The HF Homer uses soft copper tubing securely bolted to a plastic box, mounted on a PVC pipe mast.
Build the HF Homer
by Joe Moell KØOV
Updated from my Homing In columns in the April and May 1990 issues of 73 Magazine
Updated from my Homing In columns in the April and May 1990 issues of 73 Magazine
Some years ago, I conducted a mini-survey to check our preparedness to hunt down jamming on the HF bands. I started down the ARRL Official Observers list for a section of southern California. (This was before the OO program became the Volunteer Monitor Program.) I called those who were listed as being involved in HF monitoring and asked each one if he (no YLs were on the list then) was equipped to perform mobile radio direction finding (RDF) on any HF band. After getting three quarters of the way through the list without finding anyone who could do it, I gave up in dismay.
Most Volunteer Monitors are very good at looking up a callsign and sending out a notice to a Novice with key clicks, but they can't go out and find a non-identifying jammer or a noisy power line on the DX bands. There are plenty of mobile foxhunters to find repeater jammers on VHF-FM, but very few hams have equipped their vehicles for HF DF, or "huff-duff," as the military folks used to call it.
Unless one of the members lives next door to the jammer, a team of only fixed stations cannot make a positive identification. Eventually, someone is going to have to go mobile to track down the exact location and document the case. The more mobiles there are in the field, the sooner it will happen.
Mobiles don't need pinpoint accuracy in their RDF indications, because they simply "home in" in the signal, following the line of bearing to the target. Minor system or site errors are no problem are long as you keep moving along. If you can go mobile with your HF transceiver in the family car, you are already halfway to the goal of becoming a mobile HF T-hunter. All you need is an antenna and an RF attenuator.
Fortunately, it turns out that on the HF bands a simple RDF loop is very effective for closing in on groundwave signals. By adding this capability to your HF mobile installation, you can track down interference problems in your area. Besides jammers, you can locate other QRM sources such as noisy power lines and cable TV leakage.
I can hear some of the veteran VHF T-hunters scoffing at the idea of hunting jammers with an old-fashioned loop. It's true that loops are not competitive with beams and dopplers on two meter FM T-hunts. But on the HF bands, dopplers and beams are out of the question for mobiles.
There are more sophisticated mobile RDF setups for the HF bands, but how many hams are willing to spend the time and dollars to implement them just to hunt an occasional jammer? The HF Homer, on the other hand, is so simple that just about any HF mobile enthusiast can build and use it. When interference comes on, it's too late to start the project, so get the parts together and start building now.
I adapted the HF Homer from a design used by the US Army in the 1950s. The hand-held AT-340/PRC RDF Homing Antenna covered 20 to 39 MHz and worked with field portable receivers that were predecessors of the "manpacks" of today. Surplus AT-340's are hard to find now, because they were snapped up by hams back when ten meter foxhunts were popular.
The HF Homer gives the same performance and ease of use as the Army loop, but it has a lower frequency range (18 to 30 MHz) and it's mast-mounted for mobile hunting. The loop is 13-1/2 inches in diameter on a mast two feet above the van roof to minimize proximity effects. The SENSE mode was selected by a toggle switch on the AT-340 case, but it is relay-activated from inside the vehicle in my design.
The sharpest bearing indications are in the NORMAL mode, which provides a figure-8 antenna pattern. There are two broad response peaks and two very sharp nulls in a 360 degree rotation of the antenna, indicated on the receiver's S-meter as you turn the mast.
Peak response occurs when the incoming signal is in the plane of the loop, and the nulls occur when the signal is "through the loop." Usually, you'll use the nulls instead of the peaks to determine the line of bearing. This gives two possible directions for the incoming signal, 180 degrees apart.
Closing S1 picks up relay K1 and puts the HF Homer in the SENSE mode, changing the antenna response pattern to favor one of the two peaks. The purpose of the SENSE mode is to resolve the 180 degree ambiguity of the NORMAL mode peaks and nulls. Once you have practiced a bit, you can take a bearing much faster than I can explain how to do it. You'll see how it's done later, in the section on adjustment.
If you have experimented with HF loops in the past, you'll notice some differences between the HF Homer and typical ham designs. This is not a shielded loop. Many loops have a shield to suppress the "antenna effect" and couple only to the magnetic component of the incoming signal. Such designs require a separate vertical sense antenna to resolve the 180 degree ambiguity.
