CB and Ham Radio Techs Love Their Bird Wattmeters

[joeqsmith]

Still here. Not had the time yet. Also the AD8307's I landed are possibly fake. Need to do a test rig

I assumed these were all fakes.  Outside of that shift problem I see with the AD8310's their performance has been very good.

[bd139]

Still here. Not had the time yet. Also the AD8307's I landed are possibly fake. Need to do a test rig

I assumed these were all fakes.  Outside of that shift problem I see with the AD8310's their performance has been very good.

Yeah I don't mind fakes that do what they say on the label. What I do mind is when I get shipped something else 8 pins instead which has been relabelled

Awaiting stuff order to test this but the Queen dropped dead so everything is delayed ffs.

[joeqsmith]

Yeah I don't mind fakes that do what they say on the label. What I do mind is when I get shipped something else 8 pins instead which has been relabelled

I was repairing an old meter the used a high voltage op-amp.   The op-amp was no longer available from my usual suppliers.  I ended up making a circuit to replace the op-amp just to move ahead with the repairs.  In the end, I had found a supplier in China that claimed to have these parts.  I assumed these would be fakes that were remarked.  I bought two of them and made a test fixture to test them (before ever thinking about installing one).   They matched the datasheets and I have one in that meter today.   The other is taped to the PCB just in case it fails again.

Thank you China for saving my meter!!!   

[xrunner]

You had mentioned earlier, 
"Well, I don't think there is any question about it. Things like this have cropped up before, and it has always been due, to human error ... "

The old Agilent VNA I own is a bit of a pain to drive.   Most of the time, I run it from the PC using the same software I wrote for the other VNAs I own.  The advantage of having a common interface is they all basically drive the same.   

The LiteVNA with Dislord's firmware allows me to change the drive strength for both synthesizers.  Its a pretty crude and the noise floor isn't all that great.   Still, for the $130 they sell them for with a few bits added to the mix, it throws up some decent numbers.   Its not as good as the original NanoVNA for lower frequencies.  Then again, my Agilent VNA is limited to 300kHz so I still keep my old HP around for low frequency experiments.   

...

Is the error at the start of the data sets an artifact how the Rigol works?   Is it effected by changing the start freq or slowing the sweep rate?   Is there an AC/DC coupling that you can set to DC?   Seems like there would be a way to correct it as I doubt it's due to the attenuator.

Well I got out a Nanovna-h last night and tested the 40 dB att. and it showed a flat attenuation, so I knew I had done something wrong or forget something. Something a little wrong, but not a lot wrong ...

You know technology changes with time. The fact they had three sets of tracking generator levels you can set manually is a function of it's design. Maybe it's automated in newer and better units but not this one. I just hadn't thought about those settings for a while. Anyway it works correctly so I'm satisfied.

Can you export the data to a Touchstone file and upload it here?   We could then do a better job comparing results.

I haven't needed to export any data from it except screen prints, so I have to check that. I think it's bin and ascii files for data. I mean if you really want one I'll do it but I'm ready to move on from this point, since I know it can handle 10W with cooling, and that it's attenuation wasn't affected.

OK I attached a zipped csv file, the only other choice in bin.

[joeqsmith]

I downloaded the manual for your Rigol and started going over it.   I didn't see anything about DC coupling.   Oddly enough, one of the first pictures in the manual also shows that problem at the start of the sweep.   I was surprised to see a fair bit about measuring VSWR.  Almost like they were trying to target the hams and if they actually marketed it as an antenna analyzer like I have seen some of the ham equipment sellers do with the low cost VNAs.   

I was more just curious about the Rigol's capability with the Touchstone.   I'll have a look at the file and see if I can overlay the data.  Just visually looking at it, it seems on with the three I looked at. 

It's good when things make sense....

[joeqsmith]

Your data compared with what I collected with the LiteVNA.

