EMRFD Message Archive 11604
Message Date From Subject 11604 2015-09-08 08:49:54 Rod files have been uploaded to show xtal filter scans On 9/05 I replied to Ravi r.e source coupled JFET oscillator, and included a
description of a scalar network analyzer I built to sweep filters and
I attempted to attach files showing the filter sweeps, but they did not come
So, I uploaded the filter sweep .jpg files to the file area....
I used a program running on a PC called KST to generate the images.
Very powerful software, and allegedly one can use it to generate
plots in real-time.
For your viewing pleasure,
11605 2015-09-08 10:10:47 Ashhar Farhan Re: files have been uploaded to show xtal filter scans I don't see why we need to sweep it anymore. you can plot it anyway on a computer. here is how...you need :1. a manually tuned signal generator.2. power meter based on pic with frequency counting as a part of the firmware.Now, as you manually tune around, the pic will take readings at different frequencies and send it to a pc where it can be plotted. the sweep needn't be linear or uni-directional either. those things can be ironed out in the software.the power meter too needn't be a perfectly caliberated log detector. instead a lightly biased germanimum diode based detector can be calibrated in software as well.- f 11607 2015-09-08 19:44:47 kb1gmx Re: files have been uploaded to show xtal filter scans 1. a manually tuned signal generator.With enough stability and resolution.... Now that AD9850 or SI570 and kinare easily available for acceptable prices this is easy.However in the days of olde that was not true. The solution was a frequencycounter (at tool not everyone had) and to get stable RF a VXO usingsaid same crystals. A 2.2 khz filter means you need to measure to thenearest 10hz and be able to tune a signal generator to that and keep it there.any FM in the generator shows up as a voltage that's not stable especiallyon the skirts of sharp filters. Most general purpose signal generators werenot up to the task and those that were often didn't fit the budget.For either of the above a diode detector with 16db preamp can be calibrateddown to -50db and good up to about 0db at the input. I'm thinking somethinglike a 2n2222 and a 1n5711 diode. This is also useful for other things. Betteryet is the Circuit from W7ZOI using two diode and an opamp, good powersensitivity and linearity. If that's not sensitive enough a preamp ahead ofthe detector is a solution.Now I skip both. Use a noise source and down convert from the filter frequencyto audio and use Spectran. View spectrum on PC. No sweeping and all that.2. power meter based on pic with frequency counting as a part of the firmware.Now, as you manually tune around, the pic will take readings at different frequenciesand send it to a pc where it can be plotted. the sweep needn't be linear or uni-directionaleither. those things can be ironed out in the software.A viable solution but is that the easiest way and easily reproduced for a personthe first time? Better as a established kit. Also the meter does not have to readas power it can be voltage across a known load. Same thing only voltage mostpeople can measure with good accuracy thanks to DMMs.Allison 11608 2015-09-08 20:25:11 DuWayne Schmidlko... Re: files have been uploaded to show xtal filter scans I used a pair of simple diode detectors feeding a dual opamp in the simple SNA I built. The rest of the SNA is a AD9850 controlled by an Arduino, and a small graphic display. I measure the output going to the Device Under Test, and input coming back from the DUT. Then compute the db gain or loss of the signal.
Only have about 50 db range, but for what I do it is more than adequate. An advantage I found with this method is that I don't have to worry about the non linear output of the DDS over a large frequency range. Alignment is simply connect a cable between the input and output, start a sweep ,and adjust a couple of pots for full scale readings reading on the instrument. A function in the software makes that very easy. I have information on my blog along with some of the functions I added to the basic software.