OM0ET | UltraLight Magnetic Loop antenna
The UltraLight Magnetic Loop MC-20 is a 7-band(+CB) Ham radio QRP antenna based on very popular Ver.4 with the same dimensions, but completely new tuner. The antenna has a foldable construction, designed for easy transfer in the special designed cardboard box or any 17" laptop bag. This antenna was designed for 40m to 10m bands + CB. The main loop is almost 1m in diameter and antenna itself is almost 1,3m tall(without tripod - is not included). Foldable boom is made of a solid 25mm PVC tube.
New dual gang Air Variable Capacitor is connected in serial fashion because of the very low resistance in a whole antenna circuit what is very important to secure a high Q and high efficiency of my loops.
Combination of a new variable capacitor and custom made PCB inside the box improves the frequency range of this Magloop antenna from previous (Ver.4 from 7MHz - 28.900MHz) to 7MHz-30MHz.
Its small dimensions makes this antenna a perfect buddy for your vacation, trip to the nature or just working QSO's right from your living room, balcony or garden by enjoying your coffee and having relax at any time. Due to a wide frequency range, quiet reception and selectivity is this Magloop great solution also for SWL's (Short wave radio listeners).
For my measurements I use the Mini1300 Antenna Analyser and antennas were tested with the XIEGU X5105 or mcHF HF SDR Transceivers. The SWR on all bands is better than. 1:1.5. Automatic tuner is not required.
Weight of the antenna is only approx. 1kg and with the carboard box 2kg. Band switch or counterpoise is not required at all.
It's a QRP antenna for RF power 0 to 20W (max. 10W CW,FT8/DIGI / 15-20W SSB) depends on the desired band.
Please do not exceed the max. power limit of 20W! It may cause a fire on the capacitor plates,
permanent damage of capacitor or failure of the PA in your transceiver!
HF Small Transmitting Loop Safety Compliance Distances FCC, ICNIRP, and Canadian Guidelines
The Main Loop system
The Main Loop is made of an excellent quality coaxial cable BELDEN H1000 (made in Holland) which is 10,3mm thick in outer diameter. Inner conductor is made of solid Bare Copper 2,62mm thick core which allows to hold the perfect circular shape of the loop without deformation of gravity. In all my Magloops is connected only the inner core. Outer shield is disconnected for improve the SWR results and less sensitivity of nearby objects.
In the middle of the Main Loop lenght is located the mark (heatshrink) which inform you where the Loop have to be inserted in to a Plastic Holder on top of the Magloop Antenna Boom.
The Coupling system
Quick installation of my Magloops is my priority and therefore I made the small coupling loop with a BNC socket. The clamp on the Coupling box allows you to attach the small loop on antenna boom in a second.
Great for Experimentators
The "small" coupling loop is made of 3,4mm thick solid copper wire attached with a mounting eyes on both ends, which allows you anytime to do your own modifications or easy exchange to the other experimental loops.
The heart of all the Magloop Antennas is a Variable Capacitor, which is located in the Tuner box. In my antennas was used the enclosure made of ABS plastic with sealing against the rain shower or dust (but the Tuner box it self is not fully waterproof). The Main Loop is connected to the Tuner box with two SO-239 connectors (sockets) and two PL-259 on Main Loop with goldened center poles, which improves connection and reduce loses. Tuner box is also equipped with two clamps for very quick installation on the antenna boom.
New variable capacitor used in my Magloops is connected in serial fashion due to a minimal loses in the antenna circuit, which has three positive advantages:
1. improves Q-value and efficiency of the Antenna on all bands
2. allowes to work with higher power up to 20W
3. antenna will not change the SWR value when human hand is close to the tuning knob and is easier and faster to final tune
For more comfortable tuning is this Capacitor equipped with the 1:3 gear reduction and larger plastic knob. In the MC-20 is for the first time used a high quality custom made PCB which includes a preparation for the RF meter modul, which could indicate in the future an antenna resonance while tuning. Lack of the SWR meter should not be then so critical problem.
New flexible clamps for easy and firm mounting of components on the antenna boom. For a firm grip, it is necessary to tighten the clamp to two clicks. Releasing the clamp is easy (see picture), pull both rings apart from each other to the sides:
The Mounting adapter for a Camera tripods
With help of my friend Lev - OK2PLL we have designed and made this CNC machined 1/4' camera tripod mounting adapter. Is suitable for any standard camera tripods. With this adapter is very easy to mount entire antenna on the tripod and also very comfortable 360 degree rotating this antenna on it.
The Feed line
Connection between the Antenna and Transceiver is done by the very soft and flexible Coaxial cable HELUKABEL C/U RG58 with waterproof BNC male (clamp system) connector. Usable lenght of this cable 4,5m is sufficient to operate in the safe zone of 2 or 4m away from the Magloop when we are transmitting (If we use max. 20W). HF Small Transmitting Loop Safety Compliance Distances FCC, ICNIRP, and Canadian Guidelines read here.
