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Bias tee modification of HiLetgo RF amplifiers

Hi folks, There are some inexpensive RF amplifiers available in the hobby market by various names. They may be called LNAs, if you consider 3 dB noise figure as low noise. I purchased two of them from Amazon from a seller called HiLetgo. However documentation is sparse and the design is not all that great. People have had frustrating experiences with this type of LNA. Information regarding power supply to this board is practically non-existent, with voltage suggestions ranging from 5V to 12V ! Some even obtained the "magic smoke". Nonetheless they are reasonably cheap and therefore modifications can be done to make them useful. Let us now take a closer look at the board. Figure 1. The amplifier without any modification. Fig.1 shows the board without any modification. There are two SMA connectors and provision to externally power the board. The active element is an MMIC, with N02 as the marking. Other users have identified the MMIC as INA-02184 from HP. It seems to m
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Digital modes with VUSDR and Quisk

Hello all, VUSDR is a popular TxRx SDR in India. Inspired by Peaberry SDR, it can also be used in Linux machines with Quisk as the software. In this post, I won't go into the details of configuring Quisk for normal SDR. Instead, assuming that it is already done, I shall go into the details of configuring it for digital modes especially configuring for WSJT-X for Ubuntu 16.04. As for normal Quisk configuration, I might blog about it in future. A word of caution ! These steps worked for me, but I cannot guarantee that they will work for you. So let's get started ! First download and install WSJTX from the following link. https://physics.princeton.edu/pulsar/k1jt/wsjtx.html You can double click and install the .deb file or can use terminal to install. I used the following command to install it (remember to open a terminal and navigate to the folder where the .deb file is present before typing this command) sudo apt install ./wsjtx_1.8.0_amd64.deb Next step is to in

Using FTDI USB to serial converter in Linux - Ubuntu

I recently purchased an FTDI USB to serial converter - FT232RL. However I could not use it properly in Windows. With some googling, I could find a way to use it under linux. Following are the steps to be used in Ubuntu to get it working. Open a terminal and type the following commands. sudo modprobe ftdi_sio sudo chmod 666 /sys/bus/usb-serial/drivers/ftdi_sio/new_id nano /sys/bus/usb-serial/drivers/ftdi_sio/new_id In the file that got opened, type 0403 8a8a and save it. The number can be found by typing lsusb in another terminal. Now unplug and re-plug the module. Type  ls /dev and you should see /ttyUSB0 in the list. Now use some serial terminal (like screen) to view the data ! For opening a screen session, the following command is used. Here 115200 is the baud rate. sudo screen /dev/ttyUSB0 115200

A simple guide to installing and using RTL-SDR and related software in Ubuntu

Hello all ! In this post , let me help you install and use RTL-SDR and related software in Linux , specifically Ubuntu . The software being installed are  GNUradio and GQRX . GQRX I have tried this procedure in several systems running Ubuntu 14.04 LTS as well as Mint OS ( which is based on Ubuntu ) . The procedure assumes that you have access to root password and knows basics of Linux terminal. Moreover you need a working internet connection. If you don't know how to use the terminal , then please watch some youtube videos on the same . So let's start ! Step 0 Install Ubuntu ! This is the right decision that you can make . Linux is ideal for developers and hackers ( I mean hackers like Richard Stallman and not crackers ) . Step 1 Open a linux terminal ( Ctrl+Alt+T) and type the following command sudo apt-get update You will be prompted for the password . Give it . It won't be shown on the screen . This will update your Ubuntu installation and install th

Some experiments with double balanced mixers and GNURadio

Hi all, This post is all about frequency mixing , specifically double balanced mixers using diodes or ring mixers , commonly used in communication circuits . The circuit diagram of a ring mixer is given below . (Courtesy : Radio-electronics  ) Schematic of a double balanced mixer.  As you can see , this makes use of two transformers and a four diodes . For most of the HF work , switching diodes like 1N4148 suffice . However , for better performance Schottky diodes like 1N5711 can be made use of . For more information on the working of this mixer and construction aspects , I strongly recommend the excellent video by W2AEW on ring mixers given below .  So what I wish to explain in this video is a set of experiments carried out using a double balanced mixer which I shall call DB mixer for convenience :) The test gear consists of a DDS VFO , a crystal Colpitts oscillator , a variable  power supply , CRO , RTL-SDR and the PC sound card . The software tools used are GQRX and

The trouble with double balanced mixers

Hello folks ! I never knew that overdriving double balanced mixers can actually reduce their very purpose of carrier suppression . I found this out while watching a video on microwave mixers . This problem was plaguing my Bitx40 , one of the reasons why I didn't put a linear stage on it and come on air . Instead of using its own LC VFO , I use a DDS VFO external to the Bitx40 . It had stupendous amount of carrier in its output . Trying to figure out the cause , I changed the diodes , rewound the transformers , but nothing worked out . However reducing the drive level alleviated the problem . After doing a few simulations of this in TINA-TI and obtaining the results , I did the same with the actual Bitx40 PCB . The CRO output looks much better now compared to the previous cases . The tests on a receiver too is encouraging as I can hear my sound as an SSB signal in it . Needless to say , the BFO stage has to be tuned to match the crystal filter's range to ensure best operation

Receiving NOAA weather images using RTL-SDR

HI all , In one of my previous posts , I explained how to receive ISS SSTV images (see  RECEIVING SSTV FROM ISS ! Steps involved in decoding when using MMSSTV ).Today I will describe reception of APT images from NOAA series of satellites using RTL-SDR dongles . The steps are outlined below . Record the WBFM signals from one of the NOAA weather sats ( NOAA 15,18 or 19) . You can use any of the satellite prediction software like Orbitron,GPredict etc to do the predictions . The recording can be done using any the SDR software like SDRsharp , HDSDR or GQRX . I use GQRX as my lab PC is Linux powered (see  Lab / Shack PC running Linux !  ) . The recording should be in .WAV format with the filter set tot the right bandwidth . Import the .WAV file into Audacity . Change the project rate to 11025 Hz and split the stereo track into two ( If u don't know audacity , this can be done by clicking the small arrow button near the tracks ) . Delete one of the tracks and make the other track