K2 problem or is it the antenna?

[Darwin, Keith]

My K2 will not give more than a few watts out on 40 meters when driving
my antenna.  Into a dummy load it gives full power.  On 30 meters with a
different antenna the rig is fine.  I wondered if it was a problem with
the rig but I saw some other things that make me think it's an antenna
problem.
 
The antenna is a ground mounted vertical fed with 30 feet of RG-213 to a
Heath manual tuner in the garage.  From there, RG -8x takes the signal
all the way to the shack.  I go to the garage with my MFJ analyzer and
adjust the tuner for a match on my operating freq.  I did this and got a
1:1 match at 7040.  I then went to the shack and confirmed the same SWR
at the rig.
 
Hook up the rig, key it and the SWR meter shows very high SWR.  Rig is
generating hardly any power out.  Recheck with the analyzer and SWR is
fine.  Hmm.  I'm thinking the issue is power related.  Could it be that
my antenna system has a problem that only shows up when you hit the
system with a few watts and doesn't show when the analyzer hits it with
milliwatts?
 
Last night I tried it again and noticed the resonant frequency had
shifted from 7.040 to 9 MHz.  I think it is time for an antenna / tuner
/ coax review.
 
- Keith -
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[Don Wilhelm-3]

Kieth,

If the K2 works fine into a dummy load - and some of your antennas, then the
problem is not with the K2!

You likely have a piece of coax (or antenna) that is failing with power - it
could be an arc-over situation or something like that.  Try moving the dummy
load to the garage first, then on out ot the antenna.  If the dummy load
works fine at those locations, it is not the coax, look at your antenna for
the problem.

The fact that the resonant frequency shifts on you says the most likely
place for the problem is the antenna, but coax can act like a tuned circuit
too, so check it all.

73,
Don W3FPR

> -----Original Message-----
>
> My K2 will not give more than a few watts out on 40 meters when driving
> my antenna.  Into a dummy load it gives full power.  On 30 meters with a
> different antenna the rig is fine.  I wondered if it was a problem with
> the rig but I saw some other things that make me think it's an antenna
> problem.
>
> The antenna is a ground mounted vertical fed with 30 feet of RG-213 to a
> Heath manual tuner in the garage.  From there, RG -8x takes the signal
> all the way to the shack.  I go to the garage with my MFJ analyzer and
> adjust the tuner for a match on my operating freq.  I did this and got a
> 1:1 match at 7040.  I then went to the shack and confirmed the same SWR
> at the rig.
>
> Hook up the rig, key it and the SWR meter shows very high SWR.  Rig is
> generating hardly any power out.  Recheck with the analyzer and SWR is
> fine.  Hmm.  I'm thinking the issue is power related.  Could it be that
> my antenna system has a problem that only shows up when you hit the
> system with a few watts and doesn't show when the analyzer hits it with
> milliwatts?
>
> Last night I tried it again and noticed the resonant frequency had
> shifted from 7.040 to 9 MHz.  I think it is time for an antenna / tuner
> / coax review.
>
> - Keith -
>

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[Ron D'Eau Claire-2]

Keith asked:

My K2 will not give more than a few watts out on 40 meters when driving my
antenna.  Into a dummy load it gives full power.  On 30 meters with a
different antenna the rig is fine.  I wondered if it was a problem with the
rig but I saw some other things that make me think it's an antenna problem.
 
The antenna is a ground mounted vertical fed with 30 feet of RG-213 to a
Heath manual tuner in the garage.  From there, RG -8x takes the signal all
the way to the shack.  I go to the garage with my MFJ analyzer and adjust
the tuner for a match on my operating freq.  I did this and got a 1:1 match
at 7040.  I then went to the shack and confirmed the same SWR at the rig.
 
Hook up the rig, key it and the SWR meter shows very high SWR.  Rig is
generating hardly any power out.  Recheck with the analyzer and SWR is fine.
Hmm.  I'm thinking the issue is power related.  Could it be that my antenna
system has a problem that only shows up when you hit the system with a few
watts and doesn't show when the analyzer hits it with milliwatts?
 
Last night I tried it again and noticed the resonant frequency had shifted
from 7.040 to 9 MHz.  I think it is time for an antenna / tuner / coax
review.

------------------------------------------

By getting consistently good output into a dummy load, it looks like you've
eliminated the K2 as the likely source of the problem.

