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Home , Noise (electronics), Shortwave radio

Locating RF Interference at HF

A proven and practical approach to dealing with RFI from grow lights and more.

Tom Thompson, WØIVJ longer ranges, however, the might be ing set to LINE, the RFI might be line interference (RFI) in- heard only at HF. So, HF RDF to get you related. in VHF range can be a real time saver. See creased dramatically in my neighborhood RFI from consumer devices that appears www.arrl.org/power-line-noise-faq for recently. Locating the sources was not at regular intervals across the band likely more information. easy, due in part to the distances involved. comes from a switching-mode power sup- The typical range for a consumer device I also found that RFI from consumer de- ply. If the noise is pulsing it could be a bat- that meets the applicable FCC Part 15 or vices can be problematic. While FCC Part tery charger. Sharp periodic ticks could be 18 emissions limits is usually no more 15 and Part 18 rules define emissions limits from an electric fence. Variable speed mo- than a few hundred feet. Some of the for most consumer , the limits tors in appliances, like washing machines, sources in my area, however, were more are high enough to allow interference to increasingly rely on electronic speed con- than a half-mile away. The usual “sniff” nearby radio receivers. FCC rules protect trols and switching power supplies. See also methods weren’t practical, and without an all licensed radio services from harmful in- Light Bulbs and RFI — A Closer Look for initial heading, the sources were difficult terference, and the operator of an offending an additional discussion on FCC rules and to find. Furthermore, they were primarily device must correct the problem. Therein interference from modern energy-saving HF sources. I needed a radio direction lies the rub — someone must first find the light bulbs.1 finder, but an HF handheld Yagi was not device in order to identify the operator. an option! Since the FCC generally does not provide Locating the Noise Source Power-line noise, especially if it affects Looking for Noise Sources RFI locating services, the burden became mine by default. only the lower frequency HF bands, can Some noise sources are caused by arcing sometimes be caused by a source several power lines, which, at close range, can wipe Some Typical RFI Sources miles away. However, if the source is a out all bands from AM broadcast to beyond Switching-mode power supplies, usually consumer device that meets the FCC limits, 70 centimeters. The noise is relatively con- associated with consumer electronic de- it most likely will be located in your home stant and uniform across the spectrum. It vices or battery chargers, often spew RFI at or a neighbor’s home. In this case, always sounds like a constant harsh raspy buzz ev- very high levels. They can emit in start by temporarily turning off the main erywhere you tune, and can often go away a regular and repeating pattern of ­spectral breaker to your residence while listening during periods of rain or high humidity. peaks, ranging from about 50 to 70 kHz, to a battery-powered radio. Also, disable Many power companies lack the resources which exhibit a growling sound that may any battery-powered devices. If the source to find and fix noise sources in a timely drift slightly in frequency. Such RFI noise proves to be external to your home, you can manner. Thus, hams can attempt to locate “signatures” can sometimes help you use the procedure from Mike Martin’s RFI such sources as an aid to their power com- distinguish between power line noise and Services web page to find the residence.2 pany. Finding a distant source can be diffi- noisy consumer electronics. If the audio This approach works well when consumer cult. Nearby, you can track power line noise noise bursts from your receiver seem to stand still on an oscilloscope with trigger- at VHF or UHF right down to the . At 1Notes appear on page 39.

Figure 1 — An RFI tracking system.

QS1411-Thomp01 Loop Strength Step Meter Attenuator HF Receiver

30 20 10

Figure 2 — Tracking loop antennas. Left to right: 24-inch copper loop, 20-inch aluminum loop, 16-inch #22 AWG wire loop with plastic tubing.

