[Microwave] Measurement interpretation.

[Dr. Gerald N. Johnson]

On Wed, 2007-04-11 at 16:09 +0200, DAKA Technology Johannesburg wrote:
> Hi all,
>  
>     I have a question regarding what an analyser will display when a
> WLAN is connected!
>  
> I have a WLAN card that operates in the 5.8GHz band and allegedly gives
> out +20dbm (OFDM modulation) and runs at a 25MHz channel spacing.
>  
> I connect this to an old but calibrated, and trusty TEK 492, press the
> max hold button and select peak store.
>  
> The display shows the expected shape of the channel occupancy but the RF
> level is too low. For this board it shows a peak RF level around 20 db
> less ie about 0dbm.
>  
> I do understand that the resolution bandwidth will effect the displayed
> results (currently set to the 492's max of 1MHz) and note that the
> displayed RF level is about 10db lower when going to 100KHz resolution
> bandwidth.
>  
> My question is that for a WLAN unit that is giving out what the
> manufacturers specify (say +20dbm) what should I expect to see on the
> analyser. Is there a relationship between the analyser bandwidth, the
> WLAN channel width or similar specifications that I can use?
>  
> Thanks & 73 to anyone able to help.
>  
> Dave ZS6BNT / G3ZGZ
> 
I think probably that the data per carrier is being spread ten times
wider than the 1 MHz bandwidth of the analyzer. That's how spread
spectrum clocks claim to reduce interference levels, simply by spreading
wider than the standard analyzer bandwidth.
-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer