> 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,
Really? The most successful 'scope in history. > 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. Apparently, you don't know what an HP 3400A is. Stick to political blogs. -John =============== > 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.