QST ® – Devoted entirely to www.arrl.org November 2014 33 devices are within a few hundred feet of the ham. There are, however, some important The Grow Light Problem exceptions. A very cooperative manager of a hydroponic store allowed Larry Benko, WØQE, Not Your Typical Source of RFI and me (Tom Thompson, WØIVJ) to test some of his ballasts and lights. Also, one grower loaned me his equipment for the day during his “lights off” period. Using a line In my experience, the most insidious and impedance stabilization network (LISN), we measured conducted emissions 40 dB problematic RFI generators are high- above FCC Part 18 limits. The RFI in the HF spectrum from these ballasts can easily power lighting systems, particularly grow be heard a half-mile away. These products are available from multiple vendors; some lights used for cultivating plants indoors. have a sort of FCC sticker, but appear to have never been tested. The RFI is of such Although classified as Part 18 devices, a magnitude that common mode ferrite chokes alone do not eliminate the interfer- they are subject to similar emissions limits ence. Larry and I developed filters that decreased the RFI from S-9 +40 dB to S-5 as A, B as Part 15 devices. Since these devices measured on my IC-7000 from a short distance. Recently, an employee from the can cause detectable RFI for blocks if not local power utility company said that about half of his RFI complaints were from grow light ballasts. In my experience, the 40 meter band seems to be where that sort of miles, they would appear in many cases RFI is the strongest. to be exceeding the FCC limits. One grow light tested in the ARRL Lab exceeded the Awww.w0qe.com/RF_Interference/grow_light_electronic_ballasts.html Btomthompson.com/radio/GrowLight/GrowLightBallastFilter.html applicable Part 18 FCC limits by 58 dB, and several that I have tested exceed Part 18 FCC limits by more than 40 dB. While the techniques in this article can be used to locate a wide range of RFI sources, my run multiple bulbs totaling several hundred to the source. Driving around with a mobile primary objective was to track down grow watts on a 12 V system. Grow lights, on rig can also work, especially if the source lights. Almost overnight, they had become the other hand, can require more than a is some distance away. However, I found the primary source of harmful interference kilowatt. The radiating antenna is generally that a small tuned used with affecting my station in Colorado. the house wiring and associated cabling. To a shortwave receiver and a good S meter be clear, the bulbs themselves, whether they (Figure 1) works best. Many amateurs keep a close eye on their RF are halogen tract lights or high-pressure level. If an increase oc- sodium grow lights, are not the problem. The Loop Antenna curs randomly, and appears to coincide with It is the poorly filtered electronic ballasts A loop antenna is bidirectional. You can periods of human activity such as weekends that cause the problem. See the sidebar, The rotate the loop easily if you hold it above or evenings, it may be a consumer device. Grow Light Problem. your head with the feed point at the bottom. Power-line noise can also occur at random In this position, vertically polarized signals intervals but is often weather related. If, If you can determine the on/off sequence of peak when the loop is turned edgewise however, the noise comes and goes at regu- the RFI, listen to your radio when the RFI to the source. Additionally, a deep null in lar intervals that appear to be controlled by begins. The noise sounds stronger and has the signal occurs for vertically polarized a timer, then a grow light ballast is a likely a burbling sound to it until the lamp warms signals when the loop is turned 90 degrees culprit. These systems generally cycle on up, which is generally less than 5 minutes. from the peak position. In other words, the and off daily in approximately 12 to 16 hour A free program, Audacity, will enable you signal is nulled when looking through the intervals, although this timing sequence to make an excellent audio recording from loop toward the source. That sharp null is 3 may vary depending on the plant. Another your receiver audio output. most useful for determining the direction of the noise source since most consumer RFI clue is the distance over which the inter- Finding the RFI Source seems to be vertically polarized as long as ference can be heard. Typical consumer Once you have an idea of what might be you are further than about one hundred feet devices will fade away in 200 to 300 feet. causing the RFI problem, you still need from the source. Grow lights, on the other hand, can be prob- to find the source. Figure 1 shows a block lematic to well over 1000 feet. diagram of the HF RDF system that I use. My loops are shown in Figure 2. They all So far in my neighborhood I have tracked Grow light RFI is often prevalent in the consist of a tuned larger loop that is four down six grow light ballasts and three halo- 40 meter band, but a Yagi antenna is times the diameter of the offset coupling gen light ballasts. Most of the grow light obviously not practical. A short dipole loop. Note that the loop antenna efficiency systems have been on a timer with a 12- has directional characteristics only for is much lower than that of a full-size di- hour on/off sequence. Some halogen yard horizontally polarized signals. RFI from pole. Signals are much weaker than what lights, however, might be on a timer that is consumer devices seem to be mostly verti- you typically hear with your base station turned on and off at regular intervals. Grow cally polarized. Besides, the short . The efficiency of the loop will light systems may also be off for a week or needs a preamp to make it effective. The increase as you increase the diameter of two during harvest, and can be on continu- preamp must have sufficient the loop or improve the conductivity of ously during germination. to prevent from strong the tuned loop material. The coupling loop broadcast stations. One locating approach conductivity is less important. Both of these lighting systems, with the is to walk around the suspect area with a As shown schematically in Figure 3, the exception of a halogen desk lamp, can handheld shortwave radio with a telescop- larger loop is a tuned circuit and the cou- employ very high-current switching-mode ing antenna. The antenna can be shortened pling loop is a one-turn link into a choke power supplies. Some halogen systems to help minimize the signal at ranges close

