Many thanks to SWLing Post contributor, Zoltan Azary, who has written an extensive theoretical analysis of ferrite sleeve loop antennas. This article has a very academic flavor and for those who are interested in antenna design, he welcomes your comments!
Many thanks to SWLing Post contributor, Pavel Kraus, for the following guest post:
Building a Drain Pipe FSL Antenna
by Pavel Kraus
Hi, I greet all DX fans and the entire SWLing Post community! I enjoy reading reading this blog and the diversity of contributions from our authors and contributors; many thanks from me for so much useful information.
The following are the construction notes of my FSL antenna, which I designed thanks to the suggestions of GaryDeBock, and other FSL designers.
The antenna is a classic design featuring 60 ferrite rods 200x 10 mm, which are placed on a plastic sewage pipe.
Pict 3: Pipe with ferrite rods and windings
Pict 4: Pipe with ferrite rods and windings
In addition, sewer pipe sections are used for the entire antenna cover. I assume that this material can be obtained in other countries as well. Continue reading →
Many thanks to SWLing Post contributor, Gary DeBock, who shares a video of his latest Ferrite Sleeve Loop (FSL) antenna: the 3″ Baby FSL.
The new design 3 Inch (76mm) Baby FSL antenna is the smallest, most compact and lightweight of the “airport friendly” FSL’s developed here recently, but it provides a very potent inductive coupling boost for weak AM-DX signals.
This demonstration video shows its huge boost to a weak daytime DX signal from 1070-CFAX (10 kW in Victoria, BC, Canada) here in Puyallup, WA, USA:
Many thanks to SWLing Post contributor, Gary DeBock, who shares the following notes and recordings from an Ultralight DXpedition in Kona, Hawaii:
April 2017 Kona, Hawaii Ultralight DXpedition
The first long-range test of a “Frequent Flyer” FSL Antenna
By Gary DeBock, Puyallup, WA, USA April 2017
Ever since the U.K.’s Graham Maynard published his innovative article about the “Ferrite Sleeve” antenna in early 2011 an enthusiastic group of DXers and tinkerers has continually refined and upgraded the design, with most of them going in the pursuit of maximum possible gain. Monster FSL models were designed with weights of up to 38 pounds (17 kg), and considering the size, weight and subversive appearance of the typical model, the general assumption was that this new type of antenna was highly unsuitable for air travel, since it would send airport security personnel into a serious panic.
This situation continued for a full 6 years, during which the FSL antenna became a star performer in the related new niche of ocean cliff transoceanic DXing. But was there another possible application for the antenna’s compact performance advantage? What if a very lightweight, high-performing model could be designed which would not only provide a huge boost in DXing gain, but fit inside a hand-carry suitcase, and routinely pass airport security screening inspections around the world? This was a tough design challenge, but well worth the effort if successful!
Since the new antenna would need the maximum possible performance for its small, lightweight size, the use of the Russian surplus 100mm x 20mm x 3mm ferrite bars was mandatory. Every possible effort would be used to make the antenna as compact and lightweight as possible, although the choice of the highest-sensitivity 1162/46 Litz wire was critical for best performance. The PVC frame would be shrunk down to the smallest practical size. Finally, in a major experimental effort here over the winter season, the first of the new 5 inch (127mm) “Frequent Flyer” FSL’s became a reality. The finished antenna had a very non-subversive appearance, and could fit inside a custom-sized plastic tote within a hand-carry suitcase. Most importantly, it could still deliver a serious amount of inductive coupling gain– roughly similar to that provided by a 4 foot (1.22m) air core box loop, but with the advantage of somewhat lower noise reception.
Because the Russian surplus 100mm x 20mm x 3mm ferrite bars are extremely scarce (without any current supply source) only five of these original “Frequent Flyer” models would be made, although alternative models using the commonly available 140mm x 8mm ferrite rods were also designed. These antennas would be somewhat heavier and larger, but these “Baby FSL” ferrite rod models could be easily assembled from parts available on eBay, fit inside the hand-carry suitcases, and still deliver a lot of DXing performance (while routinely passing airport security screening). Finally, an economic model using the commonly available 62mm x 12mm x 4mm Russian surplus ferrite bars was also designed. This lightweight FSL can be constructed for around $65 US, and can still provide a serious DXing gain boost to a stock Ultralight radio. For want of better terms, these three classes of “Frequent Flyer” FSL antennas are called the “first class,” the “business class” and “coach class” models, with FSL sensitivity scores (ferrite length x coil diameter) of 585, 490 and 300 respectively.
