Sharing antenna between KiwiSDR and HF transceiver
With some trepidation I am about to install one of the inexpensive (about $65) RF sense antenna sharing boxes with one of my Kiwis, so that I can occasionally use my ICOM 7300 transceiver without having to swap cables and completely disconnect the KiwiSDR. The switcher box has both a PTT connection to the rig as well as an RF sense, so IN THEORY, it should be OK. However, given how precious a KiwiSDR is (even more so, now that production has ceased), I am following a "trust, but verify" approach, outlined below for any comments that might be had, or flaws that are in my reasoning...
1) Connect everything up, with a dummy load in place of the KiwiSDR, then use an oscilloscope to measure the p-p voltage across the load (if any) during a continuous carrier transmission from the transceiver, set at its full 100W output on each of the 80-10 meter bands. Do this in a 15 second on, 15 second off cycle for about 2 minutes (i.e. use FT8 software to control the rig). Convert the measured VRMS across 50 ohms to a dBm value...make sure it does not exceed 0 dBm.
2) Swap out the dummy load with a "sacrificial" SDR such as an RTL-SDR dongle, old SDRPlay RSP1, etc., and repeat the transmitter output test. Verify the SDR has not been damaged.
3) Connect the KiwiSDR and repeat the transmitter test, starting at very low power level ("0%" setting on the ICOM; about 0.5 watt) and gradually increase the power to 100W while observing the KiwiSDR signal strength during transmission, to ensure it is still "OK".
Aside from this test plan, it occurs to me that adding a couple of diodes (recommended type?) across the Kiwi input would be a good insurance policy. I should also mention that I already have a 10 dB attenuator in place before the KiwiSDR, in order to keep a local MW signal (-15 dBm@1340 kHz) from overloading it, while still preserving the MW signals. This may also reduce the risk somewhat, barring a catastrophic failure in the switcher.