I bought web888 and installed it with a MLA-30+ active loop antenna.

Now I have personal FT8 skimmer for max 12 different bands (using now 7).

I developed few scripts that plot the data and it all seems logical and stable. The web888 even provides SNR data by default.

web888 is awesome device, so many possibilities and I really liked the MLA-30+ antenna, nicely thught and the outdoor unit is potted in expoxy!

#web888 #ft8 #sdr #loopantenna #hamradio

Affordable HF Loop Antenna Reviewed

Modern ham radio operators often face restrictions on antennas. This has made small antennas more popular, despite some limitations. [Tech Minds] reviews the GA-450 indoor active HF loop antenna and finds it better than expected. You can see the video review below.

You can't expect a little antenna to perform as well as giant skyhook. However, for such a small loop covering 3 to 30 MHz, the antenna seems to perform very well. We like that the active part of it has a rechargeable battery. Obviously, you will only want to use this antenna for receiving, but it would be a great pairing for an HF-capable software defined radio (SDR). Even just in the window sill with half gain, it was able to pick up quite a bit of signal on the 40 meter and 20 meter ham bands. According to the video, performance below 7 MHz was lackluster, but it worked nicely at higher frequencies.

The loop is directional and you can rotate the loop on the base to zero in on a particular signal. Of course, if the antenna were up in the air, it might be harder to rotate unless you work out something with a motor. If all you want to do is receive and you have a budget of under $100, this looks like it would be a nice portable option.

You can build your own loop and loop-like antennas, of course. Some of them can be quite portable.

#radiohacks #antenna #loopantenna #sdr

Frame Antenna Works the Low Bands

The lower the frequency of radio transmission, the more antenna that will be needed in general. [OM0ET] wanted to work the 80M to 20M ham bands and decided to turn to a frame antenna. You can see the project in the video below.

The antenna looks a lot like a magnetic loop antenna. The one in the video has seven loops forming a 520mm square. The loop is, of course, an inductor and by removing some insulation, the operator can clip a lead at different points to control the inductance. A variable capacitor resonates the antenna, so there is definitely tuning required.

The physical support for the antenna is 25mm PVC. It isn't that hard to build, but does it really work? The video shows quite a bit of detail on the construction, but we are waiting for part two which will show the operating tests. From past experience, we will guess it will work well enough, but the tuning will be sharp, meaning you'll have to retune a lot when changing frequencies.

Also, these kinds of antennas tend to be directional, so they are useful in fox hunting. We see a lot of loop antennas for hiding in plain sight or, sometimes, for portable use.

#radiohacks #antenna #frameantenna #hamradio #loopantenna

Where’s that Radio? A Brief History of Direction Finding

We think of radio navigation and direction finding as something fairly modern. However, it might surprise you that direction finding is nearly as old as radio itself. In 1888, Heinrich Hertz noted that signals were strongest when in one orientation of a loop antenna and weakest 90 degrees rotated. By 1900, experimenters noted dipoles exhibit similar behavior and it wasn't long before antennas were made to rotate to either maximize signal or locate the transmitter.

British radio direction finding truck from 1927; public domain

Of course, there is one problem. You can't actually tell which side of the antenna is pointing to the signal with a loop or a dipole. So if the antenna is pointing north, the signal might be to the north but it could also be to the south. Still, in some cases that's enough information.

John Stone patented a system like this in 1901. Well-known radio experimenter Lee De Forest also had a novel system in 1904. These systems all suffered from a variety of issues. At shortwave frequencies, multipath propagation can confuse the receiver and while longwave signals need very large antennas. Most of the antennas moved, but some -- like one by Marconi -- used multiple elements and a switch.

However, there are special cases where these limitations are acceptable. For example, when Pan Am needed to navigate airplanes over the ocean in the 1930s, Hugo Leuteritz who had worked at RCA before Pan Am, used a loop antenna at the airport to locate a transmitter on the plane. Since you knew which side of the antenna the airplane must be on, the bidirectional detection wasn't a problem.

Basic Navigation

Radio navigation owes a lot to ordinary celestial navigation and surveying. Instead of sighting a lighthouse, the sun, or a star, you sight a radio transmitter.

Using the sun and moon gives two circles (lines of positions) and you can assume your ship is not over dry land around Argentina or Paraguay. Public domain.

Consider you are in a field that has a flagpole on it and you know the exact location and height of the pole. If you are somewhere in the field and want to know where you are, you can use the pole. You sight the pole and measure the angle to the pole. Since you know the height and the angle, you can use geometry to draw a circle around the pole that you must be on.

Of course, you could be anywhere on the circle -- what navigators call a line of position. But what if you had two poles? You could draw two circles. If you are lucky, the circles will touch at exactly one point and that is where you are. However, it is more common to have two points and -- presumably -- one will be very far away from where you ought to be and one will be close to where you should be.

Even with a simple pair of loops, you can do the same trick if they are far enough apart. If station one shows an angle of 30 degrees (or 210 degrees; it is ambiguous) to the transmitter and station two shows an angle of 300 degrees, you can triangulate by drawing two lines and noting where they cross.

Improvements

A 2 MHz Adcock installation; public domain

Even so, there was a demand for something better. In 1909 Ettore Bellini and Alessandro Tosi introduced an innovation. The Bellini-Tosi system used two antennas at right angles that fed coils. A third loop moved inside the coils to find the direction. This allowed the large antennas to remain stationary. By the 1920s these were quite common and remained so until the 1950s.

By 1919, the British engineer Frank Adcock came up with a system that used four vertical antennas, either monopoles or dipoles. This arrangement wired the antennas to effectively make a square loop that ignores horizontally polarized signals, thus reducing the reception of skywaves. Adcock antennas were often used with Bellini-Tosi detectors.

Lightning Strikes

Huff Duff gear; Photo by Rémi Kaupp CC-BY-SA-3.0

In 1926, Brit Robert Watson-Watt was trying to detect lightning to help airmen and sailors avoid storms. Lightning signals are very fast, but it took about a minute for an experienced operator to line up a Bellini-Tosi detector. By coupling an Adcock antenna and an oscilloscope, Watt was able to rapidly lock onto a lightning bolt or a radio transmitter.

The military high-frequency direction finder or huff-duff proved invaluable during the war. The German U boats kept transmissions short to avoid detection, but with the huff-duff, that didn't matter. The Germans didn't figure out the technology improvement and estimates are that 25% of U boat sinking were due to the huff-duff.

Modern Times

Modern-day systems are much more sophisticated using phase locked loops and other techniques. Although some early systems like the one used by Pan Am used transmitters on the plane and receivers on the ground, most systems do the opposite. Older ADF -- automatic direction finding -- sets used motorized antennas to locate known transmitters. Modern sets use the Marconi system with multiple antennas, although the switch is electronic in this case.

Ham radio operators enjoy fox hunting -- part of the event known as "radiosport" in most of the world -- which is essentially hide and seek played with a radio transmitter. You can see more in the video below.

You might think that GPS has made radio direction finding a thing of the past. However, if you think about it, GPS is sort of a different form of radio direction finding. Instead of using a bearing of an antenna, you are measuring signal arrival time, but it is the same idea. The time delay gives you a circle from the known position of the satellite. Making multiple circles around multiple satellites gives you an exact position.

Sure, the technology is a far cry from Hertz's loop antenna. But radio direction is still a key part of modern navigation systems.

#featured #history #interest #originalart #adcock #bellinitosi #deforest #directionfinding #gps #hertz #huffduff #loopantenna #radiodirectionfinding #rdf