this is another way but i havent seen anyone using this in centuries, the last time i saw it was on a old jerrold sweeper, everything i had ever since was using the approach i described, problem with the RF method is that its quite expensive to realize, a directional coupler, sampling mixer and the oscillator and frequency counter costs money and space and also takes away from the RF power, another factor is that whenever you use a comb generator you run the risk of finding your peaks "everywhere" even in places you dont want them :)
DC or LF stuff is cheap and doesnt take up much space so i think thats why most companies opted for this approach
J Forster <jfor@...> wrote:
lothar baier wrote:
ok there are two basic ways to create a marker in a swept system, one is called RF blanking the other one is called intensity modulation, ok usually you have a control voltage thats proportional to your RF frequency, if the analyzer sweeps its basically a ramp, each point of the ramp corresponds to a certain frequency, you feed this signal to a comparator and compare it to a DC voltage thats adjustable (coming from your marker pot) anytime the ramp "hits" this threshold you get a pulse on your comparator output, you route this pulse back into your display and use it to crank up the intensity just a bit at this point and there you have a marker blip on your screen :)
There is another way. You sample the RF, mix it with a (frequency settable) oscillator, run the output through a LPF, detector, and comparator and use this output for intensity markers.
This system has the advantage that you can count the oscillator and have accurate digital markers, and, if you replace the oscillator w/ a comb generator, you get nice, calibrated pips.
Best,
-John
you could also use this pulse to turn the RF of your TG off for just a moment but then you would end up with a dark spot as a marker for a short time instead of beein brighter.
Your statement about you seein a bright blip on your screen as a marker along with the statement about you seen the marker even with the calibator connected to your RF section input makes me certain that your markers are intensity modulated !
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