CB and Ham Radio Techs Love Their Bird Wattmeters

[xrunner]

I'm at the point where I feel confident I can calibrate my power meter and get reasonable readings that would make it a very usable SWR / Power Meter. I may actually add HF (all bands below 30 MHz) if I can get away with a single calibration factor. It really wouldn't be a big deal, but most people I'm thinking about would want this for VHF and UHF.

The first ham band to calibrate is 6 m (50 MHz band). I'm going to fine-tune the calibration factor for each band in 0.1 dB steps until I get the best accuracy from lowest to highest power. This takes into account the Putnam port coupling factor (~50 dB), the additional SMA attenuator on the FWD port (10 dB), the cable losses, and the AD8307 output voltage response per frequency band. The total correction will be somewhere in the range of 59 to 69 dB but different for each band, increasing as we go from 50 MHz to 445 MHz.

In terms of error, what does +/- 0.1 dB adjustment steps do? If we have +53.0 dBm (200 W), an error of +0.1 dB yields 204 W. An error of -0.1 dB yields a power reading of 195 W. A span of 9 W.

If we have 1.0 W (+30.0 dBm), an error of +0.1 dB yields 1.02 W. An error of -0.1 dB yields a power reading of 0.98 W. A span of 0.04 W.

The test setup for 50 MHz is shown in the pic. I now have the project system inside a temporary shielded box. I have a Yaesu FT-450 HF, 6m transceiver which will give me a power output from ~5 to ~100 W from the menu. However it's not a lab-grade RF source. So unlike the guy in the video, I don't expect if I set the radio to 50 W, that it will transmit 50.0 W. It most likely won't, and I don't adjust my project to a number in a menu setting or a radio's power meter.

My hp 437B power meter is the reference measurement standard. For example, I do not expect the radio to output 100.0 W on that menu setting. But whatever it does output (probably from 95 to 105 W), my system should give the same reading as the hp (ideally). That is the cal factor I will determine and have as a constant for each band in the software.

[A.Z.]

... he should have used in the video was the 25 - 60 MHz, 5W element.

He was putting out 12W on AM.

I think you mean 12 birds, isn't it ?

[Wallace Gasiewicz]

Maybe 12 Angry Birds???

[joeqsmith]

... he should have used in the video was the 25 - 60 MHz, 5W element.

He was putting out 12W on AM.

I think you mean 12 birds, isn't it ?

Unless you're a ham or CBer, then it's Watts.   They are the gold standard after all.

[xrunner]

Love the angry birds logo. Would look good on my power meter. 

[xrunner]

Some tests starting with VSWR on 50 MHz. I used a 50 ohm dummy load, and my homebrew SWR tester load, which gives a 2 or 3 depending on the switch position.

[vk6zgo]

I will probably go  at my ignorance when you tell me, but what does CF mean in the display?

[xrunner]

I will probably go  at my ignorance when you tell me, but what does CF mean in the display?

Thanks for asking. I'm sorry if I forgot to explain that before.

It's the Correction Factor required to account for the Putnam coupler port attenuation (50 dB), the additional SMA attenuator I added to shift the power range I'm working with down more on the AD8307 response curve (10 dB), the cable losses from the coupler port, and the AD8307 log amp response which drops as the frequency increases. I have a CF for each ham band I'm using this project for. In the case of the 50 MHz band the CF happens to be less than 60 dB because the Putnam coupler loss at the FWD port is a bit less than 50 dB.

The CF is displayed now only for development and won't be needed for the final display. 

[vk6zgo]

I will probably go  at my ignorance when you tell me, but what does CF mean in the display?

Thanks for asking. I'm sorry if I forgot to explain that before.

It's the Correction Factor required to account for the Putnam coupler port attenuation (50 dB), the additional SMA attenuator I added to shift the power range I'm working with down more on the AD8407 response curve (10 dB), the cable losses from the coupler port, and the AD8307 log amp response which drops as the frequency increases. I have a CF for each ham band I'm using this project for. In the case of the 50 MHz band the CF happens to be less than 60 dB because the Putnam coupler loss at the FWD port is a bit less than 50 dB.

