Been doing some tests of my Elad FDM-DUO on HF bands with my noise-ridden lab environment. Using my HP E4421B sig gen with 30dB screened attenuator, the minimum discernable signal using PI-RX and JT4A is:
I was wondering if I was getting noise from the local environment up the coax outer or power/control leads, but those measurements were made with the coax screen of the HF antenna connected to the radio, so I guess not.
With the antennas connected (at 2200utc), I see a noise floor of -142dBm on 28MHz, only a couple of dB more than with a dummy load. On 18MHz, about the same. Across the bands from 18MHz to 30MHz, I see a few tones and squiggles, worst tones about -120dBm. Looks like I don’t have any significant local noise, at least between 18MHz and 30MHz. Interesting. Bit different on LF and VHF, where I have some work to do!