Tagged: preamp

How an LNA can Improve VHF Reception with an RTL-SDR

Over on his YouTube channel Adam 9A4QV has uploaded a video showing how an LNA work to improve signal SNR on VHF, as long as the LNA is placed close to the antenna. Adam is the manufacturer and seller of the popular LNA4ALL low noise amplifiers.

On UHF and high frequencies an LNA can help by reducing the system noise figure, but on VHF this effect is small. But if the LNA is placed near the antenna then the LNA can still help significantly by overcoming any losses in the coax cable, filters, switches or any other lossy components in the signal path. It might also help create a better SWR match for the dongle and antenna. The video has some sound issues in during the demonstration part, but on his Reddit thread Adam writes:

Well, monitoring the beacon signal on 144.478 Mhz the S/n without LNA was just 10dB and cannot improve with decreasing the gain. Inserting the LNA in line, close to the antenna, through the Bias-T the S/n improve from 10dB to 23dB.

To meet the most of the user's conditions I was using the RTL-SDR dongle and the 20 meters of RG-6 coaxial cable with F-connectors.

It is obvious that using the LNA on the antenna can improve your reception even on the VHF band. Using the proper bandpass filter instead of a single FM stop filter will give much better results.

LNA4ALL on the VHF close to antenna effect

RTLSDR4Everyone Four New Posts: Janilab Preamp Review, Why Use a Preamp?, Small ADS-B Antennas Review, SDRUno User Guide

Akos from the RTLSDR4Everyone blog has recently posted three new articles. The first article reviews the Janilab LNA Preamp which has a frequency range of 1 MHz to 3 GHz and an adjustable gain. In the review he compares reception with and without the preamp at shortwave frequencies and at ADS-B frequencies. Finally he also compares it against the LNA4ALL and LNA4HF, and notes that they generally have better specs than the Janilab preamp, but the disadvantage is needing two to cover HF + VHF/UHF, meaning an increase in costs.

In his second post Akos explains when and why you should use a preamp. Basically he explains how the lower noise figure of the preamp can help improve SNR.

In his third post Akos does a review on small ADS-B antennas. These are small whip type antennas that are tuned for 1090 MHz. In his testing he found that a telescopic antenna gave significantly better results that the ADS-B whip, but recognizes that these are designed for pilots and light aircraft owners who need a small sturdy antenna.

Finally his fourth post he shows an updated beginners guide for SDRuno. SDRuno is the official software for the SDRplay RSP, but is compatible with the RTL-SDR.

The LNA4ALL and LNA4HF vs the Janilab Preamp
The LNA4ALL and LNA4HF vs the Janilab Preamp