measuring RF field strength

Anyone know of a good field strength meter for measuring the field strength emitted by a wireless device?

Not cheap but I've used these at work and they are great http://www.zoro.com/g/00105154/k-G4262946?utm_source=google_shopping&utm_medium=cpc&utm_campaign=Google_Shopping_Feed&gclid=Cj0KEQjwjZefBRDfsY28oNjbgeABEiQA8kVt3dltNnHvZPd4IjIJd-TJyKif0cPkjK-YnKHJV8Rvo5EaAqna8P8HAQ

What 'wireless devices' are you wanting to measure?  Wireless access points?  Wireless security sensors?  Wireless portable devices?  Your 'RF' description covers a pretty broad range.

BraveSirRobbin said:

What 'wireless devices' are you wanting to measure?  Wireless access points?  Wireless security sensors?  Wireless portable devices?  Your 'RF' description covers a pretty broad range.

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Sub-1ghz wireless transceivers, such as Ciseco's SRF shield for arduino: http://shop.ciseco.co.uk/srf-shield-wireless-transciever-for-all-arduino-type-boards/ which can be set to work at 915Mhz, 433Mhz, or 315Mhz.  It's based on TI's CC1110 chip.

This is a possibility http://www.ti.com/tool/MSP-SA430-SUB1GHZ
 
You could also ask in this forum http://forum.43oh.com/ .  There are a few engineers that hang out there and know their RF stuff.

What's your budget?  Be aware that you get what you pay for with these devices, mostly in terms of accuracy and response time.
 
http://rfexplorer.com/models/
 
http://www.ebay.com/itm/Tektronix-2712-9kHz-1-8GHz-Spectrum-Analyzer-/231287797745?pt=LH_DefaultDomain_0&hash=item35d9d3b7f1
 
http://www.ebay.com/itm/Agilent-HP-8591E-9KHz-1-8GHz-Spectrum-Analyzer-/171412844003?pt=LH_DefaultDomain_0&hash=item27e9006de3
 
http://www.rigolna.com/products/spectrum-analyzers/dsa800/dsa815/

My interest in it was just to make sure I stay within the FCC Part 15 rules for transmit power, and I wasn't sure what might be available for that purpose.  The TI chip is programmable as to output power, but how much of that gets radiated depends on the antenna and the insertion loss, etc.  I can measure RSSI on a receiving chip, and convert that into field strength, but it's the same problem in reverse: unknown as to what the antenna related losses are.  Then there are the antenna gains to consider, but those are easier to closely approximate.  It would be easiest if I had a simple calibrated meter for reading field strength over a given bandwidth centered on the tx frequency.  It wouldn't make sense to pay a lot for it, because it would undermine the point of using inexpensive $14 transceivers in the first place.  If there isn't a low cost field strength meter, I will just make some overly conservative assumptions and reduce tx power accordingly so as  to guarantee I'm operating within the Part 15 power limits.
 
Ideally these sorts of measurements should be done in an anechoic chamber,  and I'm far from sure whether I would get any useful measurements without one.  I've never tried doing it before, and so I have no feel for it.  Fortunately, the FCC requirements for a hobbyist build are slightly less exacting as for something that would be sold commercially, but it's clear the objective is still to fit within the same standards for field strength (measured at a 3 meter distance from the tx).

NeverDie said:

My interest in it was just to make sure I stay within the FCC Part 15 rules for transmit power, and I wasn't sure what might be available for that purpose. 

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An RF Power Meter is what you'd ideally want, but they are $$$$.  A spectrum analyzer would put you in roughly the same ballpark for much less.
An analyzer with a tracking generator would also allow you to test the sensitivity of your receiver.
 
 

NeverDie said:

Ideally these sorts of measurements should be done in an anechoic chamber,  and I'm far from sure whether I would get any useful measurements without one. 

