#91: Basic RF Attenuators - Design, Construction, Testing - PI and T style - A Tutorial 

doesnt matter if you tell few words or a lot....it is allways informative and direct to the point....teaching talent

I was just looking how to make some attenuators and I run into you again! You are just a wealth of great information and practical implementation ! I want to be sitting right next to you and try to catch some of your breadcrumbs! Thank you again! Stay safe and have a great weekend!

Wow, I always thought that making attenuators is a complicated science, especially getting a decent flat line frequency response. But your video proved to me that it can be quite easy, thanks!

PI & T? Yes, I'd love some. On a more serious note, another excellent video.

Excellent video! Thanks for taking the time to make them. Your explanations are very clear and concise.

I'm going to put a notebook together (with graph paper of course) and follow along with these videos and even build some of the stuff you've got here. Thanks for taking the time to make these!

One trick I picked up for similar attenuators and terminations is to stack a number of smd resistors to get the desired value. 3 150 ohm larger ones make good 50 ohm terminations. For attenuators it is a good way to get more precise values and somewhat better frequency flatness. I am not sure why it works. Probably stacking helps reduce stray inductance. Made a small cal set with a power splitter like this for my VNA that turned out almost as god as the original N sized ones for that application. For some reason I had good luck with the 1218 size resistors.

WOW!!!!!!! THANKS FOR WALKING US THRU YOUR NOTES,... EXCELLENT DESCRIPTIONS!!!... GREAT DEMO!!! THANKS!!!

Wow! Another great lesson. I keep coming back to your channel to learn and refresh my memory. I remember my college professor always telling me when dealing with RF circuits "Keep 'em short, neat and tidy." Great to see such accuracy by keeping these same principles in the 20dB attenuator you built. Now, if I can only find a good used RF spectrum analyzer to do the same thing....

Thank you for your time in a full explanation, your patience and knowledge is appreciated! 73 ' David K8KEM

Fun: Yes that was ! I'm 77 years old and still enjoy tinkering around. 73 Leo

Very informative! Never thought it could be so simple!

Excellent. Amazing the bandwidth acheived!

The best channel in youtube. Keep up the good work.

just found the channel, thanks for all the education you provide

Loving how you constructed the attenuator!

Que buen video, muy bien explicado. Necesito hacer un atenuador y me sirvió bastante tu enseñanza. Gracias

Very nice. Wonderful. Sometimes the simple things are so rewarding .... ! Make several videos this way for us, the guys like me, that sometimes need go back to the basics ....

Thank you for your video. Excellent! I need to make an attenuator. It so much cheaper than buying one. Thanks for the inspiration.

What is fun is to do the exact same circuit with Long THC leads and see your high end response skew. Another nice video!

I must agree your videos are excellent I always look forward to the next one. Thanx Gary

Thanks for the heads up once again Alan - almost purchased an attenuator on eBay but now I'll make my own. Thanks for explaining and your valuable time. 73 de GI8WFA.

Thanks for the video, I really need an attenuator by tomorrow and amazon wouldn't get it to me soon enough. So this will work temporarily.

This is awesome! Thanks so much for explaining this.

Another nice video!! I have done the same thing to make various values. I use the same type of connectors, but round. The attenuators fit perfectly inside brass tubing available at most hobby shops.

It's still a very good video though. I did build the version with the series 120R resistors and the response was 20dB +/- 0.1dB to 3GHz on a VNA. The return loss at LF was 'only' about 40dB (because 120R isn't the ideal value of course) and it degraded to about 28dB by 3GHz. However, the resistors fractured when removing it so I would also advise soldering some additional bracing around the structure to protect against PCB flexing when twisting it during fitting/removal from a test setup :)

Great video!! This video made me think about making a diy feedthrough 50ohm termination for my oscilloscope...🤔

Great explanation!

Great video ! Thanks so much

That's a good design, and a great construction technique! Thanks for sharing! I would not have thought to suspend surface mount components in the air like that, like old style leaded resistors, but it clearly works well.

Thanks for your input. Traditionally, I have bought mostly HP and Textronix but Advantest seems like it's a top end unit from my limited observation. I too like the ole Tek 465B scopes. I was once a FE for DEC and traveled around the nation with the VAX/VMS platforms. During that time we ALWAYS drug 465B's around. Rumor was leaving it at the office could get you dismissed, mot sure that was true. Hi I appreciate your videos, some of it proved to be a good review and I have learned as well. 73

