QRZ Forums. Tags: antenna hamradioconcepts icom dstar kj4yzi loop antenna mfj loop receive loop antenna review yaesu fusion. So i finally got around to checking this thing out. A powered receive loop that covers khz to 30mhz, and has the same characteristics as their magnetic loop antenna, but no tuning required.
Not designed for transmitting, however if you have an HF radio capable of transmitting on antenna A and receiving on antenna B, then you can open up your ears and null out the noise.
You can see in this video how it eliminates the high level of interference from power and gives more received signal. You answered some questions of mine on w and a wire on FB, today. I want to ask others on this Any guesses? I'd like to buy one of these, but shipping here, to Korea, would likely be pretty bad, as they are in a big box. Have been thinking of building and trying a simple flag antenna out, as soon as I can get around to finding the torrid, and resistor I need, here in Seoul.
The loop I use gives me anywhere from S units in noise reduction and an S-Unit increase in signal over my doublet, depending on how it is orientated to the primary noise source. AF6LJMay 18, AF6LJ likes this. KK5JYMay 18, Last edited: May 18, You must log in or sign up to reply here. Show Ignored Content. Share This Page.
Your name or email address: Password: Forgot your password?Revised Dec 22, corrected text errors and reworded some areas to make clearer. Related pages coaxial cable and especially skin depth.
Please read the Radiation and Fields page. Small loops are often referred to as "magnetic radiators". Folklore claims a small "shielded" loop antenna behaves like an electrical sieve or filter, sorting "good magnetic signals" from "bad electrical noise".
Nothing is further from the truth! At relatively small distances a small magnetic loop is more sensitive to electric fields than a small electric field probe. The ratio of electric to magnetic field sensitivity is sometimes called or can be described as the "field impedance". In the near field region, a high field impedance indicates a dominant electric field. A low field impedance indicate has a dominant magnetic field. The field impedance actually varies with distance when close to the antenna, and it can also vary with direction or angle.
Although fields have different ratios close to the antenna, at distances of about one wavelength the field impedances of small antennas are virtually indistinguishable from each other. It would not include wide-spaced stacked beam antennas, or antenna physically significantly more than a wavelength in widest dimension. Once we understand fields near an antenna, we might picture our antennas differently. We often find antennas don't respond to signals and noise like we thought.
Best of all, we won't be as susceptible to the "noise" caused by rumors and folklore! Very close to a small loop antenna but not necessarily near the open ends of the small loop where the tuning capacitor is the magnetic field dominates. Current is essentially uniform all around the loop circumference, while voltage has a nearly straight-line increase as we move to the tuning capacitor area. Since most of the loop area has uniform current and only a small concentrated area has the highest voltage, the magnetic field clearly dominates over most of the loop area.
Magnetic fields are effects derived from the actual moving of charges current flow. The magnetic effect is related to current, and if it is proportionally large compared to voltage or capacitive coupling the field is described as having a " low " impedance. This is similar to the description used in circuits, where a system with high current and low voltage is said to have "low impedance".Ragchewing on 75 meters with the locals several hundred miles can be a lot of fun.
The summer months, however, with their high static and noise levels, can be brutal on the ears. I have found that a small receive-only loop antenna can be used to make the situation much more tolerable. This page describes an easy-to-build loop that I have built several times for myself and friends.
We tend to congregate on 3. The perimeter length of the loop is 12 feet, and it is in a diamond shape. It is approximately 4 feet wide and 5 feet tall.
The Small Vertical Loop Antenna for HF Reception
It is certainly possible to use the loop in the shack, although I find the performance to be better when the loop is outside. A er up against the garage Introduction Design Parts List Assembly Checkout and Adjustment On-the-Air Introduction In order to improve reception, it is necessary to improve the signal to noise ratio. Common 80 meter antennas such as low dipoles, inverted Vees, or verticals, suffer on receive because they have a nearly omnidirectional response pattern.K9AY Receiving loop antenna for top band.
While the desired signal is arriving from one direction, noise can arrive from all directions. A loop antenna such as the er improves this situation because it has broadside nulls at very low wave angles. Most radio signals within several hundred miles tend to arrive at much higher wave angles above 45 degreesand at those angles, the loop response is nearly omnidirectional. Often times, noise is relatively local, and arrives at a low angle.
The loop can be oriented to reduce the reception of this noise. Less noise, same signal, improved signal to noise ratio. Technically, the er is a single-turn shielded loop antenna.
Some sources state that the shielded nature of the loop provides additional noise immunity by shorting the noisy electric field to ground while responding to the magnetic field. Because of that belief, this type of antenna is also called a magnetic loop. I'm not sure if I believe that particular theory, but in any case, the loop can improve reception of short-distance radio signals. In my experience, this type of antenna is most useful for short-distance work in the summer months.
