WSE (Weak Signal Equipment) A joint effort by SM5BSZ Leif and SM7UFW Niklas.
(Dec 17 2011)
The WSE RX2500 is a converter that converts 2 radio frequency signals to audio signals that fit a four channel 96 kHz 24 bit sound card.

The input signals are centered at 2.5 MHz and the useful bandwidth is over 90 kHz. Together with a Delta44 sound card, WSE RX2500 provides the hardware for an SDR (software defined radio) receiver such as Linrad with a bandwidth of 93 kHz centered at 2.5 MHz.

The WSE RX2500 is intended for use together with other converters that bring radio frequencies of interest to 2.5MHz. Such converters are easily designed with standard technology, but to fully utilize the exceptional dynamic range of the RX2500 some non-standard solutions are required.

There are WSE converters that match the performance of the RX2500. These converters use crystal oscillators only to avoid noise floor degradation and therefore several converters are used to provide a wide frequency coverage with a limited number of crystals.

The WSE converters provide a receiver having a first intermediate frequency of 70 MHz. The WSE RX70 converts to 10.7 MHz and the WSE RX10700 converts from 10.7 to 2.5 MHz. The frequency coverage at 70 MHz is 0.5 MHz. Other converters convert from amateur bands to 70 MHz in 0.5 MHz wide segments. The output of these receivers is four audio channels that form two baseband signals that fit a four channel soundcard such as the Delta44.

The WSE RX2500 was sold in the years 2002 to 2010 in a quantity of about 50 units for a price of 4200 SEK excluding VAT. The WSE project is now closed but there is some left-over from the project that we offer here: WSE surplus

WSE RX2500 technical data

Input Two BNC connectors for two receive channels.
Nominal input impedance 50 ohms.
SWR < 2 for frequencies between 2 and 4 MHz.
Maximum input RF power +25 dBm. Note that the wideband input is unprotected. A single pulse with a voltage above 6V could damage the input transistor.
Output Four audio channels in a 15-pin D-sub with pin connections that fit a Delta44 soundcard. Unsaturated output voltage 4 V RMS (11.3 V peak-to-peak) Output load impedance > 5000 ohms.
Bandwidth 92 kHz at -3dB.
Supply DC +15V and -15V at 0.6A (18W) The supply is connected on a 9-pin d-sub.
pin 9 = DC ground
pin 5 = +15V DC, 0.6A
pin 4 = -15V DC, 0.6A
Sensitivity Noise floor in 500 Hz bandwidth -140 dBm (NF = 7 dB).
Gain 10 mV RMS input voltage, measured with the RX2500 connected, typically produces an unloaded output voltage (in two channels) of 850 mV RMS.
In-band dynamic range 1 dB compression point -11 dBm (156 dB above noise floor in 1 Hz bandwidth)
Weight 1.5 kg.
Size 48 mm   x   218 mm   x   350 mm.

The RX2500 fits to a Delta 44 soundcard. It is a good idea to make some modifications, the Delta 44 soundcard suffers from spurs and noise due to several inadequacies in the design. The sensitivity to ground loop currents can be eliminated and the flat noise floor can be improved by about 3 dB. Read more about the Delta 44 soundcard modifications here.

System performance data for WSE RX2500 used with a modified Delta 44

Sensitivity System noise floor in 500 Hz bandwidth with the Delta 44 in minimum gain mode -133 dBm (NF = 14 dB).
System noise floor in 500 Hz bandwidth with the Delta 44 in maximum gain mode -138 dBm (NF = 9 dB).
In-band dynamic range Level for A/D saturation -13 dBm.
Noise floor relative to near saturating carrier at 10 kHz frequency separation with Delta 44 in minimum gain mode -147 dBc/Hz. (Interference signal within the passband)
Out-of-band dynamic range Level for 1 dB gain compression +15 dBm outside 2.4 to 2.6 MHz.
Level for 1 dB gain compression +3 dBm outside 2.45 to 2.55 MHz.
Third-order intermodulation Two signals at - 20 dBm produce third order intermodulation below -105 dBm (IP3 > 22.5 dBm) if both signals are within the passband. For signals outside the passband, third order intermodulation is lower. At a frequency separation of 200 kHz, IP3 is in the order of +35 dBm.

The WSE RX2500 is designed by SM5BSZ, Leif. A detailed description is available here: details of the RX2500

Some general information about the WSE converters is available here: the WSE converters