Upper limit for signal strength measurements?

[tustinfarm]

I believe it was posted somewhere that a 1 mW input signal strength (0 dBm) is tolerable for long periods, and 10 mW (10 dBm) for short duration. My question is, what would be the upper limit for measuring the signal strength, in dBm or peak voltage, etc. where the readout has validity. I am assuming that 0 dBm is tolerated but is beyond the limit of measurement utility.

I am experimenting with WSPR mode transmissions at a 0 dBm and below on 7 or 14 MHz, and it would be great to use the SDRplay as an additional confirmation of the transmitter power output at the levels I am working with. Of course, I could use an input attenuator, but I'd like to know how high I could directly measure on the SDRPplay RSP1 without using one.

[Mike2459]

I'm just speculating here but I think the accuracy can be maintained until the onset of ADC Overload.

[glovisol]

Hi guys,

An RSP Processor is capable of measuring up to 0 dBm with a specified precision of better than 1 dB. My own RSP-1A + SDRuno has consistently given me a precison of +/- 0.4 dB and gave same precision today, when I did the tests uploaded below. To check this of course you must extend the range in SETT, as shown below.

Tests were done at 5 MHz, but precision has been the same at all frequencies I ever tested. When you increase the level above - 50 dBm you must start reducing the gain, in order to avoid the OVERLOAD ALARM. Also, when you come up to 0 dBm the RSP becomes "nervous": it shows the right level for a few seconds, then it starts "complaining" and the level shown becomes erratic, but please consider you are pushing in ONE MILLIWATT of power!

I even dared to go for a split second to + 10 dBm after setting the gain to minimum and the darn thing showed +10 dbm all right! No time to take a pic., though.

In any case it is so easy to make a PI attenuator using precision resistors I do not see the point of gettig this far and risk burning out the front end. The beauty of it is that you can CALIBRATE the attenuator with the RSP itself and SDRuno, so there is no danger whatsoever of making measurement errors.

More, for $ 15 or so you can find on Ebay a 30 dB (0.5 dbsteps) electronic attenuator which provides fantastic performance, even though up to now I had to use it manually because I was unable to find the programming software. Look here:

https://www.sdrplay.com/community/viewt ... f=5&t=4152


Cheers,

glovisol

[tustinfarm]

Glovisol,
Huge thank you for posting all of that detailed information...that's enough to give me the courage to give it a try. I don't need to go above 0 dBm, and am mainly interested in verifying a -10 dBm level (0.1 mW), so it looks like I should be "OK". I have the original RSP1, and hopefully that will perform similarly to the RSP1A that you are using.
Regards,
Bruce KX4AZ