I use a Thunderbolt GPSDO plus TADD-1 distribution amp as a reference for my spectrum analyzer, signal generator, scope and counter. These all share a common earth chassis ground. I usually work on boatanchors but recently wanted to get into SDR and I bought the UBitx HF SDR transceiver kit. Calibration is needed and in firmware is done by zero-beating to WWV or Signal Gen on 10.000000 MHz carrier. I couldn't do it because of a loud birdie around 10.000.000 Mhz. The UBitx has 12MHz and 25MHz crystals so I didn't think the radio was the source. I quickly found that with UBitx powered off, and just using a broadband antenna into my SA, there is a -60 dBm signal at 10.000.000 MHz. I got rid of the TADD and focused on just one coax Freq Ref between Thunderbolt and any device on my bench other than the SA. If coax is disconnected from Thunderbolt, signal disappears (< -130 dBm) so coax is acting as antenna. I thought the Thunderbolt must be poorly shielded but I also have a Lucent GPS XO/Rb pair shielded like a tank and also a Leo Bodnar GPSDO reference and I see the same 10 MHz -60 dBm spur on my SA with these also. I changed to RG-402 semi-rigid shielded coax and same thing. I have a FLEX radio about 10-15' away from my workbench and it's noise floor goes down to -120 dBm and no spur there. Is this expected for any GPSDO as frequency references on the workbench?
Jerry