Topics

KPA 1500 ATU Issue


Jeff Clarke
 

A friend of mine has a KPA1500 that's having strange issues with the ATU. The SWR on his Hygain TH6 tri-bander is kind of high in the CW band because it's tuned for SSB. When he goes down to CW on 20 meters it's maybe a 2.4 :1 SWR. When you switch in the ATU with the amp in the standby position it gets the SWR down to an acceptable level. When you put the amp into the OPER position the SWR jumps up and causes the amp to fault. It also does this also for his 80 meter and 40 meter dipoles when you get away from the resonate frequency on those bands. Same issue with the TH6 on both 15 and 10 meters where it's not near the resonant frequency. This makes the amp pretty much unusable on frequencies where the SWR is around the 2:0 range or a little above that without putting an external antenna tuner is line after the output. He doesn't want to use it this way and risk blowing the final transistors again.

According to the KPA1500 manual  "At lower amplifier outputs up to about 800 W, or when using your driving transceiver “barefoot” at 100 W, the ATU will match loads up to an SWR of 10:1 on 80 through 10 meters and 5:1 on 160 and 6 meters. At 1500 W the tuner will match an SWR of about 3:1" The SWR on his antennas are well below these SWR readings but the ATU doesn't seem to be working as designed?. My friend is pretty frustrated right now because he just got his amp back from Elecraft (after having no amp for 4 months) to repair two final transistors that blew. He's only owned it for about 10 months. He was really looking forward to being HP again since he's not a LP guy. Lucky for him it was still under warranty and was fixed for free. I wasn't so lucky with my KPA500 and it cost me $600 to ship and have it repaired by Elecraft for blown final transistors.  Now he's not sure he wants to own a solid state amplifier that's so picky about SWR (and having to use an external antenna tuner) that he's just thinking about just selling it and going back to a tube amplifier.

Has anyone else had a similar issue with the ATU? I remember when he first bought the amp a little less than a year ago and we hooked it up it didn't act this way.

Jeff KU8E


K9MA
 

The first thing that occurs to me is that something is going wrong with the antennas or feedlines at high power. Does the SWR go high in the OPER position at 100 W, or only at higher power?  Does he have another amplifier he can try with those antennas?

Another possibility is that the ATU is actually failing, but that seem unlikely if the SWR goes back down at low power. I've been running my KPA1500 into antennas with over a 2:1 SWR for a couple years with no problems.


73,
Scott K9MA

On 7/2/2020 14:23, Jeff Clarke wrote:
A friend of mine has a KPA1500 that's having strange issues with the ATU. The SWR on his Hygain TH6 tri-bander is kind of high in the CW band because it's tuned for SSB. When he goes down to CW on 20 meters it's maybe a 2.4 :1 SWR. When you switch in the ATU with the amp in the standby position it gets the SWR down to an acceptable level. When you put the amp into the OPER position the SWR jumps up and causes the amp to fault. It also does this also for his 80 meter and 40 meter dipoles when you get away from the resonate frequency on those bands. Same issue with the TH6 on both 15 and 10 meters where it's not near the resonant frequency. This makes the amp pretty much unusable on frequencies where the SWR is around the 2:0 range or a little above that without putting an external antenna tuner is line after the output. He doesn't want to use it this way and risk blowing the final transistors again.

According to the KPA1500 manual  "At lower amplifier outputs up to about 800 W, or when using your driving transceiver “barefoot” at 100 W, the ATU will match loads up to an SWR of 10:1 on 80 through 10 meters and 5:1 on 160 and 6 meters. At 1500 W the tuner will match an SWR of about 3:1" The SWR on his antennas are well below these SWR readings but the ATU doesn't seem to be working as designed?. My friend is pretty frustrated right now because he just got his amp back from Elecraft (after having no amp for 4 months) to repair two final transistors that blew. He's only owned it for about 10 months. He was really looking forward to being HP again since he's not a LP guy. Lucky for him it was still under warranty and was fixed for free. I wasn't so lucky with my KPA500 and it cost me $600 to ship and have it repaired by Elecraft for blown final transistors.  Now he's not sure he wants to own a solid state amplifier that's so picky about SWR (and having to use an external antenna tuner) that he's just thinking about just selling it and going back to a tube amplifier.

