[time-nuts] OT: Power level reference

[J. Forster]

> 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.
>
>
>