34 November 2014 ARRL, the national association for Amateur Radio® www.arrl.org Tuned Loop

Coupling Loop

Figure 4 — Details of the 20-inch loop.

Balun

where F is frequency (Hz), L is inductance in mind that antenna efficiency gets worse (H) and C is capacitance (F), we find that for lower , or smaller loops, or the loop can tune from 40 through 10 smaller wire diameters. If the RFI is much meters. You may need to make the loop greater than the band noise, you may pre- slightly larger than 20 inches to cover the fer the much lighter 16 inch loop. As you Coax lower part of 40 meters. get closer to the noise source the RFI will become stronger so the RFI to band noise The 5-inch diameter coupling loop of ratio improves. #12 AWG copper wire is encased in a piece of 0.25 inch plastic tubing. The balun is The Step Attenuator 3½ turns of RG–174 through two FairRite You may need a step attenuator when sig- To Receiver 2643540002 type 43 material cores (see nals become very strong close to the noise QS1411-Thomp03 Figure 4). I use an SPDT (center off) toggle source. I built a three-section Pi to switch in 1200 pF for 80 meters resistive attenuator with 10 dB, 20 dB, and Figure 3 — Circuit schematic diagram of a and 5400 pF capacitors for 160 meters. 30 dB sections. Combinations of these tuned loop. The center off position is for 40 through values will give an attenuation range from 10 meters. 0 to 60 dB in 10 dB steps. See Chapter 22 of The ARRL Handbook as well as QST for balun on the coaxial feed line. The tuning Loop Performance and 6, 7 Considerations details. capacitor resonates the loop at the fre- Connect the loop to your transceiver, mak- quency of interest. A loop inductance calcu- ing sure the transceiver cannot transmit. lator may be found on the web.4 [One-turn You can hear the noise level increase when loop inductance is − 0.016a ln( 8 ab) 2 you resonate the loop. Tuning is sharper. µH, where a and b are loop and wire diam- Even though the VSWR is not very low, eters in inches — Ed.] I could measure the resonance with an I used a capacitor with a MFJ259 analyzer on all bands except 160 built-in 8:1 reduction drive and a capaci- meters. tance range of 16 to 390 pF.5 The 20 inch Let’s say that normal band noise is S-5 diameter loop made from 0.5 inch diameter using a dipole on 40 meters, where S-9 aluminum has an inductance of 1.2 µH. corresponds to –73 dBm, and let’s further Using say that your receiver minimum discernable 1 F = signal (MDS) is –125 dBm. At 6 dB per 2π LC S-unit, S-5 corresponds to –97 dBm (28 dB above the MDS). The Table 1 three loops shown in Loop Antenna Details for 40 Meters Figure 2 have the char- Loop Diameter Loop Material Conductor Diameter acteristics shown in (inches) Antenna Gain Table 1 for 40 meters. 24 Copper ¼" –13 dBd The 20 inch loop will 20 Aluminum ½" –19 dBd hear the band noise 16 Copper 0.025" –27 dBd 9 dB above the MDS (#22 AWG) of the receiver. Keep Figure 5 — Noise receiver front view.

QST ® – Devoted entirely to Amateur Radio www.arrl.org November 2014 35 T1 +8 V U1 C7 0.0022 J1 10 dB 20 dB 30 dB NE602A R6 27 k +8 V C11 BN-43-2402 8 C4 R5 R9 27 k 0.0022 R7 2 1 4 4 S1 S2 S3 C9 R8 5t 38t 1 R10 6 #28 #28 2 5 1 μF 2.7 k 2.4 k U2A 7 2.7 k 2.4 k C5 C8 0.047 11 0.22 U2B 3 1 μF LT1014 C10 0.047 R21 R24 R27 6 7 5

