#545b

Episode 545b
Warning! do not connector your radio to a spectrum analyzer without the correct external attenuator. I will show you how to choose one
• #285 250 watt 20db att... Building a 250Watt 20dB attenuator
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[@NikiBretschneider]

You don't always need a calculator to convert dBm to W, especially if you don't need exact precise number. Think about dBm as if it is integer. The least significant digit gives you multiplication by 2 (+3dB) or division by 2 (-3dB), the rest gives you the order. So 30dBm is 10^3mW which is 1W. 40dBm 10W, 50dBm 100W, 60dBm 1kW etc. This is easy. But the last digit. +3dB means doubling that power, so if 40dBm is 10W, then 43dBm is 20W, 46dBm is 40W and 49dBm is 80W. You can also use substraction, where -3dB means half power, so if 50dBm is a 100W, then 47dBm is 100W/2 = 50W, 44dBm is 25W and 41dBm is 12.5W. So you can easily get last digit 0, 1, 3, 4, 6, 7 and 9. Then there is something, you have to remember (similar to +3dB means doubling that power) - +5dB means multiplication by cca 3.2 (I know this is not easy to remember). Substracting 5dB means division by 3.2, but this is not usefull at all. So. If 40dBm is 10W, then 45dBm is 32W. And using previous method you can get ±3dB - 42dBm is 32W/2 = 16W and 48dBm is 32W · 2 = 64W. And if you look at that numbers, you can easily convert any integer dBm value to W without using calculator. It is simple, easy to use and gives you profesional look and feel :3.

[@JuliusLemonhead]

Yes good tips if you want to guess the near value, personally I prefer to be correct.

[@jspencerg]

Thanks for detailed constructions and experiments. Your 20dB attenuator build videos inspired me to make my own. I just finished installing a 30dB 150W attenuator in an aluminum box using old laptop's fan/liquid radiator to keep it cool. Attenuation is a level 30dB until 1GHz. I'm going to install thermistor to measure temperature response when I get rf power source big enough to push it. Maybe build an amplifier? Only have an HT radio now.

[@davefoord1259]

Always use 90% of your bench withh for junk and 10% for what youre working on

[@heikosoeder]

Dont see any junk there !

[@marklowe7431]

Best video I've ever seen on the topic. Cheers.

[@skylabby]

Thank you for the explanation, much appreciated.

[@Swede4Trump]

Greetings from Sweden! You,Sir, just got yourself a new subscriber 🎉

[@IMSAIGuy]

Thanks and welcome

[@TheArtofEngineering]

You legend!!!! What I was looking for!!! Thank you.

[@vidasvv]

Also, even tho you set radio to low power you can get a big spike before it actually goes to low power. I was messing around with my Kenwood TS-2000 and was surprised how much power came out even tho I had it set at 5W. LOTS of people fried their amps! TNX 4 upload. 73 N8AUM

[@danielmorgan7702]

Very good explanation. Glad to see you using a pen and paper to show your math.

[@PowderMill]

Funny you mention using pen + paper to show calculation results… I was just watching a school district board of “education” from my hometown in NJ. I was watching at my daughter’s home with my 2 Granddaughters, both in their mid-20’s. One has a doctorate in molecular genetics and works in breast cancer research at Sloan Kettering. The other is a robotics geek (PROUD GrandPa of way smarter gals! 👍🏻 ) who’s currently working on a NASA ground propulsion project. The assistant to the district Superintendent spoke at length about STEM programs being “out of reach” for most students. Of course that got groans from the girls. They are both the product of that school system and graduated just a short while ago and spoke highly of their experiences. The woman then began with “math is dark arts and magic” and “it is a known fact that math is racist”… Her racist diatribe went on and on and her ideas had zero basis in reality or science. Huh.. HUH..!??! WTF? This is truly insane. I am so, so, so HAPPY most of my grandkids are now out of that crazy school system, but I wonder just how bad public school education has become in America and the West. It’s definitely not a funding problem, my daughter and son-in-law pay over $30k per YEAR in property taxes (on their $750k 4200sqft home) and 3/4 of that is for the schools. Average annual cost per pupil in that district: K-12 = $22k. The woman who spewed her idiocy and hateful comments earns $165k/yr and the Superintendent earns just over $245k/yr. While I greatly respect teachers (for the most part..), the bureaucrats in charge are insane and are earning insane wages to spew their “woke” nonsense. Everyone is equal despite color/sex/religious beliefs/etc.. The great things in life are always created by meritocracy. Look at the space program in the 60’s through 90’s… (not that we ever really landed on the moon 🫣🤣). It would not have succeeded in anything if they had ignored math and science. In some ways I’m happy I’m an old fart, out of school and retired from the workforce. The world has gone mad. 😢🇺🇸

