Garbled K2 SSB Signals

[Dake Holloway, K4EQ]

I completed my K2 earlier this week and everything seems to be working
great. However, I have discovered one problem. Received SSB signals from
7180 to 7185 kHz are garbled even with the NB and preamp off. Thus far I
haven't observed this problem on any other frequency. Any ideas what may be
causing this?

 

Dale, K4EQ

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[Don Wilhelm-4]

Dale,

That is an old problem often referred to as WAOF (Weird At One Frequency).
That frequency region is where the PLL frequency and the VFO frequencies
cross.  Those two signals can couple together producing the condition
that you observe.  The fix is to reduce the opportunity for those
signals to couple together.

Make certain that C88 on the bottom of the RF board soldered between
pins 12 and 13 of U4 is on the correct pins and has the shortest
possible leads.  Also the length of the leads for RFC15 and C91 should
be as short as possible at the connection point with U4 pin 16.

If that does not take care of it, flush cut all pins and component leads
in the vicinity of U4 and U6 including the R-paks to eliminate anything
that could act as an antenna.  Also above the board make certain the
varactors and capacitors in the VFO and PLL area are seated completely
down on the board - long leads will cause the signals to couple together.

The last gentleman who had this problem reported that the above efforts
did not stop it entirely, but when he covered the U4 area with
electrical tape, the problem went away.  Now, I can't explain why the
electrical tape would have that effect, but give it a try.

73,
Don W3FPR


On 5/4/2014 9:11 AM, [hidden email] wrote:
> I completed my K2 earlier this week and everything seems to be working
> great. However, I have discovered one problem. Received SSB signals from
> 7180 to 7185 kHz are garbled even with the NB and preamp off. Thus far I
> haven't observed this problem on any other frequency. Any ideas what may be
> causing this?
>

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[Matt Zilmer-2]

Hi Don,

Electrical tape is slightly resistive, at least the ones I've used. At
Idealab (Pasadena, CA - tech incubator), we used electrical tape to
"lightly ground" sections of a proto RF PCBA we were developing. Doing
this snubbed out some parasitic oscillation that we never really
understood.  One of our grad student techs found this by accident.

Murphy acts in strange ways, sometimes.

73,
matt W6NIA

On Sun, 04 May 2014 09:35:32 -0400, you wrote:

>Dale,
>
>That is an old problem often referred to as WAOF (Weird At One Frequency).
>That frequency region is where the PLL frequency and the VFO frequencies
>cross.  Those two signals can couple together producing the condition
>that you observe.  The fix is to reduce the opportunity for those
>signals to couple together.
>
>Make certain that C88 on the bottom of the RF board soldered between
>pins 12 and 13 of U4 is on the correct pins and has the shortest
>possible leads.  Also the length of the leads for RFC15 and C91 should
>be as short as possible at the connection point with U4 pin 16.
>
>If that does not take care of it, flush cut all pins and component leads
>in the vicinity of U4 and U6 including the R-paks to eliminate anything
>that could act as an antenna.  Also above the board make certain the
>varactors and capacitors in the VFO and PLL area are seated completely
>down on the board - long leads will cause the signals to couple together.
>
>The last gentleman who had this problem reported that the above efforts
>did not stop it entirely, but when he covered the U4 area with
>electrical tape, the problem went away.  Now, I can't explain why the
>electrical tape would have that effect, but give it a try.
>
>73,
>Don W3FPR
>
>
>On 5/4/2014 9:11 AM, [hidden email] wrote:
>> I completed my K2 earlier this week and everything seems to be working
>> great. However, I have discovered one problem. Received SSB signals from
>> 7180 to 7185 kHz are garbled even with the NB and preamp off. Thus far I
>> haven't observed this problem on any other frequency. Any ideas what may be
>> causing this?
>>
>
>______________________________________________________________
>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]

Matt Zilmer, W6NIA
www.elecraft.com
831-763-4211  x129


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[Dake Holloway, K4EQ]

Thanks again Don. I shortened one lead on C88 and made certain that
everything around U4 and U6 was as tightly flush cut as possible. Also, I
put electrical tape all over the U4 area. There's not much activity up here
on 40 meters now, but fortunately there was a weak station around 7182, the
offending area. Unfortunately, he was garbled. Back to the fortunate thing .
. . I don't work much SSB and rarely in the 7180-7185 area, so this won't
bother me a whole lot. Nevertheless, if you or anyone have other
suggestions, I'm open. Gracias.  --Dale, K4EQ

-----Original Message-----
Sent: Sunday, May 04, 2014 9:17 AM
To: '[hidden email]'
Subject: RE: [Elecraft] Garbled K2 SSB Signals

Thank you so much Don, Those are excellent suggestions and I will get right
on it today. I feel some comfort in knowing it isn't just my radio. In other
words, misery loves company.  :-)  --Dale

-----Original Message-----
From: Don Wilhelm [mailto:[hidden email]]
Sent: Sunday, May 04, 2014 8:36 AM
To: [hidden email]; [hidden email]
Subject: Re: [Elecraft] Garbled K2 SSB Signals

Dale,

That is an old problem often referred to as WAOF (Weird At One Frequency).
That frequency region is where the PLL frequency and the VFO frequencies
cross.  Those two signals can couple together producing the condition that
you observe.  The fix is to reduce the opportunity for those signals to
couple together.

Make certain that C88 on the bottom of the RF board soldered between pins 12
and 13 of U4 is on the correct pins and has the shortest possible leads.
Also the length of the leads for RFC15 and C91 should be as short as
possible at the connection point with U4 pin 16.

If that does not take care of it, flush cut all pins and component leads in
the vicinity of U4 and U6 including the R-paks to eliminate anything that
could act as an antenna.  Also above the board make certain the varactors
and capacitors in the VFO and PLL area are seated completely down on the
board - long leads will cause the signals to couple together.

The last gentleman who had this problem reported that the above efforts did
not stop it entirely, but when he covered the U4 area with electrical tape,
the problem went away.  Now, I can't explain why the electrical tape would
have that effect, but give it a try.

73,
Don W3FPR


On 5/4/2014 9:11 AM, [hidden email] wrote:
> I completed my K2 earlier this week and everything seems to be working
> great. However, I have discovered one problem. Received SSB signals
> from
> 7180 to 7185 kHz are garbled even with the NB and preamp off. Thus far
> I haven't observed this problem on any other frequency. Any ideas what
> may be causing this?
>

______________________________________________________________
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[k6dgw]

Be aware that most black electrical tape is very slightly conductive.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

On 5/4/2014 6:35 AM, Don Wilhelm wrote:

> The last gentleman who had this problem reported that the above efforts
> did not stop it entirely, but when he covered the U4 area with
> electrical tape, the problem went away.  Now, I can't explain why the
> electrical tape would have that effect, but give it a try.


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