I had no idea single-band boards were so inexpensive. There is a Japanese supplier who will sell a board delivered to the US for $21. The softrock boards though, sound like they are better documented. I just wish that either supplier had down-loadable manuals so I could get a better idea what the off-board needs are and what software is available/required. BTW my PC is running Linux. Is that a bad thing?
On Wed, May 14, 2008 at 3:47 PM, Dave Wade <[EMAIL PROTECTED]> wrote: > > --- In [email protected] <soft_radio%40yahoogroups.com>, > "Patricia Wilson" > <[EMAIL PROTECTED]> wrote: > > > > Thank you Carlos, a useful answer. > > > > I am rather new to this SDR thing and have a really newby question. > > Where in the chain between antenna and speaker should the signal be > > sampled by an SDR? The Nyquist limit imposes a sample rate of at > > least twice the highest frequency component so if you want to sample > > at the input RF and that RF is 29 MHz then you need a sample rate of > > 58 MHz which is not only pretty fast but will also produce a LOT of > > data very quickly. On the other hand if you mix it down to a first > > IF you lose the possibility of digitally filtering out unwanted > > signals earlier in the signal path before they have a chance to > > overload something. > > > > As with nearly everything in engineering it is a trade-off. But > > where do most SDR's do the sampling? > > It depends on what you mean by "most". There are probably more "baseband" > SDRs (in effect direct conversion) "in the field" as they are reasonably > cheap to make and can be very versatile. The Softrock series of boards > > http://www.wsplc.com/acatalog/SOFTROCK-RXTX.html > > each of which can be squeezed to cover most of an amateur band using a > single crystal, are probably the most populous. There are also a number of > home brew designs. I myself have the Elektor (Dutch Magazine) design which > is general coverage. Providing you use a pair of mixers with 90 degree out > of phase carriers you can easily eliminate unwanted side bands and even > demodulate FM digitally. By putting the mixer close to the antenna you > don't > get the same blocking issues you get with traditional multiple conversion > Receivers, and the image problems are much reduced. > > These are also useful as add-ons to traditional receivers when tuned to the > IF frequency and used to replace the filtering function. In this case you > may still get issues from the higher level mixer, but you do get a very > versatile set of filters. In addition you can use software (I forget its > name and google is no help) that will simultaneously decode and display > multiple CW signals at once... > > On the other hand I feel that direct sampling receivers must offer the way > forward. Sampling directly at RF will give the best fidelity of signal. > Trouble is at present its more expensive :-( > > Dave > G4UGM > > -- Patricia Wilson Apache Junction, AZ Member NRA, BMWMOA, AMA, ARRL WB8DXX BMW '06 R1200RT "Graues Gespenst"
