RSP2, HiZ input and the Nooelec 9:1 balun
Posted: Mon Jun 05, 2017 12:25 am
I see in the "guide to using the HiZ port" the balun secion shows the little Nooelec 9:1 balun being used. When I tried that setup with a fan dipole, I had massive 60Hz modulating the incoming RF. This was assumed to be a grounding issue..... my antennas are bonded to the incoming power ground rod as well as the incoming water service where they all enter the building but I measure maybe 50mV AC between the PC ground and the antenna shield due to stray ground currents in the house. This should be trivial, but the Nooelec balun has DC continuity from balanced input to unbalanced output and I suspect the resulting current on the shield was modulating the signal.
The fix was simple. If you examine the underside of the balun PWB, you will find two tiny solder pads shorted together by a thin trace. My guess is that they made provisions for breaking the DC path by cutting the foil and replacing the direct connection with a SMD capacitor. I didn't have a suitable SMD cap so I simply cut the trace and installed a conventional 0.001uF disk cap. Works GREAT. No DC continuity, no AC hum and excellent signal strength.
Note that simply cutting the foil is not sufficient.... you need an RF path, hence the cap.
Paul
The fix was simple. If you examine the underside of the balun PWB, you will find two tiny solder pads shorted together by a thin trace. My guess is that they made provisions for breaking the DC path by cutting the foil and replacing the direct connection with a SMD capacitor. I didn't have a suitable SMD cap so I simply cut the trace and installed a conventional 0.001uF disk cap. Works GREAT. No DC continuity, no AC hum and excellent signal strength.
Note that simply cutting the foil is not sufficient.... you need an RF path, hence the cap.
Paul