71.5 249 787 C12 R20 R22 R23 R25 R26 R28 3 95.3 95.3 61.9 61.9 53.6 53.6 0.22 C14 12 C3 R12 27 k U3 C2 0.0022 C17 LM78L05 NPO 0.01 R11 R15 27 k 0.0022 R13 13 1 REG 3 C15 R14 +8 V In Out C1 14 R16 9 R1 2.7 k 2.4 k Gnd R2 U2D 8 2 1 k C13 0.047 0.22 2.7 k 2.4 k U2C C25 C26 100 k 1 μF 12 C23 C16 0.047 4.7 μF 4.7 μF MV2105 D1 10 4.7 μF

+4 V C22 5 Gnd 1N5711 7 U4B 1 μF C27, L1 Tap D3 See Chart +8 V 6 Coil D2 R35 100 μF 100 1N5711 R31 +8 V 10 k LC Chart R18 5.1 k C24 LT1014 10 2N3904 3 4 C18 Band C7 (pF) L1 (uH) Turns AWG# Core R17 S4 R33 Q1 1 8 R29 U4A U4C 6 50 105 28 T80-6 80 m 2 5.1 k 5.1 k R32 C20 10 k C19 1 μF 2 J2 40 m 68 5 35 28 T50-6 11 9 100 k 1 μF 20 m 72 1.2 17 28 T50-6 R34 20 R19 5.1 k + 100 μF R30 270 3 Tuning Range (MHz) M1 0-1 mA 1 80 m 3.17 - 4.02 − QS1411-Thomp06 40 m 6.65 - 7.36 +8 V S5 20 m 13.04 - 14.45 D4 R3 +4 V BT1 1 k BAT46 2200 2200 R4 Decimal values of capacitance are in microfarads (µF); C21 C29 C6 C28 9 V μF μF 1 k others are in picofarads (pF); Resistances are in ohms; 47 μF 4.7 μF k=1,000, M=1,000,000.

QS1411-Thomp06

Figure 6 — Direct conversion noise receiver schematic diagram. BT1 — 9 V battery C27-80 m — 6 pF, NPO R1 — 100 kΩ, ¼ W C1, C4, C5, C18, C20, C22 — 1 µF, 50 V C27-40 m — 68 pF, NPO ceramic capacitor R2 — 1 kΩ, 10 turn potentiometer ­ceramic capacitor C27-20 m — 72 pF, NPO ceramic capacitor R3, R4 — 1 kΩ, ¼ W C2 — 12 pF, 25 V NPO ceramic capacitor D1 — MV2105 varactor diode R5, R8, R11, R14 — 2.7 kΩ, ¼ W C3 — 0.01 µF, 50 V ceramic capacitor D2, D3 — 1N5711, Schottky diode R6, R9, R12, R15 — 27 kΩ, ¼ W C6 — 47 µF 16 V electrolytic capacitor D4 — BAT46, Schottky diode R7, R10, R13, R16 — 2.4 kΩ, ¼ W C7, C11, C14, C17 — 0.0022 µF, 50 V film J1 — BNC female connector R17, R18, R19, R33 — 5.1 kΩ, ¼ W capacitor J2 — stereo female connector R20, R22 — 95.3 Ω, 1% , ¼ W C8, C10, C13, C16 — 0.047 µF, 50 V film L1-80 m — 50 µH, 105 turns #28 AWG enamel R21 — 71.5 Ω, 1% , ¼ W ­capacitor on Amidon T80-6 core R23, R25 — 61.9 Ω, 1% , ¼ W C9, C12, C15 — 0.22 µF, 50 V L1-40 m — 5 µH 35 turns #28 AWG enamel on R24 — 249 Ω, 1% , ¼ W C19, C24 — 100 µF, 16 V electrolytic capacitor Amidon T50-6 core R26, R28 — 53.6 Ω, 1% , ¼ W C21, C29 — 2200 µF, 16 V electrolytic capacitor L1-20 m — 1.2 µH 17 turns #28 AWG enamel R27 — 787 Ω, 1% , ¼ W C23, C25, C26, C28 — 4.7 µF, 25 V tantalum on Amidon T50-6 core R29 — 10 kΩ potentiometer capacitor M1 — 0 – 1 mA meter R30 — 270 Ω, ¼ W

