Solving Amateur Radio Ground Loops Ford Amateur Radio League Educational Program David Treharne, N8HKU June 23, 2018

Table of Contents What are Ground Loops How do you know you have one? Solutions Audio Headphones USB

What are Ground Loops? Connections between pieces of equipment that contain a data (audio or digital) signal and ground or return signal. The data signal going from one piece of equipment to the other, then back, forms a loop, which can form an antenna. The direct connection between the devices is only part of the story: there can exist a second ground connection between the power supplies of the equipment: This forms a big loop that can act as an antenna.

Ground Loops in the Radio Station RF Energy Power Power Power USB or Serial Power Audio Audio Power Audio

What are the Effects of Ground Loops? Audio: Howling or echoing in the headphones or speakers during transmit This destroyed the audio amplifier in the FARL powered speakers Distorted audio on transmit (hear it in the Monitor or get complaints over the air Radio Stuck in Transmit: VOX feeds back on itself, will not turn off. Computer audio feedback keeps the rig in transmit Digital: Radio stuck in Transmit: command to turn off transmit gets blocked Computer to Radio connection lost or unreliable. Computer undergoes a reset Other: A connection between a rotator and an Arduino automatic antenna interface destroyed 2 Arduino microcontroller and 1 USB Hub.

Solutions: Break the Ground Loop! Audio: Use Isolation Transformers: Rigblaster contains them.$120 and up Can make your own. Buy it: Ground loops are a problem with Ipod or Iphones with audio connection to a car: Commercially available stereo isolation transformers can be purchased for less cost than buying your Own! $9 for 2. Digital: USB Isolation Device. IC based transformer- see block diagram. Inexpensive ones are low speed, but fast enough for Rig control and audio codec. $19. Other: 120V Isolation transformer or break the ground. The Arduino problem was that the 30V secondary of the rotor transformer was grounded. Opened the ground, problems solved.

FARL Station for 2018 Field Day For the FARL Station, we have had audio in the headset and the external speakers, and a lot of dropouts on the USB connection between the radio and the computer. We have the MPOW stereo audio isolator at the radio output, feeding the split signal of the headphones and the speakers. Audio issues are eliminated. We have the DIYMore USB Isolator, based on the ADUM 3160 IC, set up for its first use this Field Day. Last year, the Rig frequency and the Logging program band were different, resulting in possible dups and the need to reorder the log file post event. A solid rig USB connection will eliminate this concern. This USB isolator has proven to solve a major problem at N8HKU’s home station with disconnection of both the Rig interface and the audio interface. Digital modes were unusable, along with Rig frequency tracking. We look forward to a solid operating event this year!