Attenuators to measure power on handheld 5 watt & 10 watt radio - Page 1
Forum section: electronics / rf-microwave

author: u666sa
author_rank: Frequent Contributor
timestamp: October 25, 2024, 10:00:07 am
content: I just got me TinySA Ultra and need help choosing attenuators for measuring sensitivity and power.Target is a handheld radio. Stock power is about 5 watts. Modified with 21700 batteries and output transistor it can go above 10 watts, perhaps as high as 15 watts.If I get 25 watt 30 db attenuator (this onehttps://aliexpress.ru/item/1005002544651127.html)and also2 watt 30 db attenuatorand connect them in series, is that okey to measure the power? Perhaps I should get 40 db 25 watt. Please suggest.How about sensitivity with the signal generator. TinySA Ultra minimum goes to -115 db. So is 30 db 2 watt attenuator okey for sensitivity?

author: CaptDon
author_rank: Super Contributor
timestamp: October 25, 2024, 12:57:19 pm
content: You could put the attenuators in series but of course the most powerful one has to be first in line on the transmit side. As for receiver sensitivity testing, there may be to much external leakage to make a meaningful measurement. Communications analyzers used for testing receivers are extremely carefully shielded inside and generally a very high quality cable is used between the tester and the unit being tested and as few adapters as possible!! For power measurement you would be far better off with a real dummy load rated for at least 25W and a quality inline wattmeter rated for the frequencies of interest. Using the tiny SA for power measurements with external attenuators is very inaccurate.

author: radiolistener
author_rank: Super Contributor
timestamp: October 25, 2024, 07:04:46 pm
content: its better to use 40 dB attenuator with about 2x higher power rating than expected power on the input.If the power is still too high on 40 dB attenuator output, you can add secondary low power 20 dB attenuator.For 5-10W it will be enough. For 100W it may need to use 30 dB secondary attenuator.

author: CaptDon
author_rank: Super Contributor
timestamp: October 26, 2024, 12:55:51 am
content: Also be aware the higher power attenuators may be marked with IN and OUT. Not all attenuators can handle the rated power from either side!!

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: October 26, 2024, 05:29:06 am
content: 30dB means reducing the power by 1000. So 15 watts becomes 0.015 watts.You just need one big attenuator to put at the radio, and the second attenuator after that can be much smaller, since the input power it sees is only 15mW.I might be wrong, but the TinySA only takes 0dBm. So you need a second attenuator (like maybe 20dB) but it could be much smaller.

author: Randy222
author_rank: Frequent Contributor
timestamp: October 28, 2024, 04:58:28 pm
content: Max input power of the meter is what you worry about.Buy a 20w -40db, and a 20w -20db. All the cheap ones I have used have bad VSWR beyond 3GHz.You can use the -40db for your testing. Plenty of attenutaion charts online to look at, -40db is a factor of 1/10000, 15/10000 = 0.0015W = 1.5mWUse -60db is you want to stay below 1mW.I would perhaps 1st measure your radio output with a VSWR/Power meter and a 20 or 50w dummy load, add fwd and reverse power and call that your total radio Tx power that you need to handle in attenuation with the SA.Also recommended to cap your SA ports with 50ohm load (terminator) caps when the ports are not being used.Per the Sa Ultra documentationhttps://tinysa.org/wiki/pmwiki.php?n=TinySA4.SpecificationAbsolute maximum input level of +6dBm (3.981mW) with 0dB internal attenuationAbsolute maximum short term peak input power of +20dBm with 30dB internal attenuationSuggested maximum input power of +0dBm (1mW) with internal attenuation in automatic modeFor best measurements keep input power below -25dBmhttps://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-dbm-to-watts