# Tag Info

16

When the tone is present, it is because the antennas are out of phase. One antenna's signal will be leading the other; which one is leading depends on which one is closer to the transmitter (provided that the antennas are less than 1/2 wavelength apart, so that the phase difference will always be less than 180°). When we switch from the lagging signal to ...

7

There are a few radios that support diversity reception, but only to minimize effects of propagation rotation and multipath, not to increase data rates. This isn't true MIMO. It's more like SISO where the input is whichever one of two antennas has the strongest signal. Which brings up another point - data. There really isn't that much data being used on ...

5

OK, this is an interesting one. At first blush you could achieve this with two tuned magnetic loops at right angles to each other (visualize an egg-beater) and a 1/2 wave vertical for the omnidirectional part. Of course, someone has thought of this crossed loop arrangement before, in 1907 Bellini and Tosi invented the Bellini-Tosi Goniometer: A coil is ...

4

First, a "ground wave" is difficult to estimate since it is so dependent on all kinds of things, most importantly frequency and second the conductivity of the ground (or, water). Buildings in an urban area can result in diffraction of the ground wave among buildings that can create strange areas of signal strength and signal weakness that are virtually ...

4

The important thing is that the antennas are in phase. That is, at the instant the electric field is pointing up on one antenna, it's pointing up on the other antenna. Otherwise, they won't add constructively. In the worst case, they are 180 degrees out of phase and they cancel. Keeping the antennas in phase can be accomplished any number of ways. If the ...

4

There is, but it depends on the characteristics of the cable and the frequency of interest. There are online calculators that can do the work for you. For instance the two lengths of your cable have the following attenuation (almost none for RG-58) and phase delay. The phase delay is noticeably different, but as I haven't evaluated the antenna design I ...

4

Theoretically yes, if you carefully control the lengths of the cables and the placement of the antennas. This is called a phased array. However, you would get a far better improvement in range by using an antenna which is not a rubber ducky, like a 1/4 wave whip or a dipole. Rubber ducky antennas are electrically shortened, making them smaller. The price of ...

3

Yes, it is possible given two antennas at orthogonal angles to adjust the relative amplitude and phase between them and create vertical, horizontal, or anything between polarization. You can even create circular polarization of either chirality, or elliptical polarization. However, this does not solve the problem of the antenna interacting with the mast. ...

3

I recommend eliminating the array altogether and instead put a single patch antenna inside the rocket body facing upward. The frequencies of GPS signals will freely penetrate a non-metalic body, nose cone, and parachute. Place any other electronics below the patch antenna so as to not obscure its view of the satellite constellation. A patch antenna in ...

3

The hex grids can fit more transmitter/receivers into the same space, resulting in greater power output per square meter. But more importantly, the one you pictured also has independent transceivers so they are individually field-replaceable. The computer that runs it all does diagnostics on startup and can flag the bad ones so they can be fixed right ...

3

Yes, element spacing and geometry most definitely has an effect on radiation resistance in the real world. Radiation resistance is essentially that part of the signal which is not lost in some other fashion, be it resistance of the elements, the feed line, the ground, etc. In free space, the difference either spacing or phasing make would be miniscule (or ...

3

I don't know about mechanically steerable arrays, but there are several hams locally here that swear by a four-square electronically steerable arrays. The setup is typically done for 40m and is an array of four 1/4λ verticals arranged in a square 1/4λ apart. You run one feedline to a remote switch located in the center of the square and 4 identical length ...

3

There is no single "destructive interference frequency". There is maybe a frequency where destructive interference occurs in a useful direction. It can be shown that for any array, at any frequency, for any given polarization, there exists at least one (and often more) nulls in the radiation pattern, which must occur due to destructive interference ...

3

Look at the radiation patterns in all cases, and do that before you start plotting over frequency. What looks like "destructive interference" only happens in a certain direction, where the spacing and phasing of the elements result in a smaller far field strength. This is just a hole in the radiation pattern - the power is going somewhere else. As ...

2

The Christman feed system using 84 and 71 degree lines is an example in ON4UN's Low Band DXing book where 1/4 wave ground mounted verticals are used. The line lengths are calculated from feed line impedance and driving impedance of each antenna in the array. If the antenna configuration is changed so does the driving impedance, and the phase shift will no ...

