Author Topic: Measuring 2.4g ISM in time domain  (Read 749 times)

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Offline Harvs

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Measuring 2.4g ISM in time domain
« on: December 13, 2016, 12:58:57 pm »
I'm working on a personal project in order to learn more about RF, in particular up in the 2.4GHz ISM band.

So I'm having a go at building an RF front end (LNA/PA) for a Wifi chipset to hopefully increase its performance. Only it doesn't have switching control outputs for the LNA/PA.

It seems simple enough to build a coupler and feed a detector circuit to trigger when the chipset is transmitting, but my question is how would one go about measuring the switching performance in terms of time to switch on and off?

My lab is kind of setup for digital and analog sensor work apart from a USB VNA, so is there any way to observe this on a 200MHz DSO?  Is some sort of down-converter the answer?

Any points in the right direction would be great.
 

Offline w2aew

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Re: Measuring 2.4g ISM in time domain
« Reply #1 on: December 13, 2016, 01:05:07 pm »
One thing that you'll have to be very careful with is the timing of the turn on of the PA.  Carrier sense might not be fast enough to enable the PA and still maintain the integrity of the preamble of the OFDM transmission. If the beginning of the preamble is truncated, the signal won't be able to be decoded in the receiver.
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Offline Harvs

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Re: Measuring 2.4g ISM in time domain
« Reply #2 on: December 13, 2016, 01:48:51 pm »
One thing that you'll have to be very careful with is the timing of the turn on of the PA.  Carrier sense might not be fast enough to enable the PA and still maintain the integrity of the preamble of the OFDM transmission. If the beginning of the preamble is truncated, the signal won't be able to be decoded in the receiver.

Thanks, this is really why I want to be able to measure it.  The makers of these wifi boosters seem to be able to get it to work, with a spec of 1us switch time:
http://www.ebay.com/itm/4W-2-4Ghz-WiFi-Wireless-Broadband-Amplifier-Power-Range-Signal-Booster-Extender-/232168129340?hash=item360e4c833c:g:cHMAAOSwA3dYSVWd

The integrated SMD PA's I've been looking at from Skyworks have typical rise and fall times of about 0.5us to 0.75us.  So if I can get a detector + comparator timing to be < 0.25us.

This video shows pretty much what I'd like to try and build, they show switching times around 0.8us.
 


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