rf sniffer with sdr radio or tinysa?

Good afternoon..Ive been using a chinese sdr radio with a short AV line and a 101k cap..it this safe or what would you recommend me? its sniffs TX signals ok but doesnt pickup IF like a 17mhz RX crystal signal at test points..I also have a TinySa but I only use it as a signal generator, becuase Im afraid to damage the front end with the AV line and cap thing..