Electronics > RF, Microwave, Ham Radio

Cheap RF signal generator any good?

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Merlysys:
Looking for a simple RF signal generator to test antennas in the 2.4-2.5 Ghz.
I came across this cheap unit. It doesn't have the buttons and displays of the typical unit as it is USB controlled. I don't need the accuracy, just the ability to create an RF signal in the desired range (yes I will keep power output to lowest)

If this unit not a good buy what basic unit would you recommend?

Specs
Output frequency range 138MHz-4.4GHz,
Stepping: 1kHz
Output power (for reference): 150M-3.2DBM; 250M-3.4DBM, 500M,-3.4DBM; 750M-2.8DBM, 1000M-3.4DBM;
1500M-3.6DBM; 2000M-4.0DBM; 2500M-2.8DBM; 3000M-1.8DBM; 3500M-3.6DBM
Spectrum of the input frequency range of 138M-4.4GHz
Frequency Accuracy (after calibration): +-1k @ 1GHz
Low-noise input signal amplitude:-70DBM @ 0.5G

http://www.ebay.ca/itm/138MHz-4-4GHz-USB-SMA-Source-Signal-Generator-Simple-Spectrum-Analyzer-138M-4-4G-/351805484236?hash=item51e93daccc:g:4D0AAOSwU-pXqX7W

tggzzz:
Harmonics can be an issue.

Cheap RF sig gens often have a PLL/VCO which is divided down digitally to get the lower frequencies. The consequence is that the high frequencies are a "reasonable" approximation to a sine wave, but lower ones are a square wave. Whether that matters depends on what you are trying to measure, how you are trying to measure it, what is in the UUT, and what extra filtering you could add to the testbench.

I suspect, but have not checked, the unit you refer to has a PLL/VCO operating 2.2-4.4GHz.

uncle_bob:

--- Quote from: Merlysys on August 13, 2016, 02:04:30 am ---Looking for a simple RF signal generator to test antennas in the 2.4-2.5 Ghz.
I came across this cheap unit. It doesn't have the buttons and displays of the typical unit as it is USB controlled. I don't need the accuracy, just the ability to create an RF signal in the desired range (yes I will keep power output to lowest)

If this unit not a good buy what basic unit would you recommend?

Specs
Output frequency range 138MHz-4.4GHz,
Stepping: 1kHz
Output power (for reference): 150M-3.2DBM; 250M-3.4DBM, 500M,-3.4DBM; 750M-2.8DBM, 1000M-3.4DBM;
1500M-3.6DBM; 2000M-4.0DBM; 2500M-2.8DBM; 3000M-1.8DBM; 3500M-3.6DBM
Spectrum of the input frequency range of 138M-4.4GHz
Frequency Accuracy (after calibration): +-1k @ 1GHz
Low-noise input signal amplitude:-70DBM @ 0.5G

http://www.ebay.ca/itm/138MHz-4-4GHz-USB-SMA-Source-Signal-Generator-Simple-Spectrum-Analyzer-138M-4-4G-/351805484236?hash=item51e93daccc:g:4D0AAOSwU-pXqX7W

--- End quote ---

Hi

Test antennas how?

A network analyzer (which this is not) is a much more common thing to test antennas with.

Bob

Kalvin:
One can test antennas with a signal generator and a simple SWR bridge. Something like these:

http://pe2er.nl/wifiswr/
http://www.w1ghz.org/QEX/A_UHF+_VSWR_Bridge.pdf

uncle_bob:

--- Quote from: Kalvin on August 14, 2016, 01:37:23 pm ---One can test antennas with a signal generator and a simple SWR bridge. Something like these:

http://pe2er.nl/wifiswr/
http://www.w1ghz.org/QEX/A_UHF+_VSWR_Bridge.pdf

--- End quote ---

Hi

Neither one of those are anything you are likely to have just sitting around. They also aren't all that easy to put together unless you have microwave PCB material running around. Once you get them "close" getting them reasonably well calibrated is an interesting process. The point being that the SWR (or return loss) bridge tacked on to a signal generator like the one in the original post can easily cost more than the generator he's looking at.

Bob

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