services, LLC as well as an employee
of Elecraft providing support and servicing of their Classic Line of
products.
Barry contacted me a few months ago to report the chirping (popping)
problem and sent me his K2 for service. I spent a good amount of hours
researching this problem where I was able to reproduce what Barry was
hearing. It was through his wonderful description of how to produce the
problem that I was able to reproduce the same issue on a number of K2's
I have here in the shop including my own personal K2 #5099.
With that said, I must emphasize that the great majority of K2 users
will not be affected by this issue. There have been reports of chirps or
pops during tuning in the past. Most were resolved by running CAL PLL
again and making sure that the bottom cover was installed on the unit
after plenty of warm up time. This is still the first line of defense
when dealing with this problem. Unfortunately for Barry, this did not
solve the issue he was hearing. And while I can explain why the issue
occurs, I can't really explain why it is worse for some units than
others except to say that the K2 was designed to use readily available
through-hole parts with 5% and 10% tolerances and that it's possible
those tolerances add up in certain circumstances. And, it must be
remembered that the K2 is a 22 year old design. The fact that this
design still produces a rig with the performance numbers it has after 22
years and is still available as a build-able kit is a great tribute to
Wayne and Eric's vision and implementation.
The issue: audio chirps and pops were being heard while tuning only when
there were strong signals on the band within +/- 50KHz of the VFO
frequency being tuned. These chirps were being heard every 5KHz of
tuning. This happens to be the tuning boundary of the K2 PLL Oscillator.
In a nutshell, at the 5KHz boundary, the PLL chip was programmed with
new divide by registers and then the PLL Oscillator was moved to the min
or max end of its range depending on the direction of tuning. Between
these two operations was a brief period (a few milliseconds) where there
was some instability while the closed loop of the PLL circuit settled
down after the change in boundary. This produced a large voltage spike
from the output of the PLL chip that caused the integrator circuit
feeding the VCO varactors to sweep the VCO 50KHz or so in a few
milliseconds. If there was a large signal in that frequency range, it
was heard as a chirp or pop. It would be like spinning the VFO knob
50KHz in 8 milliseconds. This is why these chirps are not heard when
there are no signals on the band in the area of tuning.
As I was able to reproduce this issue, I believe in the past, I just
simply blew off what I heard as atmospheric noise while I was tuning,
especially on noisier bands like 40m. Barry could really hear it on 20m
where there was less atmospheric noise but large signals on the band.
This is especially exacerbated when tuning through the lower part of 20m
during a contest where strong CW and digital mode signals made this very
noticeable. Again, most users will not notice this especially if tuning
slowly through the band. When using a tuning rate of 100Hz or 1KHz, it
may be more noticeable as you are hitting the 5KHz PLL Osc boundary
quicker.
As I explained to Barry, I would never have noticed this before he
explained how to produce it. Now that I know what it is, it drives me
crazy. And I am not describing this to bring it to light for all of you
(although I know many of you will try to reproduce it now - sorry). As
Wayne explained to me, this type of PLL tuning design was fairly popular
(and cutting edge) at the time and many radios of the time might produce
similar results.
What I came up with for Barry was a simple one-shot circuit that would
punch the AGC line of the IF Amp during the 5KHz tuning boundary to
dampen the volume for about 15ms to prevent the audio chirp. It monitors
the chip select line of the PLL chip which happens when the process of
setting the divide by registers is going to occur at the beginning of
the PLL boundary reset. The pulse dampens the IF Amp long enough to
allow completion of the boundary reset and prevent any strong signals to
be heard that may be in the VCO sweep that follows.
Again, the vast majority of users will not notice this issue, and as I
mentioned, it may be at different intensities on a per unit basis. I am
trying to develop a very small SMD version of this one-shot circuit for
Barry to test out. This is not a documented mod as yet and has not been
approved by Wayne and Eric in any manner except for experimental
purposes. I just wanted to explain where things are at before this
conversation became speculative or confrontational.
I will be happy to answer any questions that may come up.
73,
Dave W8FGU
------ Original Message ------
From: "Macy monkeys" <macymonk...@charter.net>
To: elecraft@mailman.qth.net
Sent: 11/21/2020 9:53:35 AM
Subject: Re: [Elecraft] K2 purchase considered
Me neither. #586.
John K7FD
On Nov 20, 2020, at 10:13 PM, Vic Rosenthal <k2vco....@gmail.com> wrote:
Strange. I have K2 #725, which received various mods over the years, but I
never noticed anything like a loud pop, nor do I recall a mod for it.
Victor 4X6GP
On 21 Nov 2020, at 4:41, barry halterman <kthre...@gmail.com> wrote:
I will throw my two cents in on this. Quite frankly, I do not see how a K2
got the reviews it did over the years. I put one together in July to do
something during lock down. After assembly, which was really a pleasure,
and in two or three weeks after, I noticed a disturbing pop when tuning
around strong cw stations. The s meter would jump to maximum signal
strength and my ears took a beating with the loud pop!
The rig went back to Elecraft for evaluation and I was told with this type
of PLL circuit design, this is the nature of the beast. Having known this
irritating pop is nature of the beast, I would have saved my money!!
I want to say that Elecraft made a modification to help with the strong
pops and I am very thankful for that and the the terrific service, but the
pops are a big annoyance to me even with the suppressor.
I still am evaluating if I want to keep this thing or put it up for sale.
K3bo
On Fri, Nov 20, 2020, 9:11 PM Macy monkeys <macymonk...@charter.net> wrote:
Agree. I have had a parade of 'better' rigs come and go through the
shack...but my K2 built over 20 years ago is still here.
John K7FD
On Nov 20, 2020, at 5:41 PM, Robert G Strickland via Elecraft <
elecraft@mailman.qth.net> wrote:
John...
Jim has the resume to back up his opinion(s) which I do not have. His
view point always merits serious consideration. For myself, building the K2
was/is one of the "peak experiences" I have enjoyed as an amateur radio
operator. While I now use a K3s - and it is a "better" radio - I have
continued to use the K2 regularly over the years. I never fail to smile
when it powers up, and the two of us go on the radio journey of the moment.
It is my go-to radio for field day. When I bought it there were no other
options, while today, the KX2/3, K3/s, K4 are all excellent radios that
should be considered; you can't go wrong with any of them. That said and
speaking for myself, I would sell any of the "better" radios in my
possession before parting with my K2. When you go on to better and better
rigs, you'll never regret the time spent with the K2. This reads like a
"testimonial," and I suppose that it is. No offense to anyone meant. Just
one ham's opinion.
...robert
11/20/2020 06:54 PM, Jim Brown wrote:
On 11/20/2020 10:07 AM, John Daws wrote:
Am really tempted to get a K2 to use alongside the above- I have an
experienced builder here in the UK.
Everything I have read about the K2 excites me!!
Most of the fun of the K2 is in the building. The newer rigs (K3, K3S,
KX3, K4) are better radios.
73, Jim K9YC
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--
Robert G Strickland, PhD ABPH - KE2WY
rc...@verizon.net.usa
Syracuse, New York, USA
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