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Mesure IMD with Two Tone and TinySA Ultra

 

Hi Group, I'm an Ham Radio operator and I need to mesure the IMD for the modulation in SSB. I just built a two tone generator so I can inject 700hz and 1900hz at the same time to mesure the IMD but, I'm at my first steps with RF electonics and the TinySA Ultra. Does anybody can take me by the hand and tell my what setting I need to do with the TinySa Ultra in order to mesure the IMD.? Let's say for the test that I will? transmit at 14.245Mhz USB 100Watts in a dummy load. I built a RF sampler 40db attenuator so I can feed the TinySa without blowing it.? thanks? ?73 from VE2IBN (Canada).
 

Firstly, 100 watts is 50 dBm, so the output power after your attenuator (50dBm - 40dB = 10dBm) will exceed the permitted 6 dBm for the TinySA. Although I would highly recommend not to exceed 0dBm at the input, for all signals including harmonics.
 

Use 30 dB extra attenuation between the -40 dB sniffer and the tinySA input
Set LEVEL/EXT GAIN to -70 dB
Use the MEASURE/OIP3 and enter the two test frequencies (in case of USB: 14245700 Hz and 14246900 Hz, do not use the decimal dot when entering frequencies)
and set the span to 25 kHz
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Designer of the tinySA
For more info go to

 

Hi:
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As noted elsewhere, you'll need more attenuation in a form that can handle the power. I usually start my test chain with a 50db 100 watt attenuator and then add others as needed.
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The neat built in function in the TinySA is really useful, but most amateur (and commercial) radio specifications for IMD are described in terms of the individual distortion components and how far below the "carrier" level they are in "dbc" the worst ones are - you may still need to examine the spectrum manually to determine the numbers you want.
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The ARRL has a document describing how they conduct these measurements in their review labs and this is the usual way of arriving at the numbers used in their IMD measurements. It's important to set up the levels correctly for the tests.
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I also have a number of short videos about doing this with other equipment (since the time the original TinySA lacked the resolution for doing this using the ARRL specs), but they might still be of some help in understanding the overall process.
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hopefully this is not confusing the issue...
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M
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Which brings up a good point.? When testing for weak signals such as IMD you should first look for the strongest signal that your device will be exposed to.? That includes other signals that may be present at the location you are at.? My Anritsu Sitemaster and Cellmaster both alert me with a tone to warn me that a high level signal above it's allowable level is present.? This may be a high powered FM or TV station at the site.? Also, you may be tempted to reduce attenuation to be able to see the IMD, only to allow another signal to cause damage to your device.

Joe, K1ike

On 1/5/2025 4:19 AM, MaxPi via groups.io wrote:
Firstly, 100 watts is 50 dBm, so the output power after your attenuator (50dBm - 40dB = 10dBm) will exceed the permitted 6 dBm for the TinySA. Although I would highly recommend not to exceed 0dBm at the input, for all signals including harmonics.

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