[Elecraft] KAT500 Key Line Interrupt when in BYP mode?

[Barry Baines]

Mike:

> On Sep 2, 2018, at 11:27 AM, Michael Blake via Elecraft <elecraft at mailman.qth.net> wrote:
> 
> When the KAT500 is powered on but in the Bypass mode will it still open the key line to the KPA500 at the preset level (3.0:1 in my case) if the load suddenly goes above 3:1?

To confirm, is your SWR 3.0:1 or 2.0:1??

According to the KAT500 manual (page 21) you can use the KAT500 Utility Program to set VSWR thresholds for keying an amplifier, “Also, you can set an SWR threshold at which the key line will not close to enable the external amplifier to protect it from excessive SWR.”  These thresholds can be set for all bands or individual bands.  This would presumably work with bypass mode as bypass is defined as bypassing the tuning elements in the tuner’s matching network while the tuner’s SWR meter continues to function and the antenna selector will still switch to the antenna chosen for a particular band.  

I haven’t made adjustments using the Utility Program so I cannot speak from personal experience nor do I know what the default values are for VSWR threshold as I’m not currently where my ham station is to confirm.  You will need to experiment carefully to ensure that you get the intended results.

Also keep in mind that the KPA500 protects itself.  See page 19 of the KPA500 manual (“Fault Conditions”) which discusses SWR measurements by the KPA500 itself where “minor faults” in VSWR will result in a 3 dB reduction in output (“Attenuator Faults”) and continues to operate (if the SWR improves the attenuator is removed).  In the case of severe SWR problems the amplifier goes into standby (“Hard Faults”). Hard faults require intervention by the operator to place the amplifier in ‘operate’ presuming that the cause of the excessive SWR has been resolved.

The more basic question is what SWR levels the KPA500 will operate. According to the KPA500 manual (page 17) the amplifier is designed for 1.5:1 or less (the amplifier SWR LEDs are green).  Between 1.5 and 2.1 the LEDs are yellow, and above 2.1 the LEDs are red.  I could not find a reference in the manual that defines at what SWR level an “attenuator fault” or a “hard fault” due to high SWR are generated, but this suggests that an attenuator fault presumably happens when SWR is above 2.1 which is why I’m wondering if there’s a typo in your first sentence regarding current SWR.

The KAT500 manual (page 21) also notes, “The Elecraft KPA500 amplifier also works efficiently into a load SWR of 1.5:1.  Suggested values are 1.8:1 to launch an automatic tuning operation and 1.2:1 for bypass.”   


Hope this helps,

Barry Baines, WD4ASW
(Currently in Boston, MA)

> 
> The situation is a remote autotuner connected to a 33’ vertical that I use for bands that I do not have a resonant antenna.  On those bands the KAT500 is in the BYP mode.  A remote switch brings all of the antenna choices in on a single coax which connected to the KAT500.
> 
> 73 - Mike - K9JRI
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