Roger > > The problem that has made me unable to go totally SDR, and for which I > really wish I had a solution, is that I do weak signal contest work [50 > MHz to 24 GHz] but live in an environment where during a [VHF and up] > contest I have more than 1 full-legal-power-on-multiple-bands station > operating within a few miles of me [one a multi op]. The extremely > high RF levels from inband signals from these stations trash the front > end of any radio [SDR or not] that I have had available to me that > doesn't have a narrow roofing filter [1st IF filter] to greatly > attenuate the inband signal [as long as it is outside the roofing > filter]. Given that the multiop stations usually have the lower four > bands [50-432 MHz] continuously occupied at 1.5 kW output, this is a > great problem on these bands. ---snip--- > I wonder if a hybrid approach such as something with an architecture > like the Orion I or II might offer the best of both worlds in terms of > performance in the environment described.
It seems to me that what you want is a high dynamic range VHF/UHF SDR. There are two projects that I am aware of that have started to address this; one is the High Performance SDR project and the other is the Microwave SDR project. Details of HPSDR can be found at :- hpsdr.org A VHF transceiver is planned, but at the moment most of the work is being done on OZY/JANUS/PHEONIX etc for HF; the VHF version is some way off. Probably a bit further down the road is the microwave SDR project, details of which are at uwsdr.berlios.de uWSDR are currently developing a 144MHz version, with other bands (50-432MHz) planned. Performance should be excellent - the 144MHz Rx will use a high-performance I/Q demodulator IC with a 24 bit ADC; the Local Oscillator will be divided down from a 2.3GHz synthesiser to give low phase noise etc. etc. It will take several months to complete development, but I'm guessing that the 144MHz version could be very popular. regards Grant Hodgson G8UBN for the uWSDR team
