Cheap 16-bit SDR RX / TRX - WEB-888 and TRX-DUO

Thanks to the rapid development and the wide use of SDR technology, it is possible to buy interesting devices at very reasonable prices. In addition, SDR technology allows new features to be added and devices to be upgraded without the need for intervention in the HW design.

For example, the software allows reception over the entire range up to 60 MHz and multiple users can listen in different segments independently. Each can use a different type of mode, and each can even use the built-in decoders - CW, FAX, RTTX, FT8, etc.

Here is the basic information on two very nice SDRs at reasonable prices.

WEB-888 16-bit SDR receiver HF + VHF

WEB-888 is an all-in one SDR receiver with 16-bit ADC LTC2208. The receiver is housed in a metal box and includes a LAN port. In addition, it also has a built-in GPS receiver - this allows you to tune the oscillator. The SMA connector for the REF signal can serve as a reference signal input, but also as an output of the internal generator, which is synchronized with the GPS. There are also GPIO outputs on the front panel for connecting an antenna switch that can be controlled from the WEB-SDR. The SDR can be used in a wide range: from a web-SDR receiver for 13 users, FT8 skimmers, to an eight band receiver for CW/RTTY/DIGI skimmers.

Main functions:

- Broadband: 1 KHz to 62 MHz and 118 MHz to 145 MHz

- 16-bit ADC DDC architecture SDR

- ADC chip LTC2208

- 61.44 MHz real-time bandwidth

- Built-in GPS module

- Gigabit Ethernet

- Reference clock input/output

- 24.576 MHz, 0.5 ppm TCXO

- 6 GPIO for antenna switching

- Zynq7010 FPGA with dual A9 ARM

- Alpine Linux 3.20 with Linux 6.6 Kernel

- WebRX-based browser SDR experience

- KiwiSDR web socket protocol for applications

- WSPR, FT8 skimmers, and other decoders

- 13 RX channels and 13 spectrum channels simultaneously

- Read-only root partition to prevent SD card corruption

- Aluminium enclosure

- Dimensions (with connectors): 115x70x25 mm

You can buy it there: HamParts.shop

TRX-DUO two channels 16-bit SDR receiver, 14-bit transmitter up to 60MHz

The TRX-DUO is similar in concept to the WEB-888, but includes a pair of 16-bit ADCs and a pair of 14-bit DACs. It is a full-featured dual TRX with a frequency range up to 60MHz. This concept makes it possible to use the two RX chains to phase each other and achieve diversity reception. Or create a SO2R TRX. Thanks to the SDR concept, it is possible to insert an SD card with different applications. From an SDR TRX to an eight band receiver for CW/RTTY/DIGI skimmers. 

Main functions
- Broadband: 10 KHz to 60 MHz
- Double 16-bit ADC DDC RX architecture SDR
- ADC chip 2x LTC2208
- Double 14-bit DAC TX architecture SDR
- DAC chip AD9767
- 61.44 MHz real-time bandwidth
- Sample rates 125 MS/s
- Gigabit Ethernet
- Zynq7010 FPGA with dual A9 ARM
- Read-only root partition to prevent SD card corruption
- Compatible with RedPitaya SDR board
- Aluminium enclosure
- Dimensions (with connectors): 115x70x25 mm

You can buy it there: HamParts.shop

Technical articles:

Here you will find simple technical articles to get you started experimenting with SDR. Most of the time it is very simple, just copy the image to the SD card and then proceed to the web interface. Watch out for the right type of SD card.

There is link to the blog.

Pre-installed SD cards:

To simplify the work with SDR we offer pre-installed SD cards. Simply insert these into the SDR and proceed according to the notes in the technical article.

You can buy it there: HamParts.shop

Cooling:

The enclosure of SDR also includes a fan. However, it does not include any dust filter. In the TRX-DUO, the fan is also very small and noisy. If the fan stops, it can very easily destroy the ADC or CPU. For these reasons, I offer an additional fan that easily slips onto the SDR. It allows you to adjust the fan speed and includes a basic dust filter.

You can buy it there: HamParts.shop

RF limiter protection:

It is very important to note that these SDRs have no input filter or protection. The SMA input is connected directly to the ADC via a transformer. Therefore, it is important to keep two things in mind:

- connect the RX antenna through a filter that limits signals to a maximum of 30 (60) MHz (antialiasing)

- protect the input from strong RF signals (custom transmitter) and storm surges

To protect the input from strong signals and spikes, we offer RF limiters. Their feature is to limit the RF signal amlpitude to a certain maximum value and thus protect the device. More information can be found on our website: RF LIMITERS

 QO-100 at CN3A

Together with Vasek OK1VVT during CQ WW SSB 2024 on CN3A we talked and thought about what could be done on VHF. Besides future plans with 2m EME I thought about the QO-100 satellite. Since I have been building LNBs for several years, not only for this satellite, it was "just" enough to finish the rest :)

For several years I have been using an Adalm pluto SDR TRX with additional front end boards for VHF remote control (70 MHz, 144 MHz, 433 MHz). So I decided to use this SDR together with a great SDR program - SDR Console. For the RX I used my LNB ext OSC - that is an LNB with the ability to hang a PLL using an external 10 MHz normal. This GPSDO also serves as a reference signal source for the Adalm Pluto. I also found a nice 10W PA in China. I just had to add some more parts like LAN and PoE filters, DC-DC converter with filters and mount it in a box with a heat sink. 

I printed an ice cone feed as an antenna. Outdoor box is connected only with one CAT-5 FTP cable. There is common power supply with LAN filter and PoE injector - all in one enclosure.

LNB: LNB ext OSC MK3

Adalm Pluto: with EXT REF

LAN and PoE filter: with protections LAN PRO-FIL

ICE CONE FEED: web of author

Common 24V power supply with filters

GPSDO board with LNB bias tee, Adalm Pluto PA and DC converters

Testing output power

First test at CN3A without the dish

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The first test on CN3A was done without dish antenna in January 2025. Despite the opposite polarization of the transmitting antenna and simple support of the antenna on an improvised table, it was possible to listen to the beacon. After tuning to the FT8 frequency, I was surprised that I easily decoded several stations. I tried transmitting with 6W RF power into the wrong polarization and it worked :) The first QSO was very easy and thanks to Libor OK1ALX for the test! After the first CQ an avalanche of calling stations came down.

After a month it was time to go again for 14 days of working relaxation on CN3A. Apart from work and CQ WPX SSB I planned to finish the equipment for QO-100, buy a dish and holder and mount everything.

After a couple of days, Jirka OK1RI and I went to get some food and drink supplies and also visited the local “hardware” street in Safi. After an exchange of greetings and a commented (in Czech) demonstration of photos of the antenna on a mobile phone, the seller brought us the antenna and the wall mount. Even a first year engineering student would be ashamed of this mount... but better than nothing :)

After installing and pointing the antenna, the increase in signal strength was significant. The gain was around 30 dB and our own signal is at S9 level. When there is more time, we will sit down to SSB, where it will be much more fun compare to FT8...

All QSOs are confirmed over LOTW.