36 November 2014 ARRL, the national association for Amateur Radio® www.arrl.org T1 +8 V U1 C7 0.0022 J1 10 dB 20 dB 30 dB NE602A R6 27 k +8 V C11 BN-43-2402 8 C4 R5 R9 27 k 0.0022 R7 2 1 4 4 S1 S2 S3 C9 R8 5t 38t 1 R10 6 #28 #28 2 5 1 μF 2.7 k 2.4 k U2A 7 2.7 k 2.4 k C5 C8 0.047 11 0.22 U2B 3 1 μF LT1014 C10 0.047 R21 R24 R27 6 7 5

71.5 249 787 C12 R20 R22 R23 R25 R26 R28 3 95.3 95.3 61.9 61.9 53.6 53.6 0.22 C14 12 C3 R12 27 k U3 C2 0.0022 C17 LM78L05 NPO 0.01 R11 R15 27 k 0.0022 R13 13 1 REG 3 C15 R14 +8 V In Out C1 14 R16 9 R1 2.7 k 2.4 k Gnd R2 U2D 8 2 1 k C13 0.047 0.22 2.7 k 2.4 k U2C C25 C26 100 k 1 μF 12 C23 C16 0.047 4.7 μF 4.7 μF MV2105 D1 10 4.7 μF

+4 V C22 5 Gnd 1N5711 7 U4B 1 μF C27, L1 Tap D3 See Chart +8 V 6 Coil D2 R35 100 μF 100 1N5711 R31 +8 V 10 k LC Chart R18 5.1 k C24 LT1014 10 2N3904 3 4 C18 Figure 7 — Noise receiver inside view. The two modules are plug-in coils for 20 and Band C7 (pF) L1 (uH) Turns AWG# Core R17 S4 R33 Q1 1 8 R29 80 meters. U4A U4C 6 50 105 28 T80-6 80 m 2 5.1 k 5.1 k R32 C20 10 k C19 1 μF 2 J2 40 m 68 5 35 28 T50-6 11 9 100 k 1 μF 20 m 72 1.2 17 28 T50-6 R34 20 R19 5.1 k + 100 μF R30 270 3 Tuning Range (MHz) M1 0-1 mA 1 80 m 3.17 - 4.02 − QS1411-Thomp06 40 m 6.65 - 7.36 +8 V S5 20 m 13.04 - 14.45 D4 R3 +4 V BT1 1 k BAT46 2200 2200 R4 Decimal values of capacitance are in microfarads (µF); C21 C29 C6 C28 9 V μF μF 1 k others are in picofarads (pF); Resistances are in ohms; 47 μF 4.7 μF k=1,000, M=1,000,000.

QS1411-Thomp06

R31 — 10 kΩ, ¼ W R32 — 100 kΩ, ¼ W R33 — 5.1kΩ, ¼ W R34 — 20 Ω, ¼ W R35 — 100 Ω, ¼ W SW1, SW2, SW3 — DPDT toggle switch SW5 — SPST toggle switch T1 — primary 5 turns #28 AWG enameled, secondary 30 turns #28 AWG enameled on Amidon BN-43-2402 core U1 — NE602 or SA602 oscillator/mixer U2 — LT1014 or equivalent quad operational U3 — LM78L05, 3 terminal 5 V ­regulator. Figure 8 — Triangulation example using in a local park. [Image source: www.scribble maps.com, copyright 2013 Google]

