We have completed the final construction and integration of our DX Engineering 8 Circle Receive Array Antenna System for the Low Bands. We built our array to cover 160m, 80m and 40m some time ago. We also had previously constructed a second entry and grounding system to connect our shack to the new Receive Array System. In this post, I’ll cover the completion of the feedline and control system and the integration of the Receive Array into our shack control systems. The picture above shows the control console for the 8-Circle Receive Array (second box down on the left) as part of the Antenna Control Stack in our shack.
The diagram above shows the components in the 8-Circle Receive Array System that we are building. We used all of the components in shown above in our installation including the optional Receive Feedline Choke (DXE-RFCC-1) and Receive Preamplifier (DXE-RPA-1).
The first step was to build and install the delay line for the 8-Circle Receive Array System. The delay line ensures proper phasing between the forward and rearward elements in the receive array and is used to create a directional pattern which suppresses noise and unwanted signals from the rear of the array. The delay line is made from a specific length of 75 ohm coax (the same coax that is used in the rest of the system) and is installed in a coil next to the Array Controller. We also terminated the control cable on Array Controller. The control cable carries 12V power for all of the active electronic in the array (12V, 250 ma) and the selection of the control cable must account for the potential voltage drop between the shack and the Array Controller. Our cabling is quite long (approximately 500 ft) so we choose a Heavy Duty Control Cable (DXE-CW8-HD) from DX Engineering. We paralleled spare pairs in the cable with the 16 ga. power and ground leads to ensure that we did not have significant voltage drop in the control cable.
The next step was to run a length of 75 ohm coax from the Array Controller to the shack entry point. We choose to install a Receive Feedline Choke in the feedline due to its long length and its installation on the ground (as opposed to buried which would have been impossible in our woods due to roots and rocks). The choke prevents the shield on the feedline from conducting signals from local noise sources or AM radio stations nearby. These problems, if not corrected, would distort the directional pattern of the Receive Array and create higher noise levels in the system. The choke needs to be installed 20-30 ft from the edge of the 8-Circle Receive Array in the feedline. The unit requires a good ground so we mounted it on a 5/8″ x 8 ft ground rod which we drove into the soil. We used a pair of standard ground rod clamps to mount the Receive Feedline Choke on the ground rod. We then secured the feedline and control cables to the ground every 6 ft or so using Metal Anchor Pins from DX Engineering.
Once we got the feedline and control cables near the house, pulled them through the PVC conduit we installed to get them across our yard and to the shack entry point. We then terminated them on the ground system and static suppressors that are explained in the article on the construction of our second shack entry system.
Finally, we ran the feedline and control cables into the house and to our shack.
We use high power on the low bands (1 KW) so the Receive Array’s active electronics must be powered down and the elements grounded when we are transmitting. The Array Controller handles these steps when power is removed from the control cable to the array. To allow for safe switchover of the array between receive and transmit, the power must be removed from the array a few milliseconds before our transmitters and amplifiers switch to transmit. These steps are accomplished via a Sequencer. In a single radio system, a DX Engineering Time Variable Sequencer Unit (shown above) would handle this job including the required time sequenced keying of an associated transceiver and amplifier.
Our shack has a total of four transceivers configured as two SO2R operating positions so we used our microHAM MK2R+ SO2R Controller (the unit on top of our Icom IC-9100 Transceiver in the picture above) to control the overall sequencing of our transceivers and amplifiers and the DX Engineering Sequencer to provide fast switching of the power to the Receive Array under control of the MK2R+.
The DX Engineering Sequencer is the last element in the control cable before it terminates on the Receive Array Control unit (shown above). This device uses a rotary switch to control the selection of one of 8 directions that the Receive Array can electronically pointed in.
Due to the length of our feedline, we choose to install a Receive Preamp in the feedline. This unit is installed close to the radio and is powered from the shack 13.8V power supply.
The final element in the feedline is a 75 ohm to 50 ohm transformer from Wilson Electronics which converts the 75 ohm feedline from the Receive Array to the 50 ohm impedance at the antenna terminals on our Icom IC-7800. The IC-7800 has a provision to use a separate Receive Antenna and we configured it to do this by default on the 160m and 80m bands.
With everything in place, we began by testing the Receive Array system with our Transceiver set at a low power level (10 w). Once we verified the operation of the Sequencing System, we turned on the amplifier and verified proper operation a high power. The entire setup worked perfectly and the receive Array is much quieter on both 160m and 80m than our transmit antennas. This enables one to “hear” weaker signals on these bands much better. The array is also noticeably directional as expected. I am anxious to operate on the low bands a few evenings (and early mornings) to see how well the system performs but the early indications are very good.
– Fred (AB1OC)