# Tag Info

## Hot answers tagged vlf

6

If you zoom in on these signals, there are labels describing what the stations are. Example, many of the signals around 20kHz are military: If you mouse over the labels, it will expand them. You can zoom with the mouse wheel or with the controls in the "Waterfall view" section.

6

There are plenty of ways to make antennas smaller. Unfortunately, all of these things also make the antenna less efficient. Economics provides a compelling proof: if efficient, small, low-frequency antennas could be realized, why do AM broadcast stations erect huge, expensive towers to support their enormous antennas? Antenna inefficiency isn't necessarily ...

5

I don't think it will work to add suppression to the fence. The fence charger is designed to support heavily reactive loads by generating pulses every second or two. The pulses are formed by dumping the charge of a capacitor bank through a step up transformer. Any additional reactance will be a very minor load delta. My experience (several miles of e fence ...

4

"Ferrite" is not a fungible material. There are many kinds of ferrite materials, each with very different properties. To make a comparison, you need the material datasheets, which answer questions like: What is the relative permittivity? What is the loss at the frequencies you intend to use them? What is the Curie temperature of the material? You can see ...

4

At 4 kHz you could use your laptop as a rudimentary two-channel oscilloscope. First find out if it has a useful two-channel input sound card, and find a way of recording a stereo 16-bit WAV and processing it. Octave or Python would work, or you could write your own. Then build a circuit like this, adjusting parameters to suit: simulate this circuit –...

4

A squarish shape antenna is the best sender/receiver There is no practical basis for this assertion. Wavelength of the 15Khz [SIC] frequency is around 14990 meter [SIC] The formula for the reasonable approximation of wavelength is $$\lambda (in\space meters) = \frac{300}{Frequency\space in\space MHz} \tag 1$$ Since 15 kHz is 0.015 MHz, it has a ...

3

Below is a rough estimate of the near fields calculated by NEC4.2 for an elevation of 3 meters above level Earth from a transmit antenna and system as generally described in the OP, and the followup comments of the OP. "Use with due diligence."

3

Estimating the near field is best done with modeling software or empirical measurement. The details of the antenna construction and environment (the ground and any nearby conductive objects in particular) can significantly impact the near field. That said, 100W is not much, and often regulations specify that no particular evaluation need be done if the ...

3

display_qt is a GNU Radio example program. It does not display any actually existing electromagnetic signal but internally generates a 1500 Hz sinusoid. The code creates a sine source and a noise source, // Source will be sine wave in noise src0 = analog::sig_source_f::make(rate, analog::GR_SIN_WAVE, 1500, 1); src1 = analog::noise_source_f::make(analog::...

3

The point of a huge antenna is efficiency. Ground rods alone will result in a very small signal being received, and high transmitter mismatch. VLF antennas are massive and require both very large grounding radials as well as antennas. The links from the VLF page at Wikipedia, especially the Long Wave Radio Club of America and K4NYW's page on vintage Navy ...

3

Your method only crudely measures the magnitude of the feedline impedance, without taking into account the fact that it is probably a complex value, with a phase shift between voltage and current. Also, the output impedance of most modern audio power amplifiers is very low — usually way less than an ohm. I'm surprised that you get any useful answers ...

1

I want to add to Phils answer. The VLF around 3-30 kHz are used for submarine communication. From WikiPedia: VLF radio waves (3–30 kHz) can penetrate seawater to a depth of approximately 20 meters. Hence a submarine at shallow depth can use these frequencies. A vessel more deeply submerged might use a buoy equipped with an antenna on a long cable. The ...

1

See the US allocation of frequencies for the source data for some of this. Right now, the current users of VLF/LF are either maritime mobile, radio navigation, time frequencies, or aeronautical use. There are a few stations that have experimental privileges, as ARRL mentions. The bandwidth for these bands drops dramatically, often only a few kilohertz. ...

1

If you're going to be using this antenna strictly for reception, then increasing the windings is fine, but as the previous answer stated you're on increasing inductance, and when you increase inductance, you are by nature adding more radiation resistance. So, for transmitting that is not ideal at the wavelengths of VLF. These are small loops and can only ...

Only top voted, non community-wiki answers of a minimum length are eligible