I do not consider it to be a good DX antenna, although it has been used for DX by some. When winter comes, and 80 meter noise tends to drop naturally, the advantage of the loop often disappears. Please note that the er is a receive-only antenna. In order to use it, it is almost a necessity that your radio provides a separate receive antenna input jack. This antenna, like most receiving antennas, will have very low output compared to transmit antennas.
In some cases, a preamp can be useful.Noise and common mode noise. Power line and other noise sources. Note: The top of this page has links to various receiving antennas such as Beverage, "magnetic" loop, and vertical low-noise DX receiving antennas.
This area deals primarily with low noise antennas, and discusses effect of antenna directivity on weak-signal reception. My local wintertime Hz BW noise, compared to a sample of signals, on one night was:. This chart also shows why a direct distance-corrected multiplier does not work! Every hop adds significant attenuation, as does a signal travelling near the earth's magnetic poles.
This is over times difference in power levels at my receiver. This illustrates how important the combination of antennas, location, and propagation W4ZV is one sharp hop away are, rather than power, location, distance, or antennas alone. Differences between signals from the same area can be quite pronounced. Before talking about receiving antennas for lower frequencies, it is important to understand a few basics.
We all understand the primary reason we use special receiving antenna systems is to improve signal-to-noise ratio. On the surface this sounds like the same reason we use directional transmitting antennas, but there are some very important differences between transmitting and receiving applications. It uses directivity, with results based on noise being evenly distributed in all directions.
These rankings are most accurate in the frequency range of AM broadcast, or 80 meter bands when:. The receiving location shows a nighttime increase in noise level.
In other words, the system is not limited by local or internally generated noise, instead being limited by skywave or propagated distant noise. Thunderstorms or other local noise, such as power line noise from specific directions, does not dominate the receive system noise floor.
RDF directivity will be an almost perfect indicator of what you can expect from your antenna as long as:.
If antennas are within two dB of each other in directivity RDFa lesser ranked antenna may outperform a better ranked antenna. This is because:. In a majority of cases, the following RDF directivity table shows relative performance of antennas in ascending order:. Directivity Myth One common rumor or myth is that higher antenna gain results in improved reception. Gain is an unreliable way to predict receiving ability on frequencies below upper UHF!The K6STI Receiving Loop This relatively unknown antenna does an amazing job pulling weak low band signals out of man-made noise backgrounds.
Perhaps it seems a little too complicated, but I found it well worth the effort it took to design and build one. It is a terrific performer and has greatly exceeded my expectations. This is a low, medium size, horizontal loop with some very interesting characteristics. It has an omnidirectional, fairly low angle pattern with a deep overhead null like a vertical, yet it rejects vertically polarized RF energy and responds only to horizontally polarized energy.
It offers a 25 to 30dB improvement in signal-to-noise ratio over a vertical for man-made noise. This is often the predominant noise type in densely populated urban and suburban areas. Results often seem magical as signals that are covered by noise on a vertical antenna become perfectly readable upon switching to the loop.
A typical antenna is about 21 feet 6. Mine has 23ft 7. It is double-fed with ladder line in diagonally opposite corners to maintain good balance. The feedpoint is at the center of the ladder line.
Coax from the receiver is connected through a matching network with a transformer and series resonating capacitor in the secondary, built in a weatherproof enclosure.
For a 21 foot loop, there is a small impedance stepdown on 80m and a larger ratio on m. The antenna can be built with remote band switching, as I did with mine. It works well on 80 and has been surprisingly good on I had not expected much.
It is often my best performing low noise receive antenna. Low band operators who have already used Beverage antennas are nearly always disappointed with the K6STI loop. Beverages will 'spoil' you for any other low noise receive antennas, but many hams do not have room for them. If you want to reduce atmospheric noise and you do have some room for Beverages or phased verticals, both of which are directive, then those antennas would be a much better choice.
Likewise, the WA2WVL cardoid loop array provides good directivity over a narrow bandwidth if you have the room- about 80 feet on 80 meters. QST, Augustp. They might benefit from the use of a receive preamp, and so might the STI loop, to a lesser degree.
I do not use a preamp with mine, however. It is a good idea to add a highly selective tuning network ahead of any preamp to avoid receiver front-end overload.
K6STI and W6KUT, who built the first loop, noticed an apparent improvement of 1 to 2 S-units even when there was no detectable power line noise present. I have also seen this behavior in my antenna. STI reasons that in populated areas the noise background may consist of many individual man-made noise sources which, in composite, are characterless.The best performing receive antenna tested was an active loop design by John G8CQX upon which my receiving antenna is based.
I was particularly impressed by the stability of Johns amplifier design regardless of the construction methods used. Initial daytime tests with a 1 Metre diameter loop proved the loops ability to receive signals over several octaves and with much reduced local QRM levels.
However, tests after dark revealed overloading of the loop amplifier from powerful SW broadcast stations. The cure for the signal overloading was to increase the standing current in the loop amplifier devices taking care not to exceed the safe collector power dissipation.
