CB and Ham Radio Techs Love Their Bird Wattmeters

[bd139]

Oh crikey. Don’t spread that cancer 

[joeqsmith]

I've noticed these little boards on Ebay -

eBay auction: #402653782431

They have an AD 8310

https://www.analog.com/en/products/ad8310.html#product-overview

which accepts a range of -77dBm to +18 dBm (95 dB). It outputs a voltage as the power changes. You could write up a little microcontroller program to read the output, do some conversion, and use a small display. Wouldn't be too awful hard. Heck I might play with that idea this summer. Looks like they are all in China though. Be interesting to see what it would do as far as accuracy.

 

Looks like they have a complete meter with display.  They had the foresight to allow adding an external attenuator.   This one has a USB interface:

https://www.amazon.com/Taidacent-Instrument-Calibration-Attenuation-Adjustable/dp/B07K1V2GC5/ref=pd_rhf_dp_s_pd_sbs_rvi_sccl_2_7/138-7979421-3740615?pd_rd_w=GRtxt&content-id=amzn1.sym.afb460dc-fa69-4440-8ffa-68f8a04f70ba&pf_rd_p=afb460dc-fa69-4440-8ffa-68f8a04f70ba&pf_rd_r=7WBJKJEZCKZV661GBJM1&pd_rd_wg=2e3eP&pd_rd_r=69a99afd-b196-4bfb-a2a5-92ada2cbf100&pd_rd_i=B07K1V2GC5&psc=1

I would like to make something in-line that can read both directions without a switch.   Maybe two of the boards you show.  They are cheaper than the parts on Digi-key. 

Coupler from one of my experiments.  Need something better for a Watt meter shootout.     

[joeqsmith]

Picture showing the backside radiation pattern off my two bean can waveguide at 2.52GHz measured with the LiteVNA.   Maybe difficult to rotate a semi in a sphere but a quad with GPS could certainly make a basic sweep of it.

That pic looks like something from the Non linear plasma reactor debacle -

https://www.eevblog.com/forum/dodgy-technology/the-non-linear-plasma-reactor/

 

Do they use a Bird meter to measure the output power?   If not, that could be the problem.   The hams and CBers will never accept the data unless the gold standard is used for measurements!   

[xrunner]

Do they use a Bird meter to measure the output power?   If not, that could be the problem.   The hams and CBers will never accept the data unless the gold standard is used for measurements!   

Output power?

What output power ... it exists only in the imagination at the moment. 

[joeqsmith]

Here is the detector, micro and LCD.   I would need two of these and then have to do the math.   Better to just make the whole thing.

https://www.amazon.com/Attenuation-Digital-Display-Strength-Frequency/dp/B08HN4HF9B/ref=pd_sbs_sccl_2_3/138-7979421-3740615?pd_rd_w=dZwAj&content-id=amzn1.sym.f20cd814-1d01-49fb-93a8-83020525ea50&pf_rd_p=f20cd814-1d01-49fb-93a8-83020525ea50&pf_rd_r=Y5M0HRBYSVESCSQW91SW&pd_rd_wg=5hpli&pd_rd_r=47ef9edf-608d-4d78-95d4-9edc2b2e56ce&pd_rd_i=B08HN4HF9B&psc=1

[joeqsmith]

Do they use a Bird meter to measure the output power?   If not, that could be the problem.   The hams and CBers will never accept the data unless the gold standard is used for measurements!   

Output power?

What output power ... it exists only in the imagination at the moment. 

[xrunner]

The printing on the PCB sez 0.1 to 600 M but the advertising sez 1M to 8G LOL.

Yea try one. I'm still going to get the basic board and see if it evens warrants further effort. If not I can stop there. Baby steps ... 

[joeqsmith]

Baby steps ...

Agree.  I want to make sure I can get a decent coupler before looking at the detector.    This was my last attempt at a wide-band coupler for the 1M-30MHz range.  Plan to to scale it up using the larger cores.   

[joeqsmith]

Some data off the higher power coupler.   Once the dope dries, I'll try running some power through it.   

[joeqsmith]

I came across Charlie Morris from New Zealand who also made a Watt meter.   
 

