At 08:30 PM 12/1/2009, J. Forster wrote...
In fact, on the Tek 7704 or 7704A (I forget which) there were "No Cost" options of maximally flat frequency response OR best pulse response. OR!
Sure, if you're using a 150 MHz to try and measure accurately at 100 MHz, you're not going to get absolute accuracy. I'm not familiar with that particular scope, but would bet the difference appears as peaking at the extreme. In the absence of circuitry which deliberately changes it, the response of an analog scope is (very nearly) Gaussian.
Can you quantify the difference between those options when measuring a 50 MHz (1/3 BW) signal?
Since the OP is a ham, I assume his quest is relative to commonly available power meters for that market, most of which can't be expected to do better than 20% accuracy, maybe 5% at the high end ( http://www.telepostinc.com/lp100.html ).
Sure, you can buy an uncalibrated 3400A (good to ~150W), and get some unknown amount worse than 5% accuracy. Or a 432a (good to a whole 10 mW!) for <$100, plus another $100+ for the mount/cable. Now you've got something which is good to a couple of %, with an _extremely_ limited range (and practically useless for many ham applications).
A Gaussian scope is predictably off ~3% @ BW*0.3. A decent scope will have a vertical amp accurate to a couple of percent. With a 1% load, you can measure at the 5% level of a $400 dedicated wattmeter (from < 1 uW to 400W, and to the 2000W ham limit if you invest in a 100:1 probe), for little cost.
"Accurate...simple and inexpensive." Many non-appliance-operator hams will already have a scope, so the cost is a $10 resistor (for a 100W rated Caddock, which should be good for a few seconds of full power, enough to make the measurement).
Finally, as I've already mentioned, one can make a simple peak detector using a rectifier, and measure the DC voltage off that.
_______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
