CB and Ham Radio Techs Love Their Bird Wattmeters

[EE4all]

Thus comes the irony of this thread as 1dB error would be a far greater error than a Bird meter. 

I am just pointing out how we typically allow a bit when we talk about dBm, but then people become critical about error in watts because it can seem like it is bigger, but it's actually not.

[xrunner]

What's the page in the manuel where they describe how to adjust the chopper ?

In the old manual I have it's on pg. 6-9.

[Kosmic]

What's the page in the manuel where they describe how to adjust the chopper ?

In the old manual I have it's on pg. 6-9.

Ok this is part of the DC calibration of the meter. Personally I would not touch that part. What did you connect on the input ? normally you need a Boonton DC range calibrator.

[xrunner]

Ok this is part of the DC calibration of the meter. Personally I would not touch that part. What did you connect on the input ? normally you need a Boonton DC range calibrator.

Well I might not touch any part of the thing if I didn't have to, but it's here and useless unless I try ...

Yes I realize I don't have the range calibrator, but again I don't have it and I'm not going to buy one, so what am I left to do? I attached a sensor with a 50 ohm load. I followed the instructions and it works now and wasn't working before. If you want me to I'll connect it to my Agilent 8648A and show some the readings vs what the Agilent is set to. It's very accurate for hobby use. I measured the power from my "test transmitter" a Baofeng HT with a 40 dB att. in front of the sensor, the same as I did with my hp 437B and the power was off by .03W from what the hp read. 

In a commercial setting you would need to get it set up with data from a sensor properly, but I'm not in a commercial setting and I have seen that it works very well, so it is what it is.

[Kosmic]

No worries, if it's working for you that's great.

[Kosmic]

My offer of calibrating you sensors still stand. I was also thinking of creating an adaptor for my Fluke calibrator to imitate a Boonton DC range calibrator. So eventually, I should also able to do the DC calibration.

[joeqsmith]

Thus comes the irony of this thread as 1dB error would be a far greater error than a Bird meter. 

Of course, that assumes the Bird meter has slugs that are matched to the range we are interested in.     For example trying to measure 100W with a 100W slug,  its +/-10% of full scale  or 90 - 110 Watts or 49.5 to 50.4dBm. (check the Bird manual)   

Seems to be less than 1 dB error ....

Which I am guessing is +/-0.5dBm so very close to the bird.   Then again if he meant +/-1dBm, 79.5-125.8 Watts which I think is your point.   (check my math)

Hams may not want to spend the $$ for slugs and use what they can find cheap used.  Use that same 100W slug at 1W....        Then we need two, one for forward, one for reverse, then we need to manually calculate.....    Funny part is then they get in a bar fight over the errors...    

Been playing with waveguides and have a cheap thermistor mount from a training kit.  When I first started out,  I worked all their examples.  For power, rather than Watts or dBm, I measured everything in Smith's.   

***
Then, isn't there correction graphs in the Bird manual as well....

[xrunner]

You have the HP.  Why did you purchase the Boonton?   Do you have the thermistor or diode sensors for it?

About three or four years ago I was told by a ham friend (call him B) that his friend (call him A) had obtained some sort of power meter from a ham flea market and was planning on using the parts to make some other contraption.  Ham B told me that ham A had tried to get the power meter to respond from a HT transmitter by connecting it directly to the sensor, and that he didn't attenuate the transmitter so who knows what happened to the sensor. Ham A did not know how to use the meter properly so ham B suggested I call ham A and offer help.

I found out it was a Boonton 42A microwattmeter (an analog meter) with sensor. After talking to ham A for a while, and hearing what he did to it, I said it's probably shot now. After a few more minutes of talking, ham A decided to just give me the whole mess.

I brought it home but I could not get the 42A meter to work reliably although when it did work it looked like the sensor was OK (amazingly). I needed parts to fix the meter but I could not locate any so I shelved that project.

However, I hated to see the sensor just sitting there, as it had appeared that it was OK. I thought I'd take a chance. I found a Boonton 4220 Digital meter for $87. I checked it out with the sensor and it appeared to work just fine, in fact it was and is amazingly accurate given the fact I did not have any Cal data for the sensor. So that is how I got into Boonton power meters I didn't need any other brand of power meter because I have HP that is true, but since it started out free I ended up with it.

Do you have the thermistor or diode sensors for it?

Diode sensors.

The Boonton 42A meter came with a 51011 (4B) 100 kHz to 12.4 GHz, -60 to +20 dBm

I recently bought a 51010 (4A) 100 kHz to 7 GHz, -50 to +10 dBm

Both work reasonably well with the Boonton 4220

So the answer is, no, I do not really need this meter or sensors, but so it goes for many other items of test equipment I possess.

