[Milsurplus] [ARC5] DAG HFDF Sense Antenna.

[Kenneth G. Gordon]

On 2 Apr 2021 at 17:53, Hubert Miller wrote:

> > The 180 degree ambiguity is impossible to resolve without that sense antenna, BTW
> 
> Is this strictly true?

At MF and HF, most definitely.

> If the loop is not balanced to ground, has one side grounded? 
> Granted, the pattern may be less marked, but it does indicate directionality.

The normal loop, without the sense antenna, displays a very, very narrow null when it is 
broadside to the signal being heard. The trouble is that null is on BOTH sides of the loop. 
Therefore, resulting in a 180 degree "ambiguity". In other words, either side "points" to the 
same station, so the operator can never tell which is correct.

The "sense" antenna causes the phase of one of the peaks of the loop to be stronger than 
the other, forming a so-called "cardioid" shaped radiation pattern, thereby indicating quite 
clearly which direction the signal is coming from.

The "cardioid" null is 90 degrees to the nulls exhibited by the plain loop without the sense 
antenna, and is not nearly as "strong" as the nulls of the plain loop. But it suffices.

It takes some practice to get it right.
 
> I feel I vaguely recall  an actual commercial application of this fact.

If there was such, it undoubtedly depended on the frequency of use.

Ken W7EKB