[@VE9ASN]

Simply an excellent and wonderfully informative video! 73!

[@IMSAIGuy]

Many thanks!

[@3asyrider75]

You can set Baofeng to low 1w and use the cheap 2w attenuators

[@ernieschatz3783]

Finishes with "umm." 😂 The rest was good stuff.

[@phyru]

Perfect! Thank you very much!!!!

[@YGurin-gw7su]

Thanks, good video

[@bruceblosser384]

the UV-5r does have a low power setting, which might make things a bit easier!! :) -- Also, if you transmit on simplex, say at 146.000MHz, check out the 3rd harmonic! You could stand 4 or 5 blocks away, and the signal on 438MHz would be almost as strong as the 146MHz signal!

[@JIMMYPOP7505]

Very good video

[@douglasbutler4360]

Rather than that big custom boat anchor, you could have used the two 3dB ribbed attenuators for -6dB leaving less than 1W left. Then used the smaller 10dB and 30dB attenuators to get a total of -46dB. That would be the right attenuation with none of the attenuators overloaded, without having to custom build anything.

[@Mr.Leeroy]

and a lot more unknown non-linearity inserted

[@TheMrjogas]

👍. Im not good in this for now just learning is any tool that can check antena quality how good that antenna.

[@totallysmooth1203]

Seems to me the best thing would be to buy or build an attenuator anvil of some kind with increments of 10,20,30,40, 50 or whatever.

[@ch-_-radi6455]

Thankyou 🎉 73

[@Travis141123]

Thank you. I have a unit on order, hopefully I get it. I have been using a SDR dongle to observe output, but it's bandwidth is limited.

[@diabolo3506]

Hello. On the baofeng UV5R you can lower the RF power through menu # 2 TXP. Put the UV5R on LOW and you will get 1W, which will be better manageable with small attenuators than on HIGHT with 5W. Regards

[@user-xj8oh6fo2f]

Diabolo 14:12

[@TheEtbetween]

Thanks

[@nateitkin8279]

Excellent video, but I thought the tinysa could handle a maximum input level of +10dBm or 10 mW. Clearly 0 dBm would be very safe, but did I misinterpret the tinysa specs?

[@Johnyrocket70]

I need to reduce the radio output of 10 watts to 7 watts to feed my amp. Can I use one of these? What do you recommend?

[@IMSAIGuy]

you need a 1.55dB attenuator rated at 3 watts. That is a pretty special value.

[@patrickleugue6190]

Thanks for your series on the tinySA. Could you make a video using an alternate way of sampling the WT signal for the tinySA using a directional coupler and attenuators?

[@IMSAIGuy]

ok tomorrow

[@IMSAIGuy]

kzbin.info/www/bejne/laupopeaZ8lgo9E

[@kurchak]

@@IMSAIGuy wow, now that's what I call a fan-attentive creator! This is better than Amazon's 2-day shipping.

[@Ibelieve218]

where can i get the sma i tried ebay unless i did not search right.also if i connected my tiny up to the radio to use it as a signal generator do i still need attenuation

[@IMSAIGuy]

search: sma attenuator there are lots of them. If used as an output (generator) you do not need one.

[@NikiBretschneider]

Yes, you need the attenuation in recever tests too. TinySA as an generator is capable of +16dBm (40mW) at its output, but typical S9 is -60dBm (1nW) and is sometimes tricky to lower the tinySA output. There is something where you can lower output to -40dBm, but it is a little bit tricky - it doesn't work with AM modulation and I am now not sure whether it works together with FM modulation, or not.

[@californiakayaker]

I'd use the W9AC samplers equivalent.

[@Ibelieve218]

I notice some have the hook up direction and some don't? As far as I understood makes no difference which way you connect the attenuator.

[@IMSAIGuy]

99% you can hook up either way. only very expensive specialized ones might have a one way hook up

[@th-mb6qs]

If I have a 125w Radio that I want to use with the Tiny SA which attenuator would I need?

[@IMSAIGuy]

at least 51dB 125watt

[@th-mb6qs]

@@IMSAIGuy Thank you sir

[@mysteriousbikingsociety]

So if I were to attach the tinysa to an antenna that I have outside, would that mess up the tinysa without attenuators? If so, what would I need to put in between it and the antenna to save it?

[@IMSAIGuy]

no it is fine I do it. but there is a odd chance to pick up some static electricity which will zap it dead.

[@mysteriousbikingsociety]

@@IMSAIGuy gotcha, would grounding it fix that? Thanks, I’ve been looking everywhere for this answer!

[@IMSAIGuy]

no, it won't. the first versions were pretty sensitive. the ULTRA version has some protection diodes now.

[@mysteriousbikingsociety]

@@IMSAIGuy Gotcha, I appreciate it!

[@dennisschultz1175]

What do you need to be able to use the antenna on the UHF side?

[@IMSAIGuy]

The same restrictions apply. I limit things to

[@dennisschultz1175]

@@IMSAIGuy So if I did my homework as you instructed, I should be fine with a 40 db attenuator as long as I do not use over 5 watts on either side correct? How much does using an antenna vs. direct connection change the attenuation if any?

[@IMSAIGuy]

@@dennisschultz1175 It will be hard for an antenna to pick up much all by itself. so no attenuator is needed at all if the transmitting source is a reasonable distance away.

[@dennisschultz1175]

@@IMSAIGuy Thank you for your response and for this video series on the Tiny SA. I even appreciate the math lesson on how to use the calculations on this! (hopefully my math is correct). Because of you, I just bought one!

[@musicforDRUMIES]

​@@IMSAIGuyso if the radio is like 3 inches away, is it still dangerous? I was wondering about it because I usually have a radio like that at work, and I wouldn't want to fry my tinySA by accident.

[@angelodemichele]

Sorry, I do not understand very well. 4.5W is divided by 100, 20db and not 20dbm, right? so the first attenuator must have a power dissipation of about 36.48dbm (4.456W)?

[@IMSAIGuy]

4.5W is 4500mw 10*LOG(4500)=36.5dBm

[@angelodemichele]

@@IMSAIGuyyes, this is clear to me. I did not understand how much power of the 4.5W was dissipated by the first attenuator (the one with 250W max). Now I understand the power indicated on the attenuators indicates the max power applicable to the input. ex. 5W, 3dB attenuator would take a 5W input and cut it in half and disapate 2.5W. in your test the first attenuator support 250W and dissipates a power of 4500mW-44mW = 4456mW. thanks

[@rdsandy11]

Wouldn't you have to load the input of the TinySA to 50 ohms, or is 50 ohms the rated impedance of the TinySA?

[@IMSAIGuy]

All spectrum analyzers have 50 ohm inputs

[@rdsandy11]

@@IMSAIGuy so SA no but O-scope inputs, yes?

[@IMSAIGuy]

@@rdsandy11 the inputs to scopes are 1M ohm also many have an internal 50 ohm load that can be switched in if wanted..

[@rdsandy11]

@@IMSAIGuy Thanks for your great content.

[@wernerpeter9706]

Hello, this is a very interesting topic, especially for me in the hobby area. But I can't handle your arithmetic. The milliwatt to dBm conversion is ok. At 9:00 you subtract -20 dB from the attenuator from the calculated 36.5 dBm with the result 16.5 dBm. dB is a relative specification for gain/attenuation while dBm is an absolute measure based on log 1 mW. In the example, -20 dB is attenuation by a factor of 10. The 20 dB attenuator should turn the 4.5 watts into 0.45 watts or 450 mW or 26.5 dBm. Do I have a mistake here?

