With inclement weather forecast over the Xmas period I was keen to try and implement some form of remote switching of the 144MHz and 1296MHz EME antennas. The antenna feeds terminate in a waterproof cabinet at the base of the mast with a common feeder run back to the shack.
I had in the back of my mind to use a Raspberry Pi (RPi) connected via WiFi to control the relay switching and manage the cabinet environment. The latter being to maintain the inside of the cabinet at a suitable temperature to ensure no damage occurs to the equipment due to condensation.
I already had a “Power-Pi” configured and working. To get the basic antenna switching to work I would need to provide suitable voltages to power the RPi plus relay switching module (5V) and RF relay (~26V).
My son, Kristian (2E0KGG) is home with us for Xmas and he had amongst some of the RPi / computing goodies he brought with him a couple of BattBorg modules. I’d not heard of these before, but they looked just the job for this project. My original plan was to use a spare Dell laptop PSU (19.5V) to power the RF relay and then one or more voltage regulators to drop down to 5V. The BattBorg would now provide the 5V.
My only reservation with all of this was just how much noise (electrical) would be generated, and what impact would all this have on my EME noise floor, especially having it all located right at the base of my antennas.
Everything was put together quickly with each module attached to a backboard which was then installed in the cabinet, in between the rain showers! I took a few screen captures from my SDR setup so I could compare the noise floor and birdies before and after applying power to the cabinet. From the very quick tests done so far, there’s no apparent increase in the number of birdies within the EME section of the band, or to the noise floor! Given all of this was lashed together quickly and is not screened, I was VERY surprised.
I plan to do further tests over the coming days choosing times when most of the TV’s should be off and with the antennas pointing up at the cold sky. With the lower noise floor it should give better indications of the impact of this kit on my EME receive capabilities, plus any impact on other sections of the two bands.
Assuming the results are positive this will all be tidied up and the control hardware housed in a metal die-cast box.