Author Topic: CB and Ham Radio Techs Love Their Bird Wattmeters  (Read 176271 times)

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Offline xrunner

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1100 on: June 02, 2023, 12:35:17 am »
Putnam coupler directivity plot. Markers at four ham bands of interest.
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Offline joeqsmithTopic starter

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1101 on: June 02, 2023, 12:56:23 am »
I keep thinking it would be fun to do some sort of shootout.  I've forked out this amount of cash to test handheld multi-meters to failure.  Not being a ham or CB radio hobbyist, I don't have that same level of interest.   Maybe we could reach out to these companies to see if they would be interested in it.  It's a lot of time to invest as well.  No way I would make a ham review where I just unbox them, blab for a half hour how great they are, and give them all five stars.   :-DD   

I swore I had posted data for the couplers but searching this section, looks like I did not.   The video shows the directivity printed on the one coupler as 30dB @25MHz and 50dB@1MHz.   

When I made the one that was actually used during the video, it measured 65@1M and 40@30MHz.  (see attached)  Isolation was better than 50 and the flatness was <0.7 total.   Good enough that I chose not to correct for it but I think if we did a shoot out, I would go ahead and add correction to shave some of that error out. 

Offline joeqsmithTopic starter

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1102 on: June 02, 2023, 12:32:46 pm »
This was some of the data I collected for the 19dB coupler.   Directivity isn't very good and of course it dissipates more heat.   

Offline EE4all

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1103 on: June 02, 2023, 12:36:45 pm »
What coupler is this now? A homemade one or commercial one? I am losing track...  :-//
 

Offline joeqsmithTopic starter

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1104 on: June 02, 2023, 02:41:07 pm »
What coupler is this now? A homemade one or commercial one? I am losing track...  :-//

The only commercial couplers I have are for microwave use, except an old Mars SWR meter I have.    For this thread, everything was homemade. 

I suspect the confusion is from my video showing the labeled coupler and post stating 30dB @25MHz, where the graph is showing 30dB and 50MHz.  Same coupler.   The graph is showing where that 19dB coupler ended up at.   

Offline xrunner

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1105 on: June 02, 2023, 07:11:42 pm »
I keep thinking it would be fun to do some sort of shootout.  I've forked out this amount of cash to test handheld multi-meters to failure.  Not being a ham or CB radio hobbyist, I don't have that same level of interest.   Maybe we could reach out to these companies to see if they would be interested in it.  It's a lot of time to invest as well.  No way I would make a ham review where I just unbox them, blab for a half hour how great they are, and give them all five stars.   :-DD   

Yea most of the ham reviews are not technical at all. Mostly just look and feel ... here's what it looks like hooked up and operating. They don't check the specs of the TX or RX or other technical things. A few months ago I invited a ham friend over because I had tested an HF receiver (FT-450) to measure the minimum discernible signal and SSB sensitivity (2.4 kHz BW) to see if it matched the ARRL labs measurements. It did exactly. He watched me go through it and was amazed. I said remember this day because you are the only ham that I know of that has ever seen this type of test being done.  :)

Quote
I swore I had posted data for the couplers but searching this section, looks like I did not.   The video shows the directivity printed on the one coupler as 30dB @25MHz and 50dB@1MHz.   

When I made the one that was actually used during the video, it measured 65@1M and 40@30MHz.  (see attached)  Isolation was better than 50 and the flatness was <0.7 total.   Good enough that I chose not to correct for it but I think if we did a shoot out, I would go ahead and add correction to shave some of that error out.

You got very good specs at HF frequencies. Of course I'm more interested in mine working up to the 70 cm ham band. I found a little calculator that sees to be useful regarding this directivity issue and what kind of errors to expect. Will report on it this evening ...
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Offline xrunner

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1106 on: June 03, 2023, 12:26:07 am »
I found an online calculator that is useful called "Calculate uncertainty of ReturnLoss and VSWR given coupler directivity"

https://owenduffy.net/calc/rlu.htm

It gives answers consistent with what you would derive with more work using the chart from the Electronic Design article linked earlier here -

https://www.electronicdesign.com/home/article/21201015/directional-power-measurements-and-the-effects-of-directivity

For example, say you have a forward power of 100W and reverse of 4W. That calculates to be a SWR of 1.50 on paper with no other considerations.

