From time to time people ask about QSK and amplifiers on the Flex, and about suitable values for TX Delay in the radio setup. Tonight I had the 'scope hooked up and looked at the key line on my 6300 and the RF output envelope from my amp. With TX Delay set to zero I see RF output start approximately 3 mS after the keyline is asserted. The keyline goes inactive again approximately 4 mS after RF goes away completely. With the Elecraft KPA-500 there is no hot switching even with the TX Delay set to zero. The attached 'scope image shows the keyline on the top trace and the output of the amplifier on the bottom trace. This is a single 30 wpm dit. (The waveform is the same with the amp on or off, only the RF output amplitude changes.)
For amplifiers with relays in the keying circuit you will need to add the appropriate TX Delay to prevent hot switching your amp. I just wanted to point out that with the KPA-500 (which has PIN diode switching) this does not appear to be necessary. I suspect it's true of the KPA-1500 as well as it also has PIN diode switching, but I don't have one of those. (I wish!)
73,
Doug K4DSP
P.S. The odd artifacts on the RF output envelope are due to aliasing on the digital oscilloscope. You wouldn't see that on an old fashioned analog 'scope.
For amplifiers with relays in the keying circuit you will need to add the appropriate TX Delay to prevent hot switching your amp. I just wanted to point out that with the KPA-500 (which has PIN diode switching) this does not appear to be necessary. I suspect it's true of the KPA-1500 as well as it also has PIN diode switching, but I don't have one of those. (I wish!)
73,
Doug K4DSP
P.S. The odd artifacts on the RF output envelope are due to aliasing on the digital oscilloscope. You wouldn't see that on an old fashioned analog 'scope.
Posted 6 months ago
