CB and Ham Radio Techs Love Their Bird Wattmeters

[A.Z.]

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.   

check this

https://www.nutsvolts.com/magazine/article/a-discussion-on-dbs-and-rf-power-meters

and in particular the notes regarding the response above 330MHz

[joeqsmith]

Saw his squiggled red line.  What about it?

[xrunner]

check this

https://www.nutsvolts.com/magazine/article/a-discussion-on-dbs-and-rf-power-meters

and in particular the notes regarding the response above 330MHz

I saw that a long time ago. It's of no relevance to me, because he's using analog circuits trying to get a DVM to respond as well as he can over the bandwidth he's interested in. I don't need any of that because I have a microcontroller to do the job with cal constants and/or compensation equations. You can see how I did it for the previous two power meters I made if you go back in this thread, but there are a lot of posts ...

[xrunner]

I've built two power meters with the AD8307 and AD8310 (in this long thread). They work well but were built and tested with low power signals which didn't cause any problems. Power levels up to only 10 mW. The previous one meant for ham bands only would read higher powers - but that was tested after it was put inside a shielded case. The use of that with higher powers meant that it needed an external attenuator attached in-line outside the box.

This project is being tested with high power emitters within a foot of the project electronics. The AD8307 is extremely sensitive and even though the power is fed to the coupler and from the coupled outputs to the boards with coax, the boards are not shielded and the input to the AD8307 can pick up RF easily due to the unshielded input traces.

I added several quick & dirty RF shields, and ferrite chokes. They are lame at the moment but I need to prove that shielding is the next problem. I put the HT inside some metal window screen, and grounded that. I made a small enclosure from cardboard, and put metal tape around it. I put the two AD8307 boards inside it, and grounded it. I put two ferrite chokes on the wiring to the AD8307 boards, and one choke on the power supply wiring.

Next I removed the 50 ohm load from the output of the Putnam, connected a 40 dB attenuator, and connected my 437B to it. Now when I transmit my development system and the 437B will measure power at the same time. This will prove to me that they are or are not in agreement.

I've measured the Baofeng HT many times using my hp 437B power meter. It's not a labratory-grade RF source, and so is probably going to vary a few tenths of a watt.

The results are as follows:

hp 437B vs development system (watts)

VHF low power
1.6 vs 1.7

VHF high power
4.5 vs 4.3

UHF low power
1.3 vs 1.3

UHF high power
3.6 vs 3.7

So now I'm confident that the cal constants are good, the attenuation values for the ports are good, and the system can read correct powers. But the shielding is not good enough because I tried another transceiver - a Yaesu FTM-7250D - which can transmit up to ~50 W. I don't have any shielding that I can put the radio inside. So any power I used higher than the low power setting, 25 or 50 W, caused improper readings on the development system (too high), whereas at the same time the hp 437B gave correct power numbers. The same thing happens when using the Baofeng HT on UHF if I do not enclose the little radio in the window screening.

So I think I want to work on a better temporary shield box for the development system. I do not want to commit to buying any new case, an Arduino Due for faster processing, or further programming work regarding a larger OLED display with on-screen graphics for the user, until I am sure it can reliably measure power from a more powerful transceiver.

[A.Z.]

check this

https://www.nutsvolts.com/magazine/article/a-discussion-on-dbs-and-rf-power-meters

and in particular the notes regarding the response above 330MHz

I saw that a long time ago. It's of no relevance to me, because he's using analog circuits trying to get a DVM to respond as well as he can over the bandwidth he's interested in. I don't need any of that because I have a microcontroller to do the job with cal constants and/or compensation equations. You can see how I did it for the previous two power meters I made if you go back in this thread, but there are a lot of posts ...

I was mainly focusing on that 330MHz issue he had, as for the microcontroller, that can cover a lot of sins, yet we're dealing with RF so shielding and all the usual precautions still apply, and then the input circuit is still analog, and it can't be amended just because there's a microcontroller (oh and I've been following this thread from the beginning)

oh and since you named microcontrollers

https://vk8rhradioprojects.com/power-swr-meter/

https://www.egloff.eu/index.php?option=com_content&view=article&id=260&Itemid=1970&lang=en

HTH

[joeqsmith]

I've built two power meters with the AD8307 and AD8310 (in this long thread). They work well but were built and tested with low
....

