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  2. Calibrating an RF detector

Re: Calibrating an RF detector

Paul G8AQA
 

Just a few experiences with the AD8310 which is the low frequency (440MHz) version of this range of devices.

Linearity was good but there was quire a large variation of output voltage with frequency so we havr ro calibrate at each frequency of interest.  The 50MHz calibrators are usually used for thermal power meters. 

The filter capacitor CLPF should not be omitted as rectified RF can otherwise appear on the output.

We encountered problems with the regulation of the supple and ended up using one of the A/D inputs of the Arduino processor to compensate for variations.

Examination of Fig 15 on the AD8317 data sheet will show the variation of input impedance with frequency.

It will pay to read the data sheet carefully to see how well it will suit your application.

Paul G8AQA


On 27/08/2017 08:17, willis.mj@... [ukmicrowaves] wrote:
 

Hi Terry,


I have of of those and also one of the OLED versions. I calibrated it against a signal generator which I believe is fairly accurate. It was within 2dB and much better in relative accuracy rather than absolute accuracy, i.e. measuring changes in power, so for example very useful to determine an amplifiers 1 dB compression point. You said you don't have one of those but they are often made available for testing at microwave round tables, as are good quality power meters that you can compare against. The next RT near you can be determined from the UKUG website. There may also be a local amateur with the right gear that can help.

Bear in mind that these chips have some thermal drift so you also need to calibrate against temperature. In practice, they are not really for accurate metrology but as very useful when used with a direct ional coupler to verify the TX is more or less working.

Mike 
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