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The smallest SDR Upconverter you known? Let me know!
2 is an improved and scaled down version of my previous SDR HF
The objective was to replace the passive mixer by an active, and then we can even compare with the SBL-1 in the previous version.
And because there was already a power supply needed for the crystal oscillator, i choose to use the mixer IC SA602.
It was easier to obtain than the IE 500 or SBL-1, which is anyway quite large, and not suitable for SMD placement.
there is a SMD relay to automatic switching from HF to VHF
if you disconnected the supply voltage (unplug the USB).
The entire board is designed for SMD components, so that ready-made available coils can be used.
That was a bit of searching on the Net, but ultimately still went well. The filter values were then also be adjusted, in order to be able to use default values of inductances and capacities.
is still mostley the same as in the previous HF Up-converter
version . A
standard SDR stick can receive from about 50 MHz, for the E4000
tuner series, and from 25MHz, for the RT820 tuner series.
The input filter for HF is a Low-Pass T-Filter 0 to 52 MHz, this time with default values of coils, so it should be easy to made. Some of the capacitors must be placed “double soldered” to each other, in order to get the right values.
The output filter is a high pass Pi-filter remained so, default values could also be used, which otherwise would not have been the case. The initial frequency of the output filter is raised slightly to 110 MHz to suppress the strong free FM stations on the FM band here in Europe.
The crystal block must works on 3.3 volts, the three diodes bring the operating voltage down at about 3.2 volts. These three diodes may also be replaced together with one resistor of about 82 ohms.
However, the signal from the crystal block remains much too high for the SA602, so that a 3dB resistor-pad some weakening is obtained.
The mixer mixes the incoming signal (1 - 50 MHz) from the HF band, with the crystal of 125 MHz, and on the output, we then can find the HF band 125 MHz to 175 MHz in our SDR receiver program.
The advantage of the crystal of 125 MHz, compared to eg 100 MHz, so that we do not end up in the middle of the FM band with strong mixing signals. Outside some airplanes that could still beaming, it's pretty quiet there after 125 MHz.
In our SDR program (eg HDSDR or SDR #), we propose using an offset of 125 MHz, and then our zero-point is also shown as 0 MHz .
As to be expected, immediately after building, and connecting the cables to the antennas, it schould been working fine.
In this version, cheap RCA inputs chassis are used, and that is not a problem even on HF and VHF .From the original stock-antenna that was supplied with the SDR stick, is only the coax cable reused here. This must cut on the antenna base, and directly soldered on the output mark of the up-converter board.
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