SWR


n3bud
 

Just wondering if anyone else sees significant differences in SWR readings on the K3, the KPA500, and the KAT500?  
 
I get a fairly low reading on a 40 delta loop I made on an MFJ Analyzer.  However, the K3 reads a 2.1 with the tuner and amp in bypass/standby modes, tuner reads 1.2, and amp reads a 1.4.   With amp placed into operate and tuner left in bypass the K3 reads 1.5, the amp 1.4, and tuner reads 1.2.   I suspect this means the amps input needs to be tuned somehow.    I know, just use the tuner and all is well but I'd like to know why this is occurring. 
 
Thanks,
Mike, N3BUD
K3, KPA500, KAT500 


ke9uw
 

Different lengths of interconnected coax. None of those readings need any tuning.


Greg Mitchell
 

same problem for me. I can't even run power on 160m into a dummy load with the amp/tuner on bypass, but if they are in line it works fine.

On Sat, Jun 12, 2021 at 1:25 PM n3bud <n3bud@...> wrote:
Just wondering if anyone else sees significant differences in SWR readings on the K3, the KPA500, and the KAT500?  
 
I get a fairly low reading on a 40 delta loop I made on an MFJ Analyzer.  However, the K3 reads a 2.1 with the tuner and amp in bypass/standby modes, tuner reads 1.2, and amp reads a 1.4.   With amp placed into operate and tuner left in bypass the K3 reads 1.5, the amp 1.4, and tuner reads 1.2.   I suspect this means the amps input needs to be tuned somehow.    I know, just use the tuner and all is well but I'd like to know why this is occurring. 
 
Thanks,
Mike, N3BUD
K3, KPA500, KAT500 


Bob Evans
 

Mike,

You know, SWR is different at different places along your coax so when you see different measurements in different components, that is normal.  This is more obvious as the SWR at the antenna is higher and almost negliable if the antenna is flat.  You can experiment by pulling out the coax that goes into your tuner (I assume goes directly to your antenna) and plugging that into your K3 as an interesting test.  While I wouldn't expect them to be exact, they should be much closer and prove to you that SWR is different at different places up and down your coax.  You could also add a random length of coax to your antenna coax and I'll bet your analyzer gives you two different readings (compairing with and without extra coax).  If you want REALLY good SWR, add 1000" of RG-58 and try 10M...just kidding, because at that point, there won't be much signal left even though your SWR will look great!

I'll leave it to one of the engineers on here to explain why but as an appliance operator, that is what I've observed in practice.  ;-)   

Good luck,
Bob K5WA


Lou W7HV
 

Complex impedance changes along the coax.  SWR remains constant, except for decreasing due to loss in the transmission line as you move away from the load.


n3bud
 

K3 reduces power out when it reads high and lights up high SWR.   Lengths of coax jumpers made only slight difference.  Made up new jumpers first and installed them from rig to amp and amp to tuner.  

On 6/12/2021 2:17 PM, ke9uw wrote:
Different lengths of interconnected coax. None of those readings need any tuning.


n3bud
 

Thanks now I know I am not alone.

On 6/12/2021 2:21 PM, Greg Mitchell wrote:
same problem for me. I can't even run power on 160m into a dummy load with the amp/tuner on bypass, but if they are in line it works fine.

On Sat, Jun 12, 2021 at 1:25 PM n3bud <n3bud@...> wrote:
Just wondering if anyone else sees significant differences in SWR readings on the K3, the KPA500, and the KAT500?  
 
I get a fairly low reading on a 40 delta loop I made on an MFJ Analyzer.  However, the K3 reads a 2.1 with the tuner and amp in bypass/standby modes, tuner reads 1.2, and amp reads a 1.4.   With amp placed into operate and tuner left in bypass the K3 reads 1.5, the amp 1.4, and tuner reads 1.2.   I suspect this means the amps input needs to be tuned somehow.    I know, just use the tuner and all is well but I'd like to know why this is occurring. 
 
Thanks,
Mike, N3BUD
K3, KPA500, KAT500 



n3bud
 

Thanks Bob, Took measurements first with everything out of line and then adding back in with both K3 and MFJ Analyzer.  The main issue seems to occur when the amp is in standby

mode, other changes are minor when adding or removing things

On 6/12/2021 2:31 PM, Bob Evans wrote:
Mike,

You know, SWR is different at different places along your coax so when you see different measurements in different components, that is normal.  This is more obvious as the SWR at the antenna is higher and almost negliable if the antenna is flat.  You can experiment by pulling out the coax that goes into your tuner (I assume goes directly to your antenna) and plugging that into your K3 as an interesting test.  While I wouldn't expect them to be exact, they should be much closer and prove to you that SWR is different at different places up and down your coax.  You could also add a random length of coax to your antenna coax and I'll bet your analyzer gives you two different readings (compairing with and without extra coax).  If you want REALLY good SWR, add 1000" of RG-58 and try 10M...just kidding, because at that point, there won't be much signal left even though your SWR will look great!

I'll leave it to one of the engineers on here to explain why but as an appliance operator, that is what I've observed in practice.  ;-)   

Good luck,
Bob K5WA


Mark Morin
 

Lou is technically correct that SWR remains constant along the feedline (except due to losses) and that the complex impedance changes with position whenever there is reflected power. Many will argue against this statement but it’s true based on the definition of SWR (ratio of voltage amplitude at a peak position of the standing wave, to voltage amplitude at a minimum point of the standing wave).

Many “SWR” meters don’t actually measure true SWR, but impedance at the point where they are connected, compared to 50 ohms. Since the impedance changes along the line, it’s normal that such an impedance-based meter will give different readings at different locations. Even if it’s not strictly the line SWR, it is still a useful measurement because it reflects (no pun intended) what a transmitter at that point would experience. 

This topic typically provokes debate. 

Mark VA2MM 


Wes Stewart
 

(As a late friend and engineering mentor used to say, "I love solving these old familiar problems that just keep popping up.")

I addressed something similar years ago.  See my comments in: http://elecraft.365791.n2.nabble.com/K3-SWR-Numerical-Indication-td7643839.html

Wes  N7WS




On Saturday, June 12, 2021, 10:24:54 AM MST, n3bud <n3bud@...> wrote:


Just wondering if anyone else sees significant differences in SWR readings on the K3, the KPA500, and the KAT500?  
 
I get a fairly low reading on a 40 delta loop I made on an MFJ Analyzer.  However, the K3 reads a 2.1 with the tuner and amp in bypass/standby modes, tuner reads 1.2, and amp reads a 1.4.   With amp placed into operate and tuner left in bypass the K3 reads 1.5, the amp 1.4, and tuner reads 1.2.   I suspect this means the amps input needs to be tuned somehow.    I know, just use the tuner and all is well but I'd like to know why this is occurring. 
 
Thanks,
Mike, N3BUD
K3, KPA500, KAT500 


Jim Brown
 

On 6/12/2021 12:29 PM, Mark Morin wrote:
This topic typically provokes debate.
Because of ignorance. The science has been established for a century.

73, Jim K9YC