I do not want to commit to buying any new case, an Arduino Due for faster processing, or further programming work regarding a larger OLED display with on-screen graphics for the user, until I am sure it can reliably measure power from a more powerful transceiver.

I think I had ran tests to 300W with mine.  I'm limited by the load I have.   I do have those boards mounted inside that PCB case and they are in a separate cavity from the digital electronics.   Seems like it shouldn't be a problem. 

I did order a new 8307 to repeat some of the tests I had ran with the 8310.  I picked one of the ones that has the case.   Plan it to measure it as is for starts, then see if I can improve it.   Will let you know once it arrives.   

[xrunner]

OK Joe, thanks. I ran into a few wiring problems (small wires breaking inside the insulation) but I got those under control.

I did make myself a ghetto shielded enclosure for testing this project. It looks so good I think I'll start selling them on Ebay.

 

No, it isn't anything for sale but it does function for my purposes. I have a setup now that simultaneously measures power output from the Putnam coupler (hp 437B) and at the same time my development system is measuring the power from the FWD port (50 + 10 dB atten.). I'm comparing the 437B reading with my system reading. I think this is the best way to calibrate my cal constants for each ham band I'm designing this for (50, 146, 222, 445 MHz).

What you see on the lab bench is a Yaesu FT-450 transceiver. It's for HF and 6m. I'm using it for a high power test at 50 MHz, up to 100 W. I can test up to 50 W with a mobile transceiver on 146 and 450 MHz. The only other band I need to test at high power is 222, but I don't have any transceiver for that band. But I can simulate a high power by bypassing the 60 dB attenuation from the Putnam and injecting a signal of correct amplitude from my Agilent. For example, a 100 W (50 dBm) signal would be -10 dBm after 60 dB attenuation, and that is the level the AD8307 board would see. So injecting -10 dBm directly into the AD8307 board, combined with the proper cal factor, is the same thing, and will read 100 W on the display. But in the end using a genuine high power test is the final and best way to put the stamp of approval on it.

So up next is to check out 50 MHz at high power (and lower powers as well) and see if my design is giving the right reading there. Will report back ...)

[joeqsmith]

I'm a firm believer in aluminum foil.   I bet I have used a few boxes of it during my career.   

When I had rebuilt that 100W JFW attenuator,  I used a part from Barry Industries to replace it.  I think they spec that part to 1dB error.   The 300W Bird attenuator I think has a fairly wide error as well.   It all adds up.   I cal'ed mine basically the same, using the signal hound as the reference.  Pretty much why I said in that video that there are a lot of errors I am not accounting for. 

[joeqsmith]

Watt meter shoot out with the Bird 43...

[xrunner]

He used a Bird 4314 with a 10 W slug for FM. The accuracy is +/- 5% of full scale (in this case 10 W). So it can be off by 0.5 W on any reading over the scale. So his measurement is really 4.0 W +/- 0.5 W so it could be any power from 3.5 W to 4.5 W. Of course he never says anything about that. But he reads the Bird meter and it's 4.0 W, no questions asked.

The RS-70 read 3.06 W. I looked up the accuracy of it and it states "+/- 5% over the range 0 to 200 W (not of full scale)". So the reading of it is 3.06 W +/- 0.15 W. So the power measured could fall anywhere from 2.91 to 3.21 W.

It's very plausible that the actual power of the MD30 is >= 3.21 W but <= 3.5 W, somewhere in that range, if you are gathering data from at least these two meters.

In other words if the radio is low 0.5W from the factory, and the Bird is actually reading 4.0 W - 0.5 W error, then the actual power could be 3.5 W.

He didn't measure the actual power with an order of magnitude better commercial or scientific meter, (no the Bird is not that) so he really has no "reference" power level to check the MD30 against. I've measured many ham transceiver power outputs (with commercial grade equipment) and they rarely agree exactly with what the manual states, and these radios are much more expensive designs than little $130 rig. 