From April 9-12 a Mini-DXpedition was conducted on a 6th floor oceanfront room at the Royal Kona Resort Motel in Kona, Hawaii. This was the first of many long-range DXing trips based upon the performance boost provided by the compact new antenna– which was specifically designed to easily pass through airport TSA security checkpoints. A 5 inch (127mm) “Frequent Flyer” FSL antenna was packed inside a matched-size plastic tote within a hand-carry suitcase, and breezed through TSA security screening in both the Seattle and Kona airports (without even a single question ever being asked). This was one of the “first class” Frequent Flyer models described previously, and was used to boost DX station gain on a 7.5″ loopstick C.Crane “Skywave” Ultralight radio. This combination was effective enough to track down many exotic Pacific Island stations (540, 621, 1440, etc.) at S9 levels during transmitter-site sunset skip propagation into Kona, as well as Asian TP-DX of varying strength around local sunrise.
This Kona trip was primarily designed as an anniversary celebration with my wife, so before we took off I had (somewhat reluctantly) agreed that DXing would have a secondary priority to sightseeing over the four days. Because of this there were many frequencies that could not be investigated in Kona, but I knew very well which Pacific island stations were tough challenges in both North America and Japan, and I was determined to go after them with a vengeance. 540, 621 and 1440 would all receive serious attention in Kona– not because they were great challenges in Hawaii, but because most DXers in both North America and Japan needed all possible information about them if they were to have any chance of reception at all. Besides this I was eager to try my long-range luck chasing exotic Asians around local sunrise with the innovative FSL antenna, but I knew that east-west propagation was almost totally dependent upon solar activity– and as it turned out both the A and K indexes shot up after our arrival.
Overall the Kona MW propagation to the Pacific islands was exceptional around local midnight (as expected), but the sunrise propagation was somewhat challenging for long range Asians. Perhaps the biggest success of this entire trip was the interest and excitement that the “Frequent Flyer” FSL antenna series (the major experimental project here this past winter) has inspired among DXers who routinely travel to foreign countries and other faraway venues. As I write this Craig Barnes of Wheat Ridge, Colorado is conducting his own 5 inch “Frequent Flyer” FSL- based DXpedition to Hawaii. Good luck, Craig!
[Note: a selection of audio files have been embedded in the post below, but all audio is available to download and stream via the links provided.]
531 6DL? Dalwallinu, Australia Presumably the one with the same-sounding announcer and program as the one on 630-4QN at the time (at 1547 on 4-9; see MP3 for 630-4QN), but it didn’t seem to be exactly parallel (maybe a time zone delay?)
540 2AP Apia, Western Samoa This station features a lot of Samoan music (with both male and female announcers), and dominates the frequency in Kona at night as long as it transmits. Unfortunately it doesn’t follow the listed PAL sign off time of 1000, but runs past this time routinely, which made it tough to track down an exact sign off time during my limited sessions. My guess is that it signs off sometime between 1030 and 1100. The following MP3 is of S9+ level Samoan Christian worship music at 0931 on 4-9. This overwhelming signal was one of the most awesome recorded during the entire DXpedition:
558 Radio Fiji One Suva, Fiji Somewhat of an underperformer considering its South Pacific location and (nominal) 10 kW power level. My guess is that the station has some transmitter and/ or antenna issues. Here is some fair level male speech with island music at 1001 on 4-9, which was the strongest signal it managed during the entire trip
621 3RN Melbourne, Australia This LR network station would start to fade in just when Radio Tuvalu was about to sign off (around 1000), although it never provided any serious competition for the exotic station. This MP3 was made just after Tuvalu’s sign off at 1006 on 4-9
621 Radio Tuvalu Funafuti, Tuvalu A very tough station to track down on the mainland, but certainly a “piece of cake” in Kona. Routinely has sign off at 1003 UTC, preceded by island choral music and the national anthem (sung by the same choral group). Around 0950 a female announcer begins the routine by giving a monolog news broadcast about 5 minutes long, typically followed by an island music song right before the fixed 5-minute sign off routine. The latter two features are included in the following 8 minute recording (at near S9 strength) made at 0955 on April 10
The usual female announcer with her 5 minute news broadcast at near S9 strength at 0955 prior to the sign off routine on April 11. The lady giving the correct pronunciation for “Tuvalu” is at the 11 second point
630 4QN Townsville, Australia This 50 kW station was far and away the strongest Australian signal heard throughout the trip. Unfortunately it wasn’t in the same time zone as fellow LR network stations on 531 and 558 in Western Australia, making parallel checks seem dubious. Here is a typical signal at 1543 on 4-9
657 Pyongyang BS Pyongyang, N. Korea This bizarre station was far and away the strongest Asian heard during the trip– almost like it was a South Pacific semi-local. When solar activity cooled off it could blast in with serious power, such as at 1555 on 4-9
693 UnID-TP This mystery signal showed up at 1604 on 4-9, after NHK2 (JOAB) sign off. Obviously there is male speech and some kind of backup music at various times, but I’m totally unfamiliar with stations on this frequency (except for JOAB). Any hints or suggestions? This station only showed up on 4-9; rising solar activity brought in only 690-Honolulu splatter on the other three days
1035 Newstalk ZB Wellington, NZ Received late in sunrise enhancement at 1611 on 4-12, this was a rather modest signal from the Kiwi big gun, which never seemed to get anywhere close to its Oregon cliff strength during the entire trip
1098 V7AB Radio Marshalls Majuro, Marshall Islands One of the regular Pacific island stations received in Kona, and one of the best bets for Mainland reception. The frequency has very little QRM, although Newstalk ZB could be weakly received in between the island music songs after around 0900.
