Hot answers tagged

5

See SigiWiki: This wiki is intended to help identify radio signals through example sounds and waterfall images. Most signals are received and recorded using a software defined radio such as the RTL-SDR, Airspy, SDRPlay, HackRF, BladeRF, Funcube Dongle, USRP or others. https://www.sigidwiki.com/


4

The ambient noise on HF is so high that such a low noise figure will not appreciably improve performance. On 20 meters, the minimum ambient noise temperature you will encounter is about $3 \times 10^6 \:\mathrm K$, which corresponds to a noise figure of about 40 dB. Noise goes up with wavelength, reaching $3 \times 10^{10} \:\mathrm K$ or 80 dB around 1 MHz. ...


4

If I were to design an amplifier, I would always design an amplifier with low noise anyway. Nope! For a power amplifier, you'd do a different tradeoff; the noise figure of that amplifier nearly doesn't matter at all, whereas the capability to produce a high output power does very much. Same goes for other aspects of amplifiers, things like linearity/...


4

The gain becomes an issue only if its ridiculously low. The main purpose of an LNA is to lift the signal well above any noise of the following stages, and often that can be done with a gain of several dB. However, the fact that they didn't advertise it, makes it suspect.


3

Here's one from the designer of fldigi. http://www.w1hkj.com/modes/index.htm


3

TDD and FDD are two methods of achieving a two way path (duplex) between two communications nodes (i.e. transceivers). They are mainly of interest for cell phones and digital data devices (e.g. WiFi). A Google search of "TDD FDD" will lead to several informative explanations. FDD is Frequency Division Duplex. In this case the two nodes select ...


3

An earlier Answer mentioned LNAs would be “of some use only if ... the noise power from the antenna is higher than the noise floor of your receiver” (quote). That statement appears in need of some clarification. If the receiver, on its own, has a high noise figure, or is preceded by a (long) lossy feedline (which contributes/adds to the system noise figure) ...


3

A LNA amplifies signal and noise. It is of some use only if: the noise power from the antenna is higher than the noise floor of your receiver, and the LNA has a lower noise floor. Many VHF/UHF receivers already have sufficiently good noise performance that one or both of these things is not true, and so adding an LNA will not improve performance. Typically,...


2

20-25 meters of RG-6 coaxial cable has significant loss at 739 MHz. RG-11 coax has significantly lower loss than RG-6. Unless there is an issue with your LNA, I expect that replacing the RG-6 with RG-11 will give you the signal boost that you are looking for. What you could do in lieu of replacing the coax is add a low-noise preamp right at the dish, to ...


2

These specifications mean: VHF yagi antenna This tells you the general kind of antenna it is: a Yagi intended to operate at VHF: "very high frequency". 12dBic gain This means that in the antenna's direction of maximum gain, it will receive 12dB more power than a theoretical circularly polarized antenna which receives power equally from all directions....


2

It's hard to say whether your active antenna would work properly if provided with 3.3 VDC instead of 5 VDC. I doubt that any damage would be done, but I'm not the engineer that designed the antenna. You might consider adding a boost regulator (and the other parts it requires) to your circuit, which could convert 3.3 VDC to 5 VDC. Here's such a part, ...


1

Phil's answer is sound from a technical perspective since there is not sufficient data to fully answer the question. From a more pragmatic perspective, if you wish to increase the 12 dB SINAD sensitivity of your receiving system, you should: Minimize feedline losses Increase the gain of your antenna Your required 5 dB improvement in sensitivity is usually ...


1

300 kHz channel at 436 MHz sounds a lot like your spectrum analyzer might be seeing that are at twice the frequency – 872 MHz would be a typical 2G cellular network frequency, and 300 kHz might be around the bandwidth of a 2G channel. Try and tune to your SA to 872 MHz.


1

If the antennas are cheap and easy to build, why not build two and use one for TX and one for RX, then use a common RF sense antenna switch such as MFJ-1707 to switch between the two. This allows you to have one coax to your transceiver and two antennas. Control lines for switching are also accommodated in many of these types of antenna switches. Typical ...


1

Whether you can use an omnidirectional antenna to replace a directional antenna depends entirely on the minimum signal-to-noise ratio required by the receiver, and the amount of noise arriving from directions other than the wanted signal. Without this information, your question does not have a yes-or-no answer. And if you are going to go to the effort of ...


1

Is there any way to independently test the two parts of the circuit -- the antenna and the amplifier? Perhaps use a 1 megaohm through-hole resistor to directly connect your RF source to the big "antenna feed" pad, completely bypassing the antenna, to test the amplifier section? It appears to me that the version 1.1 circuit board has a ground pour covering ...


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