UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Woodsons SR-12 receiver

GW3OQK Andrew · 28th Aug 2016, 7:17 pm

I can't resist having a go.

I see the PIM switch switches it into a condition for DF. That's AGC off, manual gain and BFO on. The meter then indicates audio output level. Disconnect the main aerial. The loop would be turned for a sharp audible null, corresponding to minimum meter reading, and the DF bearing and ship's heading noted.

If required the 180 degree ambiguity is resolved by connecting the main aerial to the sense terminal on the front of the receiver then turning the loop +/- 90 degrees (Perpendicular) until the loop signal is in Phase with the main aerial giving max Indication on the Meter. (One side would be somewhat stronger than the other.) There would be a Pointer on the loop's rotator wheel which would show the correct direction. (Refer to manual!)

Next apply correction from the DF calibration curve, and add the ship's (corrected) heading from the compass to get true (or magnetic) bearing from the ship.

I suggest PIM means Pointer Indication Meter and wait for the correct explanation.

73, Andrew ex MN R/O and DF bearing taker.

28th Aug 2016, 7:17 pm	#13
GW3OQK Andrew Pentode Join Date: Apr 2011 Location: Swansea, Wales, UK. Posts: 144	Re: Woodsons SR-12 receiver I can't resist having a go. I see the PIM switch switches it into a condition for DF. That's AGC off, manual gain and BFO on. The meter then indicates audio output level. Disconnect the main aerial. The loop would be turned for a sharp audible null, corresponding to minimum meter reading, and the DF bearing and ship's heading noted. If required the 180 degree ambiguity is resolved by connecting the main aerial to the sense terminal on the front of the receiver then turning the loop +/- 90 degrees (Perpendicular) until the loop signal is in Phase with the main aerial giving max Indication on the Meter. (One side would be somewhat stronger than the other.) There would be a Pointer on the loop's rotator wheel which would show the correct direction. (Refer to manual!) Next apply correction from the DF calibration curve, and add the ship's (corrected) heading from the compass to get true (or magnetic) bearing from the ship. I suggest PIM means Pointer Indication Meter and wait for the correct explanation. 73, Andrew ex MN R/O and DF bearing taker.