CB and Ham Radio Techs Love Their Bird Wattmeters

[A.Z.]

why don't you put the coupler inside a separate, external, enclosure ?

[joeqsmith]

Running a least squares fit of the 50MHz data for a reference.  Then calculate a 4th order polynomial for the 50MHz band.  So only one set of coefficients being used for the entire frequency range.    I then use the center of each data set (or frequency sweep, roughly -25dBm) to determine the offset from the reference.  So you end up with 4 coefficients plus an offset per band for your cal factors.   You could make it more complex but this was basically what I had planned to do with mine originally.  But because I was working below 50MHz, it was linear enough I decided against it and just went with the simple point slope. 

If we selecting the region of -60 to 4dBm, to get us into the somewhat linear region, we can see the effects of now compensating with the offset and poly fit using the baseline circuit and after my mods.    Hopefully this makes some sense. 

I did cut some more of the PCB and tried a few other tweaks but I'm splitting hairs with it.     

[xrunner]

why don't you put the coupler inside a separate, external, enclosure ?

Yea I am considering all my options including that. but I asked one of my ham friends today whether he'd prefer components mounted in two separate enclosures or just one. He said "one" which is what I would have guessed. So now you know.

[A.Z.]

you may put the coupler inside a slug

[xrunner]

Received supplies I didn't have on-hand. RG-400 for connection from coupler to rear panel and connectors for same: rear panel bulkhead SO-239 and N female. Ordered more than I need to have stock on-hand.

As I mentioned before, the previous two power meters I made used the Arduino UNO board. The second one was a little laggy, due to the graphics I implemented and the the Arduino UNO's clock of 16 MHz. It is also limited to 32 kB of flash which I was close to maxing out.

I considered obtaining the new Arduino R4 Mimima which has 256 kB of flash, 32 kB of SRAM, and a clock of 48 MHz. It appeared that the Arduino store had them for $20, but I didn't have an account there and I don't want to make yet another account on another online store just for one item.

I did check Mouser which I have an account with, and they say they are getting the R4 Minima in early Aug:

487
Expected 02-Aug-23

700
Expected 04-Aug-23

and the price is also $20. Matter of fact, I think I'll go ahead and purchase two of them right now so I'll be in line for shipping. Mouser is good for me because I actually live close to them and I can get orders the next day. When I get the Minima, I plan on upgrading the second power meter I made to that board, which I will post about in this thread. This may require an updated CAD drawing for the rear case panel due to different USB port on the Minima. There is also the possibility of a UPS strike which is the carrier they use (see note below).

Anyway, I ordered and received an Arduino Due from Mouser for now which has an 84 MHz clock, 512 Flash, and 96 kB SRAM. It actually comes with a clear mounting plate. The shield I'm using with the Mega board right now will simply plug right on the Due and, after re-compiling, will run with no other changes, but faster. So I can keep working with the software and I won't run out of flash nor be irritated by laggy response caused by any graphics bling I want to put on the screen.

I'm still narrowing down the case I want from Amazon's selections. After that I'll have to get on to the task of mounting the components, which will include 3D printing replacement front and back panels for the case, and all custom mounting plates etc. for the inside. That's one thing I can do CAD work on, but I really don't want to fire up the 3D printer now due to the hours of electrical usage & heat it generates, which around here right now, isn't something I need more of.


Potential UPS strike and how it may impact your orders

A potential strike by UPS workers starting on August 1 may cause disruption to the shipping of your orders. The Teamsters union voted to strike if no agreement is reached with UPS by the time the current contract expires on July 31.

What could this mean for you?

    Any strike could cause a delay in shipping of your orders from August 1.
    Other carriers may also be affected, as they are likely to be busier than usual during this time.

What can be done to mitigate issues?

    We will do everything in our power to continue providing you with the best possible service during this time.
    We will continue to process same-day orders, but the strike may still impact how long it takes for them to reach you.
    We advise that you plan ahead for any needs you may have and order early where possible.
    We continue to monitor the situation and look for ways to minimize its impact on you.

[joeqsmith]

More than enough horse power to perform any corrections you come up with.  Tough to overcome the coupler's directivity. 

[xrunner]

Have you ever used a conductive paint for RF shielding? If so, where did you obtain it?

[joeqsmith]

Recently...

https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg4635781/#msg4635781

https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg4649296/#msg4649296

[xrunner]

Where did you obtain the Sandstrom products "Silver Lining"?

https://sandstromproducts.com/products/conductive-coatings/

I can't find it for sale at all except from the company that makes it, and they say this -

*This product is sold in manufacturer batch size volumes only with a 5 gallon minimum order. Please contact our sales team at CS@SandstromProducts.com, to make inquiries.

Five gallon minimum order? 

[joeqsmith]

They may not sell it to you.  Wouldn't hurt to ask.   Otherwise MG Chemicals may be your best bet.  The stuff I used for the 3D printed horns worked about as good as the OEM horn with five coats.   

[xrunner]

Transferred project to Due board. Only change needed was to remove the analogReference(external) call because on the Mega I wanted a 3.3 V reference instead of it's 5 V default reference.

