Operators growing plants indoors need to provide supplemental lighting for photo-synthesis of their plants. Typical lights options include fluorescent, LED, or high pressure sodium (HPS) or metal halide (MH). The HPS and MH lamps are available up to 1000W per lamp and require a ballast for proper operation. The old school ballasts were originally magnetic, but recent developments in switching power supplies have created electronic ballasts which are prone to square wave generation and can be rich in harmonics and RFI. These electronic ballasts are subject to FCC part 18 emission rules but many are imported into the USA from foreign countries that fail to test for emissions per the requirements of the FCC rules. With the legalization/decriminalization of marijuana in many states and the proliferation of “grow” and “hydroponic” stores selling electronic ballasts in attractive color packaging to non-industrial users means that these devices need to meet the consumer limits of FCC part 18 in order to be legal.
In many cases the ballasts do not meet FCC requirements and radio spectrum users including amateur radio operators, public safety users (fire, police, emergency vehicles, hospitals, etc) have reported significant “noise” or radio frequency interference (RFI) from “grow” lights and other RF lighting devices. In some cases he level of conducted emissions from these devices is so high that, as a practical matter, one RF ballast operated in a residential environment would create interference to radio communications throughout entire neighborhood. These electronic ballasts produce so much noise that anyone (including police seeking illegal operators) with an AM radio can tell what is going on inside a home. Being anonymous and trying to fly under “the radar” is not easy when you are generating significant RF interference to radio communications.
Interference from grow lights has been shown to be problematic at distances of over 1,000 feet. This is well over three times the distance one might expect from a legal Part 15 or 18 device, i.e., one that meets the applicable FCC limits. In addition, they are typically controlled by a timer, cycling on and off at precise times every 12 hours or so. RFI in the 40 meter ham band (7 MHz) band is a good indication of grow light operation in the neighborhood. Directional interference (from a beam pointing in a certain direction for example) could also indicate the direction of the interference.
It must be emphasized, however, that grow lights are being used for a wide variety of indoor horticulture. For example, other uses include growing indoor vegetables and household, ornamental and exotic plants. The mere presence of a grow light is not proof that illegal activity may taking place in someone’s home.
Notable products that cause reported problems include: Lumatek LK-1000 electronic ballast
Technical Solutions To A Grow Light RFI Problem
As with any RFI problem, the solution of the “Source-Path-Victim” RFI problem is to eliminate or suppress the source, block the path, or protect the victim device with various filters and chokes for the path(s) to the victim.
Source RFI solutions include changing to magnetic ballasts, using FCC compliant ballasts, or using filters connected to the ballast usually on the AC and the lamp side. Regardless of which cure is attempted, be sure to choose a filter or other components that are properly rated for the current and voltages involved.
Although common mode chokes are another popular and effective solution in cases involving conducted emissions, the specific brands of grow light cable size and associated connectors may make them impractical without additional consideration. For example, you may need to temporally remove a connector or add an extension to the cable for the choke.
Keep in mind that snap on ferrites and slip on ferrite beads are not as effective as ring toroid ferrites at HF. Toroid rings are donut shaped, and you’ll need to pass the cable end through the center hole multiple times. We suggest the F240-31 ring toroid on the input and the output of each ballast. Usually a 10 pack of F240-31 is a good starting point to attack the ballast problem. Typical installation of ring toroids is HERE and F240-31 ring toroids are available HERE.
Note: In most cases, common mode chokes are easy to fabricate. Simply wrap the cable around a toroid core several times, typically eight or more, in order make one. Be sure to keep the toroid as close to the RFI source as practical.
Path RFI Solutions include choking the source path which may be radiated (most common) or conducted (through the AC line common to the source and victim). The F240-31 ring toroid on the AC side of the ballast usually suppresses RFI conducted to the AC line which acts as a large transmitting antenna to neighborhood receivers. Radiated RFI can be suppressed by electronically shielding the source (in a conductive box that is grounded for example) or reducing the power to levels which limits the RFI distance. Additionally the victim path (from radiated RFI) can be protected by using F240-31 toroid rings on the receiving device antenna coax to suppress common mode RFI conducted to the receiver via the outside of the coax braid.
Victim RFI Solutions include F240-31 ring toroids on the AC power line, and antenna coaxial feed lines at the receiver.
Grow Light RFI Kits
Palomar Engineers suggest the F240-31-10 10 pack of ring toroids as a starting kit and another 10 pack of FSB31-3/4-10 snap on ferrite beads (3/4″ hole) for smaller wires or wires that can not be disconnected. In either case wrap multiple turns of the wire through the center of the ferrite.