[Milsurplus] DFing receiver LO emissions

[J. Forster]

The ARN-7 is an airborne unit with a small antenna, designed to DF
powerful stations for navigation.The bigger the loop, the better the S/N
should be and the bearing accuracy also.

That said, I still doubt ship location by LO DF was anything but a cover
story.

-John

================

>
> 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
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