The HF Homer takes advantage of the antenna effect to resolve the ambiguity in the SENSE mode by properly combining the electrical and magnetic field pickup. In the NORMAL mode, the antenna effect is cancelled by properly configuring the L2/L3 coupling coils. This eliminates the shield and the separate whip, simplifying construction.
There are no exotic parts in the HF Homer. You should be able to assemble it in a evening or two. I made the loop from 1/4-inch O.D. soft copper tubing. You will find it in the plumbing section of your local do-it-yourself store, intended for supplying water to refrigerator icemakers. It comes in a coil, so you won't have to form it into a circle. Cut the tubing to 39 inches.
Use solder lugs and 10-32 hardware to mount the tubing on the 4-3/4 X 2-1/2 X 1-1/2 inch plastic case. I soldered the tubing and lugs directly to the bolts, to eliminate the possibility of bolts working loose and making an intermittent connection. (Intermittents were a problem with the Army's collapsible version.) Solder the bolt and lug to the tubing before fastening it on the box, so you don't melt the plastic.
The mast is 3/4-inch Schedule 40 PVC pipe. The coax and relay control signal leads go down the inside of the pipe. Mount a 3/4-inch slip-type PVC pipe cap to the box using 6-32 hardware. Match-drill the pipe cap and box for the wires.
Bolt a 1 by 2 inch piece of unclad perf board in the box to terminate the external leads and to mount K1 and R1. I used a subminiature relay with a 5 volt coil. That allows me to use the unit on foot with a "sniffer" that has a 6 volt battery supply. R2 drops the voltage when I use the vehicle electrical system. If you only intend to use the loop in the vehicle, you can substitute a relay with a 12-volt coil and eliminate R2.
Tuning capacitor C1, shown in the middle of the box, must be an air variable type. Small air variables are becoming hard to find. Try your local surplus emporium or electronic swap meet. Dan's Small Parts and Kits at (801) 515-6373 has a nice Millen 100 pF air variable with a long shaft. Measure your capacitor before mounting it, as it might be too bit to fit on the box side wall.
Wind L2 on a 1/2-inch diameter form, with the 25 turns spaced for a coil length of two inches. I used rod stock from a local plastics supplier for the form. The tap is 8 turns from the right end. L3 is a length of solid AWG 22 insulated wire formed into a single-turn link over L2. Its leads are lightly twisted as they go over to K1 on the perf board.
Leave a little slack so the link can be moved along the length of L2. You will find the exact position of L3 during alignment. My link is over the tenth turn from the left end, held in place with a dab of hot glue. Put yours there for starters.
You can hold the loop out a car window by hand to take bearings, but I don't recommend it. There will be random interaction with the vehicle, causing errors. You will have a hard time getting bearings while driving. And imagine the sore muscles and wet, cold fingers you'll get on a rainy night outing. So do the job right and make some sort of rotating mount for the mast.
Put a 360 degree compass indicator on the mast for accurate triangulation. Set the pointer to indicate one of the two nulls. It's hard to tell when you are looking exactly through the loop, so set the mast to indicate 90 or 270 degrees relative to vehicle heading and visually line up the loop so the plane is exactly to the front and rear. Use bolts or glue at all PVC slip joints so nothing twists.
Before you go out to clean up the bands, spend some time in your driveway setting up your HF Homer and getting used to its operation. Besides the loop, you will need a well-shielded receiver and attenuation system, all securely mounted in the vehicle for convenience and safety.
A stable test signal for each band is a great help in alignment. A QRP milliwatt rig is fine, or perhaps you have an old VFO or signal generator. I use a TTL oscillator I built to check crystals for activity. Start the alignment on 15 meters. Be sure the vehicle is in a clear area, away from overhead wires.
First, tune the loop to resonance. With S1 in the NORMAL position (relay open) and the loop plane in the direction of the test signal, tune C2 for maximum S-meter reading. Locate the receiver so that you can see the S-meter when tuning, because you won't be able to find the exact peak by ear. Use your attenuator to knock down the signal if the S-meter reads over S9. Most S-meters are less sensitive to small changes when readings are in the upper scale region.
