CB and Ham Radio Techs Love Their Bird Wattmeters

[xrunner]

Does it work better than a Bird meter?

If your talking my meter vs. a Bird (Joe made a different design than I did but same log amp board) and you want in-line capability, then as it stands, a Bird is what you want. Other than that, you need to buy slugs for the Bird for different ranges, and for mine you need to buy an external attenuator for higher power ranges over +13 dBm, such as testing a 100W transmitter (+50 dBm). But since mine has a wide range (-73 to +13 dBm) you may only need to buy one high power external attenuator.

One big advantage this design has is it can measure way, way lower ranges than a Bird ever can. I think the lowest power slug you can buy for a Bird is 1W which is +30 dBm. Mine can go down to -73 dBm (if you like watts that's 50 picowatts). I just checked that today and it's spot-on at -73 dBm. You would want those ranges to check your RF test equipment for example. A Bird cannot measure those ranges. But with a big enough attenuator I can measure any power a Bird can. So in that respect the Bird is more limited than this design.

[joeqsmith]

My goal was to measure 100mW.  With a direct connection to the coupler, the floor is about -40dBm or 100uW.  50W would be the upper end without adding attenuators between the coupler and detectors.   I've tested it to 300W but that's the limit of what I have for attenuators (for the load side).   
Frequency wise, I was looking for 1-50MHz with a 0.5dBm flatness.   

I display the power to the load, forward, reverse and %modulation live.  I am also displaying dBm and Watts.  Rather than most PC Wattmeters I saw from the main players that capture at 1SPS,  mine is a bit over 6000SPS.   Hardware filter is still set around 2kHz.   Good enough to see audio.

Accuracy is hard to say.  I can easily force the system errors to match with my spectrum analyzer + what ever attenuators I add but absolute accuracy would require that I buy a Bird Watt meter and compare it.  We all know that is the ONLY way to measure the real power. 

[xrunner]

The second version of "Power Meter" (I know catchy name eh?) is completed. It measures RF power from -73 to +13 dBm, or any higher level with an input attenuator. For most of the frequency & power range it's +/- 0.5 dB accurate*

It has an integrated correction factor calculation which is applied per the settings controlled by the encoder. This selects the frequency being measured and a 5 or 25 MHz step size for selection scrolling up to 500 MHz. If you select Zero freq. the CF is 0.

The front display shows both dBm and watts, the correction factor freq., step size. the actual CF being applied, and the voltage output from the AD8307.

*Compared to an Agilent 8648A output setting

For those interested in the parts used -

Arduino UNO  clone board
Breakout shield
AD8307 Log Amp board
3.3 V regulator for display
0.1 uF electrolytic & mylar caps
Rotary encoder w/push button
2.4" white I2C OLED display
Aluminum electronics case
RF pigtail and SMA bulkhead connector
Copper tape for shielding
Custom designed 3D printed front and back panel
Custom designed slide-in mounting plate
Custom software

[bd139]

Looking really good 

So when do you think you can publish the design, it'll get cloned and be available on Aliexpress for $20? 

[Grandchuck]

Nice work, xrunner!

[xrunner]

Looking really good 

So when do you think you can publish the design, it'll get cloned and be available on Aliexpress for $20? 

You know I do think some people would buy the thing. But there's junk like this all over Ebay for $30 -

eBay auction: #394185448364

I would not sell it for that price it'd have to be more than double to even be worth the trouble and recover some costs. I just don't want to be bothered with customers either. 

[joeqsmith]

I just don't want to be bothered with customers either. 

The hams would be calling you non-stop.  I can see it all now:   

* I can't get it to work.
* It doesn't match up with my Bird meter.
* I connected it to my radio and now it won't turn on. 
* What's an attenuator?
* How do I use this to measure my SWRs?
* Jim Billy Bob here, KQX8D, Extra Class.  I own an HP8753E that I use to tune my antennas.   I'm only stating that so you know I'm not one of those hams.  I bought your meter thinking I could take it up the side of a mountain and when I got it, there was no battery. What battery do you recommend?
* I dropped it after climbing my 100' tower and it doesn't work now.  Can you help?

