CB and Ham Radio Techs Love Their Bird Wattmeters

[xrunner]

I'll be taking my time on this project and the weather is actually helping. We have a voluntary electricity conservation notice today because of the heat so we aren't supposed to turn on unnecessary electrical devices. So of course I can't solder wires today. But using my computer is mandatory.

 

For testing I'm simply connected the AD8307s to each port (FWD & REV) with male/male SMAs. I also got a more appropriate type of shield so I can transfer the project to a Due board later if I want to.

I'm also looking at some different styles of project enclosures on Amazon but needing that is a ways off at the moment.

[joeqsmith]

Maybe you could print a custom Bird 43 looking case for it, complete with a dummy slug that is actually the selector knob to turn it on/off and select the various functions.

[xrunner]

Maybe you could print a custom Bird 43 looking case for it, complete with a dummy slug that is actually the selector knob to turn it on/off and select the various functions.

So if it looks like a Bird then it must be as good?  Hmmm ... interesting idea, I must think more about this.

I'm getting the basic project bread-boarded now. Should be able to read some outputs from the AD8307s and calculate power (uncorrected at this point) if all goes well.
 

[xrunner]

Friday Evening Update

A breadboarded setup was tested and the results were in-line with expected values for this initial look. I have the Putnam coupler, two AD8307 channels (FWD & REV), an Arduino Mega board, and a white OLED display.

I tested one frequency in four ham bands: 6m (50 MHz), 2m (146 MHz), 1.25m (222 MHz), 70 cm (450 MHz). The power applied was 0.0 dBm. At this point there are no corrections in the software for the known response of the AD8307 which falls off a bit the higher the freq. is, so I can see the raw results. However, I did correct for the coupling loss of -50 dB per port. Later, all the bands will have corrections applied in the software. The correction (band) will be selected by the user via a button. I foresee needing just one correction factor per band.

Readings:

50 MHz: -0.06 dBm FWD, -24.8 dBm REV
146 MHz: -0.45 dBm FWD, -25.61 dBm REV
222 MHz: -1.48 dBm FWD, -27.55 dBm REV
450 MHz: -3.55 dBm FWD, -28.19 REV

The coupler has a 50 ohm load attached, which should in theory give an SWR of 1:1. But as you can see the directivity issue (which is a factor for all couplers of this kind) is clearly there on the REV channel, so we know that contributes to errors. I had measured an approximate directivity in my earlier tests of 25.5.

I calculated the SWR from the 50 MHz readings just for fun and got 1.12. Not bad for a first test.

[joeqsmith]

So if it looks like a Bird then it must be as good?  Hmmm ... interesting idea, I must think more about this.

Equivalent to putting stickers on your bicycle to make it go faster.  I was a kid once and am sure it works!    

I picked up a vintage Narda X-band coupler a while back for my waveguide experiments that has a 33dB directivity.   These all look like they were metrology grade with cal data for lab use.    It made a big improvement in my measurements.

[vk6zgo]

So if it looks like a Bird then it must be as good?  Hmmm ... interesting idea, I must think more about this.

Early model Coaxial Dynamics units look like a Bird & are exactly as good---perhaps better?

[xrunner]

So if it looks like a Bird then it must be as good?  Hmmm ... interesting idea, I must think more about this.

Early model Coaxial Dynamics units look like a Bird & are exactly as good---perhaps better?

Yes I know - I used to own a Coaxial Dynamics meter with a selection of slugs. Since I have much better power measuring instruments now I sold it at a good price to a ham friend, who is thrilled to own it. 

[joeqsmith]

My vintage analog meters.  I found someone to buy them both.   

[xrunner]

Cute - a meter with a kitty cat on it. 

[joeqsmith]

That was made by WAWASEE Electronics out of Indiana.  I had a friend who worked there for a while.

https://worldradiohistory.com/hd2/IDX-Short-Wave/Archive-Ham-Radio-IDX/IDX/70s/Ham-Radio-197612-OCR-Page-0047.pdf

[xrunner]

That was made by WAWASEE Electronics out of Indiana.  I had a friend who worked there for a while.

https://worldradiohistory.com/hd2/IDX-Short-Wave/Archive-Ham-Radio-IDX/IDX/70s/Ham-Radio-197612-OCR-Page-0047.pdf

Interesting. I've never heard of that company. I'll ask some of the local hams if they have.

I'm working on some cal constants for the bands I'll be using: 6m, 2m, 1.25m, and 70 cm. The input power can be up to 200W (+53 dBm) as specified by the Putnam coupler. Therefore, the coupled output that the AD8307 could see, would be up to +3 dBm max (53 - 50). This is not a problem. Most hams will not use more than 50W, but I do know a few that have amplifiers for VHF (2m) that could reach 100 or maybe 200W. But not many.

