Boy all sorts of old ideas being resurrected. But it's hard to look it up if you don't know the name.
A PLL does not have to lock on an absolute frequency, if you use the right kind of phase comparator you can lock on any frequency that is a multiple of the reference frequency without having a large divide by N counter. By using proper component you make the locking range to be barely wider than 1/2 the reference frequency, for example; If you use a reference of 10 KHz and your PLL bandwidth is about 5.5KHz, as you change the frequency determining components the oscillator to a higher frequency let's say from 7Mhz to 7.0035, it tries to move but the PLL pulls it back at down to the frequency that it was at 7.000Mhz,if you keep turning the knob so the the oscillator's natural frequency has moved 7.0055 MHz the original 7.000MHz can't be locked but the higher frequency 7.010MHz can be locked. What it ends up doing is stabilizing the frequency at some value, because if there is a slow drift, it corrects for it, the price you pay is you can only dial frequencies that are multiple of the reference frequency. This inexpensive way of locking a VFO to frequency is often referred to Huff & Puff. Typically you use some low frequency such as 100Hz so your VFO can change is small steps, with a SDR that is not necessary since it has 48KHz to 192KHz window, you can take bigger steps By the way Varicaps are reversed biased for operation so they use practically no current at all. Do a Google search on Huff & Puff, here is a link to get you started; There are several kinds there that are very simple. < http://www.hanssummers.com/radio/huffpuff/minimalist/index.htm > Here is a Huff & Puff stabilized oscillator that uses a inexpensive PIC CPU ($1) to stabilize the oscillator. < http://kd1jv.qrpradio.com/QRPTX.HTM > At 04:22 PM 4/15/2006, you wrote: > Someone build this for us all to use in SDR! > > I want to mention an idea I once had in the 80's I told someone > about and they said someone had done it but I never did run across > an example of anyone doing it anywheres since then. Maybe it is > out there somewheres. Its a PLL idea. A logical circuit evolution of sorts. > > You can take a frequency counter and sample its latter digits and > then use that data as a PLL control where the frequency counter > loops to the vfo with a vco signal to a Varicap diode. This means > you have to unlock it then tune the vfo and then relock it. I did > see an idea not long ago close to this idea somewheres on the net, > but it was not exactly as I see it here. >This will make sine wave vfo's popular again. But you can keep your >square wave detector circuits in the i.f. so don't get me wrong here. > > The vco control signal is a matter of sampling an up or down > count movement in the frequency counter in the finer resolution > ranges of the circuits dividable counters. A simple chip or two and > a transistor and perhaps a diode are required in the sampling > circuit to create a vco voltage. > > I suspect that a high resolution frequency counter that runs in > real time terms; and not at a slow gate period, will be > best. Sampling the digits in the 10 to 1 Hz range. The idea can > then become standard in most frequency counters sold for amateur > radio use. And work with any vfo idea one has. Which means that > it is a universal application for all vfo's. I feel that the vco > signal must have a good amount of current so that one can use two > or three Varicap diodes parallel or merely one depending on the > frequency of the vfo. VLF range vfo's might require two or three > parallel Varicap diodes to do the trick in obtaining enough > capacitance change. Hence this is for VLF to HF use. A parallel > resitor to the Varicap diode circuit will match the current load > when only one Varicap diode is required in a vfo. > > If anyone runs across an idea along these lines or even developes > a circuit for this then let us know. This really is a logical idea > and a most usefull idea. And its about time it was made. > > Finally, a simple circuit board can be made that can be added to > any frequency counter; will also do the trick. I hope it seems > simple enough an idea and hopefully will be simple once someone > with fast designing abilities gets ahold of an idea for it. > >Dan > > > >_____________________________________________________________________ >Call Anyone, Anytime, Anywhere in the World - FREE! >Free Internet calling from NetZero Voice >Visit http://www.netzerovoice.com today! > > > > > >Yahoo! Groups Links > > > > Cecil Bayona KD5NWA www.qrpradio.com "Windows the worlds most successful software virus" Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/soft_radio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
