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If you have a 1W transmitter, make sure the attenuator is at least double the power. Most handhelds are 5W so plan that you may accidently output the max. What lots don't know is attenuators can change when they heat up, if the resistor(s) to ground disconnects or goes open then you potentially?can overload your tinySA.? This is why in a lab directional couplers are used.? Attenuators are either a T or pi configuration 1 or 2 resistors to ground. For HAM use either is OK as long as it can safely dissipate?the power.

On Tue, 21 Jan 2025 at 12:44, Matthew Rapaport via <quineatal=[email protected]> wrote:

Not 10 watts, 1 Watt! Yes it's much more than the minimum needed to protect the unit, even to get a decent undistorted signal. I can only say try it--what have you got to lose?--and see what nice signals, esp with LNA on, (measured harmonics and all) you get.

Not 10 watts, 1 Watt! Yes it's much more than the minimum needed to protect the unit, even to get a decent undistorted signal. I can only say try it--what have you got to lose?--and see what nice signals, esp with LNA on, (measured harmonics and all) you get.

Never connect a transmitter directly to the tinySA, an external 60dB 10 watt attenuator would be a good place to start. Can get cheapies at Aliexpress and like someone else said check with a nanoVNA. Ham swap meets is another place to check, often able to pick up a directional coupler as a lot of people don't understand their function. The other potential problem is DC, not sure if the frontend of the tinySA has a cap to stop DC, but on HP and other Spec Analy it's common to use a DC blocker at the input. Eric would be able to answer this one.

On Tue, 21 Jan 2025 at 04:32, Joe Tomasone via <joe=[email protected]> wrote:

I just received the TinySA Ultra.? ?As a first practical use, I want to measure spurious emissions from my various transmitters.? ?However, I understand that there is a maximum of -25dbm on the low input, and a maximum 30dbm internal attenuator.? By my calculations, this falls far short of even a 1w transmitter.??

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Am I correct in assuming that connecting a 1w transmitter (an HT, say) to the TinySA via SMA cable to the low input will be definition require a minimum of a 25dbm attenuator plus the internal 30dbm attenuator to get a 1w signal under the -25dbm low input threshold?

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I just received the TinySA Ultra.? ?As a first practical use, I want to measure spurious emissions from my various transmitters.? ?However, I understand that there is a maximum of -25dbm on the low input, and a maximum 30dbm internal attenuator.? By my calculations, this falls far short of even a 1w transmitter.??

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Am I correct in assuming that connecting a 1w transmitter (an HT, say) to the TinySA via SMA cable to the low input will be definition require a minimum of a 25dbm attenuator plus the internal 30dbm attenuator to get a 1w signal under the -25dbm low input threshold?

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I put 80dB attenuation between 1 Watt and the SA! Very good signal resolution. I do NOT like to use the internal attenuator because using it means you CANNOT use the LNA and the LNA is your friend!

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Matthew KD6KVH

You will need a bit more attenuation than that. And still more if you want the most accurate measurements possible.

The math is simplest if you do the calculations in dBm (dB referenced to 1 milliwatt). 1mW = 0 dBm. 1W =?+30 dBm. 10W =?+40 dBm. For HTs and QRP rigs, perhaps the most important number is that 5W =?+37 dBm.

The maximum permissible input to the tinySA Ultra is?+6 dBm (4 mW). If you are applying a?+37 dBm signal, you need 31 dB of attenuation to decrease that to?+6 dBm, more than the 25 dB external attenuator that you proposed, and a tad more than the 30 dB attenuators that are popular surplus items. And you want a bit more in case your HT produces more than 5W; I'd recommend starting with at least 34 dB, which would make you safe for up to 10W.

The internal attenuator in the tinySA Ultra is an active device, and as such it causes some distortion. That will make the device under test (DUT) look a bit worse than it actually is. For best measurement accuracy, you want the internal attenuator to be inactive, which means you need an additional 30 dB of attenuation to get down to the range where it's not used. That theoretically comes at -24 dBm, but the auto mode of the tinySA is a bit more conservative about using the attenuator; you'll get down close to -30 dBm before it turns off.

For my measurements, I use a 30 dB fixed attenuator with a 20W rating, plus a step attenuator. For testing higher power radios I also have a 20 dB fixed attenuator with a rating of 150W that I can add to the chain. It's often difficult to find the rating of surplus step attenuators; it's safest to treat them as having a maximum input rating of?+17 dBm (50 mW). Some fixed attenuators specify an input end and an output end; make sure to heed those, or else you can burn out your attenuator. If you buy a used attenuator, you should test it for accuracy, which you can do with the tinySA itself using its signal generator as the source signal (procedure at ) or with another instrument such as a NanoVNA. The NanoVNA is nice because it can easily produce a display of attenuation over a range of frequencies.

For testing an HT, I would start with the 30 dB fixed attenuator plus a setting of 40 dB on the step attenuator. That would reduce the expected +37 dBm input signal from the HT to -33 dBm. Then I would reduce the amount of attenuation in steps until the internal attenuator turns on, then back off from that until it turns off again. That procedure gets maximum dynamic range and minimum distortion from the tinySA. The actual output of "5W" handhelds varies a bit, but I'd typically end up with about 35 dB on the step attenuator. Once you have dialed in the needed amount attenuation, you can set that in the tinySA so that it will directly display the actual signal levels.

ALWAYS start with at least as much attenuation as you need, adding a bit more for safety if possible. You can then reduce it to the optimum point. If you start with an inadequate amount you can destroy the front end of the tinySA, and you don't want that.

On Mon, Jan 20, 2025 at 12:32?PM Joe Tomasone via <joe=[email protected]> wrote:

I just received the TinySA Ultra.? ?As a first practical use, I want to measure spurious emissions from my various transmitters.? ?However, I understand that there is a maximum of -25dbm on the low input, and a maximum 30dbm internal attenuator.? By my calculations, this falls far short of even a 1w transmitter.??

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Am I correct in assuming that connecting a 1w transmitter (an HT, say) to the TinySA via SMA cable to the low input will be definition require a minimum of a 25dbm attenuator plus the internal 30dbm attenuator to get a 1w signal under the -25dbm low input threshold?

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I just received the TinySA Ultra.? ?As a first practical use, I want to measure spurious emissions from my various transmitters.? ?However, I understand that there is a maximum of -25dbm on the low input, and a maximum 30dbm internal attenuator.? By my calculations, this falls far short of even a 1w transmitter.??

?

Am I correct in assuming that connecting a 1w transmitter (an HT, say) to the TinySA via SMA cable to the low input will be definition require a minimum of a 25dbm attenuator plus the internal 30dbm attenuator to get a 1w signal under the -25dbm low input threshold?

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I just received the TinySA Ultra.? ?As a first practical use, I want to measure spurious emissions from my various transmitters.? ?However, I understand that there is a maximum of -25dbm on the low input, and a maximum 30dbm internal attenuator.? By my calculations, this falls far short of even a 1w transmitter.??

?

Am I correct in assuming that connecting a 1w transmitter (an HT, say) to the TinySA via SMA cable to the low input will be definition require a minimum of a 25dbm attenuator plus the internal 30dbm attenuator to get a 1w signal under the -25dbm low input threshold?

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