The lowest power I'd expect a ham to use with this project would be 1W (+30 dBm). So the lowest input to the AD8307 would be -20 dBm (after attenuation by 50 dB from port). But the occasional person might test a lower power radio with no harm done.

I'd like to use one cal constant per band, selected with a push button. I want to take some data for each band across power levels from -20 to +3 dBm. This is what the port would output if the coupler was fed actual power levels which would be 50 dB higher.

But I'll have to go directly into the input of the AD8307 board with my signal generator, because I don't have the ability to do over 50W VHF or UHF. So I'll simulate what the AD8307 would see if it actually was connected to the coupler and the input to the coupler was up to +53 dBm (or less). I'll also need to compensate for the port attenuation, which is not exactly -50 dB for each band, but I can measure that again and just create another cal constant per band for that parameter

I'm pretty sure, having worked with this log amp before, that I'll be able to select one cal number per ham band that will be satisfactory, say giving a +/- 0.5 dB error. It will correct for the variation in frequency response of the AD8307, and the slight change in response of the AD8307 at the higher power levels around +3 dBm.

[joeqsmith]

Sounds to me like you have just justified that new amplifier you always wanted.   

That one I built from a kit I believe was rated up to 400MHz (depending how you built it) and was up around the levels you want. I never needed to run the full power and built it without a spreader.   Maybe something like that would get you going.

Found it.

https://www.eevblog.com/forum/projects/home-made-pa-and-load/

[xrunner]

Sounds to me like you have just justified that new amplifier you always wanted.   

That one I built from a kit I believe was rated up to 400MHz (depending how you built it) and was up around the levels you want. I never needed to run the full power and built it without a spreader.   Maybe something like that would get you going.

Found it.

https://www.eevblog.com/forum/projects/home-made-pa-and-load/

Yea I need a bench power amp for testing these types of projects. I'm using a Baofeng HT to get up to 5W on VHF/UHF, but that only gets me so far. Might be just the project after the current one. The local hams seem to like power amps on VHF but more than a few have popped the finals in their amp due to negligence. Maybe I can grab one they don't want to fix and use that. 

I managed to get a single cal factor to get me pretty close to +/- .5 dB power measurement accuracy on all the bands up to what would be 200W (+53 dBm) except for 450 MHz. As seen in the attached chart from the datasheet, the response curve for the 500 MHz trace (and applies pretty much the same for 450 MHz) gets a little curve in it when it sees power in those bands get over about +1 to +3 dBm, and that's what I'm seeing. And of course it mucks up my grand plans for +/- 0.5 dB accuracy.

So I'll have to come up with a little extra test in the software for that one band so I can use two cal factors: one for probably 0 dBm  up to +3 dBm input to the AD8307, and the other for all powers less than that. This mainly relates to actual power input of near 100W (+50 dBm) and up, but I said it would be useful for up to 200W so I'll stand by that claim.

At least until I can't stand by that claim. 

[Wallace Gasiewicz]

Quote from: joeqsmith on June 26, 2023, 07:42:15 pm

That was made by WAWASEE Electronics out of Indiana.  I had a friend who worked there for a while.

>https://worldradiohistory.com/hd2/IDX-Short-Wave/Archive-Ham-Radio-IDX/IDX/70s/Ham-Radio-197612-OCR-Page-0047.pdf

WAWASEE products are popular with CBer's mostly and popular here in Indiana because of the local appeal. Transel was another brand that produced Watt meters that I think are a bit better for practical transmitter monitoring. Another Indiana Brand.
A very good practical Wattmeter for HF is a DRAKE. They are quite good but are not peak reading meters. They also made a meter for 6 meters. Probably as good as the Bird Meters, and no slugs.

I think you fellows are getting too serious is it time for this???

[xrunner]

I think you fellows are getting too serious is it time for this???

*** YT Video ***

LOL, that song and similar video was posted many pages ago, you missed it. 

I made progress on the software and have a somewhat operational core but I have more tweaks to do, and of course need to move to a bigger display. I added a button which triggers an ISR that sets the cal factor and coupling factor for the band you wish to use. I'm still futzing with the calibration as I will explain below. The screenshot shows its operation. Some of the info is for debugging and will not need to be shown on the final screen, such as PF (coupling factor of port) and CF (calibration factor for the band).

As shown it's measuring the transmitter of a Yaesu FTM-7250D on 2m band. The radio is on the high power setting. I previously measured this on my hp 437B as 44 W, the project meter reads 42.2 W. So that's an acceptable reading for now, but I have more tweaks to do.

