Hello,

How accurate is the tinySA measuring/calculating power readings?? I have an HT that is set to High and reads 5 watts on a Power meter.? When I hook it up to the tinySA using a 10W 40dB attenuator, I receive a reading of 33dBm.? When I change the units to Watts I get somewhere hovering at 2.19W.? I have the Level - Ext Gain set to -40 to take into account the attenuator.? My question is, and please correct any assumptions or math I'm doing, but shouldn't the 5W output from the HT be giving me somewhere around 10 log (5000) = 36.99 dBm and measuring near the 5 Watts?

Thanks,

Brian

3dB difference is 50% difference in power so the power reading makes sense versus the dBm reading
What is a HT?
What frequency?
What tinySA input are you using?
Did you do a level calibration for that input?
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Hi,

-I'm testing with a Yaesu FT3D Handheld Radio and a Baofeng UV-B5.? Both give me similar readings.
-Testing on 146.52 MHz
-Low input
-I did Config - Level Cal with both inputs connected as instructed on the First Use Wiki page.

I don't know of any way to measure if my attenuator is truly 40 dB.? I thought maybe if the advertized 40dB is not accurate then what I enter into the Ext Gain would make my reading off.

Thanks,
Brian

You can check your attenuator using the tinySA.
Connect CAL and RF using a short SMA cable
Then set MODE/CALIBRATION OUTPUT/30MHz
Write down the measured level of the 30MHz signal
Insert your 40dB attenuator between CAL and RF
Write down the measured level of the reduced 30MHz cal output and calculate the real attenuation.

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But on 146 MHz the attenuation may be different...
Mirek

Check the spec of the attenuator
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And you may use the 5th harmonic at 150 MHz
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On Sat, Dec 10, 2022 at 02:14 PM, Erik Kaashoek wrote:

And you may use the 5th harmonic at 150 MHz

Works like a charm!!

There seems to be a penchant for announcing the arrival of your new Ultra.
Mine arrived yesterday and I love it!!!!!!!!!

Thank you Erik, ? ? ? ? ? ?larry

On Sat, Dec 10, 2022 at 02:14 PM, Erik Kaashoek wrote:

And you may use the 5th harmonic at 150 MHz

Thanks.? I checked the attenuator with the instructions above and found it to be 40dBm as advertised.? (-27.2 dBm vs -67.2 dBm).??
My handhelds are still all measuring around 2.7 Watts at 146.52.
At 14.3 MHZ on AM I get around 3 Watts on what should also be measuring 5 W.??

Any other suggestions???

Brian

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Brian,

Do you have any other tool to measure their output power?
Do you have a power level spec of these devices with uncertainty boundaries?
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I do. I have a Power Meter directly connected to my handheld that measures 4.35 W when transmitting.

Brian

I did some extra testing of the power level measurements.
In Watt the accuracy I get after level calibration is about +/- 20%
Almost 50% deviation is way above what I ever observed.

If you have a scope you can use the scope with a 50ohm load in parallel with the scope input to measure the output of the 40dB attenuator in Volt peak-peak and use an online calculator to convert to watt

If you measure the tinySA cal output at 30 MHz (MODE/CAL OUTPUT/30MHz), what do you get?
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On Mon, Dec 12, 2022 at 07:59 AM, Erik Kaashoek wrote:

output at 30 MHz (MODE/CAL OUTPUT/30MHz)

The output at 30 MHz (MODE/CAL OUTPUT/30MHz) is -27.8 dBm.

Unfortunately, no scope.??

Brian

?The only other behavior I questioned is that my Wattmeter for the handheld doesn't read anything when the radio is connected with the attenuator in between it and the wattmeter.? I'm assuming that the power into the meter is too low to read with the attenuator?? It's not the most expensive thing.? Does that make sense?

Thanks,

Brian

Yes,
Do you have any data on the accuracy of the watt meter?
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Can you measure the 30MHz cal output and, when is measures -27.8dBm, do
CONFIG/MORE/LEVEL CORRECTION/INPUT LEVEL
and enter -26.2 as actual power
This should remove some of the difference.

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What type of wattmeter are you using and how is it terminated?

If is not terminated with a 50 ohm load (i.e. a mismatched antenna) the power reading may be in error.

Hi,

Here's what I did.? Let me know if I need to perform any steps differently.

Mode / Cal Output: 30 MHz
At the 30 MHz measurement I did:
CONFIG/MORE/LEVEL CORRECTION/INPUT LEVEL
Then entered: -26.2 x1

I did my measurements again and it's still at 33.5 dBm.

My wattmeter is a Surecom SW-33 Plus terminated with a??5-20W DUMMY LOAD.

I guess my question at this point is it time to get ahold of a new TinySA and see if my current unit may be messed up?

Thanks,

Brian

Brian,

Your measurement technique and math are both correct.

(EE and extra class license here so I know enough to be dangerous!)

I looked up your SWR meter and it is spec'd as "Accuracy: mean +/- 5%".

I'm not exactly sure of what is meant by this, % of reading or % of full scale.

Instruments rated at % of full scale may not be very accurate at the low end of course.

So I looked for reviews for your power meter, some guys say it's accurate, some not.

Probably a lot of operator misunderstanding or error though.

Anyway, if I understand correctly you measure 4.35 watts with your power meter and 2.7 watts with the Tiny.

So 36.4 dbm and 34.3 dbm respectively.

If the power meter is reading 5% high then you would actually have only 4.13 Watts or 36.2 dbm.

If the Tiny is 10% low 2.95 Watts or 34.7 dbm would be your output.

36.4 and 34.3 is a difference of 2.1 dbm. (Check my math - I didn't take the time to).

Assuming one device low and the other high brings the measurements closer but you still have enough difference to question a bit while realizing we can't expect HP/Agilent type accuracy out of these inexpensive but wonderful instruments. I am very happy with my TinySA. Considering the low cost I think it's accuracy is fine for purpose. I do have an ancient HP432A calibrated probably decades ago to compare it to and it's pretty good.

Hopefully you can come up with a 3rd option to narrow this down. Maybe take your HT to a club meeting or hamfest and find someone with another instrument to try. Good luck.