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[K1] Internal Noise Bursts every 12 seconds or so

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WB4SON

[K1] Internal Noise Bursts every 12 seconds or so

I just completed assembly of a 30m/20m K1 up through the point of Receiver
calibration. Everythings has gone smoothly and all tests and alignment
steps were completed successfully. I can hear a 1 uV signal very clearly
on both bands.

However, there appears to be some internal periodic noise. It is very
raspy in nature and it repeats every 12 seconds. I'm guessing it is being
generated by one of the two internal CPUs. I hear it on battery power with
a shorting plug installed on the antenna, on any frequency and on both
bands.

Basically I hear a low level burst noise that lasts for 1/2 second, with
about a 1/2 second gap, followed by a 3 second burst, then silence for
about 8 seconds. The entire pattern repeats every 12 seconds

While it is very low level, comparable to the 1 uV signal that I aligned
the receiver with, it seems to modulate even strong S9 signals.

Does anyone know what this noise is and how to get rid of it?

Anyway, this glitch aside, I'm very excited.

73, Bob, WB4SON
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73, Bob, WB4SON

Don Wilhelm-4

Re: [K1] Internal Noise Bursts every 12 seconds or so

Bob,

That is not a normal situation for the K1.

The "standard" answer is that it is the result of a poor solder connection.
I cannot guess at where it could be other than to say due to the
periodic nature of the occurrence that it is associated with the MCU in
some manner.
So check the soldering of the Front Panel board closely.

There is only one CPU in the K1, and it is on the Front Panel Board -
the firmware on the band board responds only to the band change
information from the basic K1.

Soldering Tutorial 101:
All solder connections should show that the solder has flowed out fully
onto the solder pad as well as onto the component lead. If you can see
a ring around a component lead, that component has not been heated
sufficiently.
If your solder connections result in a solder "blob" that is a bad
connection (again resulting from insufficient heat to the connection).

Solder connections should look like mountains, but not like a volcano.
In other words, there should be a small and nice fillet of solder
between the solder pad and the component lead.

Some builders seem to worry about heating the component leads. The fact
is that modern components and boards with thru-plated holes will
withstand soldering temperatures for 5 seconds with no damage.
Watch the solder. It should flow out onto the solder pad and the
component lead in 2 to 3 seconds. If it does not, the iron temperature
is too low, and if that happens in less then 2 seconds, the iron is too hot.

I have repaired many transceivers where the problem was soldering -
usually because the iron temperature was too low or the builder did not
dwell long enough on the connection to allow the solder to flow out onto
the solder pad and the component lead.

Modern components and through-plated boards will sustain a soldering
temperature of 800 degF for 5 seconds or longer.

I recommend an iron temperature of 750 degF except for the KPA100 and XV
transverters which have a large ground plane - for those, 800 degF will
work much better.

73,
Don W3FPR

On 12/28/2015 8:16 PM, Bob wrote:

> I just completed assembly of a 30m/20m K1 up through the point of Receiver
> calibration. Everythings has gone smoothly and all tests and alignment
> steps were completed successfully. I can hear a 1 uV signal very clearly
> on both bands.
>
> However, there appears to be some internal periodic noise. It is very
> raspy in nature and it repeats every 12 seconds. I'm guessing it is being
> generated by one of the two internal CPUs. I hear it on battery power with
> a shorting plug installed on the antenna, on any frequency and on both
> bands.
>
> Basically I hear a low level burst noise that lasts for 1/2 second, with
> about a 1/2 second gap, followed by a 3 second burst, then silence for
> about 8 seconds. The entire pattern repeats every 12 seconds
>
> While it is very low level, comparable to the 1 uV signal that I aligned
> the receiver with, it seems to modulate even strong S9 signals.
>
> Does anyone know what this noise is and how to get rid of it?
>
>

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WB4SON

Re: [K1] Internal Noise Bursts every 12 seconds or so

Many thanks for the rapid reply, Don!

Good to know this isn't normal, and I will certainly follow your advice and
check the front panel assembly carefully, especially the solder. When I
initially checked things with an optical loop, the solder appeared to be
bright on both sides of the PCB (at least for things I could see). I did
use a 700 degree tip on my Weller WTCPT Iron and standard Kester 44 solder,
so the potential for decent soldering is there at least.