[bd139]

Had no idea they had already commoditised the idea. Might have a look at one of them as well for comparison.

Have been doing some thinking about extending the dynamic range of these power meters as a side note. I want to see if I can stick another 40dB on the front end of an AD8307. There is a solution involving an AD603 but due to the noise bandwidth that's only usable in a 200KHz span. This went down the line of thinking about adding a mixer and LO to the front end and sweeping for peak power. Then I realised I invented a spectrum analyser again. And then I realised I should probably just finish that project 

[joeqsmith]

More ham questions:

* The ham store I bought mine from claimed it's an antenna analyzer.  This is useless to me.  Can I get a refund?
* I connected it to my antenna and the meter will not display the -73 dBm your spec sheet claims.  It's actually much higher. 
* If I have a 100GW TV station in my backyard, is this thing going to work?  73 WKW8NZ

CBer questions:
* I am trying to figure out what attenuator I need to measure my 10kW amplifier.  Can you help?  Do you sell them? 
* I saw on youtube that attenuators cause errors and I need to connect it directly to my amplifier.  Is this true?   

[xrunner]

 

OK let me try to answer the questions ...

More ham questions:

* The ham store I bought mine from claimed it's an antenna analyzer.  This is useless to me.  Can I get a refund?

No but I can give you advice - seek a better ham store with more knowledgeable staff.

* I connected it to my antenna and the meter will not display the -73 dBm your spec sheet claims.  It's actually much higher. 

Oh well you have a defective antenna that isn't compatible with this meter. Please install compatible equipment before using!

* If I have a 100GW TV station in my backyard, is this thing going to work?  73 WKW8NZ

It most certainly will work and work very well in that scenario. It will register any and all power in the local environment through it's RF input.

CBer questions:
* I am trying to figure out what attenuator I need to measure my 10kW amplifier.  Can you help?  Do you sell them? 

I can help with that problem. First please let me know the brand name and model number of the amp, and a $25 consulting fee. But first read the answer below regarding attenuators.

* I saw on youtube that attenuators cause errors and I need to connect it directly to my amplifier.  Is this true?   

Of course if you saw a YouTube video whatever they said would have to be correct. Attenuators do cause errors. To reduce the errors please use coax that has Zero attenuation at any and all frequencies, and also make sure your RF connectors have Zero loss. Only then will the RF power meter read properly.

Thanks for the opportunity to help customers.

[joeqsmith]

I've been reading various papers and patents on directional couplers.   Some from the 70s to current.   Have a look at the construction:

https://patents.google.com/patent/US11309668B2/en

[joeqsmith]

This one's pretty interesting.

https://patents.google.com/patent/US9105954

[xrunner]

Received two used Hirose HCS2-110-F SMA coaxial switches. They go "click" when 12V is correctly applied and draw 90 mA.

That is all I know at the moment, more testing will occur ...

[fourfathom]

Yes, that last patent is interesting to be sure.

Here is a stupid/simple SWR bridge I made (but haven't stuffed the board or tested it yet).  It uses the classic two-transformer design, but I scaled up the sense impedance to increase the sensitivity while keeping low loading.  I used a diode-doubler detector circuit and then a resistive divider to keep the output within range of my 0-3V A-D input.  It's designed for a 10 MHz sub-one-Watt transmitter for a drift-buoy hobby project, so the likely frequency limits aren't a problem.  It's not designed to be a precision measuring device, just something that will let me check and report basic antenna matching and power output.

I'm using the bridge version with the center-tapped transformers.  The more typical one has no taps, but center taps give you a very slightly better performance.

[joeqsmith]

Received two used Hirose HCS2-110-F SMA coaxial switches. They go "click" when 12V is correctly applied and draw 90 mA.

