Loop antenna calculators suggest that a loop of that size can be tune from 40 to 10 mtrs with a variable capacitor of pF. See the tables and plot below. As stated above, my capacitor has a rating of 1 kV. This is sufficient for operating this loop with up to 5 watt power. The graph below shows the calculated capacitor voltage for 5 and watt input power. It shows that a 1 kV capacitor rating is sufficient for 5 watt in my loop. One important thing that the above graph shows, is the very high voltages across the capacitor at resonance.
I figured out a new way for mounting a coupling loop to the antenna. The female-female couplers for the PVC tubing are slightly tapered conical in the inside. This provides a tight connection when the tubing is fully inserted.
I used a half-round file to remove the taper. The coupler can now be slid completely onto the tubing of the mast.
It still has a good tight fit, but it can be moved up and down on the mast, and rotated by hand to find the best SWR. This mechanism works very well, even if I say so myself! Alternatively, you can cut the coupler lengthwise one side only, don't cut the coupler in half!
Thanks Dave KG0D for the tip. With a flat file, I made a notch in the outside wall of the coupler, and glued the square flange of the female BNC jack to the coupler.
It is strong and waterproof. As shown above, I initially fixed the top of the loop to the PVC mast with a plastic strap.
This didn't work very well. So I drilled a hole through the tip of the mast 9 mm drill for the 10 mm OD copper tubingand then cut a slit to the hole.
Homebrew Magnetic Loop Antenna 40m – 20m
See photo below. My clip-on method works great!
I have also replaced the coupling loop. My initial experiments were with a loop made of heavy installation wire. This is much more sturdy than the coupling loop made of heavy installation wire. The tubing is easily shaped by hand.
The shaft of the tuning capacitor can be turned without limitation. The capacitor is symmetrical, so capacitance is varied between minimum and maximum by turning the shaft degrees.
The tuning range is well over 10 MHz. Due to the high Q of the antenna, the resonance bandwidth is relative narrow.
This makes it difficult to tune accurately by hand. So I added a reduction gear to the shaft of the capacitor.The following review first appeared in the August issue of The Spectrum Monitor magazine. What can one say about portable antennas?
But, I wondered, could they provide their service easily and conveniently, even in the field? And, wow, I caught it in a bad way…! Most of the time, I simply hung the lightweight EFT from a sturdy tree branch.
But it does have one limitation: it requires that source of external support, which I worried could undermine some NPOTA activations. Eric had simplified this step by strapping a fiberglass pole antenna to his vehicle, thus avoiding either penetrating the ground or using park vegetation as a support. So as not to potentially harm sensitive park environs, nor be obliged to hop through time-consuming and expensive administrative hoops, I decided I would adopt an option similar to Eric: I would use a portable antenna that could stand on its own, thus not requiring external support from park property.
They responded by sending me a loaner unit to both use and review. After all, what better way to evaluate an antenna than by using it in the field? The W4OP loop arrived in early December, about one week before my trip. The main radiator is a sturdy, flexible-yet-rigid shielded cable. The tuning box is a heavy PVC box, and the tuning knob has an appropriate amount of brake and drives a reduction drive on the tuning capacitor.
The overall package feels well-built and of very decent quality. Since my review, however, LnR has designed a tripod mount for the W4OP loop which promises to make it much, much easier to deploy this antenna in the field. With the tripod mount, one would only need to pack a sturdy camera tripod, and then toss out the included stabilizing feet.
The loop operates best when raised off the ground and sitting on a dielectric base. Having no tripod mount at that point, I simply sat the antenna on a plastic storage bin which sat on top of a picnic table where I operated. And go I did. What truly surprised me was how many contacts I racked up in relatively short order on the twenty and forty meter bands using SSB at QRP levels.
I did take a few notes, however:. My excursion into the three river gorges of West Virginia——the Bluestone, New River and Gauley——took an amazing amount of planning for such a short trip. Firstly, I only had a limited amount of time to activate each site, yet these were rare sites and I wanted to log as many stations as possible at each site.This antenna is for the QRP amateur that is looking for a small antenna for home, backyard, portable or the park use, while it is also usable for hiking.
The primary design goal was to offer a loop at lower cost than what is available but with better performance, high quality construction and features not found on the currently available loops. The manual tuning version offers a tuning knob on the matchbox to allow you to physically tune by hand and the remote tuning offers the ability to tune via the wired handheld remote. The manual tuning version is M and the remote tuning version is M both versions are compatible with the 6m add-on accessory.
