microHAM Gear At Anita’s (AB1QB) Operating Position

We have continued our work on automating our station’s operation using microHAM equipment. I have integrated the second operating position into our station into the system via the installation of a second microHAM MK2R+ SO2R interface and two more Station Master Deluxe (SMD) antenna controllers. This position has a Yaesu FTdx5000 Transceiver and an Icom IC-7600 Transceiver. The integration of the FTdx5000 was straightforward and involved a cable hookup to the transceiver. I will add the Icom IC-7600 once the interface cable arrives here.

Current Antenna Control Stack

We’ve also begun to integrate the control of our antenna equipment into the microHAM system. I’ve moved our three SteppIR SDA100 controllers for our two SteppIR DB36 Yagis and our BigIR Vertical, as well as the two Green Heron RT-21 rotator controllers to a set of microHAM DATA control boxes (all of these devices have RS-232 interfaces). With these steps complete, any of our four radios can control the Rotators or provide frequency data to automatically tune our SteppIR antennas.

Antenna Switching Matrix

The biggest part of this project is the construction of a 4 x 10 antenna switching matrix. This element of the system allows any of our 4 radios to connect to any of up to 10 antennas. We built the Antenna Switching Matrix on a 4′ x 8′ board mounted on the wall outside our shack. As you can see from the picture above, this step required quite a few control cable connections as well as the construction of 40 coax interconnect cables (LMR400 Coax and crimp-on connectors were used here).

microHAM Ten Switch

Our Antenna Switching Matrix uses a set of microHAM Ten and 4+4 antenna switches along with multiple RELAY10 control boxes for control.

Antenna Switch Matrix SWR Test

It’s important to test an element like this as it is constructed to catch any errors and to ensure that the final system performance is as expected. I did a combination of continuity, voltage, and end-to-end SWR measurements on the Antenna Switching Matrix as it was built. The microHAM control boxes have a nice manual mode that is available via their front panel buttons which allowed me to configure each antenna switch manually to fully test all of the coax and control cabling in the system.

Receive Antenna Splitter And LNAs

Our antenna farm includes a steerable 8 Circle Vertical Receive Array for the low-bands, and we decided to create two separate appearances of this antenna on our switching matrix. This approach allows two different transceivers to use the receive antenna at the same time. This involves splitting the incoming signal from the receive antenna using a 2-port Splitter from DX Engineering. We also decided to include a pair of Low-Noise Amplifiers (LNAs) to boost the signals from the splitter before feeding the received signals to our antenna switching matrix. The Splitter and LNAs are 75-ohm devices. The signals are passed through a pair of 75-ohm to 50-ohm transformers from Wilson to match their 75-ohm impedance to our 50-ohm antenna switching system and feed lines. The SMD(s) control the LNAs, which have the associated receive antenna connection selected at any given time. This way, an operator can turn off the LNA at their SMD if they don’t need the extra amplification.

Antenna Matrix And Receive Antenna Control

All of this antenna switching requires quite a number of microHAM control boxes. We are also planning to terminate our 8 Circle Receive Antenna’s control lines at this point in our system. The receive antenna requires control leads to steer its direction and a sequencer capability to ensure it is not damaged by strong signals from other nearby transmit antennas. The microHAM system handles these functions easily via a combination of RELAY10 and RELAY6 control boxes, the units in the upper row in the picture above. These boxes also control the two receive LNAs.

With these steps done, we must complete the hookups of our Switchable Band Pass Filters and amplifiers to their associated SMDs. With that done, we can begin moving the feed lines for our antennas and radios over to the system. This will be the topic of our next article. For more information on our automation project, you might want to look at these articles:

• Station Automation Part 1 – microHAM SO2R And System Design
• Station Automation Part 3 – Antenna Cutover And Final Integration
• Station Automation Follow-On Project – Software-Defined Radio Integration

– Fred, AB1OC