But you want to get the errors for an individual coupler directivity so you can know what the SWR error might be. If you look at the chart of reflected power, forward power, and VSWR you will see the following (for a VSWR of 1.5 and directivity of 25 dB):

Forward Power error band: ~ -3% to +3%
Reverse Power error band: ~ -50% to +62%

So for 100W forward the error band yields: 97W to 103W
For 4W reverse the error band yields: 2W to 6.5W

Using the "Calculate uncertainty of Return Loss and VSWR given coupler directivity" calculator let's plug in some numbers using a directivity of 25 dB and VSWR of 1.5:

The calculated error band goes from a VSWR of 1.34 up to 1.69.

Now lets calculate VSWR from the errors derived from the chart.

Using the max positive errors of 103W F and 6.5W Rev we get a VSWR of 1.67
Max negative errors 97W F and 2W rev we get a VSWR of 1.34
a 3rd combination 103W F 2W R: 1.32
finally the last combination 97W F 6.5W R: 1.69

The VSWR errors the calculator gives us matches very closely what you can derive with more trouble manually in several steps from the Electronics Design chart (which is a little hard to read exact values from, hence a small error).

So for me that calculator is a good way to know what the VSWR errors will be for the coupler I'm using, and so can be included in the specifications of the "product". By the way this type of specification (VSWR errors per band) is nothing I've even seen on any piece of ham gear I've ever run across.

But hams really don't care what the exact SWR reading is anyway - they're not trying for SWR 1.45 or some other exact value. They just want it to go down as low as it can and know it's not what they consider "high" such as 2 or 3 (ish).
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Offline joeqsmithTopic starter

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1107 on: June 03, 2023, 03:50:19 am »
I think I references one of Duffy's posts on ham radio in this thread.    I would almost bet that they have an article that goes along with that calculator.  I tried searching for it but no luck.   

But hams really don't care what the exact SWR reading is anyway - they're not trying for SWR 1.45 or some other exact value. They just want it to go down as low as it can and know it's not what they consider "high" such as 2 or 3 (ish).

While I can't speak for all the hams, it does remind me of this thread:

https://www.eevblog.com/forum/testgear/nanovna-v24-sma-cal-load/msg3360956/#msg3360956

Offline EE4all

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1108 on: June 03, 2023, 04:38:10 pm »
I think you will find a wide spectrum of knowledge levels with radio operators, engineers, technicians, and etc. No reason to build barriers or point fingers to lack of knowledge. Ignorance can be found in all of us, for topics which we have not dedicated study to. Different people have different priorities.  :-+

As in engineering, the product is usually not to be overengineered, as to optimize profit and reduce waste, it is not surprising at all that most SWR meters are barely good enough for the purpose at hand. I would hope that they are though at least good enough, and they may not be, so analysis of what products are out there is welcome. The sellers will usually lower quality of products until they can't sell it anymore because it is now junk and not in fact fit for purpose.

I would love it if every meter had 40+dB of directionality, and etc. high specifications, but then everything would be too expensive.
« Last Edit: June 03, 2023, 04:44:29 pm by EE4all »
 

Offline xrunner

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1109 on: June 03, 2023, 05:16:10 pm »
I trying to hold back before I go on one of my diatribes ...  :-X
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Offline EE4all

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1110 on: June 03, 2023, 05:24:34 pm »
No need.  My comment is self directed as much as outwardly directed. It's a race to the bottom isn't it? Anti-intellectualism is also a problem, laziness to learn, etc, and the list goes on. I just try my best to not alienate any group, as then there is no chance to teach them (assuming I am in a position to even teach something).
 

Offline joeqsmithTopic starter

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1111 on: June 03, 2023, 05:42:30 pm »
I think you will find a wide spectrum of knowledge levels with radio operators, engineers, technicians, and etc. No reason to build barriers or point fingers to lack of knowledge. Ignorance can be found in all of us, ....

I don't think many would disagree with you.   Being ignorant myself in most topics.  Even if you are prone to making a lot of mistakes, I'm fine with that as I am right there.  Knowing I am ignorant and making mistakes is a side effect of growth.

Often with the hams, it's their arrogance and how they treat one another that I find troublesome.   Not being a ham, I don't normally run into it.   It's the hams who introduce themselves and in the same breath throw out their license and expect it carries some weight.  Then they take offense to my not acknowledging their life achievements. 

During my career I have had the opportunity to work with some very impressive people in various fields, most with higher levels of education.  I've never ran into anyone flaunting their education.  It's all about what you bring to the party.   

Offline xrunner

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1112 on: June 04, 2023, 12:31:22 am »
I received the second Putnam dual directional coupler (on top in the pic). It's a little different than the first one on the outside. Slightly different labels, SMA connectors, and screws.

However, it has the same response curves as the first one I received so all is well.  :clap:
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Offline joeqsmithTopic starter

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1113 on: June 05, 2023, 01:56:21 am »
Looking forward to seeing your new meter in action. 

