[K3] Sudden Hi-SWR on low end of 40M

[Terry Schieler-2]

Yesterday, during the CW contest, I noticed that my K3-100 (#474) suddenly began to "stutter" during CW transmissions on the low end of 40 meters.  I hadn't noticed this before, including Saturday, the first day of the contest.  My CW transmission had a "chattering" sound something like the braaaaap of a machine gun (and no, my fist isn't *that* good).  My first thought was RF getting into the radio, but, I've never had RF issues before and, again, nothing in the system had changed:
 
K3 > LP-100A SWR/Power meter > 4 position Ameritron RCS-4 antenna switch > dipole.  
 
I have never found a frequency on 40-10 meters that my K3's internal tuner could not handle with the only antenna I've ever used with the rig.  But the tuner could not eliminate this chattering yesterday.
 
After the contest I did some checking and noted the following:
 
1.  At 100W, the chattering only occurred from 7.0 to almost exactly 7.1 then went normal again.  CW was normal on all other bands.
2.  If I backed the power down from 100W to 50W the chattering CW below 7.1 went away and all was normal again.
3.  I checked my DX-EE parallel dipole and it was without damage or change.
4.  All coax connections in the feed line chain were tight.
5.  The meter on the K3 indicated a *tuned* SWR of 1.2 at 7.033 during the chattering but the LP-100 meter showed 4.5 and up at the same time and its alarm sounded.  I'd never even heard the alarm before.
6.  I put my MFJ 269 analyzer on the PL259 that connects the 10-40 meter dipole to the K3 and swept the bands.  No band had an SWR greater than 2.4, which the K3's tuner should (and always has) handle well.
 
All in all, the rig performed extremely well in the contest except for this new chattering issue.  I logged many stations that I could barely hear.  Now all I can think is that the K3's internal tuner somehow is losing its memory.  So I went back to each band and did a few "manual" antenna tunes.  SWR on the lower end of 40 meters tuned to 1.2 in several places but the chattering CW continues there with power above 50 watts.  Are there any tests I could perform to determine if the memory function of the K3's internal tuner is intermittent or otherwise suffering.  Thanks.
 
73,
 
Terry, W0FM
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[Rick WA6NHC]

Obviously something has changed.  One element of your system can't handle the higher RF.

Note: use of the internal K3 tuner completely negates the accuracy of the external power/SWR meter since it is 'downstream' and not at the expected 50 ohms resistive.

I'd start by replacing the patch cables, checking the choke (you DO use one, no?) for burns or other failure (replace?) and all connections at the antenna.

I'm guessing you'll find something marginally 'off'.  The analyzer won't catch it because it is very RF out.

GL es 73,
Rick wa6nhc

Tiny iPhone 5 keypad, typos are inevitable

On Feb 18, 2013, at 8:54 AM, "Terry Schieler" <[hidden email]> wrote:

> Yesterday, during the CW contest, I noticed that my K3-100 (#474) suddenly began to "stutter" during CW transmissions on the low end of 40 meters.  I hadn't noticed this before, including Saturday, the first day of the contest.  My CW transmission had a "chattering" sound something like the braaaaap of a machine gun (and no, my fist isn't *that* good).  My first thought was RF getting into the radio, but, I've never had RF issues before and, again, nothing in the system had changed:
>
> K3 > LP-100A SWR/Power meter > 4 position Ameritron RCS-4 antenna switch > dipole.  
>
> I have never found a frequency on 40-10 meters that my K3's internal tuner could not handle with the only antenna I've ever used with the rig.  But the tuner could not eliminate this chattering yesterday.
>
> After the contest I did some checking and noted the following:
>
> 1.  At 100W, the chattering only occurred from 7.0 to almost exactly 7.1 then went normal again.  CW was normal on all other bands.
> 2.  If I backed the power down from 100W to 50W the chattering CW below 7.1 went away and all was normal again.
> 3.  I checked my DX-EE parallel dipole and it was without damage or change.
> 4.  All coax connections in the feed line chain were tight.
> 5.  The meter on the K3 indicated a *tuned* SWR of 1.2 at 7.033 during the chattering but the LP-100 meter showed 4.5 and up at the same time and its alarm sounded.  I'd never even heard the alarm before.
> 6.  I put my MFJ 269 analyzer on the PL259 that connects the 10-40 meter dipole to the K3 and swept the bands.  No band had an SWR greater than 2.4, which the K3's tuner should (and always has) handle well.
>
> All in all, the rig performed extremely well in the contest except for this new chattering issue.  I logged many stations that I could barely hear.  Now all I can think is that the K3's internal tuner somehow is losing its memory.  So I went back to each band and did a few "manual" antenna tunes.  SWR on the lower end of 40 meters tuned to 1.2 in several places but the chattering CW continues there with power above 50 watts.  Are there any tests I could perform to determine if the memory function of the K3's internal tuner is intermittent or otherwise suffering.  Thanks.
>
> 73,
>
> Terry, W0FM
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[Don Wilhelm-4]

Terry,

I suggest you look for something arcing or otherwise breaking down at
some power level in your antenna system.
The K3 is showing you the SWR achieved at the input to the internal tuner.
Your LP-100 is showing you the actual SWR of the antenna.