2

A single bowtie dipole does have an impedance of about 50 ohms. However, stacking multiple dipoles with a properly-designed phasing system can change that. Here's a TV antenna that I made and use, with four phased bowties. Notice the phasing lines running between them. At the feedpoint where the 4:1 balun is, the impedance is about 300 ohms.

2

A practical approach for steerable patterns at these frequecies is to use electronically steerable arrays. These can take on various forms but a simple example consists of 2 or 4 vertical elements that are phased to steer the major lobe in the desired direction. On the other hand, a dish or high gain yagi on 60 GHz has a very small footprint. This could be ...

2

the lower coil seems to be an "ugly balun", a choke made out of coax, is this it? Sure looks like it. What is the 447mm "covered" section, though? Is it some sort of quarter-wave matching? should it also be extended if i try to match the antenna to a lower frequency? Yes, it's definitely intended as a kind of quarter-wave transformer akin to the lower ...

2

The info is in the model number BM - Bluewave Marathon E - Exposed offset 139- Frequency F - Gain 5.5dBd N1 - Connector Type H - Horizontal Polarized More info can be found here - Please note you may have to download the whole book for all info.

2

For some context, the relevant part of the cited source: The average collecting area is defined by $$\langle A_e \rangle \equiv {\int_{4\pi} A_e d \over \int_{4\pi}d}.$$ The effective collecting area of a receiving antenna is independent of its radiation environment, so this result applies for any type of radiation, not just blackbody radiation. Without ...

2

Good RG8 such as Belden 9913 has less loss than RG58 or LMR240, so as long as the thicker diameter doesn't cause you trouble, then it should work fine for your project.

2

The first is still correct, and can be evaluated at any position. The second is true only at broadside, when $\theta=0$. In your attempts, do you find that $\vec{E}_{total}$ is the same in all directions? Then you are doing something else wrong, or $d \ll {2\pi\over{\lambda}}$ Or are you accidentally including the $e^{-j{Phase}}$ in the individual element ...

1

I am sure the phasing and proper connection of the coax to the individual dipoles will get you a pretty good hemispherical CP pattern. It is easy to get confused when connecting the coax to the dipole.

1

You should be able to use a traditional offset mount: The counterweight balances the weight and the wind-generated torque of the yagi. If you want to use a different offset for either side, use simple proportions to create the same gravity- and wind-driven torques. Given the relatively small offset required, this doesn't seem too onerous.

1

The effective aperture can be expressed in terms of the antenna's gain: $$A_e=\frac{\lambda^2 G}{4\pi}$$ where G is the "linear" value of gain, not the logarithm of a ratio expressed in decibels. Assuming you are able to obtain the gain of your dipole array, this may be a more workable expression.

1

On 1) let me take you through a though experiment I created, struggling with the same problem with a ring of antennas fed to make an Omni. You can back it up by calculation later. Antennas are reciprocal devices. Gain in transmit is the same as gain in receive. If you transmit into the bottom port, the corporate feed / matching network works perfectly, ...

1

An antenna is effectively a transformer between the impedance of free space (377Ω) and whatever the feedpoint impedance is. For any antenna which has only negligible losses, and no reactive impedance at the feedpoint, the feedpoint impedance is equal to the radiation resistance. Consider this model: simulate this circuit – Schematic created using ...

1

Short answer: For an array of dipoles with equal spacing $d$, the direction of maximum gain with respect to the end-fire direction (call this $\theta_0$) can be obtained using the following equation: $\delta = k d\cos(\theta_0)$ where $\delta$ is the incremental phase difference between adjacent elements, $kd$ is in radians. ($k$ is the wave number defined ...

1

I want to design a steerable beam array antenna which has 15 dBi directivity using uniform fed infinitesimal dipole elements at 1GHz frequency occupying physical aperture. Array elements cannot be uniformly fed and steerable. Steering is most simply provided by applying a linear phase distribution across elements. Kieth is correct that gain/directivity will ...

1

Three verticals (or three vertical dipoles) arranged in a triangle, spaced less than $\frac{1}{2}\lambda$ apart should do it. Any pair of these antennas could be considered as an Adcock antenna. Each has the desired figure-of-eight response, and with the three antennas, we have three of these, each aimed sixty degrees apart. Unlike a traditional Adcock ...

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