I have a TinySA that has been kind of fun to figure out and test with. I received a couple of attenuators today through Amazon, and have finally been able to hook a radio directly up to the TinySA rather than just receiving through its antenna. However, I'm seeing power output levels that don't really make sense, from the radio I'm testing with. The attenuators I got are SMA 10w 40dB DC-3GHz and SMA 10w 20dB DC-3GHz (a 40dB and 20dB attenuator).
The test hardware:
TinySA
SMA 10w 40dB DC-3GHz attenuator
Baofeng AR5RM radio set to mid power (typically measures around 5w with my Surecom SW102).
Whatever connectors are needed to get them connected to the TinySA.
Pre-setup: I calibrated my NanoVNA, and then tested the attenuator along with the cables I'm using with my NanoVNA and measured the attenuation to actually be 41.5dB.
Configuration:
Radio -> 40dB attenuator -> short SMA-M to SMA-M cable -> TinySA device.
TinySA: "High" mode (UHF), Level/ExtGain=-41.5dB, Frequency/Center 467.6750, Frequency/Span 18kHz (doesn't seem to matter even if I set 500kHz), Units: Watts.
I don't expect things to line up exactly with the SW102. And there's no telling which is more accurate. The old words of wisdom are "Never take two chronometers to sea, take one or take three." I've got the equivalent of "two chronometers" (no third opinion to help form consensus). But what is interesting to me is that I really do have to use both the 40dB and 20dB at the same time, and calibrate the offset to -61.5dB to get an accurate reading.
The TinySA is supposed to be able to handle up to +10dB input. With only the 40dB attenuator, am I getting too close to that +10dB? As I calculate where I should be in dBm input, I 10w=40dBm, minus 40dB attenuation should bring me to 0dBm with no ext gain adjustment. And 5w is 36.99dBm. 36.99-40=-3.01dBm. In both cases, I shouldn't be approaching the danger zone for the TinySA with just the 40dB attenuator. Yet I only seem to get accurate readings if I use both the 40dB and 20dB attenuators in series.
Finally, I did test the two attenuators in series, through my NanoVNA, and they came in very close to -61.5dB when connected in series.
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dosw
I have a TinySA that has been kind of fun to figure out and test with. I received a couple of attenuators today through Amazon, and have finally been able to hook a radio directly up to the TinySA rather than just receiving through its antenna. However, I'm seeing power output levels that don't really make sense, from the radio I'm testing with. The attenuators I got are SMA 10w 40dB DC-3GHz and SMA 10w 20dB DC-3GHz (a 40dB and 20dB attenuator).
The test hardware:
Pre-setup: I calibrated my NanoVNA, and then tested the attenuator along with the cables I'm using with my NanoVNA and measured the attenuation to actually be 41.5dB.
Configuration:
Test:
Plug the radio into my SW102 with a 50w dummy load on it and retest (no attenuation):
Connect to the TinySA again, this time with a 40dB and 20dB attenuator inline:
I don't expect things to line up exactly with the SW102. And there's no telling which is more accurate. The old words of wisdom are "Never take two chronometers to sea, take one or take three." I've got the equivalent of "two chronometers" (no third opinion to help form consensus). But what is interesting to me is that I really do have to use both the 40dB and 20dB at the same time, and calibrate the offset to -61.5dB to get an accurate reading.
The TinySA is supposed to be able to handle up to +10dB input. With only the 40dB attenuator, am I getting too close to that +10dB? As I calculate where I should be in dBm input, I 10w=40dBm, minus 40dB attenuation should bring me to 0dBm with no ext gain adjustment. And 5w is 36.99dBm. 36.99-40=-3.01dBm. In both cases, I shouldn't be approaching the danger zone for the TinySA with just the 40dB attenuator. Yet I only seem to get accurate readings if I use both the 40dB and 20dB attenuators in series.
Finally, I did test the two attenuators in series, through my NanoVNA, and they came in very close to -61.5dB when connected in series.
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