***
Quick Google search for "Rigol antenna analyzer"

... 104 cm was tested with a RIGOL antenna analyzer.

https://pa0fri.home.xs4all.nl/Ant/W3DZZ/w3dzztrap%20eng.htm
 

[xrunner]

Your data compared with what I collected with the LiteVNA.

Yea that looks very nice. Amazing what can happen when the right buttons are pushed in the right sequence.

Quick Google search for "Rigol antenna analyzer"

... 104 cm was tested with a RIGOL antenna analyzer.

https://pa0fri.home.xs4all.nl/Ant/W3DZZ/w3dzztrap%20eng.htm
 

Rigol antenna analyzer? Oh boy 

[joeqsmith]

Your data compared with what I collected with the LiteVNA.

Yea that looks very nice. Amazing what can happen when the right buttons are pushed in the right sequence.

We both have different physical parts and systems. Unless you come over and get my part to test or I do the same with yours we're doing the apples and oranges thing. Maybe your parts are out of spec but your test instrument is out of cal so it's actually making it look better than it is - you know how the game goes ... 

This is a good example that if measured properly,  using two very different low end systems, located in two parts of the world, ran by two different operators, using different standards can indeed will come up with basically the same answer.  So not really an apples and oranges.  More a McIntosh and Red Delicious.   

If we try to tighten up our measurements, no doubt we would run into problems but +/- 1.5dB is a big window.  Attachments from Jürg Rüfenacht, Swiss Federal Office of Metrology and Accreditation metas,  discuss this.     

[xrunner]

Next I want to utilize the 40 dB att. to make a measurement on a RF emission with my "ham band" RF power meter (the first one I made). Thinking ahead, I had already incorporated in the software the ability to set a correction for up to 50dB of external attenuation.

But at the moment I am making a couple of systems that tell the temperature drop (or rise) in your AC/heating system so you easily know it's working properly. Pretty simple in the scheme of things - an Uno and two type K thermocouples / amplifiers. You just install one above the coils and one at the entrance before the filter. Why am I making two sets? Because I showed the one I was making for myself to my neighbor and he though it such a nice idea he wanted one too.

So I should get to the attenuator / radio testing this weekend.

[TheBay]

I prefer my Telewave 44A as it doesn't need slugs.

[virtualparticles]

I never understood why people care so much about the accuracy of a watt meter anyhow.  Not only are they incapable of differentiating between fundamental and harmonics, but it takes doubling the power twice to make 1 s-unit of difference on the other end ~ so who cares if its 22w or 29w?

The FCC cares. 

[joeqsmith]

Rerunning the first ZDTECH attenuator on the old PNA.   

[xrunner]

Hey Joe,

Sorry I've been busy with other projects like the AC/Heating temperature monitor system for one thing. Then my 3D printer threw everything it had at me for a week to try to get me to give up that hobby (multiple failures at once). But I beat it into submission in the end so all is well.

I'm setting up a test of the little 40 dB att, being used with my first power meter design (for ham bands only). Let's see what readings I get when compared to the trusted hp 437B power meter.

[joeqsmith]

I don't know about you but when if comes to my home electronics hobby, I have no schedule.      Otherwise, I may have to call it work...  Take your time, no rush on my account. 

I had fired up the old PNA the other day to run another test and thought why not see how the data compared.  Completely different set of standards, cables and adapters.  I'm amazed how well that $130 VNA performs.   

[xrunner]

The little attenuator that could - now can't. 

Although I hadn't taken pics yet, I had transmitted using low power on 145 MHz through the 40 dB att. into my homemade power meter, and then into the hp 437B as a check. They both indicated 5.2 W. I was satisfied everything was working OK, I got ready to take pics and next transmission I got no power indicated on the 437B (which made me very nervous because there is a $300 sensor being used).

Switching over to my power meter, I got an indication of very low power (since mine reads much lower than the 437B.) After sanity checks with the 437B 0.0 dBm calibration output, I realized the 40 dB att. had developed a flaw.

