Don is assuming your 'scope is calibrated! No scope is good enough to work properly if it's out of calibration, Hi!
Usually the most dependably calibrated piece of test equipment in a Ham shack is the DMM. They are robust and stable unless really abused. A simple RF rectifier circuit such as that included for power measurements in the DL1 can be used with your DMM to check the calibration of the 'scope. If using the DL1, keep in mind that the voltmeter circuit in it measures *half* the applied RF voltage to provide a greater power range without burning out the diode. Since your 'scope measures peak-to-peak and the metering circuit in the DL1 1/2 the voltage, the peak-to-peak reading on your scope should indicate 4 times the DC voltage shown on the DMM attached to TP1 of the DL1. Of course, you can rig up your own RF rectifier, using the circuit shown in the DL1 schematic (it's on the Elecraft under Manuals and Downloads web site). For best accuracy check the forward voltage drop in the diode you are using and add that to your readings as described in the DL1 manual. A diode like the 1N5711 used in the DL1 will have a quite low drop - in the range of 0.15 to 0.2 volts. A common silicon switching diode will also work but will have a forward drop in the range of 0.6 volts. For best accuracy, you want to apply enough RF to be well above the forward drop voltage, but not so much you destroy the diode. If your scope is okay at a low voltage, compared to the DMM, it's probably fine. It's rare for a 'scope to be off on other ranges. Their calibration is done by setting the gain of the amplifier circuits. The step attenuator at the input is usually very stable and, unless it's been abused with too much voltage applied, seldom causes significant error. Don warned you to use a 10X probe with your 'scope. That's one very important reason. Most 'scopes that I've seen can only handle a few volts applied directly to the vertical input without damaging them. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