QST ® – Devoted entirely to Amateur Radio www.arrl.org November 2014 37 The HF Receiver zero beat between the tones heard on the Triangulating a Source An AM receiver (FM will not work) that upper and lower as you tune the You can triangulate to find the source. In covers the HF bands (or at least the band receiver. addition to your locating equipment you where the RFI occurs) is essential. The need a magnetic compass. Calibrate the shortwave receiver should have an exter- Learning to Use Your RFI compass for the magnetic declination for Detecting Equipment nal antenna jack and preferably a signal your area (see www.ngdc.noaa.gov/geo- I built a small test (see the strength indicator. You can add an S meter, mag-web/#declination). Use the following QST in Depth web page for the details) to to an inexpensive receiver by finding the steps as a guide. practice using the equipment.8 The little AGC line and amplifying it. The receiver transmitter radiates a small signal on 7159 (1) Take a reading at your house and rotate must have good sensitivity with an MDS at kHz. You can orient it for either vertical or the loop for a null. The RFI source should least –120 dBm. You can use a small trans- horizontal and practice locat- be located along the line perpendicular to ceiver like the FT-857D, FT-817, DZKit ing it. I found that the horizontally polarized the broadside of the loop. HT-7, or IC–7000, but make sure that it signal is much weaker than the vertically cannot transmit. (2) Walk about 500 feet perpendicular to polarized signal at various distances. the direction from the line where the null I built a small direct conversion receiver With the test transmitter oriented vertically, occurred and find another null. The RFI (Figure 5) with a built-in attenuator, S meter, turn your loop edgewise to the source to source will again be located along the line and battery. The circuit diagram is shown get a peak while determining if the signal perpendicular to the broadside of the loop. in Figure 6, and construction technique is is getting stronger or weaker. Orient the shown in Figure 7. The NE602 IC is used (3) The lines should cross at the source and loop broadside to get a null to determine as an oscillator and mixer. The audio output diverge beyond the source. Hold the loop in the direction of the source. Using vertical from the mixer is filtered and amplified by front of you and rotate your body back and polarization works in most cases for find- four of the in the quad package. forth until the null is well defined. Site an ing grow light RFI. Larry Benko, WØQE, Each is an active object on the landscape by looking through and I have spent some time learning search low-pass filter with 20 dB gain per stage. the small coupling loop. Point your com- techniques.9 With a little practice, you Between amplifiers, ac coupling provides pass at the object and record the reading. will become an expert at locating the test a roll-off at about 200 Hz. oscillator. The roll-off is at 3 kHz with (4) Repeat steps (2) and (3) after moving 48 dB per octave attenuation in the stop about 500 feet in the other direction from Locating RFI in Sources your house. band. Another quad operational ampli- Locating a known RF test source and locat- fier provides buffering and detection. The ing an unknown RFI source can be very (5) Go to www.scribblemaps.com, click NE602 oscillator is a varactor-tuned Hartley different. With an unknown source, the on Create Your Map Now, and type your with plug-in coils for 80, 40, and 20 meters. direction and polarization are not known. street address, city, and state in the Search The varactor diode is tuned with a 10-turn However, I have found that assuming a window. Use the ± controls on the top right potentiometer, and a meter reads the varac- vertical polarization initially is a good start. to zoom so that all of your reading points tor voltage to give an indication of the are on the map. Use the Draw Lines com- received frequency. Since the NE602 has Tracking a Source mand to draw lines from each point using a conversion gain of about 20 dB the total Use the following as a guide to tracking a the compass readings you recorded. Zoom gain is about 100 dB. The input impedance source. so the intersection of the two lines is on the of the NE602 is 1500 Ω so I used a broad- (1) If you can hear the RFI on the loop near map. Now pick a place on the map so that band transformer with a 5:1 turns ratio to your house, tune the receiver so that only a new line can be drawn perpendicular to match a 50 Ω input. An emitter follower the noise source is heard. Twist the loop one of the two lines on the map. Go to that drives a pair of low-impedance headphones. for maximum signal while holding the loop location with your loop and receiver and Also, the output of the last active filter is over your head. get another compass reading using the null rectified using an active and a peak method described in step (2). Place this line (2) Walk in the direction that the edge of the detector. I use the same meter to read the on the map just as you did previously. Due loop is pointing. If the signal gets weaker, varactor voltage and signal strength. This re- to measurement errors, these three lines walk in the opposite direction while con- ceiver has an MDS of better than –130 dBm. will not intersect in a point but will form a tinually twisting the loop for maximum triangle instead. This is the triangle of con- If you are tracking down a noise source signal. As the signal gets stronger, switch fusion. Ideally the RFI source lies within or that is on a particular frequency, transmit a in more attenuation to keep the S meter at near this triangle. carrier on that frequency with a small wire about half scale. connected to the noise receiver antenna. (6) Go to the triangle location on the map (3) Once the signal is strong, twist the loop Locate the carrier and note the varactor with your equipment and zero in on the for a null and continue to walk in the same meter reading. You should be able to tune source. in the RFI source using the varactor meter direction; now you will be looking through reading. Since this is a direct conversion the loop for a refinement in direction. Figure 8 shows the results of this process receiver, you will hear both upper and lower (4) Alternate between maximizing the sig- when it was performed using the test trans- sidebands simultaneously. The receiver nal strength and refining the direction until mitter and done in a nearby park. If you are is exactly on frequency when you hear a you think you have located the RFI source. not sure that you have compensated your magnetic compass correctly for magnetic