Noticed the low SN has a catch diode.   Was it later added internally?

Yes, that last patent is interesting to be sure.

Here is a stupid/simple SWR bridge I made (but haven't stuffed the board or tested it yet).  It uses the classic two-transformer design, but I scaled up the sense impedance to increase the sensitivity while keeping low loading.  I used a diode-doubler detector circuit and then a resistive divider to keep the output within range of my 0-3V A-D input.  It's designed for a 10 MHz sub-one-Watt transmitter for a drift-buoy hobby project, so the likely frequency limits aren't a problem.  It's not designed to be a precision measuring device, just something that will let me check and report basic antenna matching and power output.

I'm using the bridge version with the center-tapped transformers.  The more typical one has no taps, but center taps give you a very slightly better performance.

IMO, nothing I show was very complex.  The coupler is the heart of what I was attempting to demonstrate.   Making something that would cover the frequency range of that 07 demo board and not require fitting would be much more difficult. 

[xrunner]

Noticed the low SN has a catch diode.   Was it later added internally?

The datasheet doesn't indicate they have a diode internally. I think some of these were in a system wired in parallel. I will check for internal diode when I test them further.

If I were to sell these power meters, should I do it the Chinese way - meaning I wouldn't include any documentation or instructions? I was gaming out how I would respond to a customer and it would go down like this -

Buyer: "I connected the power meter to a 50 W ham mobile radio. It worked for about 2 seconds and now it doesn't even light up the display and it smells strange!"

Me: "Well first of all, did you read the instructions included with the unit?"

Buyer: " No! There were NO instructions included! I thought there was something amiss."

Me" "Well that's the problem right there. You admit not reading anything and you realized something was missing.

Buyer: "But why were they missing?"

Me: "Environmental waste reduction initiatives. If you already have this meter and just bought another one, you wouldn't need another set of instructions."

Buyer: "But I never had one before!"

Me: "You should have contacted me to get the instructions then. I can't be responsible for you not understanding how it operates if you didn't even want to go to the trouble to get documentation. I'm under strict controls to reduce paper waste. The documentation also includes a red warning label to be installed by the RF input so you will be advised not to go over the power limit."

Buyer: "Warning? Red label? What warning!"

Me: "However, since you reached out I will be happy to send you the instructions and warning label so you will understand where you went wrong - at no charge to you! Also a sneek preview of new upcoming products."

Buyer: "    "

[joeqsmith]

Based on my experience with hams, assuming you actually took the time to document it and included the manual it would go down like this -

Buyer: "I connected the power meter to a 50 W ham mobile radio. It worked for about 2 seconds and now it doesn't even light up the display and it smells strange!"

Me: "Well first of all, did you read the instructions included with the unit?"

Buyer: " No!"

Me: "No problem.  Did you read the very first sentence that stated WARNING .....  "

Buyer: " No!"

Alternative:

Me: "No problem.  Did you read the very first sentence that stated WARNING DO NOT EXCEED 18dBm MAX.  AVOID STATIC DISCHARGE.  "

Buyer: " I saw that and was confused.  Your document should be in VSWRs and Watts.  And BTW, ESD is not real.  "

Let's continue.....

Me" "Well that's the problem right there."

Buyer: "I have been a ham for 50 years now and I know what I'm doing."       

Me: "Me, so are you trying to tell me that at one time you knew how to read? "

Buyer: "I'm telling you your products are very poor and I demand a refund for this burned up worthless device!"

Me: "But you didn't pay for it.  I gave it to you for free."

Buyer: "I'm an extra class!!!  Do you even have a license???!!!" 

Me: "No"

Buyer: "That explains why you don't understand why we hams love our Bird meters!"   

Buyer: Proceeds to measure their 5W radio with a 100W slug.  Wants to measure their SWRS and flips the 100W slug.  Is pleased with their ability and question why so many people are clueless. 