[@IMSAIGuy]

4.5w is 4500mW is 36.5dbm. if you have a 20db attenuator this would then measure 16.5dbm.

[@wernerpeter9706]

@@IMSAIGuy Got it now. My mistake was the 20 dB attenuation rate of 10. -20 dB means 10 x voltage loss but 100 x power loss (volt / 10 * ampere / 10). 4.5 watts becomes 45 milliwatts or 16.5 dBm. For all those who couldn't follow my thoughts: 36 dBm - 20 dB = 16.5 dBm is correct, but 36.5 - 20 is the wrong calculation method :-)

[@AECRADIO1]

Holy low signals Batman! 50dB of attenuation is required to safely feed the TinySA? Good to know..certainly no input protection on that instrument.

[@dennisschultz1175]

5 watts (lowest I can get on mobile) should be 36.99 dbm so a 40 db attenuator should work correct?

[@user-xj8oh6fo2f]

12:17 Is it directional? I see you connected radio to the OUT and tinySA to the IN.

[@IMSAIGuy]

all attenuators are bi-directional

[@user-xj8oh6fo2f]

@@IMSAIGuy Yep that was I thought. But IN/OUT labels are a bit confusing.

[@IMSAIGuy]

@@user-xj8oh6fo2f I kept forgetting it was an attenuator and not the load connector so I could say in/out in/out

[@IMSAIGuy]

in/out out/in

[@IMSAIGuy]

also confusing

[@jbammi]

I am trying to understand why you would connect your Tx to tinySA this way. Why would you instead now use a simple RF sampling, where you have a straight through path, and using a simple few turns of wire, sample the RF to a sampling port, and feed that to the tinySA. Much safer, don't have to worry about the wattage of the TX or any impedance issues etc etc, and much cheaper. Am i missing some obvious point?

[@IMSAIGuy]

that would be great for any spectral measurements and I use it all the time. for calibrated power measurements an attenuator is needed

[@IMSAIGuy]

Make sure your RF tap is attenuating enough. At 100 watts you need lots and lots of dB loss

[@IMSAIGuy]

A 60dB 10W attenuator is something anyone can buy. A dummy load with RF tap is more on a DIY thing that many cannot or will not do.

[@IMSAIGuy]

One can always just use the supplied antenna on the TinySA and no connection is needed

[@NikiBretschneider]

Near field coupling gives you some attenutation, but there is a huge amount of (near field or strong enough) signals coupled to input of that spectrum analyzer, so you are completely unable to know what origins from your DUT (transmitter) and what comes from somewhere else.

[@dustoff499]

Dang, you have to do math? Then piggy back an entire stock of attenuators just to check a handheld radio? Oh my…

[@dustoff499]

Suddenly a $60 device is not $60.

[@IMSAIGuy]

Nope, and a $1000 machine won't to it either, you need attenuators.

[@AECRADIO1]

A 6dB attenuator will be perfect for a 4 Watt signal, and 5 Watt power handling capacity. Of course, it depends on max. input signals allowed with the Tiny SA. I do not know its maximum input signal allowed. 6dB might not be enough attenuation.

[@IMSAIGuy]

NO! 6dB is not enough! the max input to the TinySA is +10 dBm. that is 10 milliwatts. 4 watts is 4000 milliwatts or +36 dBm. I would not want to run more than 0 dbm into the TInySA so you need at least 36 dB of attenuation

[@aronhighgrove4100]

The use of watts and dbm at the same time a bit confusing. Your attenuator can handle a certain amount of power (like any component) and at the *same* time it also dissipates some of this power. But besides attenuating it still needs to feed the remaining power through it, that's where it's power rating matters. In short how much signal power can an attenuator handle, and how much power does it attenuate. Both could be specified in dbm, but the signal power it can handle is specified in watt.

[@IMSAIGuy]

attenuators are specified in dB and Watts. dB is relative, Watts is absolute

[@kurchak]

Too bad HP can't make laptops as well as they can SAs and calculators.

[@TheGadgetwiz]

You have my calculator! Best calculator ever designed. DeVry?

[@IMSAIGuy]

I worked at HP so got a discount.