I recently decided to add an attenuator to my 1.5Kw 50ohm dummy load. I found an online PI attenuator calculator that allowed a different input and output impedance. I thought if I used 3 stages and lowered the impedance in each stage I could start with an input of 100K as to not effect 50 ohms of the dummy load(and also not have any real power attenuation in the first stage). I copied the formulas for the page into a spreadsheet so I could quickly change the input impedance/attenuation/output impedance and have the spreadsheet calculate the total impedance and the power dissipated in each resistor. Luckily I simulated the circuit and it was off by a factor of 100. Being it was only a large resistor network, I then calculated it with a DC input by hand with EET101 skills, this matched the simulator. After asking numerous times on online forums, I only got responses that it's the wrong way to do it. I finally built an current sense RF sampler with an PI attenuator(50 ohms in and out) on the output, I again missed and got 68db instead of 60, but the thing works and I'm tired of fighting it. But I've never been able to comprehend why the previous method didn't work(at least mathematically), my spreadsheet outputs the same values as the online calculators. Someone suggested that the online calculators are incorrect when the input and output impedance are not the same(even though they specify that is what they do) I finally left it as the calculators are wrong so I could sleep at night. chemandy.com/calculators/matching-pi-attenuator-calculator.htm care to take a shot at this? It's purely academic at this point, but somewhat important to my sanity. KO4SWI QRZ

Keep up the good work!

Thanks mate, You videos are priceless!

Great video, thank you for the info and saving me a couple of bucks :)

Great Job and thank you. I give you an A++

Good example of construction technique for RF stuff!

That is excellent and helps me alot thankyou!

I love this videos. Thanks!

perfect! please do more vids on RF stuff

Thanks for the video! Your soldering job was pretty interesting - surprised you managed to make that work lol.

Excellent explanation as always , a very useful bit of diy . Similar video on DC blockers would be great , should you be looking for suggestions , given how expensive they are to buy off the shelf.

thank you very much Sir for this video!

You explained that so well, +++++

Thank you so much for your videos! :)

Nice video, thanks for sharing it :)

amazing all that math looked so boring in the book..... but now it all makes sense now that you brought it to life. Thanks

Nice! I always thought that resistor has stray reactance that affect sigificantly when you vary the frequency...

Thanks for the video it came in handy the other day when i made a 30dB attenuator for a test fixture.. BTW I sent you a message on linkedin regarding a PCB i am wanting to send you.

Great job...

Sooo very true .. I strive to make one as good some day .. :) Practice makes perfect lol

Fabulous as usual. How about this idea: use three quality (cermet) trimpots and then adjust them as precisely as indicated by the equations? It would be interesting to see the resulting bandwidth performance.

Many thanks

Wow, great tutorial! Finally I know what an attenuator is, and what it's for ;) You meant it's good for couple GHz, so essentially I can build attenuator for Wi-Fi antenna (if it's needed, (because I don't have that much experience in RF stuff as you have))?

Very nice..next topic on circulators pls

thank you for video thats whats in toe works here

Very interesting video, wonder how u soldered that !

Thanks soo muchhh

Thank you

Thanks very much I'm going to make me some attenuators

Great video! If you need to calibrate this to get an exact attenuation figure, what's the best way to do that? Would little trim pots be too lossy or noisy?

@w2aew I love your videos they are very informing and explains everything in an excellent explanatory way. I have a question. How do you calculate the maximum effect these attenuators can handle? Regards Jacob, OZ2LT.

Is there a reason to use matching parallel resistors or would it be better getting the higher accuracy of using 330 || 75 for the 61.1111Ω and 270 || 3000 for the 247.5Ω resistor? To reinforce the information presented here, I created a spreadsheet that calculates Pi and T attenuator resistor values and helps me select the best parallel or series resistors from my personal collection.

Thanks for sharing. Seems I had not seen this one. What controls how flatness of the response of the attenuator? Is this mainly the construction characteristics? Would shielding the whole thing help even more than just the solid ground plane? Also, are SMD resistors better for this purpose vs. through hole? If so, just due to their size? Thanks so much for the great videos you produce.

Good video with perfect explanation. But your attenuator needs to be shielded, in order to protect it from unwanted oscillations/background RF signals. Otherwise your attenuator will not work properly. Also resistors need to be mounted correctly to make it more effective. Thanks!

Thanks. When you speak of "going to ground", is that soldering to the chassis?

Hi, what is the wattage on those resisters? Could you suggest a good way to seal the attenuator for use in a wireless test bed? And thank you for an excellent, helpful video.

So clear and simple, I think I can do it. I need to cover 0-6ghz at 3watt 10 db 50ohms. how do I alter your example? eg instead of smd resistors do I use 2w resistors (old school) and how do i cover the 6ghz extent? Note I am adding this to a 30db unit to give me 40 db. thanks Troy

Thanks

Great!

Thanks for video! What's the maximum bandwidth that normal 0603/0402 resistors can go to before the ESL is a an issue? I've been looking in Farnell at microwave resistors and they look quite expensive. Are they only required for over 4GHz for example?

