PC controlled direct sampling SDR receiver. Receiving frequency range HF and part of VHF in undersampling mode. Ideated in Italy, year of introduction 2014.

Reference market : ham-radio

General :
Frequency coverage [1] 0.0100 ~ 54.0000 MHz
74.0000 ~ 108.0000 MHz [2]
135.0000 ~ 148.0000 MHz [2]
Modulation mode CW / LSB / USB / AM / FM / WFM / DRM
Tuning step 1 Hz min
Receiver :
Sensitivity [3] CW 0.18 uV (14 MHz, 10dB S+N/N)
FM 0.4 uV (145 MHz, 12 dB SINAD)
WFM 2.5 uV (98 MHz, 12 dB SINAD)
MDS (Minimum Detectable Signal) [4] -132 dBm (14 MHz, 500 HZ BW, noise reduction off)
-138 dBm (14 MHz, 500 HZ BW, noise reduction on)
-130 dBm (50 MHz, 500 HZ BW, noise reduction off)
-136 dBm (50 MHz, 500 HZ BW, noise reduction on)
Selectivity user-defined
A/D conversion Freq. 122.88 Msps
Res. 16 Bit
Sampling out 192 / 384 / 6144 Ksps
RF attenuator 12 dB
Blocking 115 dB (2 KHz spaced signals, 10 MHz)
IP3 (3rd order intercept point) [4] +23 dBm (14 MHz)
+16 dBm (50 MHz)
+21 dBm (98 MHz)
+5 dBm (145 MHz)
Features :
Memory Unlimited memory channels
Antenna SMA 50Ω connector (HF)
SMA 50Ω connector (VHF)
Power supply 5 VDC USB
Power consumption 750 mA
520 mA with slow sample rate
Connections USB2.0
DB9 (external accessories control)
Mechanical and environmental data :
Operating temperature from 0°C to +40°C
Dimensions 110 (W) x 40 (H) x 90 (D) mm
Weight 360g

[1] Bypassable front-end RF filters for experiments
[2] ADC undersampling mode for VHF bands
[3] Without noise reduction function
[4] High sensitivity mode

Description :

The FDM-S2 is an SDR with a direct sampling architecture and the ability to manage two distinct RF spectrum channels. The project is an evolution of the previous FDM-S1 of which it inherits the software part. The heart of the electronics is the 16-bit analog-to-digital converter operating at 122 Msps and a subsequent high-performance digital downconverter based on the Xilinx FPGA (Field Programmable Gate Array). Another focal aspect in this receiver is the front-end, capable of expressing a remarkable dynamic-range but designed to allow also the experimentation of the ADC stage potential, excluding the filters that delimit the operating bands (HF of 0.01~54 MHz, VHF1 and VHF2 respectively of 74~108 and 135~148 MHz) and accessing it directly so that the receiver can be used substantially from zero to about 200 MHz. In the latter mode of course the user must be aware of the aliasing effect that leads to receive image frequencies without attenuation. Always in terms of experimentation the FDM-S2 in addition to offering itself as a traditional receiver is directed to be combined with another radio set, also transceiver, acting as an analyzer and demodulator once connected to the IF of the latter.

Among the most relevant features of this model there is a wide range of processed band, up to 6 MHz, and the possibility to activate different listening channels. In particular, it is possible to opt for two freely configurable 384 KHz wide channels where for each one set up mode and controls, as well as two completely independent receivers. The software also allows you to activate four sub-receivers if the tuned frequency falls within the same sampled interval. The FDM-S2 has an antenna input for HF and a shared input for VHF bands. A 9-pole connector is then dedicated to interfacing with external accessories, which ideally allows considerable flexibility on software control.

The software integrates all the functions expected from an advanced SDR, ie spectrum analysis with multiple graphical representations, accurate and linear measurement of the signal intensity, demodulation of all the modes including also the WFM (wide FM), user definable filter bandwidth, etc.

Performance and practical notes :

With the FDM-S2 the ELAD has undoubtedly made a device with remarkable performances that nevertheless supports positive aspects to others of different character. Among the qualities we mention the possibility of FM DX listening using the sub-sampling mode of the ADC, with similar terms the amateur radio band of 2 meters can be explored taking advantage of the features offered by the SDR configuration to observe in real time a significant frequency range. In HF listening, with good dynamic-range for advanced DX use, one notices the lack of a filter preselection filter bank that splits the HF into segments in order to improve second-order spurious responses. Another element to be evaluated concerns the power supply, the device takes advantage of the USB port but being the typical absorption of 750 mA a single line (nominally a USB port delivers 500 mA maximum, ed.) may not provide enough current. For this the supplied cable integrates a splitter for the two-port connection, the dual power supply naturally limits the use in mobile.

Valuation :

Dynamic range
Spurious response
Signal functions
Control functions
User friendly

Stars: 1=insufficient, 2=just sufficient, 3=mediocre, 4=good, 5=excellent

Review :

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