Offline xrunner

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1114 on: June 05, 2023, 02:14:11 am »
Looking forward to seeing your new meter in action.

I'm gathering parts as we speak. This is a long thread and if anyone doesn't know, I made two different power meter projects in this thread (and Joe also made his own take). The controller was an UNO board and the log amps were AD8310 and AD8307. They were not through-line meters but meant for measuring power from a source and checking for power output problems. One was for HAM bands only, the other for a wider bandwidth with no gaps.

Of course this project will measure power forward and reverse with SWR and report same on an OLED screen. Anyway, I already have my own software so adapting it for this shouldn't be too hard.  :-DD

We shall see ...  :popcorn:
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Offline EE4all

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1115 on: June 05, 2023, 02:15:09 am »
It will be interesting! All the talk about uncertainty levels when directivity is too low on a directional coupler had me a imagining a SWR meter that digitally tells you what it measures, and then ironically also follows up with, "but I am only x% certain of that," in a humorous way.  :scared:  ;D
 

Offline xrunner

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1116 on: June 06, 2023, 12:14:02 am »
It will be interesting! All the talk about uncertainty levels when directivity is too low on a directional coupler had me a imagining a SWR meter that digitally tells you what it measures, and then ironically also follows up with, "but I am only x% certain of that," in a humorous way.  :scared:  ;D

Errors could be displayed of course, but I doubt most hams would care or even want to see the words "error" or "uncertainty" on their SWR meter. Most don't care and certainly would never tell anyone on-air they had a meter designed by a local ham that had "errors or uncertainties" clearly showing on a display, especially telling some other ham that had a Bird. The ham with the Bird would giggle and tell the other guy that he should get a better meter designed by someone that knows what they're doing. Ignorance is bliss as the saying goes.

This brings up an interesting point I was just looking at the other day. I have a Daiwa CN-103L (L meaning it has a lamp which I converted to an LED). It's for use on ham bands 2m (144 to 146 MHz) and 70cm (420 to 450 MHz). It's a simple thing and has no switches to tell it what band it's on (only for the expected power), so it operates across the entire range 144 to 450 MHz (or even wider with more error). There are no bandpass filters or the like in it (see schematic). The directional coupler is a small el-cheepo metal box with components (I can see inside through a slot) that do not match the schematic, but what is the directivity of it? I don't know and they don't say but I bet it's not nearly as good as the Putnam coupler.

Yet, the manual states it has a "Tolerance" of +/- 10% of full scale. Tolerance referring to ... all the measurements indicated on the meter face - SWR, FWD power, and REV power? There is no simple way to get a directivity curve since the DAIWA coupler box doesn't output RF, but rectified AC. No telling what would happen if I opened the metal shield and connected a measurement instrument to it - it'd probably throw the whole delicate scheme off so much I'd never get a good answer. So where did the 10% come from?  :P
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Offline joeqsmithTopic starter

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1117 on: June 06, 2023, 12:33:12 am »
Quote
So where did the 10% come from?

One technique is to lick your finger and hold it into the air and depending on the direction of air flow, that's your answer....

Compare it with your new meter, the first meter you built and your HP.  Just as long as you don't series up the meters and measure them using the same cables and attenuator with your HP,  your should get some idea if that 10% is real.  Maybe make a video of it.  I would watch it.

Offline EE4all

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1118 on: June 06, 2023, 01:06:36 am »
Don't you know you have to buy those meters in 6 packs? You need to use each one, and then get your average.  :-DD
 

Offline vk6zgo

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1119 on: June 06, 2023, 03:18:16 am »
It will be interesting! All the talk about uncertainty levels when directivity is too low on a directional coupler had me a imagining a SWR meter that digitally tells you what it measures, and then ironically also follows up with, "but I am only x% certain of that," in a humorous way.  :scared:  ;D

Errors could be displayed of course, but I doubt most hams would care or even want to see the words "error" or "uncertainty" on their SWR meter. Most don't care and certainly would never tell anyone on-air they had a meter designed by a local ham that had "errors or uncertainties" clearly showing on a display, especially telling some other ham that had a Bird. The ham with the Bird would giggle and tell the other guy that he should get a better meter designed by someone that knows what they're doing. Ignorance is bliss as the saying goes.

This brings up an interesting point I was just looking at the other day. I have a Daiwa CN-103L (L meaning it has a lamp which I converted to an LED). It's for use on ham bands 2m (144 to 146 MHz) and 70cm (420 to 450 MHz). It's a simple thing and has no switches to tell it what band it's on (only for the expected power), so it operates across the entire range 144 to 450 MHz (or even wider with more error). There are no bandpass filters or the like in it (see schematic). The directional coupler is a small el-cheepo metal box with components (I can see inside through a slot) that do not match the schematic, but what is the directivity of it? I don't know and they don't say but I bet it's not nearly as good as the Putnam coupler.