Strong island music at 0955 on 4-9 (its best performance during the trip)
1440 Radio Kiribati Bairiki, Kiribati Because of its domestic frequency this obscure station is another of the toughest Pacific island stations (and countries) to receive on the Mainland, but some very helpful identity clues were discovered in Kona (where the station is a breeze to hear). The station routinely signs off at 0936 UTC each evening, with a very loud 1000 Hz audio tone right before it cuts power. The sign off routine includes station ID’s in both the local language and English around 0932 prior to the choral music national anthem, although because of her heavy accent the fact that the female announcer is talking in English might well go unnoticed. The full sign off routine is included in the following MP3, preceded by an Island music number (during which a 1440 Spanish pest attempts a run on the frequency, only to be immediately drowned out)
The American country music format can be heard prior to the 4-bong time signal.
Prior to the sign off routine this station also uses its female announcer to give a final news update (like 621-Tuvalu). This recording is of such a news update at 0925 on 4-11, with several mentions made of the American president
1566 HLAZ Jeju, S. Korea Fairly regular with its Chinese Christian service around 1530 each morning in Kona, but never at very great strength (possibly due to unfavorable solar activity). Here at 1609 on 4-9 it is the music station playing the Chinese version of “I Would Rather Have Jesus,” in a mix with the (presumed) Mainland Chinese Yanbian Jammer
1566 Yanbian, China (Presumed location, Jammer) Because of Chinese inflection this is the apparent co-channel of HLAZ in the same recording at 1609 on 4-9; it was also received at 1600 on 4-10 with Chinese 5+1 time pips (thanks to Chris Kadlec for his assessment)
Many thanks to SWLing Post contributor, Gary DeBock, who shares the following:
Daytime DX Shootout– a new-design 4.7 inch FSL antenna ($62 construction cost) goes up against the Terk Advantage AM commercial loop ($58 on eBay) in the daytime DX reception of 650-CISL (10 kW at 160 miles, in Vancouver, B.C.).
The first 20 seconds are on the Terk Advantage, and the final 24 seconds are on the new 4.7 inch FSL (using 27 of the commonly available 62mm Russian surplus ferrite bars).
Signal strength is roughly equal, but the FSL’s lower noise advantage gives it the edge.
Thank you for sharing this comparison, Gary. You’re right: the FSL provides lower noise and a more stable signal to boot. Still, I’m impressed the Terk was able to compete! In terms of commercially-produced loops, the Terk Advantage is certainly a good one.
Many thanks to SWling Post contributor, Gary DeBock, who shares the following note about his latest FSL antenna experiment:
Medium wave DX FSL antenna phasing experiment– 1593-CNR1 (Changzhou, China, in Mandarin) boosted up to strong (S9) peaks by two 5 inch “Frequent Flyer” FSL’s at 1435 UTC on February 25th in my frozen back yard in Puyallup.
Unlike other high gain MW antennas, the FSL’s can provide cumulative gain at very close inductive coupling ranges.
I’m very fortunate to live across town from my good radio hobby pal Gary DeBock. He has been responsible for the rapid growth in Ultralight radio DXing and the construction of Ferrite Sleeve Loop (FSL) antennas. Living near each other as we do, I’ve benefited a lot from his expertise and creativity in the hobby. We’ve enjoyed visiting about Ultralight radios and antennas many times over a leisurely lunch. If you’re unfamiliar with Gary’s efforts, just do a YouTube search on his name and see just a few of the many FSL antenna variations he’s built!
