Re: Calibrating an RF detector


geoff Blake
 

First, you need to decide exactly how accurate you need to calibrate the sensor. RF power is notably fickle in this aspect. All but the best, most well equipped calibration labs are hard put to measure much better than +/- 5% over the range you speak of. Before other folk raise their pens to criticise me, at certain spot frequencies better figures are attainable.  In amateur circles I cannot see that any better than +/- 10% is necessary. Of course your amateur SWR/power meter will be much better than this :-)

OK, to sensibly and reasonably accurately calibrate a RF power sensor, you need to:

1) check the RF sensitivity of the device, i.e. RF in to outputted reading. This is the primary step and is best done at 0dB or 1mW. This is probably best done with the 1mW 50MHz reference fitted on many HP and other power meters. This power meter should have been recently calibrated - the specified power drift of the reference source is 0.7%/yr IIRC.

2) check the return loss of the sensor. Obviously, any reflected power is going to reduce the readout and make the sensor read low. This needs to be done at several frequencies over the range.

3) look at the linearity of the sensor, i.e. if you reduce the power by 10dB, the output reading should reduce by 10dB.

4) Check the noise floor of the sensor, i would expect this to be about -60dBm and would increase the error at -50dB by about 10% or so.

In practice, and in an amateur world, I would choose Francois's option first, although I would go easy on the good beer, at least until the measurements are all finished :-)

Andy's proposal, just to use the spec. sheet figures, would probably produce significantly better results that those of a typical SWR/power meter or dare I say it, a Bird model 43 system.

Good luck

Geoff G8GNZ

#################################################
Geoff Blake,   G8GNZ    JO01fq:   Chelmsford,  Essex,  UK
<geoff@...>    or   <melecerties@...>
Using Linux: Ubuntu 14.04 on Intel or Debian on UltraSparc
    and  Apple  OS  X  El Capitan  on  my  Macbook  Pro.    
                Avoiding Micro$oft like the plague.
#################################################

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

'jnt


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

Hi all, I have one of these

http://www.ebay.co.uk/itm/AD8317-1MHz-to-10GHz-RF-Power-Meter-Logarithmic-Detector-Controller-f-Amplifier-/172248001491?hash=item281ac7ebd3:g:SSoAAOSwM4xXZ9NN

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?

Cheers

Terry






Join UKMicrowaves@groups.io to automatically receive all group messages.