What exactly is the difference between these networks and a voltage divider?

Alan, thanks for your generous contributions to the electronics and ham communities! I recently scored a Spinner 745359 100 W 40 dB attenuator. It measures an accurate 50 ohms at DC and NanoVNA sweeps show 50 ohms and excellent SWR in both directions. Does anyone know if this attenuator can accept high power input to either port? The datasheet I found is almost illegible and the sheet for the modern equivalent doesn't mention in/output, so I'm guessing they're symmetrical with regard to power handling but thought I's ask before using.

lol thank you. Colorimetry and details are tipical from Canon DSLR. nice video quality and nice stuff. You have a nice workshop...

sir im in a bit of a muddle i have a rf radio output 10 watts and a unit that takes 100 mw input or less to operate if not damage will be so can you give me a pi simpe circut values please

Nice

Absolutely brilliant Alan. Thanks for sharing. Incidentally, I'm curious; some speccies have the option of a tg. On your Advantest how easy/difficult is it to install a tg? Or does the tg have to be installed during manufacture?

Needless to say, it is very very clear and easy to follow, from design to test. NOW MY QUESTION. Is it mandatory to use the SMD resistors if I aim to use the attenuator at 500 Mhz? Can I use regular resistors? Thanks in advance. Manfred.

Thanks for this useful video. As a beginner in construction, please could you tell me if I could replace R3 in your Pi version with a potentiometer to make a variable attenuator?

nice video. you have selected smd resistor I think 0805 package. I want to know do we have to consider wattage of resistor during selection. how it will impact the design.?

Hi, a little off topic but I have been looking for a spectrum analyzer with a tracking gen without the typical high cost. I have a great HP 8566B that covers almost DC to 20gigs but no TG. I can built an interface adapter and Phase Lock an external sig gen to the first LO but at best, I may have 80 dB of dynamic range. Are you pleased with the Advantest SA and any recommendations on a good SA that will go to 2 or 3 gigs?? Oh, I need the low range to be good at about 100 KHz 73,, Glenn WA4AOS

I want to build one for input to ldmos hf amp covering 160m-6m I have a place on amp board for t attenuator what type of resistor should you use metal film or carbon film can’t get a good answer can you help

If you want to seal it off. just build an enclosure with thin metal or find some old junk CRT monitors and strip them for parts. Or do what Raytheon does and build inside freight containers.

Because for SMD, capacitive effects are more important than inductance?

Hi Allen, I am going to hook up my rig 870 IF out put to a RTL dongle with a rf 20 db attenuation do you think it is enough I am not going to damage the RTL's front end??

I'm very impressed. Super great work ... I'm wondering if we measure the reflection S11 or s22 ... Are they gonna be good as well?? Or should they be close to zero as possible for an ideal attenuator or not? I really don't know.

Hi, thank for your works. Can i mesure an attenuator without spectrum analyser ?? Thanks 73's

Does it work at frequencies greater than 2.5GHz?

Hello W2AEW, can you pl explain how to design a DC block.

kindly explain how to measure self resonating frequency of capacitor

What happens at lower frequencies? Is it linear all the way to DC?

Hi, i would like to ask you some question since i have no idea about RF. First, can i build it with normal resistor or it should be better with smd resistor ? Second, will it work for the 5 -6 Ghz frequency . Thanks

I thought attenuation db rating is based on power, ie 20db (n=100), those n-formulas are for voltage db only?

I built this in LTSpice with a 1V generator and 50Ohm at the input and output and I'm getting 50mV at the output. This is a 20 ratio. What am I doing wrong??

can someone tell me why the equation of powerloss X(DB) is vin/vout? my understanding for calculation is output/input . thanks

Do these not require capacitive compensation as is used in scope probes?

I wasn't actually thinking the values would related to *bandwidth*. I just thought trimmers would be easier and more precise than paralelling resistors. My thought was *also* that trimpots (and the even the shortest means of connecting them together) would be higher in parasitics (both inductive and capacitive) than your smt-resisitors on a thumbnail. That might limit the bandwidth some. Maybe? Personally, I leave anything above 30MHz to professionals anyway.

How much power would an attenuator like this be good for on the input?

ive this sussed out thank you but there is one question still remains if i had a 27db 5 watt pi attenuator an wanted to shift it to a 10 watt 30 db pi attenuator must my R1 AND R3 risistor increase and alter not only in value but double up in wattage ??

Hi. I know its been a long time but I saw one of your video's on the 0.1-2000MHz 30dB Low Noise RF Amplifier LNA Broadband Module Receiver P5O2 . but I can't find the video, if you could be so kind has to let me know which one it is. I think I've watched nearly all of your video's and learned a vast amount of information from them. Thanks.