Compare field strength

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Peter1337
Posts: 1
Joined: Fri Sep 20, 2019 9:24 pm

Compare field strength

Post by Peter1337 » Fri Sep 20, 2019 9:34 pm

Hi,

Can I compare field strength with a SDR?
To be more specific maybe 145Mhzish to 900Mhzish. I wouldn't mind a inaccuracy of factor 3.

alanzfq
Posts: 56
Joined: Thu Oct 04, 2018 11:18 am

Re: Compare field strength

Post by alanzfq » Sat Sep 21, 2019 11:19 am

What do you want to do?
Comparing signal levels to within about 1dB is easy.
Actual Field Strength will need a standard, few, if any, SDRs are calibrated.
Alan

hotpaw2
Posts: 101
Joined: Sat Jan 14, 2017 11:07 pm
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Re: Compare field strength

Post by hotpaw2 » Sun Sep 22, 2019 12:59 am

Depending on your accuracy requirements, the response of your SDR's RF front-end and ADC might not have a flat enough response for your needs without calibration. So you would have to calibrate your SDR over the frequency ranges of interest, perhaps with a decently calibrated signal generator and some attenuators.

You would also need one or more calibrated antenna's covering your frequency range of interest, as any single antenna will not have flat gain from 100 MHz to 1 GHz, although a discone or biconical of the right size range might be a lot better than any whip or dipole. If you can't calibrate, you might get close enough (depending on your accuracy requirements) by computer modeling (NEC, et.al.) a wide band antenna at all your frequencies of interest.

You would also need your test site to be free of metal objects (reflectors) within several wavelength of the antenna, or anywhere near the path between the radiator and your antenna.

snn47
Posts: 178
Joined: Tue Dec 27, 2016 11:00 pm

Re: Compare field strength

Post by snn47 » Mon Sep 23, 2019 3:19 am

and you have to know the transmission line loss(cable& connectors), The attenuation differs with frequency, the higher the frquency the higher the attenuation.

Furthermore the antennaazimuth and elevation pattern. The elevation pattern varies among other factors with frequency antenna height, above ground, ground reflectivity and polarisation to some factors.

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