The project should work up to 200W, and the signal the AD8307 sees is (input - 50 dB) port coupling.

200W is +53 dBm, port output would be +3 dBm
100W is +50 dBm, port output would be 0 dBm
50W is +47 dBm, port output would be -3 dBm
etc.

However, the response of the AD8307 isn't as linear as one would like in the area around and above 0 dBm as seen on the chart (circled in pink), mostly for the higher frequencies. Some of this is obvious from the chart but it's also present on a smaller scale that the chart doesn't reveal as readily.

So, after a lot of playing and measuring, I came up with a solution for this project. I added a small 10 dB SMA attenuator on the output of the FWD port so the port will be -60 dB now. This will shift all power readings down 10 dB (blue line on chart) and so move the high end of what I want to measure away from the troublesome area. This will not be a problem for the AD8307.

I need to measure from 1W (+30 dBm) to 200W (+53 dBm). The output from the port before this mod would be -20 to +3 dBm. After adding the 10 dB att., the output will be from -30 to -7 dBm, and should give me a much more linear response for the higher frequencies, eliminating any "gamesmanship" needed in the software to account for non-linear curves.

Now I will re-check all the cal factors for each band and see how it looks.

[joeqsmith]

Did you look at the AD8310?  I had ran tests on one of the demo boards.  There was a switch point at -5dB where the error started to open up. 

It doesn't appear that I tested the 07 to the same degree.   I think knowing I was going to limit the meter to 50MHz, I decided against running those longer tests. 

[xrunner]

Did you look at the AD8310?  I had ran tests on one of the demo boards.  There was a switch point at -5dB where the error started to open up. 

It doesn't appear that I tested the 07 to the same degree.   I think knowing I was going to limit the meter to 50MHz, I decided against running those longer tests.

Yea I made one of my previous power meters with an AD8310. Those are the boards that had the LED. 

[joeqsmith]

You just bought boards with an extra SMA (output?).  My AD8307 boards are similar to the AD8310, with the LED and without the extra SMA.   Shown is one of the AD8307 boards.  Remember I had changed out the SMA connector they used to a higher quality part along with changing the input matching circuit.   (note the LED is on)

[xrunner]

You just bought boards with an extra SMA (output?).  My AD8307 boards are similar to the AD8310, with the LED and without the extra SMA.   Shown is one of the AD8307 boards.  Remember I had changed out the SMA connector they used to a higher quality part along with changing the input matching circuit.   (note the LED is on)

Yea these boards have an SMA for the input RF and for the output voltage, but also two solder pads for the output V too. I don't know why they used an SMA part for that. Even if you wanted the board removable (easily) from a mounting, the power leads are still soldered. Seems like a waste. They could have used the money for an LED!

 

Project was looking and acting pretty good but the accuracy was just a wee bit worse than I thought it could be. I eventually realized that these boards do not come configured with the optimal input resistance. I had forgotten about that since last time.

The input resistance of the AD8307 is 1100 ohms, and the documented solution is to add a lower R in front to get closer to 50 ohms. What these boards come with is a 47 R, which is not optimal. In parallel with 1100 R that results in ~45 ohms. The best value would be 52.4 ohms but I don't have that value. I do have some 1206 51 ohm that will fit on the pad (it's made for 0805 size). That results in a value of ~49 ohms. I installed one today on the FWD board, and it indeed improves the accuracy the last little bit to the point I'm satisfied with some limited tests. I ordered some 51 ohm 0805 today and will use one of those for the other board.

I will re-take all the cal data for each band and adjust the constants in the software after the other board is modded. Then I will take more data with higher power inputs - from a Baofeng HT (up to 5 W) and a Yaesu mobile radio (up to 50 W).

[joeqsmith]

Looks like I only bought two of the AD8307 boards, which are inside the Watt meter.   I was thinking I could repeat some of the tests I ran with the AD8310.  Even then, it's a different layout so I'm not sure it would be of much value.    You should be able to measure S11 with the board powered up.  When looking at the AD8310, I had placed two 100s in parallel at the input of the board and it looks like I may have changed the capacitors.   We swept the boards to 2GHz and tried to run a fit to correct the errors.    They worked well in the <500MHz range you're interested in.    And have an LED!

[xrunner]

Looks like I only bought two of the AD8307 boards, which are inside the Watt meter.   I was thinking I could repeat some of the tests I ran with the AD8310.  Even then, it's a different layout so I'm not sure it would be of much value.    You should be able to measure S11 with the board powered up.  When looking at the AD8310, I had placed two 100s in parallel at the input of the board and it looks like I may have changed the capacitors.   We swept the boards to 2GHz and tried to run a fit to correct the errors.    They worked well in the <500MHz range you're interested in.    And have an LED!