Has anyone else had a similar issue with the ATU? I remember when he first bought the amp a little less than a year ago and we hooked it up it didn't act this way.

Jeff KU8E


-- 
Scott  K9MA

k9ma@...


Christopher Scibelli
 

What is the SWR with the amp on but in the SSB part of the band?  Does the SWR jump there too, or does it provide a good match?  I don't know if the TH6 uses traps but it could be the amp heating up the traps.  If the SWR is low on 20 SSB with the amp on that rules traps out.

I've had the SWR climb high due to a balun about to go and then the SWR is sky-high once the balun goes.  Once again check the SWR across the whole band with the amp on and amp off. Rule out any traps and the balun before you conclude it's the amp.  An SWR of 2.4 to 1 in the 20 CW section sounds very high. I had a trapped tribander (Cushcraft A3S) and the SWR never got that high on wider bands never mind 20 meters.  Lastly, does the amp have slugs to tune the SWR for each band?  That's my last idea but I've had those slugs in tube amplifiers. I've never had a SS amplifier.

73,

Chris  NU1O


-----Original Message-----
From: Jeff Clarke <ku8e@...>
To: Elecraft-K3 <Elecraft-K3@groups.io>
Sent: Thu, Jul 2, 2020 3:23 pm
Subject: [Elecraft-K3] KPA 1500 ATU Issue

A friend of mine has a KPA1500 that's having strange issues with the ATU. The SWR on his Hygain TH6 tri-bander is kind of high in the CW band because it's tuned for SSB. When he goes down to CW on 20 meters it's maybe a 2.4 :1 SWR. When you switch in the ATU with the amp in the standby position it gets the SWR down to an acceptable level. When you put the amp into the OPER position the SWR jumps up and causes the amp to fault. It also does this also for his 80 meter and 40 meter dipoles when you get away from the resonate frequency on those bands. Same issue with the TH6 on both 15 and 10 meters where it's not near the resonant frequency. This makes the amp pretty much unusable on frequencies where the SWR is around the 2:0 range or a little above that without putting an external antenna tuner is line after the output. He doesn't want to use it this way and risk blowing the final transistors again.

According to the KPA1500 manual  "At lower amplifier outputs up to about 800 W, or when using your driving transceiver “barefoot” at 100 W, the ATU will match loads up to an SWR of 10:1 on 80 through 10 meters and 5:1 on 160 and 6 meters. At 1500 W the tuner will match an SWR of about 3:1" The SWR on his antennas are well below these SWR readings but the ATU doesn't seem to be working as designed?. My friend is pretty frustrated right now because he just got his amp back from Elecraft (after having no amp for 4 months) to repair two final transistors that blew. He's only owned it for about 10 months. He was really looking forward to being HP again since he's not a LP guy. Lucky for him it was still under warranty and was fixed for free. I wasn't so lucky with my KPA500 and it cost me $600 to ship and have it repaired by Elecraft for blown final transistors.  Now he's not sure he wants to own a solid state amplifier that's so picky about SWR (and having to use an external antenna tuner) that he's just thinking about just selling it and going back to a tube amplifier.

Has anyone else had a similar issue with the ATU? I remember when he first bought the amp a little less than a year ago and we hooked it up it didn't act this way.

Jeff KU8E


N6RV
 

I do not know if this works with all radio / KPA1500 combinations however with my K3S/KP1500 I do the following.Hopefully it i something as simple as this.

I do not use the ATU in the K3S.

Tune the ATU in each sub-band (CW, SSB, Digi) using the K3S in Tune mode and selecting ATU Tune on the KPA1500.
I believe the amplifier stores and retrieves the ATU settings on different band segments. It reads the transceiver frequency and switches to the correct ATU settings.