Even though the second CPU on the filter board is mostly inactive, no
telling what internal loops are going on that might result in it turning
that 4 MHz resonator into a periodic signal. So I'll be sure to check
around that too. Of course at this time in the assembly process, the
Filter Board is not screwed down. Don't know if that is a source of noise
or not. I'm also curious what the AGC_OFF signal is doing on that board.
I'll investigate that later.

Given that it is appearing in the audio chain (or at least post
demodulator), I am suspecting the noise is propagating over the internal
power rail.

Figures I'd have an interesting problem.

Thanks again!

73, Bob, WB4SON
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73, Bob, WB4SON

Mike Morrow-3

Re: [K1] Internal Noise Bursts every 12 seconds or so

In reply to this post by WB4SON

Bob wrote:

> Even though the second CPU on the filter board is mostly inactive, no
> telling what internal loops are going on that might result in it turning
> that 4 MHz resonator into a periodic signal.

In addition to the relays on the filter board itself, the PIC on the KFL1 board controls RF board relay K1 (the RF Attenuate ATTN relay). But that info is not likely to help isolate the problem you report.

I own K1 #175 that I built in November 2000. It was unfortunately a lightning strike victim a few months ago, ending almost 15 years of service. A most excellent radio for all thoses years.

I have never before read a report of a problem similar to what you describe, except for one in 2001 in which a burst of internal noise was generated on 20m after going from transmit to receive. This was caused by the PIC on the KNB1 noise blanker PCB, and1 was corrected by adding a 0.01 uF capacitor on the PIC's Vdd line to ground. It's a long shot, but you may want to check the installation of the similar capacitors on the Display PCB (C4) and KFL1-2 (C27).

Mike / KK5F
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WB4SON

Re: [K1] Internal Noise Bursts every 12 seconds or so

Thanks for the ideas, Mike!

Well I can rule out the Filter Board, as the noise is still there when the
Filter Board is removed.

I hoped I could remove the CPU to see if there was an issue there, but with
the CPU gone, the audio is eliminated (probably need to pull something high
or low to get the audio back).

In looking over the Front Panel Schematic quickly, my attention was drawn
to the 6 volt power supply generated on the Front Panel ("6A") and
distributed to several high gain parts of the RF board. Any noise on 6A is
going to be an issue. I also noted that there is no traditional bulk
storage cap on the input of the 78L06 regulator, U4, typically .3 to 10 uF,
and while there are a few decoupling caps on the output, the closest one to
U4 is several inches away C5. The output cap on a 78L series regulator is
typically 0.1uF mounted as close to possible. Finally the original
specified regulator has been obsoleted and a different unit was substituted.

I've seen issues with TO92 cased 78L series regulators breaking into some
strange oscillations when the input or output caps are not sufficient. So
I'm going to check that out too.

For the moment I will ignore it and move forward to complete the TX section.

73, Bob, WB4SON

On Mon, Dec 28, 2015 at 11:46 PM, Mike Morrow <[hidden email]> wrote:

> Bob wrote:
>
> > Even though the second CPU on the filter board is mostly inactive, no
> > telling what internal loops are going on that might result in it turning
> > that 4 MHz resonator into a periodic signal.
>
> In addition to the relays on the filter board itself, the PIC on the KFL1
> board controls RF board relay K1 (the RF Attenuate ATTN relay). But that
> info is not likely to help isolate the problem you report.
>
> I own K1 #175 that I built in November 2000. It was unfortunately a
> lightning strike victim a few months ago, ending almost 15 years of
> service. A most excellent radio for all thoses years.
>
> I have never before read a report of a problem similar to what you
> describe, except for one in 2001 in which a burst of internal noise was
> generated on 20m after going from transmit to receive. This was caused by
> the PIC on the KNB1 noise blanker PCB, and1 was corrected by adding a 0.01
> uF capacitor on the PIC's Vdd line to ground. It's a long shot, but you
> may want to check the installation of the similar capacitors on the Display
> PCB (C4) and KFL1-2 (C27).
>
> Mike / KK5F
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

73, Bob, WB4SON

Mike Morrow-3

Re: [K1] Internal Noise Bursts every 12 seconds or so

In reply to this post by WB4SON

Bob wrote:

> In looking over the Front Panel Schematic quickly, my attention was
> drawn to the 6 volt power supply generated on the Front Panel ("6A")
> and distributed to several high gain parts of the RF board. Any noise
> on 6A is going to be an issue. I also noted that there is no traditional
> bulk storage cap on the input of the 78L06 regulator, U4, typically .3 to 10
> uF, and while there are a few decoupling caps on the output, the closest one
> to U4 is several inches away C5. The output cap on a 78L series regulator
> is typically 0.1uF mounted as close to possible. Finally the original
> specified regulator has been obsoleted and a different unit was substituted.

I wrote previously:

>> It's a long shot, but you may want to check the installation of the
>> similar capacitors on the Display PCB (C4) and KFL1-2 (C27).

I would look closely on the Front Panel PCB (whicn I erroneously called the Display PCB above) at C4 (0.047 uF) on the 6A line to U1 pin 1 and 11. It of course is on the output of regulator U4. It would be interesting to see what happens to the noise if a similar cap was installed in parallel with C4.

Mike / KK5F
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Don Wilhelm-4

Re: [K1] Internal Noise Bursts every 12 seconds or so

In reply to this post by WB4SON

Bob,

Can you describe "noise burst" - is it more of a "tick", or if it is
longer, what is the approximate duration.
You will likely have to short the signal path at several points to
isolate it. One such point is the input to the product detector -
solder a jumper between pins 1 and 2 of T2. If it disappears, you will
have to look further toward the antenna - jumper from the base of Q3 to
ground (or between pins 3 and 4 of RP6).
OTOH, if it is still present with the jumper across T2, the next jumper
to install is between pins 2 and 3 of U3 (which should do the same as
when the K1 is muted).

73,
Don W3FPR

On 12/29/2015 12:35 PM, Bob wrote:

> Thanks for the ideas, Mike!
>
> Well I can rule out the Filter Board, as the noise is still there when the
> Filter Board is removed.
>
> I hoped I could remove the CPU to see if there was an issue there, but with
> the CPU gone, the audio is eliminated (probably need to pull something high
> or low to get the audio back).
>
>

WB4SON

Re: [K1] Internal Noise Bursts every 12 seconds or so

Great advice, Don. I will try that soon.

The noise is raspy alnost static like. Not a ticking like you would expect
from digital noise.

I have mechanically probed every component lead and cant cause the noise
that way which I would expect from any intermittant connection. Nor does
rapping hard on the case cause it. It simply repeats at its own pattern
rate: 1/2 sec burst, 1/2 sec pause, 3 sec burst, 8 sec pause, endlessly
repeating.

73, Bob, WB4SON

On Tuesday, December 29, 2015, Don Wilhelm <[hidden email]> wrote:

> Bob,
>
> Can you describe "noise burst" - is it more of a "tick", or if it is
> longer, what is the approximate duration.
> You will likely have to short the signal path at several points to isolate
> it. One such point is the input to the product detector - solder a jumper
> between pins 1 and 2 of T2. If it disappears, you will have to look
> further toward the antenna - jumper from the base of Q3 to ground (or
> between pins 3 and 4 of RP6).
> OTOH, if it is still present with the jumper across T2, the next jumper to
> install is between pins 2 and 3 of U3 (which should do the same as when the
> K1 is muted).
>
> 73,
> Don W3FPR
>
> On 12/29/2015 12:35 PM, Bob wrote:
>
>> Thanks for the ideas, Mike!
>>
>> Well I can rule out the Filter Board, as the noise is still there when the
>> Filter Board is removed.
>>
>> I hoped I could remove the CPU to see if there was an issue there, but
>> with
>> the CPU gone, the audio is eliminated (probably need to pull something
>> high
>> or low to get the audio back).
>>
>>
>>
>

73, Bob, WB4SON

Edward A. Dauer

[K1] Internal Noise Bursts every 12 seconds or so

In reply to this post by WB4SON

I think there was a Sci-Fi movie in the 1950s that started that way . . .
led to a very DX QSO.