[xrunner]

 

Any way you slice it, I don't think selling easily damaged products to people is what I want to do.

Now if I made sledgehammers, that might be different ...

But then I could get sued when someone dropped one on their toe and claimed the item was inherently dangerous.

I think I'll keep it to the hobby level where I can personally interview a local if they want to reimburse me for the costs and I can explain in-person how to use it. 

[joeqsmith]

If you're selling these sledgehammers, I'll take a few...   No manual needed!

[fourfathom]

Nice Sledgehammer version above, but man, I miss Tony Levin's amazing bassline from the original.  I've spent the last hour listening to the original and several live performances with Gabriel and Levin.  This was time not wasted.

[bd139]

Buyer: " I saw that and was confused.  Your document should be in VSWRs and Watts.  And BTW, ESD is not real.  "

This made me laugh because I had that exact discussion with someone during my intermediate course 

I decided to let him cost himself money. Sometimes pain is a good education be it physical or financial.

[bd139]

Any way you slice it, I don't think selling easily damaged products to people is what I want to do.

Now if I made sledgehammers, that might be different ...

But then I could get sued when someone dropped one on their toe and claimed the item was inherently dangerous.

I think I'll keep it to the hobby level where I can personally interview a local if they want to reimburse me for the costs and I can explain in-person how to use it. 

Actually this one made me wonder how Elecraft still exists. They sold some fairly high end kits which were quite difficult to assemble. I'm surprised the average ham ended up with a working radio at all.

I mean can you imagine some of them using Jesus' soldering iron on this bastard...

[xrunner]

Actually this one made me wonder how Elecraft still exists. They sold some fairly high end kits which were quite difficult to assemble. I'm surprised the average ham ended up with a working radio at all.

I mean can you imagine some of them using Jesus' soldering iron on this bastard...

Like I said earlier, I know of no hams - none - that have made anything like that kit. In fact I can't say I know any at all that have made any sort of kit electronics.

As far as power meters, I might get this comment -

"Your power meter isn't as good as my Bird even reading low powers! If I have a 100 W slug I can read from zero to 100W. My scale goes to zero it's printed there you should check it out on the internet. Mine reads ZERO when I disconnect it. So with that I can go from ZERO to 100W!!! When no power is applied yours still reads power LOL something like 19e-12 watts, zero is still lower than that so hahaha get real dude!  "

[bd139]

Ah yeah exactly that. That reminds me of the 5334B I sold to a ham. Firstly he couldn't work it. After providing him with a link to the manual and telling him to read it, he was complaining that it wouldn't measure 0Hz when something was disconnected. The front end is basically a clipping network, unterminated MMIC and prescaler IC which is pretty unstable and picks up anything in the room when it's disconnected. Any explanations went over his head so I had to process a return at my own cost.

I've sold 700 items on ebay. I had 2 returns out of that and they were from stupid hams 

[joeqsmith]

"Your power meter isn't as good as my Bird even reading low powers! If I have a 100 W slug I can read from zero to 100W. My scale goes to zero it's printed there you should check it out on the internet. Mine reads ZERO when I disconnect it. So with that I can go from ZERO to 100W!!! When no power is applied yours still reads power LOL something like 19e-12 watts, zero is still lower than that so hahaha get real dude!  "

I helped a friend with a small dyno project.  Dyno could absorb around 200HP and used a water brake.  We used an S type sensor at the end of an arm to measure the torque.   We would stack a series of calibrated weights onto the arm and I would run a polynomial fit on that data (similar to my simulated Bird meters in the video).   Its a pretty accurate system.  The problem of was when there was no load applied,  the system did not read 0.0.  Being an engineer, I was telling my friend who cares.  It was something like 0.01% accurate.  You could see it bothered them so I think I had a Tare function which I think still wasn't good enough and I ended up coercing readings below some cutoff to zero.   The odd part is my friend wasn't some beginner.     

Where I work, I have seen similar problems, not related to electronics or mechanical measurements.