How to Find a Marijuana Grow With Your AM Radio

Marijuana Grows Create RFI

With the proliferation of indoor marijuana grows, the indoor “horticulture” industry has been booming. Chinese manufacturers are turning out indoor grow equipment at a rapid pace with little to no regulatory oversight or compliance. Because of this, there has been a significant amount of radio frequency interference (RFI).


Before we get into how to detect a marijuana grow with your car radio, you have to understand some simple mechanics of how a grow operates. To grow marijuana indoors, you need supplemental lighting necessary for photosynthesis. These lights may be fluorescent, LED, and for larger operations high pressure sodium (HPS) or metal halide (MH).  The HPS and MH lamps may be 1000W per lamp and require a ballast for proper operation.  These ballasts were originally magnetic but in the past few years have become electronic.  These devices are subject to FCC part 18 rules but there appears to be a total disregard for the FCC rules.  These electronic ballasts are manufactured in China and may have little “FCC” stickers on them but there is no evidence of any testing for compliance having been done. Because of this, a large amount of RFI is interfering with nearby electronics. As an example, one grow next to a CalFire station (California’s state fire agency) caused a continuous hum over the stations callbox speaker and interfered with them receiving radio broadcasts over their station’s PA.

indoor marijuana grow

Reports have begun to flood into the National Association for Amateur Radio about interference with their ham radios from their neighbor’s marijuana grows. The most complaints come from California and Colorado, for obvious reasons. Many ham radio operators began to see a correlation with marijuana grows and this RFI. One ham operator located 5 marijuana grows near his house due to RFI alone! Many ham operators can locate a grow simply by taking a radio and portable antennae out into their neighborhood and using the radio to triangulate the exact location of the grow.

One industrious ham operator went to his local grow shop and borrowed several lights and ballasts to test for RFI. He found that one simple light and ballast set up would cause interference up to 700 meters. From our experience, we know that most indoor grows have more than one light and ballast, which would amplify the RFI.

Field Use to Find Marijuana Grows

One narcotics officer from the San Francisco Bay Area simply turns his car radio to 560 AM when he checks out potential indoor grows. He says that he has checked out 7 indoor marijuana grows since learning about the RFI issue. All 7 times, the car’s radio showed significant interference from the ballasts inside of the grow location.

marijuana plants on tray

One ham radio operator described the interference this way: “”It can be pops, it can be a buzzing sound, whistles — just all kinds of different noises that we’ll hear.” Tom Thompson, a ham radio operator, told a Colorado newspaper, “”If I can track this down, anybody can track this down.” If I listen long enough, I can tell when they turn the lights off … You can tell exactly when the harvest is.”

There are ways that growers can mitigate the RFI produced by these ballasts. But, I don’t want to give away those tricks. The purpose of this article is for you to find them, not help them continue to hide.

Is this method of finding marijuana grows fool proof? No, it isn’t fool proof. It’s just another tool in your toolbox.

Author: Keith Graves
Keith is a retired Police Sergeant and worked in the San Francisco Bay Area for 29 years. Keith was named as California’s Narcotics Officer of the Year and is a prior winner of MADD’s California Hero Award. He has years of experience as a Narcotics Detective and a Narcotics Unit Supervisor and is a Drug Recognition Expert Instructor (IACP #3292). Keith teaches both the DRE course and the Drug Abuse Recognition Course and has taught at the Police Academy. He has developed several drug courses for the California Narcotics Officers Association, California POST and California Colleges and currently consults POST on drug investigation procedures. Keith has held other assignments besides narcotics including Training Sergeant, Patrol Sergeant, COPPS Officer, Traffic Officer, and 20 years as a SWAT Team member and Sniper Team Leader. Keith has taught thousands of officers and businesses around the world about drug use, drug trends, compliance training and drug investigations. He is recognized as an international drug expert and has testified as an expert in court proceedings on drug cases, homicide cases and rape prosecutions. Keith earned a BA in Business Management from Saint Mary's College of California and a MA in Criminal Justice. Keith is the Founder and President of Graves & Associates, a company dedicated to providing drug training to law enforcement and private industry.

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