I had tried before to get the internal element out of the 40 dB att. I didn't then because I was afraid I would break it, but now there was nothing left to do but get it out. I got out a small vise and a small punch, and after tapping on it gently for a while it finally began to move out.

Under the microscope I found where I think it developed a problem. There are three dark areas of a resistive material, and one has a flaw across it. I do not of course know how long it has been there or if it was worsened when I was testing it before when it got very hot.

There are three areas of resistive material, each connected in series. They also have a branch on each side to a common connection which goes to each of the three areas along the outside (on both sides). All the scratches on the silver were there when I opened it, not sure why they are there. Also the silver center trace is connected to others by a silver "paint", not sure why they were not a continuous connection between resistive areas.

You can see where each leg consisting of the resistive material has been hand-trimmed with a grinding tool, to achieve the desired total attenuation. The trimming is very inexact and rough per each individual leg. Someone is basically looking at a meter and going back and forth until the total att. is what is wanted. Maybe this design is used for all the models in this power range, trimming each one by hand. Not exactly an efficient model for mass-production but warm bodies are cheap where it's made.

Comments?

[joeqsmith]

With someone grinding away at the part, let's hope it's not BeO.   There were no markings on the shipper showing it contained BeO.   Did you ohm out each section to verify the fault?   Did you happen to monitor the temperature when you tried it out?  Curious if it exceeded their max temperature.   

I could try and repeat your test using the parts I have. 

[xrunner]

With someone grinding away at the part, let's hope it's not BeO.   There were no markings on the shipper showing it contained BeO.   Did you ohm out each section to verify the fault?   Did you happen to monitor the temperature when you tried it out?  Curious if it exceeded their max temperature.   

I could try and repeat your test using the parts I have.

I did not monitor the temp. It appears that the fault you see going going across the resistive "blob" or area has caused an open condition when ohming it all out. That explains why my power readings were very low.

It's not an easy thing to check due to the way it's all connected. I'm trying to think of a resistor model, consisting of individual resistors, that would correspond to the design. It's difficult because of the resistive areas. Depending on the exact pinpoint you touch with the probe, you get different readings because it's a "plane" surface of resistance - an area; essentially a square area of resistive material. It's also connected on each side left and right to the other areas all at once, so I'm struggling with what would model that ... 

[joeqsmith]

They may use that same substrate for several designs.   You would want to measure on the nodes void of any of the screened materials.  Those areas should be homogeneous.  I would expect all three to be basically the same.  You could isolate one that you suspect wasn't damaged and try to measure it.  Of course, not knowing what that material is why bother.   

[xrunner]

What to do now?

I could split up the attenuation between two attenuators. I could get a new one the same small size but this time 10 dB - that's first in-line. Then I can use one of the common small 30 dB SMA attenuators that typically can handle 2W. So for 10W (+40 dBm) input power, I could use {10 dB + 30} dB of attenuation. The brunt would be the first 10 dB (10W rating) attenuator which would lower the power to +30 dBm (1W). Then follows a 30 dB (2W rating) to give 0.0 dBm input to the power meter (for a 10W input power.) Other combos are possible also to divide up the power dissipation.

The original goal was to expand the capability of the first "Ham Bands" power meter to read very low powers, yet be able to measure up to 10W of power direct from a transceiver, simply by flipping a switch. All this trying to keep it all in the smallest case I can manage.

This is the reason for selecting these small attenuators. If you look at the inside of the first power meter ("Ham Bands") it's pretty full of stuff. I would need to add two SMA coaxial switches, a relay board (or simple transistor switching circuit), another front panel switch with indicating LED, two attenuators, and coax patch cables, and possibly a fan. However, I could move to a Nano processor board to gain space. I can also move to a little larger case too and get it all in there.

But,

I don't know about you but when if comes to my home electronics hobby, I have no schedule. 

No schedule, no schedule. Apparently no budget either. 