Also note that the design is water resistant with seals on the toggle switch and variable capacitor shaft. To that end, this design has almost parts, many of which require considerable machining to achieve excellent fit. In addition, the coupling loop assembly easily adjusts in height to guarantee an optimal match on all bands.
The height adjustment is accomplished by loosening the plastic thumb screw, adjusting the height and relocking the thumbscrew. While height adjustment is not mandatory when changing bands, extremely low SWR can be achieved if one takes the time to adjust the coupling loop height.
The loop comes with 4 machined, powder coated stabilizing feet that attach by custom locking thumb screws. Also standard is a no-mar clamp for affixing the antenna to a table or railing. A tripod option is now available.
The adapter mounts with the same red thumbscrews that are used for the stabilizer feet. The main tuning variable cap is dual gang and does not make use of the lossy grounding fingers.
Rather, the 2 gangs are connected in series. A reduction drive makes for easy tuning. We have just completed the 6M option. On 6M the system behaves more like a quad loop- broadbanded and gain about equal to a dipole. One full rotation of the variable cap is only KHz on 6M, making tuning extremely simple. Maximum radiation is at right angles to the loop as would be expected with a larger circumference loop in terms of wavelength. A unique tuning scale on the front of the enclosure makes for getting the loop tuned to each band extremely easy.
Calculators such as Pacific66 may have limited use in specifying an L or C for a loop, but cannot possibly predict real world efficiency because it does not ask for the information required for that calculation.
The AA5TB calculator is better but can be confusing to the uninformed, because the -3dB bandwidth an easily measurable quantity in the calculator is a dependent variable and loss resistance is an independent variable. As an example, the efficiency figures quoted on the Chameleon loop site are grossly optimistic because they apparently based on their SWR curves put zero 0 into the Added Loss Resistance field.
The most comprehensive calculator would be from Owen Duffy at:. In the case of the Chameleon loop, we used their SWR figures. There may be a bit of differential in the Chameleon results as they say the loop was varied in height above ground during SWR data taking.
We are all about optimal efficiency. Coupling expert design, high quality components and precision manufacturing, we feel our Loops consistently outperform other manufacturers.
LNR Precision Inc. Skip to content. Random Product.Search this site. Sub Pages Start Page. Buying A New Radio. Codar AT5. Early Voice Recordings. G3XBM History. Homemade Recordings. Mental Health Links. MF and LF. Nanowaves - Optical Communications. Network Radio.
Some External Links. Stroke Update. Virtual amateur radio. Recent site activity. Going Deeper At the bottom of each page in the sidebar you will find a list of further sub-pages to be explored. Clicking on these you will find a lot more to explore! These antennas are well known and work well, but for some reason I'd never used one apart from on and kHz where I used an 80m square magnetic loop made from standard PVC covered wire. For HF I used a 2m length of 6mm diameter copper pipe formed into a near circle as the low loss inductor.
To tune the antenna I tried a a short length of coax as a capacitor, trimming it to resonance on the 10m WSPR frequency, b a short length of mains cable, again as a fixed tuned capacitor, c a tunable pF air spaced capacitor, and d a small Jackson C airspaced variable capacitor with a small pF trimmer in parallel.
Using 5W or less, one can get away with easier solutions for the capacitor: with higher power there can be kV across it and breakdown can be a problem. Not so with QRP. This was with the antenna just taped to the back of the wooden chair in the shack in the upstairs bedroom! On 28MHz the best report so far has been from Israel at around km using 2. Ideal for the quieter solar years where having a continuous TX and RX on the band will help to spot fleeting openings that may occur.I chose to make a sling harness which goes over the shoulder, terminating with a carabiner.
Then a 2m length of Edelrid climbing rope, between myself and the pulk. The set up looks something like this. The FTnd deployed out of a pelican case, the antenna on a tripod. Laptop also deployed from the pelicase, but that is overkill for RaDAR. It might not be completely obvious, but using the pulk, I really can carry an enormous amount of gear, without any effort. In the next image, I packed the and everything into a small tactical backpack. Through the backpack in the skipulk, which made carrying and deployment very easy.ver.2.0 UltraLight Magnetic Loop - great QRP Antenna
I did have one hard lesson. Not operating from indoors, in the forest or any place where wind is no issue, the small tripod is excellent. Operating exposed near the sea is always going to be windy.
