Bradly You must define what are the enemies of the receiver.
A zero frequency SDR receiver has no IF images. but it has alias responses, so the reality is that the baseband filters (I and Q) should be >90dB down outside the passband and at the aliases. My experience is that this is where effort needs to be spent. As long as the front end does not overload (hit the P1dB) then you are pretty much OK in that part unless you land a unfortunate / unlucky intermod. My experience is for this receiver you just need to keep strong FM and TV stations from overloading the receiver. if another ham overloads the receiver, well so be it. The other thing you need to be concerned about are mixer spurs, harmonics of the mixer LO, harmonics of the products etc. Hence the good IQ LPFs. or if you have a low IF receiver, just watch the converter aliases. if you do need a front end bandpass try this one Bradly probably an overkill for a mobile/portable. http://www.temwell.com.tw/PDF/TT67709B-146M-Performance.pdf or suggest triple tuned circuit, top coupled C, using T25-2s and fixed caps with cap divider at each end. adjust by squeezing the toroid inductors. you should be able to operate it at a loaded Q of >15 with reasonable loss. regards On 14/04/2015 12:37 PM, Brady O'Brien wrote: > Hi everybody, > > I've been helping out with the development of VHF and up FreeDV and the > minimalist VHF SDR. I've gotten to the point, on the analog side of things, > that it seems appropriate to get a board made. What I've designed is a VHF > frontend for further experimentation. It's based heavily on the VHF section > of the DSP-10 ------------------------------------------------------------------------------ BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM EDT Develop your own process in accordance with the BPMN 2 standard Learn Process modeling best practices with Bonita BPM through live exercises http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- event?utm_ source=Sourceforge_BPM_Camp_5_6_15&utm_medium=email&utm_campaign=VA_SF _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