[EE4all]

But now you have 2 meters, so you can never be sure. You had better get a 3rd to be sure, in case the first 2 don't exactly agree. Heh.

[joeqsmith]

Did you return the analog section to ham A to chop up for their home project?   If not,  maybe you could use that nice case for your new Watt meter.   Maybe
you could drive that analog meter with the micro.   

[xrunner]

Did you return the analog section to ham A to chop up for their home project?   If not,  maybe you could use that nice case for your new Watt meter.   Maybe
you could drive that analog meter with the micro.

I may make you an offer you can't refuse (see The Godfather movie) on a decent power meter ensemble. Perhaps you will receive a PM soon in that regard ... 

[joeqsmith]

I am bad about collecting junk as you just never know when .... 

[EE4all]

Me too! If you get rid of something, you will immediately need it the next week. 

I submitted a web form inquiry page to custom cal about getting a certificate on this one. Did they answer? No, of course not. I think I can count like 2 times in the history of the internet that someone actually answered from a web question form. 

[xrunner]

OK, the Boonton is working well and I'm placing it back on a shelf for future use. Let's just say I'd make a pretty lousy Godfather. 

Anyway - I'm gathering parts for the power meter / SWR project, will try to focus on that now. 

[xrunner]

The previous two power meters I made in this thread used most of the entire range of the AD8307 log amp from about -73 dBm to +13 dBm. The "ham bands only" power meter could also measure higher powers with an external attenuator, but these meters were for direct measurement of power, not in-line meters to be used while operating transceivers.

In this case we are not interested in measuring very low signals such as a lab bench scenario testing our RF generator or other such interests. The measurement goal of this meter will be 0.5 W to 200 W to be used while transmitting and receiving. This equates to a range of +27 dBm to +53 dBm.

The coupled outputs, both FWD and REV (will use measured values in final design), are -50 dB. This results in a nice usable range for the AD8307 log amp of -23 dBm to +3 dBm input power. So I will be able to cover 0.5 W to 200 W input to the coupler easily.

Most of the basic details of these AD8307 power meters have been documented in this thread in previous pages so if you are curious just go back in the thread and look at the charts and data for the meters I already made. I may not repeat every detail this time but will concentrate on the differences between this and the previous projects, mainly the coupler and measuring FWD and REV power and SWR.

I gathered some of the parts to get started as you can see. What you do not see is an Arduino UNO board like I used last time, but an Arduino Mega board (and shield). I already had this, which was given to me for free (with a bunch of other such maker stuff that a local ham decided wasn't interesting to him any longer).

You may ask:

"But xrunner, why do you want to use a Mega board for this project? All those extra inputs are not needed and it doesn't have a faster clock than the UNO. That sounds pretty stupid!"

Not so fast! It does have more memory so that may be of some use (256 kB vs 32 kB). As I recall the other projects were right up to the memory limit.

"OK, you must be an inefficient coder if you need more memory. Is that the only reason you are using a Mega board instead of an UNO right now?"

I like to use graphics OK - sheesh! I also have another option I will be trying later on. The other two meters I made left a bit to be desired in terms of response time (i.e. laggy). What I'm going to try later on when I'm convinced this project is deserving of additional expenditure, is an Arduino Due board. This board has a more advanced chip that has a clock speed of 84 MHz as opposed to the UNO and Mega clock of 16 MHz.

"Hmmm - what does buying a Due board in the future have to do with what you are doing now?"

Well, it also happens to be the case that the Mega and Due boards have the same pinouts. Therefore, when I get the Due I can simply unplug the shield from the Mega and put it directly on the Due.

Enough questions!

Anyway ...  I need to check out some of the other parts. I guess I'd best see if the Mega board actually works at all so let me flash its LED. 

[EE4all]

Lol at your pre-emptive answers to critique.   

I have to give Custom-Cal credit. They did reply from my web form finally today. However, they also answered my email, sent a day later. So email is faster. The web form probably goes to a resource mailbox that they don't check as often.

[xrunner]

Lol at your pre-emptive answers to critique.   

I have to give Custom-Cal credit. They did reply from my web form finally today. However, they also answered my email, sent a day later. So email is faster. The web form probably goes to a resource mailbox that they don't check as often.

I never trust those web forms either, so glad to hear some of them actually work.

[joeqsmith]

Looks like you're making some progress.   

In this case we are not interested in measuring very low signals such as a lab bench scenario testing our RF generator or other such interests.