[joeqsmith]

Maybe that part from BECEN would fit.  It's about the same length but larger diameter.   If your plan is still very short duty cycle use to keep the temperature down, it may hold up better.   It seems like it would handle 5W in ambient without forced air cooling. 

https://www.eevblog.com/forum/rf-microwave/cb-and-ham-radio-techs-love-their-bird-wattmeters/msg4423153/#msg4423153

[xrunner]

Maybe that part from BECEN would fit.  It's about the same length but larger diameter.   If your plan is still very short duty cycle use to keep the temperature down, it may hold up better.  It seems like it would handle 5W in ambient without forced air cooling. 

Thanks for the suggestion. It may well be an option for that scenario. I chose to go ahead and order the same smaller att (10 dB, 10W) and combine it with a 30 dB, 2W size I ordered from an Ebay seller. I can add a fan if needed.

However, I can go ahead and test the switching scheme with what I have now using low power signals. This isn't a difficult thing to wire up, but something simple can fail or not work quite right just as easily as something complicated - or as they say - the proof is in the pudding. Test everything as you go, that way there will be less surprises later.

I would think that the default (safe) state is to have the 40 dB att. in the normally closed path so the user must select it to be out-of-line consciously. Then if the un-attenuated path is selected, a warning LED could light up. Suggestions accepted of course. But as we know, nothing will protect equipment from misuse / abuse in the end.

[joeqsmith]

To save some space, you could also use two input connectors and one relay.  Then cap off the direct input with one of those fancy chained SMA terminators.  Someone would have to consciously remove the cap and connect into it where if there is just a switch, someone may change it by accident.   Plus the added benefit, you now have a spare to make a second unit to sell and recover your costs. 

But as we know, nothing will protect equipment from misuse / abuse in the end.

So true. 

[xrunner]

To save some space, you could also use two input connectors and one relay.  Then cap off the direct input with one of those fancy chained SMA terminators.  Someone would have to consciously remove the cap and connect into it where if there is just a switch, someone may change it by accident.   Plus the added benefit, you now have a spare to make a second unit to sell and recover your costs.   

Yea that idea uses less (higher cost) parts true, and I think it's a good idea so I'll probably do that. Still keep the NC path for the higher powers, indicating LEDs to alert the user. I found some SMA caps with chains on Ebay. In the end anyone can forget what connector does what, get in a hurry and forget that they left the cable on the wrong connector, etc. But same story - can't protect the world from all human error.

The lower power input will cover +13 to -73 dBm as it was in the original unit. With the 40 dB attenuation switched in, the high power input will cover -33 to +40 dBm. In theory, it would actually go up to +53 (200W) if you had a 40 dB att. with higher power dissipation. The upper range for the power meter design I had been using was +13, so 53 - 40 = +13. But we want a small case so there comes the size limit of the attenuator we have to use (10 W).

I did receive the 10 dB, 10W att. today. It came from the same seller on Amazon and was selected from the list they had. However it isn't the same mechanical packaging as the 40 dB unit that failed and came in a different box. 40 dB on left side of pic. The 10 dB unit also has a decent label on it - go figure ... 

Will take frequency plot tomorrow.

Does bd139 ever check in anymore? 

[joeqsmith]

Looks like they may have reduced the materials as well.  Maybe a cost savings.   Are you going to thermal check it again?   

I don't follow too many threads but have not seen any posts from them.   You can check their stats.  Shows they were on yesterday.  Maybe busy building their super Watt meter. 

[xrunner]

Looks like they may have reduced the materials as well.  Maybe a cost savings.   Are you going to thermal check it again?   

Naw - not going to stress the thing this time. Attenuation vs. freq. plot looks good to go, within tolerance of +/- 1 dB. Waiting on 30 dB 2W attenuator, will test individually and combined with this 10 dB model.

Hmmm I could use it and test with my power meter since I already have user-selectable external attenuator selections. I'll compare a few measurements to the 437B power meter.

I don't follow too many threads but have not seen any posts from them.   You can check their stats.  Shows they were on yesterday.  Maybe busy building their super Watt meter. 

Probably got bored with this topic.