The resulting modified loop amplifier no longer overloads even with an increased loop diameter of 1. The loop diameter of 1. The active loop antenna has now been thoroughly evaluated over a two and a half year period with very pleasing results. A nice feature of the broad bandwidth loop is that no re-tuning or adjustments are required to the antenna when changing bands.
Circuit details and constructional notes. The construction of the amplifier does not appear to be very critical and four versions have been successfully built using various methods of construction.
The first used breadboard construction, the second and third built over a ground plane while the current version is built on a scrap of strip board.
BC devices have been used simply because I have a good stock of these in the junk box. Both of the transistors run with 30 mA of collector current requiring a small heat-sink to be glued to each device. The loop itself is made from multi-strand 1. The relay shown in the loop amplifier circuit diagram protects the devices from strong signals due to the loops close proximity to the transmitting antenna. The relay has normally open contacts which close when the amplifier is powered up for receiving and open when the power is removed for transmitting or when the loop is not in use.
The relay type is not critical though it should have low contact resistance. The diode D2 across the relay coil protects the rest of the circuit from the relay coils reverse E. While nothing can protect the antenna from a direct lightening strike the open relay contacts do offer some protection from surges caused by nearby thunderstorms. The loop also has a gas discharge device connected across its terminals providing a second line of defence against surges.
The discharge device itself was salvaged from an old modem. Provision has also been made to disconnect the coax cable at the antenna end to prevent currents induced in the coax from damaging the loop amplifier during thunderstorms. Transformer T1 serves a dual function of both RF transformer and R. Because most of the local QRM is thought to be due to conducted and radiated emissions from the mains wiring it was decided to place the antenna outside at the bottom of the garden as far away from the local noise sources as possible.
If such a failure should occur then L2 would provide a low resistance path for the D. D is also fitted to the enclosure to confirm the power is present. Possible improvements and things to try. Using a pair of matched devices may also give improved performance by virtue of the reduced distortion. Using devices capable of higher collector dissipation it should be possible to increase the standing current and further improve large signal handling capability.Initial results VE3CSK have been very favourable; the comparison antennas at the summer home have been a "boomerang" beverage and a ft standard Beverage.
The loop is quieter than either but requires about 20 dB of preamplification to raise the signal level to that of the Beverages. On many mornings when the Beverages are too noisy for comfortable copy the loop is often able to provide fully copyable signals. This is not to say that one should remove the Beverages and receive only with terminated loops, because there is evidence to suggest that the loop responds to signals arriving at a higher angle than do Beverages.
This means that the loop will be inferior to a 1 wavelength Beverage at least some of the time, at least equal to the Beverages some of the time, and better than the Beverages some of the time. First tests confirmed the almost identical properties like K9AY loop, there is no noticeable difference.
A preamplifier of dB gain with input filtering is a must. I highly recommend an input bandpass filter covering the 1. Like K9AY, this antenna is less sensitive to common mode current problems than an usual flag or pennant antenna.
Anyway, the main disadvantage is the need of two supports, the VE3DO loop is sensitive to the soil properties and it can't be rotated. Anyway, there is no magic, and, at least here, the K9AY loop with its single support, seems more practical.
Log in. They trashing my incoming QSL! The VE3DO receiving loop. The transformer uses a BN binocular core wound with 5 turns secondary winding and 2 turns primary winding. The secondary of the transformer connects between one side of the bottom horizontal wire and ground while the terminating resistor connects between the other side of the bottom horiz ontal wire and ground.
The shield of the coax which is 75 ohms for the turns ratio noted above is NOT connected to the common ground of the transformer and resistor. This ground isolation contributes to the very low-noise characteristics of the antenna. The coax was buried to within a foot of connection to the transformer. The same relay box as in the K9AY is used to switch the positions of the transformer HI winding and termination resistor, thereby switching the direction from which the antenna receives.
First of all, he found that the most effective height above ground for the bottom horizontal wire is " and that the best terminating resistance is ohms on m.
With these values and the wires installed taut as per the diagram, he obtained the following: Gain is dBi a 1 wavelength Beverage has a gain of about -8 dBi or less, so a preamp is required for this loop antenna Front-to-back ratio is approximately 20 dB Side lobes are down only about dB Front lobe is approximately degrees between the 3 dB points on meters TOA angle at which the antenna receives optimally is 33 degrees, somewhat higher than that of a Beverage, nominally degrees, but response is good down to about 10 degrees with less gain.
MFJ amplified receiving loop antenna testing
There is some evidence from both K8GG and W0OU to suggest that, while a ground is required thus making the antenna "ground-dependent"an extensive grounding system is not required, and a single ground rod of from ft is sufficient.
Lowering the bottom wire to a position 6" above ground level resulted in increased directivity. The comparison RX antennas are several ft Beverages and a standard pennant oriented degrees; the soil is moist to wet clay loam.