# Tag Info

13

It looks like a fibre or telephone cable strung between buildings. It sets a good precedent for setting up your antenna though - if you can get access to the other rooftop at night, and a catapault or fishing rod. Make it fairly official-looking, with some large bolts and a labels with bar codes and lots of numbers.

6

If you do it right, the bead(s) shouldn't get hot at all, and shouldn't add much loss. The impedance of the bead(s) should be about 10 x the impedance of the dipole. The current on the feedline with no balun might be about half the antenna current. With the beads on it it'll be less than 1/10 of the curent, or 1/100 of the power. Small beads (3.5 mm inside, ...

6

I know that the gap between the wall and the antenna mast that would be created using the wall mounts you mention is not for lightning damage prevention purposes. If a bolt of lightning can travel hundreds of meters from a cloud to the ground, another half-meter of air between a mast and a building won't be much of a deterrent, especially when the bolt ...

5

It should be fine. Stranded wire will take that kind of bending easily. If you were to tie and untie the knot many times you might eventually weaken and break some of the strands, but if it's tied once and left in position, it won't create so much stress. If you're worried, of course, there are alternatives — you could slide a small plastic bead onto the ...

5

The cable strung between the two buildings has two parts, a strong wire probably made of stainless steel or similar, then you can see some form of cable, as Tommexus said it's probably fibre or telephone cable, or maybe coax, hanging from the wire with lots of evenly spaced cable supports. The steel wire is used to provide a strong support between the ...

3

A half wave horizontal element at the junction between the boom and the mast with a good electrical contact between the midpoint of the horizontal dipole and the mast will create a low impedance point on the mast. Then place another half wave element down 3/4 of a wavelength along the length of the mast. You may even place two of them, one parallel to the ...

3

Nothing. A G2 storm is a common event; according to NOAA data it happens an average of 600 times per 11-year sunspot cycle. It won't hurt your radio, but it might make HF communication a little more difficult. In fact, no category of storm is expected to hurt your radio in particular, although G4 and G5 storms can cause major radio blackouts, not to mention ...

3

It's all to do with mutuals, and you can't wish them away - even for 'ideal' antennas. Consider a simple case, two elements a reasonable distance apart. Give them excitation amplitudes +1 and -1. From your assumptions, the radiated power is 2, irrespective of their locations. The power is no longer radiated isotropically, there is some array pattern, but ...

3

Think of the antenna as a whole as being many inductors in series along its length and along with that many capacitors branching off like a tree (capacitors in the air) going back to the "negative side", so parallel capacitors. The loading coil needs actual current to work with, the further up on the antenna that you mount it, the less current ...

2

Years ago I used a simulation like this one for the same purpose. The antenna you refer to is a tuned antenna, so it is not wideband. The antenna that I made is a wideband, really flat response (conversion from field strength to output voltage is frequency-independent). Conclusion: the difficulty is the design of the low-noise amplifier. Depending on what ...

2

The formula in the question is taken from page 44 of a book called The Theory of Electromagnetic Wave Propagation by CH Papas. The text says that the formula describes the radiation pattern for a center driven wire antenna. Radiation patterns normally show a graph of relative intensity which isn't the same thing as efficiency. For transmitting, the ...

2

Different beats have different attenuation at different frequencies. My gut tells me you want at least 6 dB, preferably more. Guys seem to wind their own inductors as RF chokes but not sure how much attenuation at the desired frequencies.

2

The pictures look a lot like post-socialist country big city residental area. It may as well not be, YMMV. The Yagi looks like an abandoned old analog TV antenna. Most ham installations use vertical polarization in UHF and this one looks pretty much horizontal. The cable between the buildings is not an antenna at any rate. This is a communincations cabe of ...

2

I'm not sure if this is the correct answer or not: At varying electric lengths, at any moment in time, one part of the antenna is producing the wanted field(s) and another part might be producing a canceling field(s). With a half wavelength, all you get is the wanted field and no canceling field. The canceling field (I call it that because it works against ...

1

Note: question changed since I wrote this answer. Two classic and highly effective fractal antennas are the log periodic antenna and the many variations (planar, conical, cylindrical, etc.) of the log spiral antenna. The main characteristic of both of these antenna families is extremely broad bandwidth, which can be attributed to the fractal self similarity ...

1

It isn't. Gain in the broadside (θ=0) direction isn't "efficiency". A half-wave dipole doesn't maximize that parameter, even among dipoles; it increases until roughly 1.25 wavelengths, then decreases, then generally increases again, in an oscillating way. There are nice things about half-wave dipoles (a convenient, easily-matched impedance and a ...

1

You don't need a spectrum analyzer for such low frequencies, more like a very accurate voltmeter that you can record over long periods. As the antenna, you will need something huge, I recommend the power grid. Filter everything out above 59 Hz and see what you are left with. Might have to do some different filtering to try and find Schumann resonances. Make ...

1

If you need calibrated output then you probably won't be able to do it. That's why they are so expensive. It's like a \$20 SDR dongle versus a \$2,000 spectrum analyzer, with the most notable difference being that the spectrum analyzer is calibrated and tells you how much power is at each frequency. If you don't need calibrated output and just want to get a ...

1

Consider a simpler problem: Stack two dipoles at 0.01 wavelength separation. Connect the endpoints and feed power to one of the dipoles and short the feed-point of the other. What you then have is a folded dipole. Impedance 300 ohms. Then remove the short and feed both feed-points. The impedance of each one will be 150 ohms. They are series connected on a ...

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