Re: [IRCA] Phasing /RF notch, etc.

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> I don't give up that easily. The Wellbrook Array sounds like it does
> have some good directional properties.

I do have some questions about the array that the Wellbrook site is unclear
on.  It apparently uses four loops.  How are they set?  So all four line up
in the same direction?  That would seem to work, as the inherent null of the
loops would minimize side-to-side pickup, and the phasing would null other
directions.

I have been working on a similar arrangement, but using either copper tube
loops or two of the large ferrite bar antennas.  Set them up so they null to
the sides of the desired direction, then phase them for a null towards the
rear.  Computer simulations show a very nice and tight pattern.

The problem I have been having is the leakage into the coax, per previous
messages.

I wonder how Wellbrook avoids that?  Some significant amp in the loop
itself?  How are they connected?  Just coax?  Any special isolation
techniques?  Maybe amplifying the signal way up and then attenuating it (and
the leakage) way down again?

The next phase of my own work will be set this way:

1.  Two ferrite bar antennas on camera tripods.  Both set in phase, and
nulls to the side.  I may set them to null a specific station, which would
make alignment easier.

2.  A DX Engineering RPA-1 preamp at each loop.

3.  CAT5 cable connecting each to the receiver point using metal box
shielded 110/50 ohm baluns.

4.  The DX Engineering NCC-1 phaser.

5.  All this into the Palstar R30CC in the truck.

The ferrite bar antennas may not be the best choice for low-angle reception,
but I have them already.  A couple of collapsable verticals of 20-25' height
working against a four or six wire radial base may be better.

It may be possible to use four verticals.  Combine the end two out of phase.
Combine the side two in phase.  Combine those pairs in the phaser at 90
degrees.  Vary the level of the side pair against the end pair to move the
null around the back.  This has the advantage of being used in four
directions with a bit of switching.  It has the disadvantage of losing the
side null capability of the loops.

Well, all this is a work in progress.  When I get this honed down to a
decent plan, I'll see if I can set it up for other local DXers to test.

Craig Healy
Providence, RI

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