First of all I would like to thank everyone for their feedback and suggestions. It has been very helpful.
The signal is real, and it is coming in the antenna on the 705. I used the RF Gain and ATT on the 705 (with the preamp off, thanks!) to get the received signal down in a useful range, then I compare with and without the BLP-300+ LPF on the 817 and it is definitely having an effect on the spur. That's good. For evaluation purposes I also put the LPF on the input of the 705 and it knocks it down almost completely, which is another good sign (filter working, RF coming in the front door). I am going to set up for a mock sat pass and see how it plays, but I feel a lot better about the situation. As I said (I think) it hasn't stopped me from working V/U mode into RS-44, but it is annoying. I have a BLP-200+ coming and that should be an upgrade.?
This rig is the fourth FT-817 unit I have owned, and it has been about 5 years since my last one. I had forgotten what a fun rig it is!?
72, Pete N1QDQ
N1QDQ