IQ+ Dual RX Radio for Adaptive Polarization
Performace
The IQ+ has an extraordinary performance for EME and Weak signal communication. In terms of absolute values I want to be carefully before declaring any number. I don't want to have numbers with "a lot of makeup",
One important consideration is the IQ+ is designed to work with and external pre amplifier, means the gain distribution on the entire system consider the pre-amplifier gain and noise, and for that reason will not be correct to compare the IQ+ with other radios specially design to work below 30MHz in a very polluted RF spectrum. My reference in that case are the WSE converters but with some remarks. On the WSE converters the first 3 units (RX144, RX70 and RX10700) are mainly superheterodyne receivers, only the last unit RX2500 is a real SDR.
The presence of and external pre amplifier with high gain and very low noise introduce a big complication on the receiving design chain. Everybody knows how adverse the results are when you install an external preamplifier in front of any commercial radio: you simple destroy the excellent performance, specially the dynamic range. That's why most of the good transverters have the option (not all) to bypass the internal pre-amplifier if you do EME with a mast mounted preamp.
In that case the noise contribution per stage was carefully adjusted to maximize performance. Unfortunate is not possible to have a "universal calibration" matching all the conditions and all the stations, for that reason the properly IQ+ installation will demand the calibration of one stage: the internal preamp have a variable gain and you will need to open the radio and adjust your levels to reach the maximum performance in your particular setup. This proceed can be accomplish by most of the EME operators and only few skills are needed. Without this "final calibration in-situ" your system maybe cannot perform well. A small test will be described to see if the noise increment in your pass band is enough when you switch on/off your antenna preamplifier.
IQ+ performance data
The IQ+ is build considering the presence of an external pre-amplifier, this condition makes the IQ+ a different radio compare with other SDR's and commercial rigs where the presence of and external preamp was not consider during the desing phase. Any external preampifier will have a negative impact on the dynamic range and the IQ+ is not free of this "fact" but the noise contribution is well distributed and even with an external preamplifier the IQ+ exhibit an extraordinary performance.
All measurements done without and with an external preamplifier (25dB gain / 0.3dB NF), installing the IQ+ with a preampifier with different gain and NF could affect negative or positive the performance.
Input IP3 = +7dBm (no pre-amp) , -18dBm with external preamp.
Dynamic Range = 110 dB (no preamp), 93 dB with external preamp.
NF = 9 dB
Sensitivity @500Hz BW :
- Noise floor IQ+ = -146.7 dBm
- Noise floor IQ+ with external preamp = -121.7 dBm
A/D saturation at IQ+ input = -118 dBc/Hz
A/D saturation at external preamp input = -93dBc/Hz
Local Oscillator:
- Chip : Si570BBB from Silicon Labs
- Level : -5.6 dBm for IQ+ VL and V
-10.0 dBm for IQ+ U
- Phase noise: -110.8dBc/Hz @5KHz (288MHz)
-107.0dBc/Hz @5KHz (864MHz)
- Temp stability : +/- 20PPM fro -40/85 celcius.
- Phase unbalance Port1 - Port2 :
- 0.05 deg @ 100MHz
- 0.01 deg @ 288MHz
- 0.35 deg @ 864MHz
-Amplitude unbalance Port1 - Port2 :
- 0.00 dB @ 100MHz
- 0.03 dB @ 288MHz
- 0.03 dB @ 864MHz
Copyright © 2008-2024, Eich Switzerland by Alex Artieda, HB9DRI
EME and Weak signal communication
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