It is not needed on the Due board, since it's referencing 3.3 V by default. Other than that change, there are no issues at all.

On the matter of RF shield coatings I happened across an interesting thing today. I had some neck pain pop up for the last several weeks and I eventually settled on the cause - my office chair seems to have lost several inches of max height over about ten years due to mechanical wear I guess. This was causing me to look at my monitors at a bad angle. I replaced the piston that the chair sits on, and now it's way back up where it's supposed to be. It happened over such a long period I never really noticed the change.

So what does that have to do with RF shield coatings you ask? 

Well, a decorative part fell off the chair as I hammered at the piston and it popped off. It does nothing at all but make it look nice where the welds are for the five wheel legs. I was just going to put it back on until something came to mind regarding RF shielding.

I had been wondering if common metallic spray paint like Krylon or Rust Oleum was conductive. Wow what a simple way to get what I wanted if that was true. But every topic regarding this said no no son, it's not conductive at all. It won't work for RF shielding.

So I took a look at the decorative part that popped off. It was a very shiny silver. Was it a metal part? No, it was very flimsy plastic. I scraped off some of the shiny silver coating and confirmed it's a very cheap gray plastic part. I measured ohms with a meter and wow - it's an excellent conductor (see pic)! What is this bright silver coating on the plastic ... paint?

If it's decorative paint then where do I get some? Are there some types of spray paint that really are conductive? If it's not paint, what is the coating on this plastic? Can't I achieve this at home?

[joeqsmith]

We had chromed some plastics for work back in the 80s.  I assume when they made the plastic models with chrome parts, that was also chrome.   

[xrunner]

We had chromed some plastics for work back in the 80s.  I assume when they made the plastic models with chrome parts, that was also chrome.

OK I didn't know plastic could be chromed ... learn something new every day here. 

[joeqsmith]

I showed some of the copper plating in the waveguide thread.  Once you have copper, you can chrome it.   

The last thing we tried was to 3D print using some of that high content copper PLA then sinter the part.  That was a bust.  The MGC spray worked fine for me but if you read through the thread, seems it can be problematic.   

[xrunner]

I'll use my go-to solution then ...

Copper tape.     

[xrunner]

Now that the UPS strike has been averted, Mouser says my order of two Arduino R4 Minimas has been shipped even though they previously weren't expected until Aug.

Go figure. 

[joeqsmith]

I like copper tape myself for shielding.   Easy to work with and cheap.   Someone asked about using it to line the microwave horns.    I never tried it as it seemed like mechanicaly, it would have messed things up.  Then again, I was doing some pretty crude work and getting somewhat meaningful results. 

[vk6zgo]

We had chromed some plastics for work back in the 80s.  I assume when they made the plastic models with chrome parts, that was also chrome.

OK I didn't know plastic could be chromed ... learn something new every day here. 

Yep! back in the 1960s, I picked up a small book about plating, & it showed how to electroplate various materials, such as plastic & wax.
The latter was used to fabricate hard to make parts, using a wax model, spraying it with graphite, plating copper onto that, then heavily plate the copper with the final metal required.
The result was then heated, so the wax melted out of it.
Sort of "Dreamtime" 3D printing!

[xrunner]

Kind of in a holding pattern right now until the case arrives later this week. You can see the basics of the case in the pic. The front and rear panels (which will be replaced) sit in a slot. There are additional slots along the inside. There are also twelve holes in the top and bottom for self-tapping screws. So I can design a conversion plate to match holes in the case, and have holes in the conversion plate to mount the system components: the controller, coupler, and log amp boards. I need to lay out everything and find out the best way to get it all in there.

That's the plan anyway.

[joeqsmith]

I could always send you that Nissei SWR Watt meter if you would like a smaller case.       

A few people have asked about aligning it, changing diodes ...    After seeing that review in QST which was similar to my own tests,  I took a closer look at mine and am pretty sure I know the primary cause why it is so crapolicious.  Well, maybe 60% confident.  Still, I can't understand why it made it out of the factory as no one would buy this junk as is.   May make a follow up attempting to improve it.  That or take it out to the shooting range.     Maybe both. 

[xrunner]

That or take it out to the shooting range ...

Pics or it never happened! 

[xrunner]

Received two of the AD8307 log amps in the RF shielded cases.

Looks like mine were assigned to the same quality control schmuck that inspected yours. 

Only one dent on the RF input side - isn't quite as bad as yours was. I can get the male SMA threaded on at least.

[joeqsmith]

That's too bad.  You can do what that one hammer did and jam some drill bits down there.      

[xrunner]

That's too bad.  You can do what that one hammer did and jam some drill bits down there.   

Well, tomorrow I know where that pic is going to be posted - on my Amazon review of the item. 

[xrunner]

Received two of the new Uno R4 Minima boards. Older board above in pic. Same footprint. USB 3 port now. Faster processor. Will replace board in previous power meter project with new Uno.

Another Amazon shipment now shows on the tracking -

Problem occurred

Unfortunately, a problem occurred during shipping. If you have not received your package by July 30, please come back here for an update. We're sorry for the inconvenience.

You're sorry?