MFJ-1025 antenna phasing unit
 

I've been toying with the idea of getting one of these.The possibility
of choosing between co-channel stations would be great and I already
have two outside antennas in place. Anybody have any experience with
this?

Steve M wrote:

I've been toying with the idea of getting one of these.The possibility
of choosing between co-channel stations would be great and I already
have two outside antennas in place. Anybody have any experience with
this?

Get the ANC-4, which goes down to MW.

(With three antennas and two ANC-4's you can null two co-channel stations
and hear a third; easier though with 4 antennas and 3 ANC-4's.)

The pattern from two antennas is a V that you can sweep from one endfire
to the other, opening up to a broadside I in the middle. Any separation
works but the gain is best with a quarter wave separation or more.

To null a loud MW local takes very careful adjustment (the pots aren't
really good enough, you're more breathing on the thing) unless you have an
extra ANC-4 at low gain added in as sort of a bandspread. S-meters read in dB
so you don't really get a good intuition for how fine an adjustment you're
trying to make on a local, to null it completely.

ANC-4 drawbacks (not fatal):

1. the pots go scratchy after a while, which you
will notice on loud stations you're trying to get rid of. Open the thing up,
spritz some spray DeoxIT in the two tiny holes in each pot nearest the board,
closing your eyes because it may spray back. That will free up the pot,
and then in a short while it well get very sluggishly stiff to turn; this in
turn goes away over a few weeks and it's back to normal. The scratchiness
goes away immediately and stays away. The MFJ probably has the same problem.

2. (don't know about the MFJ) the pots adjust things linearly rather than
at constant power, so adjusting phase also adjusts gain (so gain is min in the
middle and big at each end). You have to bear this in mind when searching
for the null. It would be much nicer if it worked at constant power instead.

In general, finding the null takes some talent but it does work. Very often
the null is a long thin contour in the radius and angle search you're doing,
and you have to use (say) successive relaxation to locate it. That being,
instead of

a. Adjust gain to min S meter
b. Adjust phase to min S meter
c. repeat

you do

a. Adjust gain to min S meter plus a little
b. Adjust phase to min S meter

repeat

if that doesn't work, try minus a little. The method follows a narrow
ridge better than successive exact minimization.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

Ron Hardin wrote:
and you have to use (say) successive relaxation to locate it. That being,

Successive overrelaxation, it should read.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

On Wed, 14 Jan 2004 14:15:25 GMT, Ron Hardin
wrote:

Ron Hardin wrote:
and you have to use (say) successive relaxation to locate it. That being,

Successive overrelaxation, it should read.

Thanks for the input Ron, I have a little trouble visualizing the
wiring to hookup 2 or 3 of these units to a receiver. I guess the
output of the first would go to one input of the next. Successive
overrelaxation, I think that sometimes occurs here in the presence of
Belgian ales.