[joeqsmith]

Starting out with the small kit amplifier.   The forward output from the coupler is connected to a step attenuator and set to 11dB to give me a total of roughly 30dB forward coupling.   The output of the attenuator connects to the scope.   The power output of the coupler is connected to a 30dB attenuator and then to the scope.  Basically both channels should match within reason.   Data was collected at 26.5MHz which is a good region for that little amplifier.

I compared results from 270uW to 120W.   Most of the error is due to not being able to adjust below 1dB steps.  I'll try it at higher levels and lower frequency later. 

[xrunner]

Regarding the AD8310 I perused the datasheet and it states it has an 1k input impedance. If you desire to present 50 ohms, connect a 52.3 ohm resistor in parallel with the input. You can see this in their own example in the datasheet. But what do the boards that Amazon have installed for that R? I see a 100 ohm resistor. Other people in the comments for this product noticed the same thing. So I'll have to remove that and put in a 50 ohm R (sorry no 52.3 ohm resistors at the moment).

That's why I don't trust the more built-up "power meter" that is for sale. I don't want anything in-between that chip and my testing. No telling what futzyness (is that a word?) they would have done adding more to it that I haven't approved of. 

Analog Devices have used a scale of dBV, where 0 dBV = 1 V RMS,  and so the output voltages are related to a dBV scale. If you desire dBm, and have the 50 ohm R installed, they state convert the voltage readings to dBm by adding 13 to the dBV number. So if their output from the chip is 2.5 V, it means the input is 1V RMS= 0 dBV which would be +13 dBm.

I also ran across an AD8307 board and in that datasheet Analog Devices presents a power meter design if you want to pick off readings. Should work for AD8310 too. I snipped it in case you wanted to consider anything about that for what you want to do. I just want to measure power single-ended from a transmitter for calibration purposes.

[joeqsmith]

That's why I don't trust the more built-up "power meter" that is for sale.

 
I am very interested to see how the board works.  I've seen a lot of reviews for these low boards in general (not this board specifically) being DOA. 

I'm not sure what the CB and ham groups would want for a Watt meter outside of it being in-line and maybe a peak, average and VSWR mode.   Like the guy from  New Zealand,  power to the load.   Maybe a min/max. 

***
After looking at so many products, I wonder if the two groups ever adopted the digital meter.   They may want to watch that analog display. 

[joeqsmith]

The step attenuator was replaced with fixed to avoid damage at the higher power levels. 

I ran a few checks at 7MHz.  I have not looked at the errors but it seems a bit further off than the previous tests.  These attenuators are not gold standards.  I need one of those Bird meters now. 

[joeqsmith]

Same setup at 14MHz.    Keep in mind too that I am not yet accounting for the return loss.  Just trying to get a feel how well the coupler works. 

[joeqsmith]

My scope is limited to 5VRMS when selecting the 50 ohm inputs.   To run at higher power levels another 10dB attenuator was added to both channels (40dB on each leg).

With the 20dB directional coupler, with 200W, we need 2W (which is why I pulled the step attenuator).   I have some Mini-circuits attenuators that are rated to 2W.   Thermocouples were attached to the toroids to get some idea if it will handle 200W. 

[joeqsmith]

The limit is that Mini-circuits attenuator.   The lab administrator made an executive decision to turn things up..     I let it run at 300W for about 10 minutes.  The temperature reached 47C or a 23C rise over ambient.   While the VAT attenuator did get pretty hot even with forced air, it survived.   

***
Should add, that's a difference of 22 Watts or about 0.32dBm.  Consider that the coupler is not exactly 20dB and all of the attenuators have an error.  I am not attempting to account for any of this just yet, nor am I considering the return loss.   It appears even without any sort of compensation it's well within 10%.    Of course, I have no way to know absolute until I get break down and buy a Bird meter.

[xrunner]

You know what you need to do?

You need to build yourself a power meter. 

[joeqsmith]

Looked at a few other videos of people making their own.   Like the guy from down under, most never finish the job.  Accuracy?  What's that?      