So the magnetic loop on the small tripod fell over a few times. More about the skipulk. The pulk also gives me the ability to carry multiple antenna systems. Anyway you get the idea.
Digital and phone. Normally during radar challenges, I like to work digital modes. This really helps my qrp signal get out and about around the world. Single sideband is really the worst case scenario for the radio and antenna combination. It also prevents me from having to take off my gloves and get myself cold, when I am exposed as I normally am. I hear a lot of rumors about the not actually working in cold weather. I routinely operate the at temperatures down to minus 20c.
If you continue to use this site we will assume that you are happy with it.Were you forced to remove your antenna from the roof of an apartment house? Have you no chance to hang up a long-wire antenna?
The oldest and best sold two-turn magnetic loop antenna developed by OK2ER. Its wide-band function achieved by a patented design is just excellent. No other MLA is available on the world market that can offer such wide-band coverage. This antenna is designed for QRP operation, 10 W at 3. Antennas are delivered with an individually filed test protocol. As a semi-kit, not assembled, this antenna is delivered without a test protocol. The second oldest and best sold four-turn magnetic loop antenna developed by OK2ER.
It is destined for a compromising operation at the lowest short-wave amateur bands 1. Adding the next two bands 5. Band switching is done manually. The antenna is tuned by a remotely controlled high-voltage variable capacitor using a DC motor with a flexible coupling. There is no similar antenna capable of 1. Antenna is delivered with an individually filed test protocol.
This antenna have been testing at 1. The MLA-B needs only some 5 sq. For this reason is this antenna is quite acceptable for use at and 80 meter bands as stacionar antenna in city QTH or for lower-level expeditions. It is destined for 3. It is also usable at 5. The antenna is remotely tuned by a DC motor with a flexible coupling to the high-voltage variable capacitor. The advantage is an easy and fast assebly, from unpacking to the full operation in minutes.
Antennas are delivered with individually filed test protocols. MLA-C v. The advantage is an easy and fast assebly, from unpacking to operation a dozen minutes, best in two persons As it can be completely disassembled, it can be assembled anywhere the MLA-C could not be delivered.An ongoing exploration and experiment about the use of small magnetic loop antennas for QRP low power Amateur Radio.
Not a member? You should Sign Up. Already have an account? Log In. To make the experience fit your profile, pick a username and tell us what interests you. We found and based on your interests. Choose more interests. Living and operating from a "challenging" QTH does not mean that one cannot take part in Amateur Radio. In my case our garden is too small for huge towers and long wires and there is a hill right behind the house anyway.
Instead of feeling discouraged I took this as a challenge to get QRV with minimum power, occupying minimal space and - last but not least - have the whole thing sitting indoors.
The antennas I am using are small magnetic loop antennas. Their main characteristic is the use of the magnetic component of the electromagnetic field for both transmission and reception.
The widely used Yagi TV aerial antenna for example uses the electric field component. Please be aware that even with only a few Watts transmit power the voltage at the tuning capacitor can reach several hundred Volts or even more with currents up to a few Amperes. I do not recommend this project to people with a cardiac pacemaker or ICD. Otherwise the FTND can be connected to the feed loop as well. Two brass sheets act as air gap tuning capacitor.
View all 7 components. There have been numerous reports about Raspberry Pis crashing when using the WsprryPi software. My Raspberry Pi Zero was no exception when feeding the magnetic loop antenna. These crashes usually happen right at the beginning of a transmit cycle and network connectivity is completely lost so the Pi needs a hard reset.
Oddly on some days the system crashed all the time and on other days it worked like a charm. I found the source for these crashes thanks to someone on the WsprryPi issue tracker suggesting RFI Radio Frequency Interference as one possible cause for this problem:.
As this is the "hot" part of the loop with fairly high electric fields, RF was creeping in the lead leading to these crashes.
A review of the W4OP portable magnetic loop antenna
Keeping the cable away from the loop solved the problem. And maybe it's not a bad idea to put a ferrite choke on the cable. Yes, a Raspberry PI can act as a transmitter almost without any additional hardware except an antenna. The main problem is that this output signal is a square wave. This means loads of harmonics and other unwanted signals that a good radio amateur does not want to transmit. It would not only be bad conduct but violate spectrum regulations in most countries.