anechoic chamber calibration

I've a problem calibrating an small anechoic chamber. I'm doing a calibration with a constant field – a 1.5x1.5 m surface is divided in 16 points. A certain field level is set. For every point and every frequency (I'm rising freq with 5% steps, and 6V/m field level as prescribed in CEI EN 61000-4-3) signal level of the generator is registered.
My problem is that the measurement is so long I can't do it in less than 16 hours. This is way to long. My field sensor battery wont last so long (if nothing else). Did someone do a anechoic chamber calibration? How did you do it? I'm using Rohde&Schwartz instruments and instrument drivers are made with Labwiev.

C'mon! Did anybody do a anechoic chamber calibration. How did you do it?

I have a home made anechoic chamber.
But I have not problems at all and there is only a few topics to have carefully attention.
First use as low power as possible.
Second the absortion material must cover a broadband as big as possible.
Third humidity and temperature change measurements so try to mantein them controlled.
I did the anechoic chamber with expandable polyurethane cones painted with a paint made with various kinds of ferrite powders.
It works fine for my needs from 80 to 2500 Mhz.
What models of instruments are you using ?

Ok, but did you calibrate your chamber? How did you do it?

I was looking for Agilent paper where show very clear how to use theirs instruments with anechoic chambers.
First there are not adjusts to do just replace antennas with know gain ones(REFERENCE ANTENNA) and you can start using your chamber.
Remember to use as low power as you could thats for reduce echoes .
With my chamber I use 2 to 15 mW as sweeper I use a HP8922 and for power measurement a Boonton 4200 with a type 5 sensor.
I′m really very pleasant with the results I test antennas from 130Mhz to 2.45 Ghz
(for 2.4 ghz I use as generator a modified wifi router.