The CF is displayed now only for development and won't be needed for the final display. 

Doh! I should have recognised the initials.

Back in the Dreamtime, pre-microprocessors, we had to apply correction factors manually all the time.

It was the only way to get reliable results when we often had only one instrument which had trustworthy calibration out of a group being used.
After a while, we could safely get a bit "sloppier" with things, when we found that the error of many devices was pretty much "down in the noise" as far as the effect upon results was concerned, but it was something always kept in mind.

[xrunner]

Here are the power measurement results for the 50 MHz band. This compares the power output of the FT-450D as measured by the reference (hp 437B + hp 8482A sensor) to the power measured from my development system (Putnam dual directional coupler, AD8307 log amps, and Arduino Mega controller).

Power output data is as follows (Watts):

Radio PWR Set	hp 437B	Project	Error
5	5.35	5.2	-0.15
25	24.8	25.0	+0.2
50	52.1	52.9	+0.8
75	75.4	78.2	+2.8
100	94.2	96.5	+2.3

The maximum error seen is 0.1 dB so I'm pleased with that.

[joeqsmith]

Nissei RS-70 Digital SWR/Power Meter, 1.6-60MHz, 200W. 

[xrunner]

Oh excellent. I will watch that video later this evening when I can devote my full attention to it. 

We both bought something. I just got this Baofeng UV-S9X3 HT delivered. It will give me several watts of power for testing on the 1.25 m ham band (220 to 225 MHz). None of my other radios can operate on the 220 MHz band. It was a mere $32.

[joeqsmith]

After you watch it, maybe consider buying one to repeat my tests.  There are not any good reviews from what I saw and it would be interesting to see if the results repeat.  Then again,  guessing you have better things to spend your money and time on.    All the Amazon reviews are 5 stars.  I would be generous giving it one star.

***
Interesting though, shortly after my review it is no longer available.     

https://www.amazon.com/NISSEl-RS-70-Digital-1-6-60-Radios/dp/B0188SH8VY/ref=pd_vtp_h_pd_vtp_h_sccl_1/142-4387211-6918307?pd_rd_w=TwjAE&content-id=amzn1.sym.e16c7d1a-0497-4008-b7be-636e59b1dfaf&pf_rd_p=e16c7d1a-0497-4008-b7be-636e59b1dfaf&pf_rd_r=VC8A24T747GTXYAT4A2D&pd_rd_wg=s92eM&pd_rd_r=78d40b8f-197d-493b-8909-63a1122a1b32&pd_rd_i=B0188SH8VY&psc=1

***

The SOT23 diodes are marked 400 (Under microscope, C0+.  Doing a search, I did not find anything).  Cheap design but surprised the VSWR wasn't tuned tighter.

[xrunner]

Interesting though, shortly after my review it is no longer available.     

Sold out? They must be really good meters.

Why don't I look for a different RF power meter to test either from Ebay or Amazon, in addition to getting my project working and into a nice case and all. I want to beat all the competition. 

[joeqsmith]

Similar approach:

https://www.collinsradio.org/wp-content/uploads/2015/05/Understanding-the-Bruene-Coupler-Transmission-Line-Bold.pdf

I wonder if I made a new transformer ......   could it be improved to make it a usable product without changing the artwork.   

[Grandchuck]

There is another model available: https://www.amazon.com/NISSEI-DG-503-Digital-1-6-60MHz-125-525MHz/dp/B08QJ6DGBX/ref=dp_prsubs_sccl_3/139-1436181-1811709?pd_rd_w=s9UVx&content-id=amzn1.sym.70b216e7-2402-468b-8e4e-1a721a5b73ca&pf_rd_p=70b216e7-2402-468b-8e4e-1a721a5b73ca&pf_rd_r=23HQ2XXESN8TW8H44GV7&pd_rd_wg=EzzkQ&pd_rd_r=82e0a908-903e-4bc6-8f75-e23e6e3d9cfe&pd_rd_i=B08QJ6DGBX&psc=1

[xrunner]

I wonder if I made a new transformer ......   could it be improved to make it a usable product without changing the artwork.