I'd suggest you check the connector at the rig end. Problems like this tend
to be associated with whatever it is you are changing to make it appear and
disappear, and that seems to be associated with moving that cable at the rig
end between the analyzer and the K2.

The same is true for when you saw that resonant frequency jump. That much of
a shift would account for the jump in SWR. Look for exactly what you touched
to make that change happen. Perhaps a bad connection in one of the coax
connectors?

For example, one time I suddenly saw a "problem" with my K2/100 going from
normal operation to "high current" and shut-off when the resettable fuse
opened! I was about to tear into it when my own advice popped into my head
and it gave some thought to what I had been doing. I had made some cabling
changes between the rig and my external ATU. Sure enough, the PL-259 to the
ATU was very loose. It worked some of the time but then the heating by the
RF current or a tiny movement caused by something would make the connection
open and the K2 was looking into a very high SWR and would shut down.
Tightening the connector fixed the problem <G>.

It is possible for a problem like yours to be power related. The RF current
flowing through a bad connection can cause heating and resistance changes
that don't show up at low powers or a partial short at a high voltage point
in either the tuner or antenna can cause that to happen. It can be
band-specific too, since RF current and voltage levels at various parts of
the antenna and tuner circuit change with the band. The only thing to do
there is to start working toward the antenna. Try connecting your rig
directly to the tuner in the garage with a different piece of cable and see
if the problem appears there.  

Ron AC7AC

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[Darwin, Keith]

Yep, I've done enough testing (and made enough mistakes) at work to have
caught on to the fact that if something has quit working, look first at
what just changed :-)

In this case I do have some good data that points to the antenna.  The
K2 acts like it is seeing very high SWR which agrees with the Palstar
meter which is measuring a large reflected power.  Only the MFJ analyzer
says 1:1 SWR.  I'm swapping at the connector going into the rig so the
analyzer is looking at the exact system the K2 is which includes the
power meter in the path.  If the power meter said low SWR and the K2 was
acting up, I'd suspect an issue with a connector at the rig end.

Then comes the other piece of evidence.  I've notice recently my manual
tuner settings are not holding from day to day.  The system impedance
just magically changes overnight (wind & precip maybe?)  Also, the
bandwidth of the tuned system has become much narrower.  I used to get
2:1 bandwidth across most of the 40 meter band.  Two nights ago, I
struggled to get 2:1 over 90 KHz.

I'll open the case on the tuner to see if ants or spiders have invaded.

I'll check the connections from the coax to the vertical and from the
radials to the radial plate.

I'll lower the vertical (a bit of a pain) to see if any of the hose
clamps have come loose causing the radiator to sometimes act shorter
than it's actual length.

Gee, while I'm out there, I might as well bury another 15 radials :-)

The biggest bummer is all this takes away from operating time.
Fortunately for me, Ham Radio is about lots more than operating!

73 & thanks for the input Don & Ron!

- Keith -


-----Original Message-----
From: Ron D'Eau Claire [mailto:[hidden email]]

By getting consistently good output into a dummy load, it looks like
you've eliminated the K2 as the likely source of the problem.

I'd suggest you check the connector at the rig end. Problems like this
tend to be associated with whatever it is you are changing to make it
appear and disappear, and that seems to be associated with moving that
cable at the rig end between the analyzer and the K2.

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[Ron D'Eau Claire-2]

Keith wrote:
Also, the bandwidth of the tuned system has become much narrower.  I used to
get 2:1 bandwidth across most of the 40 meter band.  Two nights ago, I
struggled to get 2:1 over 90 KHz.

----------------

Narrow bandwidth is a sure sign of a reasonably efficient, but physically
small antenna compared to the wavelength. That would cause me to look at
something intermittent in the antenna itself that is disconnecting part of
the radiator. You said it was a ground mounted vertical. Does it have any
traps or other bits beyond a vertical radiator? I'd sure look for a
connection that is opening up, as you mentioned. Possibly even an
intermittent feedline connection to the antenna.

Ron AC7AC

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[Darwin, Keith]

Good Q's Ron.

The antenna is a 28' tall home-brew vertical using telescoping sections
of alum. tubing.  I put Penetrox at all the joints to avoid issues.  No
traps or anything, just a big piece of alum sticking up in the air.  It
is U-bolted to a pressure treated 4x4 buried in the ground.   I have 15
radials buried a couple of inches down.  Each radial is 20 feet long
IIRC.  It's been up since about Nov.