Make sure the ATU is in line by depressing and holding the ATU mode button on the KPA1500. If both LEDs (ATU In & ATU Bypass) are lit the amplifier is indicating that the antenna VSWR is low enough and the ATU is automatically switched out.

Maybe your friend is doing this already. If so, then he has a strange issue.


Jeff Clarke
 

Some more information :

This amp was purchased new as a factory built unit in August 2019. When we hooked it up back then the ATU in the KPA1500 seemed to lower the SWR of all his antennas when it was inline. Fast forward to this spring when he noticed the amp was only putting out only half power. It was sent to Elecraft for repair and they determined two of the four final transistors had blown. He just got the amp back from them on Thursday when we hooked it back up. My friend is pretty adamant that there aren't any problems with his antennas. He bases this on the fact that he felt he was getting out pretty well and doing good in contests when running low power when is amp was being repaired. If the SWR was high he just used the internal antenna tuner in his TS590SG to lower the SWR.

 At first I too thought maybe there could be a problem with the traps in his TH6 and suggested to him that it just wasn't noticeable when running low power and maybe he should have his antenna guy check this out. He's not buying this from me.  I also noticed that his 80 meter dipole is resonant around 3625 and when he goes to the bottom of 80 meters the amp faults when tuning on the ATU and won't tune out the SWR. The 40 meter dipole which I recently changed a bad connector on was resonant down in the CW band but when hooked to the amp it has a higher SWR. Not sure what's causing that. The pattern I'm noticing  with his KPA1500 is if the SWR is above 2:1 with the ATU off it won't tune out the mismatch when you turn it on. I guess when I go back over to his house again I should take my antenna analyser over and check all the antennas again by bypassing the radio/amp and double check all the connectors. 

He just sent Elecraft an email and they want him to download the KPA1500 configuration file and email it to them which of course he doesn't know how to do. So I'm going have to go do that as well. My friend is a a total appliance operator and very non-technical so it sometimes gets very challenging for me to help him out.

Jeff


NS2N_PTA@outlook.com
 

Jeff take your KPA500 and see if it works any better. Wou;d be a check on the 1500s’ ATU, and

Might show any arc faults.

 

Paul NS2N

 

Sent from Mail for Windows 10

 

From: Jeff Clarke
Sent: Friday, July 3, 2020 4:21 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA 1500 ATU Issue

 

Some more information :

This amp was purchased new as a factory built unit in August 2019. When we hooked it up back then the ATU in the KPA1500 seemed to lower the SWR of all his antennas when it was inline. Fast forward to this spring when he noticed the amp was only putting out only half power. It was sent to Elecraft for repair and they determined two of the four final transistors had blown. He just got the amp back from them on Thursday when we hooked it back up. My friend is pretty adamant that there aren't any problems with his antennas. He bases this on the fact that he felt he was getting out pretty well and doing good in contests when running low power when is amp was being repaired. If the SWR was high he just used the internal antenna tuner in his TS590SG to lower the SWR.

 At first I too thought maybe there could be a problem with the traps in his TH6 and suggested to him that it just wasn't noticeable when running low power and maybe he should have his antenna guy check this out. He's not buying this from me.  I also noticed that his 80 meter dipole is resonant around 3625 and when he goes to the bottom of 80 meters the amp faults when tuning on the ATU and won't tune out the SWR. The 40 meter dipole which I recently changed a bad connector on was resonant down in the CW band but when hooked to the amp it has a higher SWR. Not sure what's causing that. The pattern I'm noticing  with his KPA1500 is if the SWR is above 2:1 with the ATU off it won't tune out the mismatch when you turn it on. I guess when I go back over to his house again I should take my antenna analyser over and check all the antennas again by bypassing the radio/amp and double check all the connectors. 

He just sent Elecraft an email and they want him to download the KPA1500 configuration file and email it to them which of course he doesn't know how to do. So I'm going have to go do that as well. My friend is a a total appliance operator and very non-technical so it sometimes gets very challenging for me to help him out.