Yea possibly ...

OK I watched the video, Basically a piece of junk - I wouldn't trust the information it gave me. I see it listed elsewhere for $90 to $100. 

The case design is weird to me. Is it supposed to sit on the table? With two coax cables pulling on it, it ain't going to stay in one position very well. It needs to be pointed at the operator to view. 

Obviously there is a microcontroller underneath the PCB calculating the powers and SWR, controlling the display (same thing I'm doing). You might be able to re-program it if you needed to. But I think it's probably doing the right math. The problem is - garbage in garbage out. Too wide a bandwidth to deal with without trying to correct the answers with correction factors per band (like I'm doing  . You have access to the tweaking pots, so if you need a project try it. 

[joeqsmith]

There is another model available:

Fool me once, shame on you.  Fool me twice, shame on me.   

[joeqsmith]

...
Obviously there is a microcontroller underneath the PCB calculating the powers and SWR, controlling the display (same thing I'm doing). You might be able to re-program it if you needed to. But I think it's probably doing the right math. The problem is - garbage in garbage out. Too wide a bandwidth to deal with without trying to correct the answers with correction factors per band (like I'm doing  . You have access to the tweaking pots, so if you need a project try it. 

It appears there are at least two PCBs.  I would have to remove the top board to get a better look.  I can imagine they left all that paint on the case and it may not have a good ground.   There is also the trimmer cap.  I would need to somehow get it onto the VNA to try and adjust it for flatness.  I would have thought with the two trim pots, the forward and reverse would have been accurate at the calibrated frequency.   Makes me wonder what their alignment procedure is, or I guess was.   

[DaneLaw]

Got a couple of cheap RF SMA Wattmeters. (both are bottom of the barrel)
One is an older USB3 fellow from China with some years on the back since I purchased it, it goes from 0Mhz to like 10 or 11Ghz, - it can both be used as a stand-alone unit with its OLED display that got a 10log frequency bank where you can have different dbm-offsets for each of the frequencies you put in.

The unit can also be hooked to a computer for graphing alongside adjustments with 3 different speed settings.
Testing HackRF signal generator output that peaks around 24.22mW at 2.445Ghz on this RF-meter..I recall the HackRF is rated as half duplex with around 25mW of max RF output-power, but got no idea at what frequency that output was rated, as the hackRF RF-power is highly variable across its output span that peaks at 7.25Ghz, though with some frequency drift from 6.9G to 7.25Ghz.. up to 6.9Ghz its spot on, but obviously with minute RF power up in those multiple gigahertz.

The other one is from this year, and got it for some cheap handhelds I purchased..
its spec-rated at max 120 watt and got a range from 125 MHz to 525 MHz according to manual.
Its this one below that costs around the same, and is not PC-compatible.. it got a few features on its screen.. shows forward & return, alongside SWR but the SWR needs some juice before the SWR reading will play along,.. the wattmeter also needs around 0.5 to 1 Watt, so not a unit for smaller values.

Wattage test on the quite popular Quansheng K5, as it is cheap as, and you can mod it with games, s-meter, pong, spectrum, and 18Mhz to 1.3Ghz span, and more or less anything under the sun. 
At 17 US delivered to DK with incl.VAT (25%) and charging cradle, - Im quite impressed with this K5 unit, and its cleaner than my Jianpai8800plua which is a radio too around 300% more and around 50 bucks, though with Bluetooth app & GPS, and all that yazz.
Quansheng K5 wattage test _ low 1.55W / medium 3.43W / high 4.94W at 146.2Mhz (battery somewhat full 8.1v) with a 20W dummy load attached.. the SMA dummyload was incl. with the wattmeter. (wattmeter-price was a tad over 30 bucks with a little shipping cost on top incl. EU-VAT/danish25%)

Wattage test of the Jianpai8800Plus (if others have tested these radios with better wattmeters would love to hear the results, to put mine into perspective, though both of these radios.. seems to be highly voltage-depended and how full the battery is' and what amount they can deliver)
Low 2.04W / High 5.87W at 146.2Mhz (battery 8.0v)

 
Manual of the latter RF SMA wattmeter, unit is fitted in a metal box with an inbuilt LIPO cell.. (front/back page)
The manual states an SWR detection range at +3watt (highlighted in the spec box upright front page, click for increased resolution).