38 November 2014 ARRL, the national association for Amateur Radio® www.arrl.org declination, you can use Scribblemaps to Generally, it is not a good idea to do any 2www.rfiservices.com/residence.htm 3www.audacity.sourceforge.net/download/ get a vector down your street and see if it work on your neighbor’s equipment. You 4www.eeweb.com/toolbox/loop-inductance agrees with your compass. might feel comfortable applying exter- 5www.midnightscience.com/catalog5. nal filters to solve RFI problems with html#part3 Next Steps 6Chapter 22 in The ARRL Handbook, Centennial some neighbors, but use your judgment. Edition. ARRL order no. 0007, available from After you think you have located the RFI Commercial filters that might do the job your ARRL dealer, or from the ARRL Store, source, make sure you have the correct Telephone toll–free in the US 888–277–5289, or are available, but I have not tested any of 860-594-0355, 860-594-0303; www.arrl. house. I generally move across the street them.10, 11 You need a differential and com- org/shop/; [email protected]. 7 and walk up and down to make sure the mon mode current filter on the ac line that R. Shriner, WAØUZO and P. Pagel, N1FB, “A Step loop is pointing to the correct house. [Close Attenuator You Can Build,” QST, Sep 1982, p 11. can handle the high current that these light- 8www.arrl.org/qst-in-depth 9 by, say within a half separa- ing systems require. www.w0qe.com/RF_Interference/tracking_ tion, the patterns of loops and sources down_rf_interference.html 10www.cor.com may be dramatically different than far Your neighbor might not even cooperate 11www.morganmfg.us/radio-products/ac-line- away. — Ed.] If you have determined the with you to turn off the power, much less filters-protectors/ 12 time when the RFI turns on, verify from let you install filters on the system. If you do www.arrl.org/grow-light-rfi across the street that you have the correct not get any cooperation, consult the ARRL house. on how to proceed. The FCC is just begin- ning to be aware of the magnitude of this At this point, take care. If this is an indoor Tom Thompson, WØIVJ, holds an Amateur problem, so a letter from the ARRL might Extra class license. He was first licensed as growing operation, you do not know what be your best solution at this time. K5BHB in 1955 in Odessa, TX at age 14. Tom could be growing in that house. You know received a BA in psychology in 1963, and a BS in in 1969 from the your neighbors and the nature of your Conclusions University of Colorado in Boulder. He worked neighborhood better than anyone else pos- RFI on the amateur bands is a growing in electronics for the Department of Commerce at the Central Laboratory at sibly can, so use your own good judgment problem. You can build the equipment to the National Bureau of Standards (now NIST) about how to approach a neighbor, or even track down the RFI. You can also remedy and National Oceanic and Atmospheric Admin- whether you should approach the neighbor the problem in most cases if you have a istration (NOAA ) for 44 years. He has applied his Amateur Radio knowledge to several proj- at all. Approaching a total stranger about cooperative neighbor. The ARRL considers ects during his career. Now retired, Tom devotes an interference problem can result in unfor- this to be such a problem that it has devoted his time to designing and building Amateur 12 Radio equipment. He is an active member of tunate reactions. People can be dangerous, a web page to it. This web page covers the Boulder Amateur Radio Club. You can reach so approach a neighbor only if you feel the legal as well as the technical aspects of Tom at [email protected]. completely comfortable and safe. ARRL the problem. can write letters to a neighbor on your be- For updates to this article, I would like to thank Larry Benko, WØQE, half, anonymously if you wish (but if you see the QST Feedback page at for sharing his transmitter-hunting skills have a visible ham antenna, it is likely that www.arrl.org/feedback. and for his technical support with this your neighbor will have a pretty good idea article. where the complaint originated). Fixing the Problem Notes 1M. Gruber, “Light Bulbs and RFI — A Closer In most cases the problem can be fixed. Look”, QST, Sep 2013.

QST ® – Devoted entirely to Amateur Radio www.arrl.org November 2014 39