[600MRG] Scoping MF XMTR Output

[J Mcvey]

If I understand the question, you want a mini scope for monitoring the keying waveform at the output?
It's all about bandwidth on scopes. I think the rule of thumb is the BW should be at least twice that of the frequency to be measured.EVen if you want the slow rate of keying displayed, the amp still has to be able to handle the RF frequency within the envelope.If you were to expand a triggered scope trace at the RF frequency, you should be able to see the amplitude ramp up every cycle until it gets to V max.
Not that's all that useful for the application, but it can refine it to that point. If not, the scope is inadequate for the purpose. It wont be accurate at the envelope rate.
 

    On Sunday, July 24, 2016 7:30 AM, Frank Lotito <k3dz at live.com> wrote:
 

 Yes, I have been triggering my scopes, both digital and analog with my keying generator.  However - back to my initial primary  question - do I need an old fashion analog scope to observe the "envelope" of the keyed transmitter output in order to check rise and fall times, power supply ripple, etc.? Any thoughts on my other questions?

73 Frank Lotito  K3DZ / WH2XHA

________________________________________
From: J Mcvey <ac2eu at yahoo.com>
Sent: Saturday, July 23, 2016 10:10 PM
To: Frank Lotito; 600 / 630 Meter Group
Subject: Re: [600MRG] Scoping MF XMTR Output

The simplest thing to do is provide an easy trigger-able repetative waveform like a from a square wave generator.
Depending on the age of the equipment, the interface between the generator and the key input has to be designed accordingly.
Alternately, you might try running a line from the key itself to the trigger input of the scope, so the trace starts on keydown, but it might miss the leading edge unless you have a delay function available on the scope.


On Saturday, July 23, 2016 9:56 PM, Frank Lotito <k3dz at live.com> wrote:


I'm looking for suggestions on how to properly apply digital oscilloscopes to take a look at the keyed envelope of my 630 meter transmitter.  I have access to 3 different working oscilloscopes, two digital:  a B&K 2530 and a Tektronix TDS 210, and an analog "looks like its gonna need a new CRT" Tektronix TAS 465 scope.

When I use my B&K 2530 or Tektronix TDS 210 to view the transmitter's output at "fast sweep speeds," all's as to be expected.  A nice clean sinusoidal waveform at the transmitter's output.  If I slow down the sweep speed to look at the RF envelope, UGH! For the B&K the displayed waveform is that of an AM modulated waveform at about 50% modulation.  For the TDS 210 the appearance is that of a rectangular array of low-density dots.  The analog scope (TAS 465) waveform appearance is what you expect to see, but intensity modulated (hum modulation in the CRT accelerating electrode power supply / CRT heater-to-cathode short?)

Product reviews of amateur transmitters commonly contain one or more photos of the keyed envelope at 60 WPM.  Beautiful, no strobe or "AM" effect or intensity modulated effect.  Is the scope used for these measurements an analog scope, such as the product evaluations in QST?

Thinking out loud, what would the keyed RF envelope look like if one were to use a recent model "almost shirt pocket sized" digital scope?

The user manuals for these 3 different scopes say nothing in particular w.r.t. viewing the envelope of a transmitter output, regardless of the modulation type, e.g. CW, SSB, AM, PSK, etc.

You suggestions are most welcome.

73 Frank Lotito  K3DZ / WH2XHA



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