Jeff

 


Dan Abell
 

This is an interesting thread from a sociological standpoint more than technological one :)

But an “appliance operator” is saying it’s not my feedline, not my connectors, not my antennas, but when I drive high power the swr appears the change...

Finally has “he” tried running to amp at reduced power and observed the swr?  (If that was already stated I apologize, just too much text :) 

Dan w3dka

On Jul 3, 2020, at 3:21 PM, Jeff Clarke <ku8e@...> wrote:

Some more information :

This amp was purchased new as a factory built unit in August 2019. When we hooked it up back then the ATU in the KPA1500 seemed to lower the SWR of all his antennas when it was inline. Fast forward to this spring when he noticed the amp was only putting out only half power. It was sent to Elecraft for repair and they determined two of the four final transistors had blown. He just got the amp back from them on Thursday when we hooked it back up. My friend is pretty adamant that there aren't any problems with his antennas. He bases this on the fact that he felt he was getting out pretty well and doing good in contests when running low power when is amp was being repaired. If the SWR was high he just used the internal antenna tuner in his TS590SG to lower the SWR.

 At first I too thought maybe there could be a problem with the traps in his TH6 and suggested to him that it just wasn't noticeable when running low power and maybe he should have his antenna guy check this out. He's not buying this from me.  I also noticed that his 80 meter dipole is resonant around 3625 and when he goes to the bottom of 80 meters the amp faults when tuning on the ATU and won't tune out the SWR. The 40 meter dipole which I recently changed a bad connector on was resonant down in the CW band but when hooked to the amp it has a higher SWR. Not sure what's causing that. The pattern I'm noticing  with his KPA1500 is if the SWR is above 2:1 with the ATU off it won't tune out the mismatch when you turn it on. I guess when I go back over to his house again I should take my antenna analyser over and check all the antennas again by bypassing the radio/amp and double check all the connectors. 

He just sent Elecraft an email and they want him to download the KPA1500 configuration file and email it to them which of course he doesn't know how to do. So I'm going have to go do that as well. My friend is a a total appliance operator and very non-technical so it sometimes gets very challenging for me to help him out.

Jeff


Bob McGraw - K4TAX
 

A systematic approach is to start at 100 watts using the amplifier and ATU. Allow the ATU to resolve a match and note the SWR value.  Then start increasing the drive from the transceiver in increments such as to attain 200 watts, 300 watts, 400 watts, and etc.   At some point, it would seem from prior descriptions, something in the antenna system is failing thus causing the SWR to increase.    Always question; connectors, jumpers, feed-line, balun, antenna traps.   

Further, using a known good 50-ohm dummy load, allow the ATU to resolve a match into the load.  Do this on each band.   This is necessary to prove the ATU integrity.  Do the same power increment tests again.  If nothing fails, then it is most likely in the components of the antenna system.   If it should fail using the dummy load, then one can suspect a component breakdown in the ATU. 

73
Bob, K4TAX


Roger N1RJ
 

An "L" network will not match 50 Ohms to 50 Ohms. Assuming starting at an
arbitrary point, the tuner will stop when it gets within the programmed
SWR window and switch itself out of circuit. To check at various power levels,
you must have a load Z that is not 50 Ohms resistive.

73, Roger

On 7/4/2020 11:43 AM, Bob McGraw - K4TAX wrote:
A systematic approach is to start at 100 watts using the amplifier and ATU.
Allow the ATU to resolve a match and note the SWR value. Then start increasing
the drive from the transceiver in increments such as to attain 200 watts, 300
watts, 400 watts, and etc. At some point, it would seem from prior
descriptions, something in the antenna system is failing thus causing the SWR to
increase. Always question; connectors, jumpers, feed-line, balun, antenna
traps.

Further, using a known good 50-ohm dummy load, allow the ATU to resolve a match
into the load. Do this on each band. This is necessary to prove the ATU
integrity. Do the same power increment tests again. If nothing fails, then it
is most likely in the components of the antenna system. If it should fail
using the dummy load, then one can suspect a component breakdown in the ATU.

