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

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.  Many (if not most) 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 station’s callbox speaker and interfered with them receiving radio broadcasts over their station’s PA. 

Ham Radio Helpers 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.

Read the rest at http://www.policeone.com/drug-interdiction-narcotics/articles/8224280-How-cops-are-catching-grow-ops