Yet, the manual states it has a "Tolerance" of +/- 10% of full scale. Tolerance referring to ... all the measurements indicated on the meter face - SWR, FWD power, and REV power? There is no simple way to get a directivity curve since the DAIWA coupler box doesn't output RF, but rectified AC. No telling what would happen if I opened the metal shield and connected a measurement instrument to it - it'd probably throw the whole delicate scheme off so much I'd never get a good answer. So where did the 10% come from?  :P

I think Daiwa just grab a bunch of known accurate mismatches, poke a suitable power level into them via the SWR meter, then check what the meter reads for each one, tweaking whatever pots are available.

They repeat this process over multiple bands, then "call it good".

As to power readings:

With "ham" type SWR meters of this style & even more so with "CB" ones, it is pretty much accepted that the power reading is fairly "approximate".
In any case, it only means something if the load is a purely resistive 50 \$\Omega\$ one.

Hams often use simple 1/2 wavelength dipoles which are around 75 \$\Omega\$ at resonance, or 1/4 wave verticals, which, in the basic form are around 37.5 \$\Omega\$, but can be "tweaked to 50 \$\Omega\$ at resonance by angling the radials downwards.
Outside perfect resonance, "all bets are off!".
 

Offline xrunner

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1120 on: June 07, 2023, 12:32:12 am »
Right now I'm sidetracked because I have a weird issue with a Boonton 4220 power meter that was working fine last time I used it. I've had it for a while like over a year and I wanted to get it off the shelf and use it for this project to measure a transmitter power out, but it seemed like the sensor had gone bad because it wouldn't zero. The sensor came from a local ham who got it at a hamfest and I suspected it has been abused, so perhaps it decided to finally fail. I convinced myself that was the case so I ordered another compatible sensor and I could not get that sensor to zero either.

So was it the power meter ... or cable? I messed with everything for an hour and then for no reason I could see, both power sensors zero'ed and calibrated. OK well now I have a spare sensor. But then a while later the new sensor wouldn't zero again. I took off the outer shell of the new sensor, and presto it zero'ed again. But then why did the original sensor stop zeroing, and what does removing the shell fix?

Right now I have no idea what's going on but I'm determined to find out!  >:(
« Last Edit: June 07, 2023, 12:49:28 am by xrunner »
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Offline joeqsmithTopic starter

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1121 on: June 07, 2023, 12:58:47 pm »
You have the HP.  Why did you purchase the Boonton?   Do you have the thermistor or diode sensors for it?   

Offline Kosmic

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1122 on: June 07, 2023, 01:49:39 pm »
So was it the power meter ... or cable? I messed with everything for an hour and then for no reason I could see, both power sensors zero'ed and calibrated. OK well now I have a spare sensor. But then a while later the new sensor wouldn't zero again. I took off the outer shell of the new sensor, and presto it zero'ed again. But then why did the original sensor stop zeroing, and what does removing the shell fix?

Do you have the 14 points linearity data for the sensor ? (4220 Manual page 4-1, section 4-5). If not, this would explain why you are struggling to zero the sensor. Normally the meter and sensor are sold together and can't be separated. If you want to pair a new sensor with a meter you need the calibration data of the sensor.

You can also validate the good working state of the sensor by applying a RF signal and connecting a multimeter on the output. You should see a DC voltage in the millivolts range if you apply a signal around 0dBm. The sensor is really just a rectifier.
« Last Edit: June 07, 2023, 02:10:26 pm by Kosmic »
 

Offline xrunner

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1123 on: June 07, 2023, 02:29:23 pm »
I have fixed the 4220. I had to adjust the chopper per the service manual, now it works perfectly (both sensors). It fell out of adjustment and was on the edge of operating correctly, hence the seemingly random results.

Kosmic, about 1.5 years ago we were talking about this in the TEA thread here -

https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg3943906/#msg3943906

Of course it would be better if I had the cal data, but amazingly it is very accurate without that (both sensors). Seems to be less than 1 dB error in my testing down to -60 dBm. Good enough for testing ham gear.

Joe, I will write more about how I got all the Boonton equipment later, can't at the moment.
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Offline Kosmic

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Re: CB and Ham Radio Techs Love Their Bird Wattmeters
« Reply #1124 on: June 07, 2023, 02:44:44 pm »
What's the page in the manuel where they describe how to adjust the chopper ?
 


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