New K3/K3S Beta Firmware, rev. 5.57: Faster response to high reflected power

[wayne burdick]

Hi all,

K3/K3S beta firmware rev. 5.57 is now available on our K3 software page. This release has enhanced protection from transient events that cause high reflected power, such as antenna or feed-line opens or shorts.

(Winter seems to be the season for such things, with high winds agitating intermittent antenna systems. In our own [brutal] testing, we set power to maximum, tuned into various loads, then applied dead shorts and opens repeatedly. No damage observed on any test unit.)

See release notes below for additional details.

For instructions on installing beta releases, refer to our K3 software page. (Beta releases are not automatically recognized by K3 Utility.)

73,
Wayne
N6KR

* * *


MCU 5.57 / DSP 2.88 / FPF 1.26, 2-16-2017
 
* FASTER RESPONSE TO HIGH REFLECTED POWER: The transceiver will now reduce drive much more quickly when transient conditions cause excessive reflected power. This roll-back in response does not change the set power level (PWR knob); instead, it temporarily reduces drive to get below the reflected power limit. This means that once a better match is restored, such as when using an antenna tuner, the set power level will automatically be restored.
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[Bill Leonard N0CU]

I frequently wonder just how much protection a typical SWR protection circuit can provide against an instantaneous discontinuity if it relies totally on a feedback approach. If the response time of the feedback circuit isn’t faster than the risetime of the voltage at the output transistors that results from a sudden failure, then it isn’t apparent to me how this approach can provide reliable protection. A well-designed feedback circuit can provide adequate protection during tune up into a high SWR. It can also provide adequate protection during CW or voice modulation since the bandwidth, and therefore the risetime, of the transmitted signal is limited by the transmitter circuitry. However, the voltage rise due to a sudden failure in an antenna or transmission line connection could conceivably result in a risetime in the 100 nsec range at the drains/collectors of the output transistors. I have never seen any specs on the response time of any SWR protection circuit, but I would be surprised if any of them can even approach the low nsec range. If the failure occurs when the transmitter is at full output, then I would expect the voltage to quickly exceed the max rating on the output transistors. This is clearly a worst-case scenario that probably doesn’t occur very often. However, I wonder how many (if any) manufacturers of ham transmitters have disconnected the antenna when their transmitter was putting out full power as part of their evaluation of their SWR protection circuit.

Bill  N0CU

[Don Wilhelm]

Bill,

Download and install the latest K3 beta firmware.  The time to power
reduction due to high SWR has been reduced substantially.

73,
Don W3FPR

On 2/18/2017 8:58 PM, Bill Leonard N0CU wrote:
> I frequently wonder just how much protection a typical SWR protection circuit
> can provide against an instantaneous discontinuity if it relies totally on a
> feedback approach. If the response time of the feedback circuit isn’t faster
> than the risetime of the voltage at the output transistors that results from
> a sudden failure, then it isn’t apparent to me how this approach can provide
> reliable protection. A well-designed feedback circuit can provide adequate
> protection during tune up into a high SWR.
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