73
Bob, K4TAX


Roger N1RJ
 

Ignore my post...it's more complicated than that!

On 7/4/2020 12:44 PM, Roger N1RJ wrote:
An "L" network will not match 50 Ohms to 50 Ohms. Assuming starting at an
arbitrary point, the tuner will stop when it gets within the programmed
SWR window and switch itself out of circuit. To check at various power levels,
you must have a load Z that is not 50 Ohms resistive.

73, Roger


On 7/4/2020 11:43 AM, Bob McGraw - K4TAX wrote:
A systematic approach is to start at 100 watts using the amplifier and ATU.
Allow the ATU to resolve a match and note the SWR value. Then start increasing
the drive from the transceiver in increments such as to attain 200 watts, 300
watts, 400 watts, and etc. At some point, it would seem from prior
descriptions, something in the antenna system is failing thus causing the SWR to
increase. Always question; connectors, jumpers, feed-line, balun, antenna
traps.

Further, using a known good 50-ohm dummy load, allow the ATU to resolve a match
into the load. Do this on each band. This is necessary to prove the ATU
integrity. Do the same power increment tests again. If nothing fails, then it
is most likely in the components of the antenna system. If it should fail
using the dummy load, then one can suspect a component breakdown in the ATU.

73
Bob, K4TAX


Lyn Norstad
 

Bob –

 

 

Ø  Further, using a known good 50-ohm dummy load, allow the ATU to resolve a match into the load.  Do this on each band.   This is necessary to prove the ATU integrity.  Do the same power increment tests again.  If nothing fails, then it is most likely in the components of the antenna system.   If it should fail using the dummy load, then one can suspect a component breakdown in the ATU. 

73
Bob, K4TAX

_._,_._,_


 

How do you do that on a KAT500?  It just goes into Bypass (not Bypass on the Mode setting, Bypass on the “Others” setting).

 

73

Lyn, W0LEN


Jeff Clarke
 

I'm not sure what using a dummy load as the load would really prove? We already know that when the SWR is fairly good (i.e below a 2:1 SWR) there aren't any issues and the ATU works just fine. The dummy load I use is always has a 1:1 SWR when I kick it in. I also believe from reading the KPA1500 manual that if the SWR is good the amp automatically bypasses the ATU. Both the ATU IN and ATU BYP LED's light up.

Jeff KU8E


Ray Maxfield
 

Jeff……… If you want reliable Date From the Test you do,

Then use a Calibrated Load.  

This is How it is done in the Broadcast World.

Wa6vab  retired.

 

From: Jeff Clarke
Sent: Sunday, July 5, 2020 9:13 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA 1500 ATU Issue

 

I'm not sure what using a dummy load as the load would really prove? We already know that when the SWR is fairly good (i.e below a 2:1 SWR) there aren't any issues and the ATU works just fine. The dummy load I use is always has a 1:1 SWR when I kick it in. I also believe from reading the KPA1500 manual that if the SWR is good the amp automatically bypasses the ATU. Both the ATU IN and ATU BYP LED's light up.

Jeff KU8E

 


David Box
 

Jeff, you can use the dummy load create a mis-match by inserting an air wound induction in series with the DL. Just measure with ant analyzer so you get about 2.5 - 3:1 mismatch at desired freq, now using this test load run the power sweep. Using the KPA1500 as test equipment means taking extra care but several ways using DL and series/parallel components you can create a reliable test mis-match.
de Dave K5MWR


On July 5, 2020 11:13:44 AM CDT, Jeff Clarke <ku8e@...> wrote:
I'm not sure what using a dummy load as the load would really prove? We already know that when the SWR is fairly good (i.e below a 2:1 SWR) there aren't any issues and the ATU works just fine. The dummy load I use is always has a 1:1 SWR when I kick it in. I also believe from reading the KPA1500 manual that if the SWR is good the amp automatically bypasses the ATU. Both the ATU IN and ATU BYP LED's light up.

Jeff KU8E

--
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