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Not necessarily.  Most cases you'd connect the meter directly to the RF output and measure the true output.  Antenna loss would be calculated (or observed) from there.
Unless you're in a very heavy RF environment, you could easily decrease the sensitivity of the analyzer to reject noise and clearly show the DUT while using antennas.
 
I suggest heading over to the Radio Reference Forum and asking the same question in THIS forum.
 
YMMV

Thanks!  I'll have a look at that forum.  I would think this is a fairly common concern, so there may already be postings there that address this scenario.

Automate said:

This is a possibility http://www.ti.com/tool/MSP-SA430-SUB1GHZ
 
You could also ask in this forum http://forum.43oh.com/ .  There are a few engineers that hang out there and know their RF stuff.

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Thanks, Automate.  43oh.com has good info.

How about an Analog Discovery?
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,842,1018&Prod=ANALOG-DISCOVERY&CFID=5049376&CFTOKEN=7351c4d47e79ca12-E163728F-5056-0201-02A9CFE8169BC6C9
 
If you are a student, you can pick it up for $99.
 

• 2-Channel Oscilloscope [*DWR there are 4 ports...maybe for differential in??  Confuses me)
• 2-Channel Waveform Generator [*DWR I've not used this]
• 16-Channel Logic Analyzer    [*DWR with protocol decoders]
• 16-Channel Digital Pattern Generator
• ±5VDC Power Supplies
• Spectrum Analyzer
• Network Analyzer
• Voltmeter
• Digital I/O
• Now supported by MATLAB / MATLAB student edition

 
I have one and use it often.  Really is a nice product, especially for the $$.  I've not used the Spec A., but I've purchased some addons for the device (so I can use BNC probes), and a few other things.
 
--Dan

drozwood90 said:

How about an Analog Discovery?
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,842,1018&Prod=ANALOG-DISCOVERY&CFID=5049376&CFTOKEN=7351c4d47e79ca12-E163728F-5056-0201-02A9CFE8169BC6C9
 
If you are a student, you can pick it up for $99.
 

• 2-Channel Oscilloscope [*DWR there are 4 ports...maybe for differential in??  Confuses me)
• 
  
• 2-Channel Waveform Generator [*DWR I've not used this]
• 
  
• 16-Channel Logic Analyzer    [*DWR with protocol decoders]
• 
  
• 16-Channel Digital Pattern Generator
• 
  
• ±5VDC Power Supplies
• 
  
• Spectrum Analyzer
• 
  
• Network Analyzer
• 
  
• Voltmeter
• 
  
• Digital I/O
• 
  
• Now supported by MATLAB / MATLAB student edition
• 
  

 
I have one and use it often.  Really is a nice product, especially for the $$.  I've not used the Spec A., but I've purchased some addons for the device (so I can use BNC probes), and a few other things.
 
--Dan

Click to expand...

That does look like a nice general purpose tool.  Is it sensitive enough and have enough resolution that it can pick up RF directly, or would it need some kind of device/circuit in front of it?  I'm guessing the latter case, and, if so, perhaps by leveraging the Analog Discovery an add-on could be fairly basic and inexpensive.
 
As a ghetto approach, I found I'm able to do a crude comparison of signal strengths using SDR# and a $10 SDR dongle with antenna.  One thought I had was to acquire an inexpensive FCC approved device that uses the same transceiver (or at least the same kind of PHY) and use it as a yardstick against the device whose field strength I'm trying to measure.  Maybe your analog discovery device could be used similarly to yield a more accurate comparison against such a reference.

NeverDie said:

That does look like a nice general purpose tool.  Is it sensitive enough and have enough resolution that it can pick up RF directly, or would it need some kind of device/circuit in front of it?  I'm guessing the latter case, and, if so, perhaps by leveraging the Analog Discovery an add-on could be fairly basic and inexpensive.

Click to expand...

 
The bandwidth of the Analog Discovery scope is limited to 5 - 10 MHz according to the reference manual.  I'm not sure it will be useful if you are looking to do measurements in the 400 MHz to 1 GHz range.