[ARC5] DF-ing.

[J. Forster]

OK. In fact, then, when properly nulled, the loop is in the worst possible
orientation for actually receiving the signal. This is done to make the
servo problem easier, since the phase of the loop signal reversesw about
180 degrees as the loop turns throughy the null position, and this can
easily be turned into a servo error signal to drive the loop to null.

Maybe, operationally, you don't need to actually hear the station you are
locked onto.

There are alternative designs:

Use a peak-seaking servo. This is done by slightly dithering the azimuth
of the loop, and tghen using a phase sensative detector on the output,
with a reference 90 deg. shifted from the dither. This is Pound Locking.

Something like this was used in the conical scan of the SCR-584 RADAR.

Another possible design would be a second loop at right angles, used to
actually receive the signal.

-John

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

> On 3 Jul 2013 at 7:25, J. Forster wrote:
>
>> My understanding of the pattern of a loop alone in free space is a
>> figure-8 with both nulls in the plane of the loop.
>
> Correct.
>
>> Adding in the sense antenna, degrades one of those nulls, (and
>> possibly improves the depth of the other) by adding in a roughly
>> omnidirectional signal.
>
> Yes, to both statements.
>
> However, as Mike points out, there are many, many factors that can degrade
> that null.
>
> Supposedly, the "perfect" result of adding a properly-phased signal from
> the
> "sense" antenna is to completely eliminate one null of the figure-8, and
> at the
> same time, enhance the other one, i.e., making it deeper and sharper.
>
> However, actually achieving that "perfect" result is practically
> impossible in
> normal use. Most of the time we have to settle for "good enough".  And
> sometimes, given external factors, that "good enough", isn't.
>
> Ken W7EKB
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