With the coupler now sorted out, the next step is to pick which IC to go with.  Of course the Bird meters are a simple magical diode detector.   Maybe I am over complicating mine.   

https://www.rfcafe.com/references/electronics-world/rf-power-output-measurements-october-1963-electronics-world.htm     

[xrunner]

I want to check the ability of the chip to read power. I'll convert the output voltage to dBm manually with a calculator to see if that is reasonably close to what I'm inputting from my Agilent RF source. If that works out, then I'll get a Arduino board running with a simple conversion from the voltage output to a dBm power reading.

I studied the AD8310 data sheet some more and started to write a very simple program for the Arduino board. I need to re-arrange the equation they gave a bit to give the answer I'm looking for which is power input to the chip and take into account the dBm conversion factor. The max voltage out of the chip looks to be below 3 V (when reading the Max power allowed). I want to be as accurate as possible so I'll want to use the external voltage ref on the Arduino board eventually, perhaps a 3.3 V ref. instead of the board's 5V ref.

I'm jumping ahead though; first I need to order the board. It's in my Amazon cart, but I might as well order some stuff I actually need also, like coffee and toothpaste. 

[bd139]

Actually built the AD8307 variant of that ages ago. Shown here with a (home made) return loss bridge connected to my old HF antenna.



I did build a digital interface for it with an arduino mini (and AVR-GCC - fuck the Arduino GUI tat)



Never finished it of course 

[xrunner]

Well there you go Joe, now I don't have to make one. 

Reminds me of Beatles Lyrics

"Nothin you can make that can't be made"
"Nothin you can do that can't be done"

Actually built the AD8307 variant of that ages ago. Shown here with a (home made) return loss bridge connected to my old HF antenna.

I did build a digital interface for it with an arduino mini (and AVR-GCC - fuck the Arduino GUI tat)

Never finished it of course 

Did you just lose interest or was there some other reason you didn't "finish" it?

I want to play with it anyway, so I'll go at least to the point I see it could make a useful power meter. Joe is the one that really needs a power meter ... 

[joeqsmith]

Actually built the AD8307 variant of that ages ago. Shown here with a (home made) return loss bridge connected to my old HF antenna.

I did build a digital interface for it with an arduino mini (and AVR-GCC - fuck the Arduino GUI tat)

Nice 3M breadboard.   

Never finished it of course 

Did you just lose interest or was there some other reason you didn't "finish" it?

I'm curious about this as well.   Did you run out of cash to by a Bird meter to align it?   

[bd139]

Actually I got cheated on, divorced, depressed and spent all my money on beer and floozies instead

Now I'm over my mid-life crisis I might actually build one and finish it 

And hell no I'm not buying a Bird 

On the actual build I managed to get a calibration routine in the code which was fun. You put a 0dBm reference in it and held the button down for 3 seconds and it recorded the reference ADC value. Then you put a known good 10dB attenuator in and press the button again and it calculated slope, intercept and stored it in flash on the MCU. I still have the code around somewhere. Will dig it out when I can be bothered (not now)

[xrunner]

Actually I got cheated on, divorced, depressed and spent all my money on beer and floozies instead

Now I'm over my mid-life crisis I might actually build one and finish it 

And hell no I'm not buying a Bird 

On the actual build I managed to get a calibration routine in the code which was fun. You put a 0dBm reference in it and held the button down for 3 seconds and it recorded the reference ADC value. Then you put a known good 10dB attenuator in and press the button again and it calculated slope, intercept and stored it in flash on the MCU. I still have the code around somewhere. Will dig it out when I can be bothered (not now)

Looks like you got the coding pretty well covered when you stopped. Yea I was thinking about also having options to tell it you have a certain attenuator in front (for measuring those 10 kW CBs  ), so the power reading it presented would take that into account. Maybe I can get a little farther than you did at least in the packaging area. At least I can't get divorved ... the other two events could happen so I better get a move on before they do.

Hey Joe (sounds like a Jimi Hendrix song),

You know we'll have it easy though, because we won't have to write the software. Yea it's true go see here -

https://www.eevblog.com/forum/chat/video-ai-that-generates-code/msg4234603/#msg4234603

All you have to do is explain what you want to the AI. You'll look like a genuis! Simply fill in the blanks below -

Hey AI! I want software to run a power meter using the AD8310 IC, running on platform ______ , and using a display of type _______.

Thank you.

Cool thing is you don't have to tell anyone the AI wrote it!