[joeqsmith]

You're acting like the "nasty know it all"  he mentions in the end.        That was a brand new out of the box Midland radio, which has an internal Watt meter and is aligned for a perfect 4.00W.   SWR was perfect as well.  So obviously the Bird is the closest at 4.0W.   You're just jealous that you don't have an old Bird smelling of piss and lavender so you too can finally make some accurate measurements.   

I tried to find details for the RS-70.   Are you sure its of +/-5% reading?  Wonder if it really meets their claims.. 

[xrunner]

You're acting like the "nasty know it all"  he mentions in the end.        

Mean and nasty, yea that's me all right. Pointing out the obvious is so anti-social. I shouldn't be allowed around nice people. 

That was a brand new out of the box Midland radio, which has an internal Watt meter and is aligned for a perfect 4.00W.   

Yea, yea, like I said. I've measured a whole lot of ham transceivers and not a single one measures exactly what the stated power output is on any setting. Sure some are close but sheesh - down to 2 or three decimal points? ICOM, Kenwood, Yaesu all need to visit the Midland factory and see how it's really done LOL. 

SWR was perfect as well.  So obviously the Bird is the closest at 4.0W.   You're just jealous that you don't have an old Bird smelling of piss and lavender so you too can finally make some accurate measurements.   

OK you're right I'm selling my hp 437B and sensor on Ebay tomorrow. But who wants junk like that when you can get a Bird that agrees with Midland CB radio manuals 

I tried to find details for the RS-70. Are you sure its of +/-5% reading?  Wonder if it really meets their claims..

That's what they claim. So it's more accurate than a Bird on the range he was measuring. But since it didn't agree with the manual, it can't be right. I mean it's stated in black and white for all to see. 

Specifications:
Frequency range: 1.6-60 Mhz
Power range:0-200W +/- 5%
Impedance: 50 ohm
Connector: M-J(So-239 (M))
Dimension: 70W x 78H x 30D mm
Net Weight: 220g

https://www.amazon.com/Youmei-RS-70-Digital-1-6-60MHz-Two-Way/dp/B077YCMSP3

[joeqsmith]

I see the +/-5% but I don't see any details on what that means.  I couldn't find a manual for it.   My google foo is lacking.

[xrunner]

I see the +/-5% but I don't see any details on what that means.  I couldn't find a manual for it.   My google foo is lacking.

No it doesn't specifically say.

My understanding is that percent of full scale accuracy specs refer to analog meters (moving coil meters) such as an analog DMM or the Bird meter, and percent of reading is for digital meters. But somebody is welcome to correct my understanding here.

[joeqsmith]

I would have no way of knowing outside of contacting the OEM, which I am not even sure who that would be.   I did find a manual for an RS50.  They claim it has three ranges, 15,60 & 200W.   If it is of full scale for each range, you're talking  +/- 0.75, 3 & 10 Watts.   Best to have the actual data than guessing.  Too bad it doesn't offer peak like the Bird.  We could buy a couple and review it.   

[metrologist]

What the hell, you guys get run off of QRZ? 

[Wallace Gasiewicz]

I have limited experience with these things. I have only seen and measured maybe 1,000 radiosNone of them are very accurate in their meters concerning their power output.The same thing goes for power meters, although they are better.I have compared these things with a HP Power Sensor with attenuators and a HP power meter.
You can calibrate the other meters with the HP and the cal will go away depending on the placement physically of the power meter. The sensor part of power meters is a relatively simple RF Bridge or Directional Coupler (whatever you wish to call it) for the most part. This coupler is not well shielded, let alone the other components.
Remember the analog meter itself is only accurate at midpoint.

Anything that makes more than a few watts will make quite the RF field around all these components.

The coax lines are suspect also. their placement will change the readings. Length of the test jumpers will change the results. Proper test coax for the HP power meters are VERY expensive. Not likely to be used.  Lets not even mention things like Pasteurnak or Shuner Cables.