On the Feed line coaxial cable and on the Main Loop coaxial cable I use waterproof BNC and PL-259 connectors with the clamp system.
Wide frequency range
Up to 7 bands + CB with only one small antenna (40m/30m/20m/17m/15m/12m/CB/10m). All the bands are countinuously tunable for the best SWR on all frequencies in this range. In addition to HAM you can count also with the AM broadcast, Air, Maritime mobile or Military service shortwave bands plus quiet reception and selectivity makes this antenna suitable also for SWL's (radio listeners). Shortwave Radio Listeners will welcome continuous antenna tune across the SW range from 6.5 to 30MHz. Here are the minimum and maximum frequency range SWR charts:
Portable Antenna to most as possible
The priority of my Magnetic Loop Antennas design is to be portable as much as it gets. And therefore is this small multiband antenna completely foldable and composed of a many dismountable or exchangable parts. Antenna fit's in to a bag for 17" Laptops. The longest part is only 477mm long. Complete setup of this antenna will take you only 2 min. on the tripod. Note: laptop bag is not included
!! NEW PACKAGING !!
The UltraLight Magloop antenna is now sent with a new cardboard box specially designed for this product, to ensure safe transport, easy storage and multiple reuse the box with your Magloop antenna.
The box is equipped with a practical handle, which allows it to be easily carried as a briefcase. The dimensions of the box are 430mm x 410mm x 145mm.
Fixations of technical foams are tailored according to our precise requirements and therefore perfectly protect the antenna parts against bumping and scratching during the handling. We use a foam material PE 30kg/m3 because of it's versatility and the possibility of combining with different materials. Therefore is widely used as a transport packaging, separators, internal fixings, etc.
PE foam properties:
- excellent absorption of bumps and shocks
- possibility of multiple reuse
- a combination with other materials
- moisture resistance
The Tripod recommended to buy
This is an affordable tripod that I tested and I recommend using it with the MC-20 antenna for its features. I use it myself too. The mounting head is fixed, without movable joints. This ensures that the antenna is stably fixed in a vertical position without tilting. Click on the pictures to to zoom in and see the dimensions and tripod features.
WARNING! In case of strong wind, the stand must be loaded or otherwise fixed to prevent the antenna with the stand from tipping over. In this case, the antenna may be damaged.
To purchase this product click on this link:
Large loop diameter: approx. 1m ( coax lenght is 3000 mm )
Small loop diameter: approx. 23cm ( wire lenght is 720 mm )
Capacitor: air type 380+320pF with a small gearbox reduction 1:4 - used in split stator fashion
Large loop is made of the Belden Venlo H1000 high quality microwave coaxial cable
Small loop is made of 3,4mm thick solid copper wire (black PVC isolation)
The foldable boom is made of 3 pieces, 25mm in diameter, PVC tubes
Total weight: +/- 1kg
How to use this antenna
Never transmit in to the antenna before you don't listen the background noise peak while tuning, it may demage your transmitter!
1. Set the desired frequency on your transceiver and rotate antenna knob to resonant frequency until you will listen the noise peak.
2. After you listen the noise peak start measure the SWR in carrier mode (FM/AM) with 5 - 15W and carefuly tune antenna for the best value ( ideally SWR 1:1,1 or 1:1,5 ).
3. Now switch to desired modulation mode and you can transmitting.
4. If you move from this frequency away you will need tune the antenna again (point 1-3).
Some close metalic objects may disturb SWR, if so you have to place antenna more away from this object or rotate the main loop to the another direction.
The elevation will improve efficiency of your magnetic loop antenna. Higher - better. Please consider the hight of your tripod stand.
This antenna doesn't need the counterpoise.
This Magnetic Loop is a wideband tunable antenna that can be used continuously from 7MHz to 31.7MHz. But that also doesn't mean that you tune it somewhere in the middle of the band and will fully tune to SWR by 2. NO! because the laws of physics cause this antenna to transmit in a narrow frequency spectrum - a few kHz, let's say 10kHz (5kHz on each side). After this de-tuning, the SWR is no longer usable and the antenna needs to be re-tuned. If it is only used for reception, then there is no need to fine-tune it and you just need to leave it tuned in the middle of the band. It may be a little annoying sometimes, but a little practice can do it. On the other hand, it is also a great advantage, as such an antenna behaves like a natural bandpass for the receiver input. Interference from nearby strong stations thus no longer overwhelms the receiver, and also in the case of using a poor quality transmitter, the antenna naturally attenuate the parasitic harmonic products. It is necessary to note a very important thing! The magnetic loop has the highest efficiency when is tuned to the best possible SWR! It is never recommended to use an additional antenna tuner as compensation if you are transmitting on an untuned frequency!
I wish you have fun with QRP activities and this antenna!
YouTube videos about this UltraLight Magnetic Loop Antenna: