Re: Calibrating an RF detector

Andy G4JNT

Feedback and PIN attenuators are fine, but how do you calibrate your 1mW in the first place?

You need an accurate power level or meter to compare with.

CMAS gates can work OK ish.   Use AC series gate which at 50Mhz will be giving a reasonable squarewave its ouptut resistance is about 10 ohms so use 39R reistor and connect to 50R load.  You now have a 2.5pk-pk square across your 50R load, that is delivering 

At the fundamental that is 2.5 * 4/pi = 3.2V pk-pk or 25mW = 14dBm
Use resistors / attenuators appropriately.

But remember that level is at the fundamental only.  If unfiltered, harmonic components will add.


On 26 August 2017 at 17:58, GORDONJ REASON gordonj.reason@... [ukmicrowaves] <ukmicrowaves@...> wrote:

to give me a 0dBm , (1 mW ) source at 50 Mhz ..............

I use a Xtal oscillator ........ and buffer .......... followed by a single , +V ,  pin diode attenuatror .

the rf output is rectified with a shottky diode .

That DC is fed to one input of an opamp .

The other input is a DC reference from a TL431 .

The output + feeds back to the PIN Diode attenuator , via a small resistor , and the opamp has a multiturn pot in the feedback path ..... 

Works like a charm ...... 

It's not inmportant to use a Crystal osc .......... the frequency is your choice .....

On 26 August 2017 at 15:54 "Andy Talbot andy.g4jnt@... [ukmicrowaves]" <ukmicrowaves@...> wrote:



First of all, download the datasheet for the AD8317 and study that to see what you've got

As the evaluation board you have "probably" has no additional DC conditioning on the output or RF gain or attenuation,  until you can prove otherwise, it'll probably do what it says in the datasheet in terms of Vout vs Pin


On 26 August 2017 at 15:50, terry.bailey@... [ukmicrowaves] <ukmicrowaves@...> wrote:


Hi all, I have one of these

I it works fine but I don't have any idea how to calibrate the readings I am getting from it. I don't have a reference source. I do have a spectrum analyser which is good to 10GHz, but it is totally uncalibrated and somewhat temperamental.

Can anyone point me in the right direction?








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