Posted by
k4vd on
Jan 26, 2019; 6:22pm
URL: http://elecraft.85.s1.nabble.com/KAT500-KPA500-Sanity-Check-Please-tp7648517p7648535.html
Hi Bob:
I'm using a very similar setup and forgot to mention the 1:1 current BALUN.
The 4:1 is outside. There's about 2 feet of coax to a window feedthrough.
Then from the feedthrough to the tuner is the 1:1 BALUN. The antenna is the
80 - 10 from trueladderline.com. Been using this model for years now.
You say "The KAT500 is set to automatically switch to BYPASS if the SWR is
less than 1.3:1. And it is set to bypass the amp if the SWR is greater
than 1.5:1."
Maybe I'm confused with the settings. In the KAT500 configuration under
VSWR thresholds I have:
Band: All
Amp Key Interrupt: 5.00
Autotune: 1.80
Bypass: 1.3
I think this should mean that the amplifier would not be permitted to
operate (key interrupt) if the tuner shows 5:1 or greater SWR. I think it
means that once the *tuned* SWR drops below 5 the amp will be keyed. Should
this be set to 1.5:1? If I really did blow the amp (I'm pretty convinced)
then, over time, this possibly was the contributing factor.
It is my amp that I think has gone bad, not the tuner.
So if the problem were caused because I was regularly running into an
antenna with >10:1 SWR (as noted by bypass SWR on the Operate tab) then I
think the problem would have been with the KAT and not the KPA. Still, I am
surprised there isn't a setting in the configuration tab that would prevent
keying the amp when a certain value of bypass VSWR was exceeded. It could
have a user setting similar to Amplifier Key Interrupt so that, as someone
else mentioned, a person could elect to operate in less than ideal
conditions while a person like me could still have some protection of
pretty expensive equipment.
I still think my amp is bad. Once out of the loop everything works well
barefoot from my rig. The KPA500 tunes just about anything I throw at it
and I'm hoping at 100 watt or less the 12:1 safety limit is not applicable.
"If your showing a Bypass SWR of 12:1 then you are outside of the range of
the KAT500. You are using the wrong balun or you need to change the 600
ohm feed line length to attain a better / lower SWR." Here's where my
misunderstand probably trips me up again. The ladder line fed dipole cut
for 80 meters should be an all-band antenna as long as I can match the load
impedance of the antenna to the radio. For the KAT500, this is a max of
10:1 at 600 watts. For maybe another manufacturer's tuner (auto or manual)
higher specs might be available? Or is there a certain point where the
antenna is just not an antenna? I've got about 10K contacts on this antenna
along with some DXCC and WAS accomplishments. It also seems to do OK in
contests.
The KPA shows the following bypass VSWRs for my antenna:
80 12.00
40 7.46
20 1.63
15 4.61
10 2.33
Changing the BALUN to a different ration would probably shift the numbers
around a bit but not necessarily improve the situation. From these reading,
technically my 80 meter band (for which the antenna is cut) is unusable
with the KAT/KPA at full power but the other bands should be fine. As long
as I fix the setting for the amplifier key interrupt then I should be able
to reduce the risk to the amp on other bands. I have no clue why it was set
to 5.
Thanks for your explanation. It helps a lot.
73,
Kev K4VD
On Sat, Jan 26, 2019 at 10:16 AM Bob McGraw K4TAX <
[hidden email]>
wrote:
> My station is a K3S, KPA500, KAT500. The antenna is a 250 ft center
> fed wire with 450 window line that runs from the feed point on the
> antenna all the way to the operating position where the 450 line
> terminates into a 1:1 current balun on the shelf just above the amp and
> tuner. I use a common mode choke between the balun and the KAT500.
> That common mode choke is a model 8232 purchased from The Wireman. It
> is 18" length of coax with about 75 ferrite beads of #43 material.
> This provides additional common mode rejection not offered by the
> balun. I can work 160M through 6M with this configuration.
>
> The KAT500 is set to automatically switch to BYPASS if the SWR is less
> than 1.3:1. And it is set to bypass the amp if the SWR is greater than
> 1.5:1.
>
> A 10:1 SWR basically says the impedance is somewhere between 5 ohms and
> 500 ohms. In order to attain this you will need to use both, depending
> on band a 1:1 balun or a 4:1 balun as likely with your antenna the
> antenna on 40M presents a Z of 3000 ohms or so. Then the length of the
> feed line is critical as it becomes part of the impedance acting as a
> matching length of line. The "600 ohm" impedance of the line is of
> little importance as you are matching the entire complex load and not
> just the impedance of the line. Many hams seem to think, incorrectly,
> they need to match the impedance of the feed line.
>
> If your showing a Bypass SWR of 12:1 then you are outside of the range
> of the KAT500. You are using the wrong balun or you need to change the
> 600 ohm feed line length to attain a better / lower SWR.
>
> The keying line between the KAT500 and KPA500 should interrupt the PTT
> line if the matched SWR exceeds 1.5:1. This is a setting defined in the
> KAT500 configuration by the user and the KAT500 Utility.
>
> The best suggestion, make changes to the antenna such that the SWR
> falls within the range of the tuner. As to the amp, connect a 50 dummy
> load to one output of the tuner {you do have one?} and then see how the
> combination of amp and tuner behave.
>
> I'd say the matching range of the KAT500 is the same at 100 watts. The
> KAT500 manual {page 2} clearly defines the matching ranges and power
> ratings.
>
> 73
>
> Bob, K4TAX
>
>
> On 1/25/2019 10:47 PM, Kevin der Kinderen wrote:
> > I'm reading the specifications for the KAT500. Typical matching range
> from
> > 3-30 MHz is 10:1 SWR for 600 watts.
> >
> > This means that if the KAT500 utility reports "Bypass VSWR" in excess of
> > 10:1 then the KPA500 should not be set to operate.
> >
> > I'm running a dipole cut for 80 and fed with 600 ohm ladder line as a
> > multiband antenna. The BALUN is right outside my window. I have the
> option
> > of 1:1, 4:1, 9:1 and 12:1 I think. They are DXE brand. My job then is to
> > pick the right BALUN to provide <10:1 SWR on the bands of interest. I
> hoped
> > this would be at least 80-20 if not 80-10.
> >
> > Not sure which BALUN is plugged in right now but on 80 meters I'm
> showing a
> > bypass VSWR of 12.00 and VSWR of 1.6:1. This means I cannot use the
> KPA500
> > on 80 regardless of the good match the KAT500 provided.
> >
> > Should the key line cables from the KAT500 to the KPA500 and the rig
> (using
> > a Flex) prevent keying the amp if the SWR exceeds 10:1 automatically?
> >
> > If I want better than that then I have to find another antenna tuner
> with a
> > wider SWR range at 600 watts or a different antenna?
> >
> > Can anyone guess at the matching range of the KAT500 at 100W?
> >
> > The thing is... I think I have a dead amp.
> >
> > Kev K4VD
> > ______________________________________________________________
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