Re: KAT500 AMP Key Interrupt Setting

Bob McGraw - K4TAX

In follow up to the question, I just checked my station configuration.  The KPA500 was in OPER mode, I activated the TUNE mode on my K3S, and then pressed the TUNE button on the KAT500.   Immediately the KPA500 switched off line, the KAT500 executed the routine to match the antenna and when completed the KPA500 came back on line.   I then pressed the TUNE button on my K3S to exit the tune mode. 

I saw no issues with the procedure or method. 


Bob, K4TAX

On 6/19/2019 4:01 PM, Rick WA6NHC wrote:
I use a K3, KAT500 and KPA500 currently.  The KPA is locked out during a KAT500 tune cycle.  Once that cycle is over, I hit the TUNE button again on the K3 to observe/confirm that the resulting tune is correct (watch the amp LEDs for SWR), THEN feel safe enough to run QRO. 

That intermediate step performs the verification at <200 watts.  It’s good to check with a bit more power as some matches vary on non-resonant antennas; what appears ‘good’ at 20 watts may be different at high power (also motivation to improve the antenna). 

A K3(S) key line lockout during tune isn’t needed but operational thinking changes may be.   In other words, Elecraft isn’t just another company, they thought it through and did it right. 


Smell Czech correction happens 

On Jun 19, 2019, at 11:32 AM, Michael Kopec via Groups.Io <michaelkopec1@...> wrote:

Thanks Bob (K4TAX).  I wonder why Elecraft never thought about this.  Any way I am operating the same way as u posted.  de Mike K8NS

On Wednesday, June 19, 2019, 10:39:09 AM EDT, Bob McGraw - K4TAX <rmcgraw@...> wrote:

I am not aware of any K3S menu value that will disable the PTT line to the amp when TUNE is active with the K3S. 

In my case, when I need to tune, I do so manually.  Thus when changing bands I have the amp set to automatically go to STBY.  Then I can use TUNE at the preset tune power value.  Once tuning has resolved a match, I then place the amp in OPER mode.

With each of my 3 antennas, I have trained the KAT500 to resolve a match for different frequencies.  For 160M it is trained every 25 kHz.  For other bands every 50 kHz.  With this method I can change frequencies via the K3S and bands and always have a matched condition.  Therefore I find no need to activate TUNE or place the amp in STBY when changing bands or frequencies.


Bob, K4TAX

On 6/19/2019 8:39 AM, Michael Kopec via Groups.Io wrote:
Bob K4TAX, is there any menu setting in the K3s that will break the key line to the KPA500 amplifier when the K3s TUNE button is engaged.  I do not hve a KAT5oo tuner but use a manual tuner and also a LDG AT-600 pro 11 auto tuner.  Now I hve to turn the amp to standby before tuning at low power as set in the K3s.  de Mike K8NS

On Wednesday, June 19, 2019, 09:16:25 AM EDT, Bob McGraw - K4TAX <rmcgraw@...> wrote:

The KAT500 interrupts the amplifier key line (sometimes called "PTT") during tuning. This is done to avoid damaging KAT500 relays by "hot switching" at high power and to protect your amplifier from wide SWR swings during the tuning process.

Some linear amplifiers, including the Elecraft KPA500, use solid state switching devices, and the amplifier key line may be interrupted at any time, even while transmitting at full power. For these amplifiers, set "Amplifier Key Interrupt Power" to its maximum value of 1500 watts, even if the amplifier cannot produce that power level. KAT500 firmware interprets 1500 as "unlimited". The KPA500 works much more smoothly if Amplifier Key Interrupt Power is set to 1500.

Other linear amplifiers use frame or vacuum relays, and often should not have their Transmit/Receive relay "hot switched" at high power. For these amplifiers, set the "Amplifier Key Interrupt Power" to a value that is within the capability of your amplifier's relay, often 30 to 100 watts. When your KAT500 starts to tune, because of a band or antenna switch, a TUNE button press, or auto tune based on VSWR threshold, it waits for the transmit power to drop below this "Amplifier Key Interrupt Power", then it interrupts the amplifier key line, waits for a tune-level signal from the transceiver, and selects the appropriate relay settings. When tune is complete and you stop transmitting, the amplifier key line is reconnected.

Bob, K4TAX

On 6/19/2019 7:06 AM, Irwin Darack wrote:
What is the function of the Amp Key Inerrupt Setting in the KAT500 Utility? 

Thanks, Irwin KD3TB 

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