There was this member who was recently asking about making such measurements. 
https://www.eevblog.com/forum/rf-microwave/swr-meter-for-signals-below-1mw/

A few other links about the Daiwa meter you mentioned.
https://www.eevblog.com/forum/rf-microwave/daiwa-cn901n-issues-technical-analysis
https://www.eevblog.com/forum/rf-microwave/daiwa-cn-901v-n-issues-directional-coupler-modification

And another just for fun.
https://www.eevblog.com/forum/projects/directional-wattmeter-project-questions-about-mixed-signal-best-practices/

[xrunner]

A few other links about the Daiwa meter you mentioned.
https://www.eevblog.com/forum/rf-microwave/daiwa-cn901n-issues-technical-analysis
https://www.eevblog.com/forum/rf-microwave/daiwa-cn-901v-n-issues-directional-coupler-modification

Hadn't seen those posts but now that I have, perhaps I made a mistake in using a commercial coupler. I mean the quality of that tin box coupler isn't so bad after all. The bonus is the components have long enough leads so that you can bend your way out of any misalignment.

 

No, I think I made a good decision.

The Mega board does seem to work, in that it flashes an LED. But then again that might not mean much considering it was tossed int a box with a bunch of electronic junk. I'll have to do a few more checks.

I next plan on checking out both of the AD8307 log amps stand-alone. Just some RF in with a known power, and hand calculating the power measurement from the Vout which is not hard to do.

[joeqsmith]

I mean the quality of that tin box coupler isn't so bad after all.

I was thinking I have handmade circuit boards with a dremel and razor blades that were at least on par with it.   

Notice that throughout this thread how the the criteria for good is that the LEDs turn on.      

[xrunner]

I mean the quality of that tin box coupler isn't so bad after all.

I was thinking I have handmade circuit boards with a dremel and razor blades that were at least on par with it.   

Notice that throughout this thread how the the criteria for good is that the LEDs turn on.   

Yes and unfortunately these AD8307 boards do not have LEDs at all! How do they expect anyone to know they're actually working? Now that I can't simply see an LED, I guess I have no choice but to check their functionality by hand!

 

[joeqsmith]

No way... They cheapened them up?   I liked having those blue LEDs.   

[xrunner]

Checking out the AD8307 Log Amps

The response curves for the AD8307 are attached. To get a power reading from the AD8307 we need two basic parameters:

Vout response is 25 mV / dB (Typ)
log intercept is -84 dBm (Typ)

Giving:

Pin (dBm) = -84 dBm + (Vout / 0.025)

Note: Log Intercept per spec sheet may be between -87 to -77 dBm will calibrate this value later (as well for Log slope of 25mV / dB)

I set up a little variable power test rig using the output of an hp 437B (50 MHz @ 0 dBm) and an hp 355D variable att. So I can go from 0 dBm to -120 dBm (I don't need to go that low though) in 10 dB steps. This is only a basic test of the AD8307 boards at the moment.

I set the power to the AD8307 to -20 dBm. I measured 1.6 V Vout.

So we have:

Pin (dBm) = (1.6 / .025) - 84

Pin = -20 dBm

I reckon that's a good start.

Bonus pic - local ham brought over a duplexer to be re-aligned to new frequencies (UHF HAM Band).

[A.Z.]

as for the AD8307 here's a pass through meter for HF which may be of interest

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

by the way on the intertubes there is a bunch of other circuits based on that log amp, for example

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

[xrunner]

Well, I got sidetracked again by HAMS. This time involving not one Yaesu FTM-400 - but two.

One local HAM burned up the final in his Yaesu FTM-400XD. It somehow got stuck "ON" transmitting high power when it was in crossband mode and it got too hot. This is a known issue with these FTM-400 radios - very poor cooling.

The final is an RDF70HUF2 part. I agreed to replace it (he already paid for the part) and the part should be here tomorrow. Then I need to get into the service menu and set the low, med, and high powers to their correct levels. Might get a free lunch out of it.

The other FTM-400DR would only boot up to the initial screen where the HAM callsign was displayed ... and halt. Nothing could make it work right, not even re-loading all the firmware (which surprisingly could be done). So that one has to go back to Yaesu for a repair cost estimate. Sorry me no can help.

I did make a little progress on the project at hand. I started over with a simple program I used to begin the last power meter projects which read the analog voltage on a channel and converted it to dBm. I just added a second channel and was testing the accuracy by reading the on-board 3.3 V supply and a voltage from a resistive voltage divider. The dBm values mean nothing at the moment, but the calculation needed (if the voltage was coming from the AD8307(s) ) is being executed.

Hopefully the HAMS won't bother me again for the next few weeks.