(25-11-2013, 02:06 PM)Yorkie Wrote: I can understand on the one hand that the probe will rectify the RF waveform and just display a DC voltage, but on the other hand, that doesn't square with the comments and the pics of traces as shown in the clips of the article which I've appended below. The wobbulator article states: "Signal levels can be too low to produce a display on the 'scope. A suitable RF probe to amplify and detect the signal will be described in the next issue of Bygones". Again, that suggests that the output of the probe should produce a display (amplified) on the scope, of an RF waveform.
The article is written correct so far as I read it David, "A suitable RF probe to amplify and detect the signal will be described" That is what that circuit does, it's no different from a standard envelope detector that you would encounter in an AM radio apart from the fact that the detector is configured as a voltage doubler.
If you modulated the 1Mhz input that you have fed into it with a sine wave then that sine wave would be shown on the output and thus on the scope, thus the diode has demodulated/detected it.
If the 1Mhz input is CW then there's no modulation, if there's no modulation then there is no modulation to detect, the detector will thus produce a constant DC output proportional to the amplitude of the CW signal fed into the detector.
The waveforms shown in the diode probe article are the typical waveforms you would expect at the output of the probe when the input frequency to the probe is swept between two frequencies (the sweep width) and has passed through a typical IF stage, they show the DC voltage output of the detector across the sweep width.
I don't know if you have used the wobbulator yet?
If not then that would be the next stage, you will need a sawtooth input to it to obtain the sweep, this is normally taken from the scopes timebase output, normally a socket on the back of the scope, however some scopes do not have that facility, if not then you can tap into the scopes timebase at a suitable point, the other alternative might be to build a seperate sawtooth generator to trigger the scope and sweep the wobbulator.
Lawrence.