The only reason your MFJ-269 would indicate a very different SWR from
the LP-100 is that while your antenna seems just fine with low power,
something changes when you increase the power.  That is usually from a
failed common mode choke, or an insulator arcing over or something similar.

Try reducing the power of the K3 to 10 watts - now what does the LP-100
indicate for SWR?  I would wager that it will be similar to that
obtained from your MFJ-269.

73,
Don W3FPR

On 2/18/2013 11:54 AM, Terry Schieler wrote:

> Yesterday, during the CW contest, I noticed that my K3-100 (#474) suddenly began to "stutter" during CW transmissions on the low end of 40 meters.  I hadn't noticed this before, including Saturday, the first day of the contest.  My CW transmission had a "chattering" sound something like the braaaaap of a machine gun (and no, my fist isn't *that* good).  My first thought was RF getting into the radio, but, I've never had RF issues before and, again, nothing in the system had changed:
>  
> K3 > LP-100A SWR/Power meter > 4 position Ameritron RCS-4 antenna switch > dipole.
>  
> I have never found a frequency on 40-10 meters that my K3's internal tuner could not handle with the only antenna I've ever used with the rig.  But the tuner could not eliminate this chattering yesterday.
>  
> After the contest I did some checking and noted the following:
>  
> 1.  At 100W, the chattering only occurred from 7.0 to almost exactly 7.1 then went normal again.  CW was normal on all other bands.
> 2.  If I backed the power down from 100W to 50W the chattering CW below 7.1 went away and all was normal again.
> 3.  I checked my DX-EE parallel dipole and it was without damage or change.
> 4.  All coax connections in the feed line chain were tight.
> 5.  The meter on the K3 indicated a *tuned* SWR of 1.2 at 7.033 during the chattering but the LP-100 meter showed 4.5 and up at the same time and its alarm sounded.  I'd never even heard the alarm before.
> 6.  I put my MFJ 269 analyzer on the PL259 that connects the 10-40 meter dipole to the K3 and swept the bands.  No band had an SWR greater than 2.4, which the K3's tuner should (and always has) handle well.
>  
> All in all, the rig performed extremely well in the contest except for this new chattering issue.  I logged many stations that I could barely hear.  Now all I can think is that the K3's internal tuner somehow is losing its memory.  So I went back to each band and did a few "manual" antenna tunes.  SWR on the lower end of 40 meters tuned to 1.2 in several places but the chattering CW continues there with power above 50 watts.  Are there any tests I could perform to determine if the memory function of the K3's internal tuner is intermittent or otherwise suffering.  Thanks.
>  
>

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[Augie "Gus" Hansen]

On 2/18/2013 9:54 AM, Terry Schieler wrote:
> Yesterday, during the CW contest, I noticed that my K3-100 (#474)
suddenly began to "stutter" during CW transmissions on the low end of 40
meters. I hadn't noticed this before, including Saturday, the first day
of the contest. My CW transmission had a "chattering" sound something
like the braaaaap of a machine gun (and no, my fist isn't *that* good).
My first thought was RF getting into the radio, but, I've never had RF
issues before and, again, nothing in the system had changed:
>
> K3 > LP-100A SWR/Power meter > 4 position Ameritron RCS-4 antenna
switch > dipole.

I've seen two versions of the RCS-4. An early version had three DPDT
relays and a later version had only two 4PDT relays. My comments here
apply to the two-relay version.

Which ANT position on the RCS-4 connects to the 40m dipole? If position
4, your remote switch may be failing. In that position the control
voltage imposed onto the coax center conductor along with the RF is
alternating current, which activates both relays in the remote switch.
If the coax connections are not solid for any reason, or if either of
the filter capacitors across the relay coils is bad, one or both relays
may be chattering.

You can check this by selecting antenna 4 and listening to the remote
switch box. If a relay is chattering you'll hear it. There's no need to
apply any RF for this initial test, but if there's no audible response
apply a steady carrier in the troublesome frequency range and listen
again. There could be an unwanted resonance due to changes in the RFC
(~7-100uH) or the capacitors that triggers the event.

Good luck,
Gus Hansen
KB0YH

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[Augie "Gus" Hansen]

There are two errors in my previous posting regarding the RCS-4 remote
antenna switch.

1) The default (off, no power) antenna position is ANT4. The ANT1
position is the one that is activated by the AC control voltage.

2) I mistyped the RFC/choke value. The value of the RFC in the remote
switch box measured with an AADE L/C Meter IIB is 70uH in circuit. It is
probably the same as the RFC in the control box that measures ~100uH.

Also note that the current version being sold by MFJ/Ameritron uses the
three-relay circuit with a modified layout of the connectors, which I
assume is to minimize any impedance bumps.

The two-relay version I mentioned in the previous post has provision for
jumpers that ground the unselected ANTx connector center conductors.
Neither of the three-relay version support this feature.

Gus Hansen
KB0YH

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