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When one of the antennas is fed 180 degrees out of phase we create a main lobe that is higher, this can be used to match the take off angle of best propagation.  The angle can be very high if the antennas are low to the ground like 40m yagis that are .5 and 1 WL above ground.  This would be a very good thing to do for changing the pattern from low angle dx to a higher angle NVIS for close in operation.  NVIS is a whole discussion in itself, but we ususally think of NVIS as being only avaiable to us from 2 to 12 MHz  Since the Ionosphere only supports NVIS angles at these frequencies.  So making a BOP set up for the 15m band is probably not a good idea.  But at 6m we have a high angle mode called Sporatic E.  Here it is very worth the effort to create a BIP BOP array.  Lets look at an example at 6 meters.

The above antenna system is 2 7 element yagis, 75 feet over 50 feet.  The pattern for this array BIP is shown next.

The main lobe is only 4 degrees above the horizon the a gain of nearly 21 dBi. If we feed the lower antenna 180 degrees out of phase by switching in a 180 degree delay line or by using a 180 degree transformer (a broad band solution) we will see this:

The main lobe is now at 18 degrees, we lost 1.8 dB of gain, but if we matched the angle of propagation we can see possibly 18-20 dB of signal gain by moving the Sporatic E signal into our main lobe.  I measured the pattern at 18 degrees in the above BIP plot and found the gain was -7.75 dbi.  So we have an overall gain of 18 degrees of 27.01 degrees in the BOP pattern at 18 degrees.  Amazing stuff when you actually here this.

Here is picture of a 5 kW StackMatch with the BOP relay built into it.

Were probing the two antenna ports that are terminated with the two antennas being driven.

Here are the two scope pictures, one driving BIP, one driving BOP.

                         BIP                                                                                           BOP

StackMatch Modification for both in phase and both out of phase control of two mono band antennas  by John, N2NU

Open up the StackMatch relay box and remove the ten nuts that hold the circuit board onto the bottom panel. Remove the circuit board, being careful to not lose the nuts, the star washers and the eight spacers that are placed between the SO-239 connectors and the board.

Using a Dremel tool, grind off the circuit board foils that connect to the NO and the NC terminals on relay 2. The NC foil is on the top side of the board, and the NO foil is on the bottom side. (See Figures 1 and 2).

Figure 1

Figure 2

Install an insulated jumper from the NO pad of relay 2 to the output of the transformer. (See Figure 3)

Figure 3

 

Re-assemble the relay enclosure.

 

Remove the control board from the box and orient the board such that you are looking at the top of the board with the LEDs on the right. Remove the following six diodes from the board:

CR3 – Located third from the top in the twelve diodes mounted next to the LEDs

CR6 – Located sixth from the top in the twelve diodes mounted next to the LEDs

CR10 – Located tenth from the top in the twelve diodes mounted next to the LEDs

CR13 – Located first in the four diodes above and to the right of the switch

CR16 – Located third from the top in the four diodes above and to the right of the switch

CR23 – Located closest to the switch in the two diodes to the left of the switch

Once all of these diodes have been removed, solder a diode (1N4004 or equiv.) with the anode end in the hole that originally held the anode end of CR23. Solder the cathode (striped) end to the mounting stud for terminal 1 of the connector block. Be careful not to short this diode to the diode to the left of where CR23 was.

Once you have completed this step, the board should appear as in Figure 4.

Figure 4

Turn the control board over and install two wire jumpers, shorting switch position 2 to position 4, and position 4 to position 7. See figure 5. Again be careful not to short anything else.

Figure 5

 

Re-assemble the control box.

Install the relay unit on the tower and connect the top antenna to port 3, one end of ½ wavelength of coax to port 2, and the bottom antenna and the other end of the ½ wavelength of coax to port 1. This is accomplished by using a Male-Male, a Tee and a Female-Female UHF connector (there is not enough clearance to use only a single Tee connector).

The above modifications ensure that all positions on the StackMatch switch are valid. When in the OFF or AUX position, both antennas will be connected in phase. When the box is on, each of the "all-three" positions feed both antennas in phase. Note that only the upper and lower LEDs light, indicating BIP operation. The individual antennas can be selected by using the normal "upper only" or "lower only" positions and the appropriate LED will light. BOP is selected by switching to the "middle only", or the former "upper two" or "lower two" positions. In each case only the middle LED will light, indicating BOP operation.