Gary uses PVC tubing, “Fun Noodle” foam cylinders, sections of curved foam, and rubber plumbing adapters almost exclusively as the core supporting structures for his FSLs, from small 3-inch models to 17-inch monsters. Gary certainly has perfected his own techniques with these raw materials; he’s an expert in combining them. He even makes PVC table structures to support his FSLs during Oregon coastal DXpeditions, as seen in some of his YouTube videos.
These materials work well, but over time even FSLs as small as 7 to 8 inches in diameter begin to sag and lose their perfectly circular shape. This seems to be caused by the shifting of individual segments of foam which are wrapped around a “Fun Noodle” core and center PVC tubing.
What possibilities are there for other materials in FSL antenna construction? It would be a fun challenge to build a small to medium sized FSL antenna that would have these qualities:
Maintain a circular cross-section without sagging
An appearance less like a threatening explosive and more like a commercial product
Use alternate construction methods for those not skilled with cutting & gluing PVC tubing
I began to keep my eyes open for likely candidates as I visited hardware stores, department stores, and office supply outlets. Eventually some ideas began to gel.
Here is a visual and descriptive list of what I used in this alternate design of Ferrite Sleeve Loop antenna. I won’t go into great detail about dimensions, quantities, and measurements, as other DIYers should be able to easily follow the general idea presented here. This article is mainly to get you thinking about other ways to construct a ferrite sleeve loop antenna.
The Core of the Matter
This 18-inch long, semi-rigid foam roller is six inches in diameter. It’s a workout and exercise aid which I found in the sports department of my local Walmart store. The cost was approximately $13. This one-piece foam is a perfect foundation for holding and protecting the fragile ferrite rods and keeping them in a circular arrangement; since the roller is in one piece there is nothing to shift around, or sag. When placed on this core, the final diameter of the FSL antenna is approximately seven inches.
So, what to put the antenna in? Something needs to suspend and protect the antenna as a substitute for the PVC frame previously used. This Sterilite tote box is the perfect size to hold the antenna. As shown in the photo, the dimensions are approximately 14-1/4″ X 9-5/8″ X 12-1/4″; the model number is 1896.
Early on, I decided that the flimsy “locking tabs” on the cover would not suffice for holding the relatively heavy antenna when carrying the tote by the handle. I drilled holes and attached a dozen small Nylon nuts and bolts to secure the cover. (Nylon avoids distorting the medium wave reception pattern of signals, as metal hardware could.)
An ample quantity of 200mm ferrite rods are needed, plus a air variable capacitor (preferably with a 8:1 reduction drive shaft), and Litz wire. 1162 strands/46 ga. Litz provides the most sensitivity but the coil will cover a greater width on the rods.
Gary likes to use waterproof medical tape, sticky side out, to hold the rods in place, but I like to use Gorilla brand tape, as it is extremely sticky and holds the rods better. My choice for the rod-to-coil spacing material is two turns of 1/8″ thick bubble wrap.
This is the foam core, ferrite rods, bubble spacer, and coil assembly prior to fitting in the Sterilite tote container. Before assembly to this point you’ll need to cut the foam roller to length using a serrated knife or electric carving knife. Two sturdy cable ties help hold all of the rods in place. A better alternative might be strips of 1/2″ wide Velcro straps purchased from a fabric shop or home improvement store.
Another key item to this construction method is the use of plastic drywall anchor screws. These are meant to be pushed and screwed into gypsum wallboard for sturdy attachment of bolts or picture hangers on walls. When screwed through drilled holes in the side of the Sterilite tote, they secure and suspend the foam roller/ferrite sleeve loop assembly. The density of the foam roller is sufficient to give a good grip to the drywall anchors. Eight to ten anchors per side are enough to hold the assembly in place. See the photo at the beginning of this article for a good view of this mounting method.
Every good FSL antenna design needs an official sounding manufacturer! With tongue firmly in cheek I’ve appropriated the name shown on this self-produced label. Clearly, a Ferrite Sleeve Loop antenna from Naughtabaum Ferrite Specialties Ltd. stands a better chance than most of passing through TSA checkpoints, right?
I hope this article has given you some new ideas for FSL antenna designs. There’s certainly room for improvement, including making the antenna’s ferrite rods look less intimidating…less like a bundle of dynamite! Perhaps the entire assembly can be wrapped with something that shields the rods from view, or you could use an opaque tote container rather than a clear model.
Be on the lookout for useful materials to repurpose. Trips to your local home improvement stores, office supply, and other outlets will give you further ideas on how to design your own Ferrite Sleeve Loop antenna.
Guy Atkins is a Sr. Graphic Designer for T-Mobile and lives near Seattle, Washington. He’s a regular contributor to the SWLing Post.
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