Ted, KN1CBR

>Message: 23
>Date: Wed, 30 Dec 2015 12:15:56 -0500
>From: Bob <[hidden email]>
>To: "[hidden email]" <[hidden email]>
>Cc: Mike Morrow <[hidden email]>, Elecraft <[hidden email]>
>Subject: Re: [Elecraft] [K1] Internal Noise Bursts every 12 seconds or
> so
>Message-ID:
> <CAPonRZ9LZcgJH+kEa__LKNe_e-CtZ1udx_xz5=[hidden email]>
>Content-Type: text/plain; charset=UTF-8
>
>Great advice, Don. I will try that soon.
>
>The noise is raspy alnost static like. Not a ticking like you would expect
>from digital noise.
>
>I have mechanically probed every component lead and cant cause the noise
>that way which I would expect from any intermittant connection. Nor does
>rapping hard on the case cause it. It simply repeats at its own pattern
>rate: 1/2 sec burst, 1/2 sec pause, 3 sec burst, 8 sec pause, endlessly
>repeating.
>
>73, Bob, WB4SON

k6dgw

Re: [K1] Internal Noise Bursts every 12 seconds or so

Well, if the bursts or spaces were primes, you may have found ET's
smartphone. I'd sure like to know the outcome once you discover that it
isn't ET.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the Cal QSO Party 1-2 Oct 2016
- www.cqp.org

On 12/30/2015 12:39 PM, Dauer, Edward wrote:

> I think there was a Sci-Fi movie in the 1950s that started that way . . .
> led to a very DX QSO.
>
> Ted, KN1CBR
>
>
>
>> Message: 23
>> Date: Wed, 30 Dec 2015 12:15:56 -0500
>> From: Bob <[hidden email]>
>> To: "[hidden email]" <[hidden email]>
>> Cc: Mike Morrow <[hidden email]>, Elecraft <[hidden email]>
>> Subject: Re: [Elecraft] [K1] Internal Noise Bursts every 12 seconds or
>> so
>> Message-ID:
>> <CAPonRZ9LZcgJH+kEa__LKNe_e-CtZ1udx_xz5=[hidden email]>
>> Content-Type: text/plain; charset=UTF-8
>>
>> Great advice, Don. I will try that soon.
>>
>> The noise is raspy alnost static like. Not a ticking like you would expect
>>from digital noise.
>>
>> I have mechanically probed every component lead and cant cause the noise
>> that way which I would expect from any intermittant connection. Nor does
>> rapping hard on the case cause it. It simply repeats at its own pattern
>> rate: 1/2 sec burst, 1/2 sec pause, 3 sec burst, 8 sec pause, endlessly
>> repeating.
>>
>> 73, Bob, WB4SON

WB4SON

Re: [K1] Internal Noise Bursts every 12 seconds or so

In reply to this post by WB4SON

I completed my K1 assembly/alignment/testing after about 27 hours. A
couple of those hours were spent dealing with the periodic noise burst on
RX.

I'm happy to report, that with the addition of a couple of 0.47uF caps on
the 6A and 6B power supply rails, the periodic noise burst signal level was
substantially reduced. I can still hear it faintly on a dummy load, but on
air tests show the signal is below the atmospheric noise level on 20/30
meters. Also, it no longer "colors" the RX signals, not even weak ones.
My final conclusion is that there was a stability issue with the 78L06
regulators due to the placement of bulk and bypass caps.

That nose was the most significant issue I had with the radio. The other
had to do with the wrong size toroids being supplied for the Filter Board.
After adjusting the turn count for the size difference, I went ahead and
used the cores, but found that the 30 meter TX power wouldn't go above 3
watts. Winding correct size cores fixed that problem.

Another minor nit came up once the metal covers were all installed. That
caused a shift of about 150 Hz in the TX offset frequency. In addition,
the built in power meter, which was surprisingly accurate with the bottom
and top cover off, is now a couple of watts off. It reads 7 watts, when it
is actually putting out 5 watts. Both of these issues are a result of
de-tuning when the covers are on. Pull the covers off and things are back
to where they were originally.

All in all, I'm very happy. The RX performance is quite good, and even the
audio derived AGC is doing an acceptable job. It was fun to put together.

Thanks for a great kit, Elecraft.

73, Bob, WB4SON
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73, Bob, WB4SON