Yes, indeed, narrow bandwidth on a shorter-than-quarter-wave vertical
can be a good sign that efficiency is up.  My antenna is fairly close to
1/4 wave and with only 15 radials, having bandwidth of about 250 KHz at
7 MHz is not unreasonable.  With the bandwidth suddenly dropping to 90
KHz, that sounds like the vertical just got shorter.  I wonder if the
top broke off? :-)

The feedline is bolted to the base of the radiator and the braid is
bolted to the radial plate.  The feedline itself is 6 months old.  I
coated the antenna end of the feedline with coax seal to prevent water
from working its way back up into the coax.  I even mounted the coax a
foot or so up the 4x4 post and brought the connection end down to the
antenna so the water would drip down and off the end rather than back
into the coax.

So I doubt it is an issue with the coax itself.

I'll find it eventually.  Maybe a bad PL259 on the RG213 coax.  Maybe an
issue inside the tuner.  One thing is sure, I won't need a solder sucker
to fix the problem :-)

73!

- Keith -

-----Original Message-----
From: Ron D'Eau Claire [mailto:[hidden email]]
Sent: Wednesday, April 19, 2006 4:36 PM
To: Darwin, Keith; 'elecraft'
Subject: RE: [Elecraft] K2 problem or is it the antenna?

Keith wrote:
Also, the bandwidth of the tuned system has become much narrower.  I
used to get 2:1 bandwidth across most of the 40 meter band.  Two nights
ago, I struggled to get 2:1 over 90 KHz.

----------------

Narrow bandwidth is a sure sign of a reasonably efficient, but
physically small antenna compared to the wavelength. That would cause me
to look at something intermittent in the antenna itself that is
disconnecting part of the radiator. You said it was a ground mounted
vertical. Does it have any traps or other bits beyond a vertical
radiator? I'd sure look for a connection that is opening up, as you
mentioned. Possibly even an intermittent feedline connection to the
antenna.

Ron AC7AC

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[Randy Rathbun NV0U]

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Hash: SHA1

Keith,

One thing you might look at, as you said, is the tuner.

I seem to recall wayyy back when I first got my ticket I had a very  
similar antenna issue. I can't remember the details too much, but it  
turned out the tuner was arcing. It was an MFJ tuner of some sort. I  
distinctly remember hearing a buzzing noise from somewhere in the  
shack when I was keying my Century 21. After listening closely you  
could hear popping coming from it.

I traced it to the tuner and pulled the cover off. Once I did that  
the problem went away. Putting the cover on made it happen again, so  
I turned the cover upside down so I could see inside and watch. There  
was a nice 1/8" arc between the coil and case. The fix was easy - I  
tried various things and ended up settling on a piece of cardboard  
between the coil and the case. It was enough of an insulator to stop  
it. Of course, I was just waiting for the day that the cardboard  
would ignite, but it never did.


On Apr 19, 2006, at 3:56 PM, Darwin, Keith wrote:

> Good Q's Ron.
> I'll find it eventually.  Maybe a bad PL259 on the RG213 coax.  
> Maybe an
> issue inside the tuner.  One thing is sure, I won't need a solder  
> sucker
> to fix the problem :-)

Randy Rathbun NV0U
[hidden email]
K2 #1981 KX1#1318
QRPARCI #10776, ARS #895, FPQRP #1292, KCQRP #1


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[Bill Coleman-2]

On Apr 19, 2006, at 12:27 PM, Darwin, Keith wrote:

> Last night I tried it again and noticed the resonant frequency had
> shifted from 7.040 to 9 MHz.

I fought a problem like this with my shunt-fed tower for 80 and 160m.  
Plagued me for months. I finally figured out the problem -- the  
toroid that formed part of the matching network was arcing.

This toroid was two T200-2 cores stacked with 44 turns tapped every  
two turns. The starting and ending turns were adjacent and that's  
where the arcing took place. The auto-transformer action of the  
tapped matching network caused the arc.

I solved the problem by switching to two different inductors, one for  
the 80m and one for the 160m matching network. The 160m inductor is  
now 40 turns on the two T200-2 cores, and there's some space between  
the starting and ending windings.

Arcing problems like this may not be evident at the 20 watts or so of  
the auto-tuner of the K2/100, but show up with 50 or more watts.  
Intermittent problems of this sort are difficult to track down.  
Inspect everything.

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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