[Milsurplus] DFing receiver LO emissions

[boeing377 at aol.com]

I put an ARN 7 ADF on my Dad's commercial fishing boat in the 1960s. It was a VERY good DF over its range of 100-1750 KHz, amazingly accurate if you calibrated the loop selsyn to compensate for ships rigging bearing distortion. It also worked well in 2-3 MHz by tweaking the band 4 osc coils which sacrificed the top end of the AM BCB in favor of the band most used by fishing boats back in the AM xmtr days. 

I tried to DF receiver emissions from other boats but the signals, if they could be received at all, were far too weak to be of any use more than about a hundred feet away if that far. It just wasn't a viable method to detect other vessels presence let alone direction. You'd see them visually before you could detect their receiver radiation. 

It takes a strong signal to get a decent bearing. On very weak signals the ARN 7's servoed loop (LP 21LM) would just hunt randomly for a null and the bearing info was useless.

73
AF6IM