As you rotate the loop in the NORMAL mode, there should be two deep nulls perpendicular to the plane of the loop and exactly 180 degrees apart. One of these nulls should be in the direction of your mast pointer. Repeat this check on 10, 12, 15 and 17 meters.
If the NORMAL mode nulls are not exactly 180 degrees apart or are very shallow, the loop isn't well balanced. Experiment with the location of link L3 on coil L2 for optimum performance on the four bands.
Next, check SENSE mode operation. Close S1 and turn the mast +90 and -90 degrees from the pointer null. One or the other directions should give stronger S-meter readings on the test signal, depending on how you connected L2/L3 leads. Mark the side of the mast to indicate the strongest peak side. Check the SENSE mode on all four bands. You will probably get best front-to-back sense indications on 15 meters, because that band is closest to design center frequency, but indications will be good enough to use on all bands.
The photo shows the loop mounted on the van, complete with compass indicator and pointer on the mast. When it was taken, I had not painted the loop and upper mast a dark color, as I usually do with such antennas to make them inconspicuous for hunting at night.
You can use the HF Homer with most 12 volt DC receivers, but some will work better than others. The receiver must be stable and well shielded. Plastic case portables such as the Sony 2001-2003 series leak in too much RF and have excessive synthesizer noise, not to mention their lack of an S-meter.
Transceivers by the Japanese "big three" ham equipment manufacturers usually work fine, but make sure that the S-meter is sensitive and fast responding. Fast AGC time delay should be selectable in all modes. The ability to turn off AGC may prove helpful.
As you get into the neighborhood of the signal you're hunting, the S-meter will read above S9, where the meter scale compresses on most rigs. This makes it harder to use the SENSE mode. Turning down the RF gain control usually won't help. That typically causes the S-meter to stop working altogether. Only a handful of radios have RF gain controls that don't adversely affect S-meter function.
While a few receivers have internal RF attenuators, most require an external step attenuator box, such as the one shown between the mast and the transceiver in the photo. Construction plans are in THRDFS and recent editions of The ARRL Handbook. The amount of attenuation switched in gives a clue of how close you are getting.
Nearby power lines and other large objects can distort the pattern of RDF loops. Keep moving and take frequent bearings to average out these effects. Be sure not to get confused into hunting local noise instead of the target signal.
Remember that vertical loops give shallow nulls on skip signals. You will probably get no null at all on Near Vertical Incidence Skywave (NVIS) signals. Test your HF Homer only on local groundwave signals. You're not going to hunt skip signals in your mobile anyway.
Sometimes when you rotate the mast to null a local signal, the received audio will begin to "echo" or get "watery." That is due to backscatter, the signal bouncing back via skywave from some distant point. Backscatter usually is not a problem because you can determine the correct null direction by observing the quality of the audio.
Do not transmit into the loop or attenuator box. Disconnect your mike in case you forget. You may want to add a coax switch to select between the loop and your regular HF mobile antenna.
The popularity of twenty meters means that it gets its share of malicious QRM. You can move the HF Homer to 20 by adding capacitance across C1 to reduce the resonant frequency. Add 82 picrofarads to cover the 17 and 20 meter bands with tuning capacitor C2. The front-to-back ratio in the SENSE mode is not as good on 20 as on 15, but normal mode nulls are very deep.
Adding still more capacitance to get to 40 meters isn't practical, because the loop signal pickup is too small on 40 relative to the antenna effect. I have experimented with larger loops to get around that problem. An 81-inch circumference loop of the same 1/4-inch O.D. copper tubing covers 40 with 330 picofarads added across C1. NORMAL mode nulls are a bit more shallow than with the 39-inch loop. In the SENSE mode, one null is deepened, and the opposite null disappears, creating a cardioid (heart-shaped) pattern. Unfortunately, the larger loop on the HF Homer box is too unwieldy for mobile in motion without some additional mechanical support.
Now you are all set to help rid the DX bands of illegal antics and electronic pollution. A final request: Please don't be a Lone Ranger. Get in contact with the ARRL Volunteer Monitoring Program and your Local Interference Committee. Working with them protects you and multiplies your effectiveness.
Text and photos © 1998 and 2025 Joseph D. Moell. All rights reserved.
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This page updated 12 July 2025