Haven't checked the SWR accuracy yet on this 125Mhz-525Mhz return/forward/swr-wattmeter, though my only tools for that would be either the TinySA Ultra with a sweep/CN-bridge or these older 130-2.7Ghz antenna analyzers.

[joeqsmith]

Most reviews, the CB/hams use a radio for a reference.   Looks like the one meter you show acts as the load.  Connect an attenuator to it's input, then add the other in-line meter and see how they compare.  Not a great test but better than nothing.

***
You could also try flipping the ports to make sure it tracks.   

[xrunner]

Most reviews, the CB/hams use a radio for a reference ...

Yep.

I scanned about 4 YT videos of reviews of the sw-33 plus. Not a single review actually tried to see if the thing met it's claimed accuracy of +/- 5% by comparing it's measurement to a more accurate standard. Some other commercial power meter generally known to be a more accurate instrument. No, a Bird model 43 is not more accurate, I'm talking a commercial RF power meter such as those made by hp, Boonton, a quality spectrum analyzer that has the accuracy, or perhaps Bird company's more accurate offerings.

The reviews simply connected it to a radio and looked at the power measured as related to the radios menu choice. It will tell you if the radio transmits power, but you can't be sure it's within the claimed accuracy.

Sure having the equipment to do a good review costs money. But it's the only way to know what you bought is worth the money.

[joeqsmith]

Pretty sure I could cover 100W up to the 2M band but 525MHz is out.   To really test the SW-33, I would need to build a new amplifier.   It does have a lot of positive reviews from the buyers.  I would believe them like all the 5 star reviews for the Nissei.   

[Wallace Gasiewicz]

Quote from: xrunner on July 16, 2023, 10:50:17 pm

Oh excellent. I will watch that video later this evening when I can devote my full attention to it. 

We both bought something. I just got this Baofeng UV-S9X3 HT delivered. It will give me several watts of power for testing on the 1.25 m ham band (220 to 225 MHz). None of my other radios can operate on the 220 MHz band. It was a mere $32.


The Baofeng is famous for putting out power quite a bit out of band, Some repeater fellas looked at some and they are not even close to being within legal specs for spurious emissions.
Don't remember if that model was evaluated

[xrunner]

The Baofeng is famous for putting out power quite a bit out of band, Some repeater fellas looked at some and they are not even close to being within legal specs for spurious emissions.
Don't remember if that model was evaluated

I checked it on my spectrum analyzer. It has a spur when set to 220 MHz, but I deemed it not significant for what I was doing. Before I had it, I tried to use a cheap amplifier that operates on 12 V, that would have put out several watts when fed with 0 dBm. But I was seeing very strange power changes when changing the input to it. When I checked that on my spec an, I saw a whole lot of spurious emissions, so it was impossible to use it to calibrate on the 220 band. If I remember tomorrow, I'll hook it back up and take a screen shot.

For the readers out there, the AD8307 responds to all RF power coming into it's input. It cannot be tuned (without other circuitry) to a specific frequency or small bandwidth. So if your transmitter has a lot of spurious emissions, it will respond to them and give you a false (high) power reading. You'd have to examine your radio's emissions on a Spectrum Analyzer to see what was going on.

However for the person receiving your transmission, on their end, the receiver is only tuned to the frequency of interest - your buddie's ham radio frequency for example, so the spurious emissions aren't a problem for communications for you two. However, they are a big problem for other people's communications.