The coax connectors mostly used are not even "N" connectors and have reflections of their own.
Even if the power meter is capable of, say 1% tolerances, all that goes out the RF window when hooked up to the radio and load.

At least the Bird devices are in a good solid case with better shielding, in my opinion. And can come with N connectors, till some CBer changes them

Having said all of that, the new digital meters appear to be much better than the old ones and however much more expensive. The old meters are still VERY useful and can prevent damage. Almost all of the time you do not need even 10% plus or minus.

Remember:  BIRD IS THE WORD!!!

[xrunner]

What the hell, you guys get run off of QRZ? 

We mentioned that the Bird was designed in the 1950s and wasn't anything special nowadays and the hams ran us off. 

[joeqsmith]

... I have only seen and measured maybe 1,000 radiosNone of them are very accurate in their meters concerning their power output...

Remember:  BIRD IS THE WORD!!!

Have you tested that same exact Midland CB?  That radio is the golden 4.0W reference standard. 

[Wallace Gasiewicz]

I have not measured a Midland M30I do not have a service manualI do not know if there are any adjustments inside the radio, some of the new surface mount designs do not have adjust pots.I do not know if this radio is packages as any other brand, although that is a standard practice in CB land, the same main board is used in different brands.
So No direct measurements of this "Golden" reference radio.

[xrunner]

By the way, the Bird element he should have used in the video was the 25 - 60 MHz, 5W element. Then the accuracy would have been +/- 0.25 W and the meter would have read in the high area of the scale, which is what you want for percent full-scale accuracy specifications. 

Can't speak for new CB transceiver designs, but the new(er) ham transceivers have a service menu that you go into and set up power level among a lot of other parameters. The days of tweaking pots with a screwdriver are long-gone. I have no idea if Midland has this or if they have a service manual that tells how to get into it. They probably would prefer CBers keep their hands out of the unit.

In theory you could set them for very exact power output into a lab setting where you have a accurate thru-line power meter and dummy load, or an accurate attenuator and terminal sensor-based power meter such as commercial meters which is what I'm using for my project. I tried to find one other person that measured the Midland M30 power output but could not.

Now, whether or not that output power remains accurate "in the field" is another story. 

[joeqsmith]

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

He was putting out 12W on AM.   

[xrunner]

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

He was putting out 12W on AM.

Right and he changed to a 25 W slug at that time (16:17 time). But the most accurate reading of 4 W would have been with a 5 W slug not a 10W slug. He apparently didn't have one, but perhaps he should budget for one. 

[joeqsmith]

Right, hard to measure 12W with a 10W slug.

[Wallace Gasiewicz]

I believe you are correct about some sort of service menu, I have seen some units without any adjustable points and I think there probably are some sorts of ways to adjust the output and other things, but the service manuals are not available and I am not able to find them.I am able to adjust these sorts of units that have adjust pots  pretty well using attenuator and a power meter, or a selective level unit, which I have, but I have no desire to do so.  Usually the owners turn everything up and blow the finals and I fix the unit and adjust things down to normal.
 I have tried to get to a service menu by punching all sorts of buttons but no luck.
The service manuals are only distributed to official repair facilities and only become available to us repair guys after someone leaks the info, usually takes years.


Quote from: xrunner on Yesterday at 12:48:07 pm

By the way, the Bird element he should have used in the video was the 25 - 60 MHz, 5W element. Then the accuracy would have been +/- 0.25 W and the meter would have read in the high area of the scale, which is what you want for percent full-scale accuracy specifications. 

Can't speak for new CB transceiver designs, but the new(er) ham transceivers have a service menu that you go into and set up power level among a lot of other parameters. The days of tweaking pots with a screwdriver are long-gone. I have no idea if Midland has this or if they have a service manual that tells how to get into it. They probably would prefer CBers keep their hands out of the unit.

In theory you could set them for very exact power output into a lab setting where you have a accurate thru-line power meter and dummy load, or an accurate attenuator and terminal sensor-based power meter such as commercial meters which is what I'm using for my project. I tried to find one other person that measured the Midland M30 power output but could not.

Now, whether or not that output power remains accurate "in the field" is another story.