Well Joe I'm beginning to wonder if the input design (the R,C,and L components) this board is using is basically crap. I'm just getting really strange readings that are seemingly nonsense - like power readings that are off by 10W on a high power input, and the higher the freq. the worse the error is. Like 146 MHz high power (44W) giving me 50W or 60 W out of my calculations from the software. I've checked my RF cal work many times over the last few days and I haven't made any mistakes there. I checked the output power from the Putnam FWD port on the SpecAn when transmitting a high power into it, and after adding back the attenuation of the port I get exactly the right answer. But something is causing the measurement to be wrong and worse when higher power is applied to the AD8307 board.

I've researched what people have done with this chip (AD8307) and the designs they are using. The most common and simplest input design arrangement is as shown in the schematic attached. Simply two caps on IN+ and IN-, and a 50 or 51 ohm resistance (in the pic two 100 R in parallel) from input to ground.

The input design this board is using, who did it is anybody's guess, is shown on the board pic attached. You can see an input cap C6. Then they have the resistor (on my original board it's 47 ohms). But it doesn't go directly to ground - there is an inductor L1 between the R and ground. Then you see the input caps for IN+ and IN-.

I checked S11 and you can see the results. The markers are at 50 and 450 MHz. The response can be a lot better. So what I'm going to do is pull some components off the front end and make it like the design that is most commonly used. Just the 51 ohm R and the two caps. I did get some proper 0805 resistors today so I will proceed to mod the board. I'll be back ...

[joeqsmith]

From what I remember, my 8307 front end was like your board.  The 8310 was more like the schematic you show for the 8307.  I had changed the input on 8307 to basically be the same as the 8310.   Basically jumped out the input C and L.  2X100 ohm to ground.  May have changed the other caps value.   Problem is I never swept those boards like I did the 8310, or don't seem to have data for them. 

Once I knew the RF gen and my Signal Hound were on par with one another, I used the bench meter to measure the voltage off the detector while I swept the level and frequency.   I still have all that software to automate the sweeping.    I think I then just did a least squares fit at the lowest frequency and then tried to do a polynomial fit to that.   Something like that.   Once I settled on that 50MHz though, all that kinda went out the window as it just wasn't needed.   

If you like, I can pick up another 8307 and repeat some of these tests.  May at least be able to give you something to compare against.   

[xrunner]

If you like, I can pick up another 8307 and repeat some of these tests.  May at least be able to give you something to compare against.

Sure if you have the time.

I removed the input cap C6, and the inductor L1, and replaced with a short wire (didn't have any Zero ohm 0805 parts). I also replaced the large SMD 51 ohm part I put in the other day with the correct size 0805 part.

I checked S11 again and it looks a lot better now. Also, I did a few quick checks of the cal constants I was using on the 445 MHz band against what they are now with this change. They are definitely not the same values as before. I edited my code with the new constants for this band and did a quick check with a Baofeng HT. I was pleased with the results that I measured using my system. So I will carefully check all cal constants for all bands I'm using and get new values. Will report on that soon.

I do note that due to:

high frequencies and higher powers being tested
TX unit nearby the measurement system
AD8307 PCBs not being shielded
breadboard and wiring acting as antennas

I can get some quirky variations in the power readings. I know what the Baofeng HT puts out in terms of power because I checked it using my hp 437B power meter. I can get the correct power reading on both 2 meters and 70 cm using my system, which is very good. However, I can also get the wrong reading for no other reason than a combination of passive and active electronics happen to be in the wrong place on the bench.

I may actually need to take a time out and design or find a 3D model that I can re-size easily for a quick and dirty little box. I can 3D print two and shield them using metal tape. I'll use one for each of the AD8307 PCBs until the testing is completed. Of course the final system will be in a shielded enclosure.

No rush I got all summer and it's too hot outside to do anything fun.

[A.Z.]

just a couple links which I hope may be helpful

http://electronics-diy.com/electronic_schematic.php?id=952

https://www.qsl.net/df7tv/pm8307.html

and then I suppose you already saw the reference design found in the datasheet

https://www.analog.com/media/en/technical-documentation/data-sheets/ad8307.pdf

[joeqsmith]

I think I straddled the first cap with two SMT resistors right to the ground planes.  This removes all that other garbage.   You may consider removed the common pads for R3/L1 and adding foil over that entire void.    Keep things flat.