CB and Ham Radio Techs Love Their Bird Wattmeters

[bd139]

I suspect that they watched a video I made on how not to blow up the NanoVNA after I saw several hams post how they had damaged theirs.   In that video, I talk about discharging the coax and I had the grill starter connector in my hand and showed shorting a BNC connector with it.  It was not my intent that the hams would see this and think it was a good idea to start shorting their connectors with drill bits but here we are (monkey see monkey do). 

Hams, don't use your calibration standards or drill bits to discharge your systems.

Normal distribution of IQ confirmed!

[joeqsmith]

Still here. Like asbestos or mould. Difficult to get rid of 

Here's an article on cleaning moldy hams:

http://www.scrumptiouschef.com/2017/01/26/how-to-clean-mold-from-a-country-ham/

[bd139]

Yuck. Glad we have food standards here 

[xrunner]

Attenuator ordered  - the adventure continues ...

Neither of my VHF/UHF rigs have a setting for 10W (5, 20, or 50W only). My box of attenuators that could get me from 50W (+47) or 20W (+43) to 10W (+40) doesn't have one rated to handle the power up-front.

But, I can use one of my HF rigs to dial up 10W at any ham band up to 50 MHz. I want to bake this thing with it's rated power and take some temp measurements. Isn't it supposed to be able to handle 10W at 100% duty cycle ... 

Anyone know what temperature aluminum melts at? 

[bd139]

Depends if you end up with aluminium or chinesium 

[xrunner]

Depends if you end up with aluminium or chinesium 

Mystery-metal?

I've been watching these videos of how things are fixed and made in Pakistan. They'll take out an engine from a truck and set it on top of a piece of cardboard and work on it in the mud. But they cast metal and make things that actually look pretty good. But the metal ... I don't even want to know what quality the metal is. You can see the piles of metal they toss into that kiln - what it all is and how it was tested ... don't ask questions. 

Oh and saftey?  They mostly work in sandals or bare feet, almost never see safety glasses worn.

[bd139]

The only reason they end up in those places is they were fixed in those places last time 

[A.Z.]

The only reason they end up in those places is they were fixed in those places last time 

would those folks fix a bird meter ?

just curious

[bd139]

The only reason they end up in those places is they were fixed in those places last time 

would those folks fix a bird meter ?

just curious

They'd hit something with a hammer until it looks like one at least 

[fourfathom]

Come the zombie apocalypse those metal casting guys will be the ones who survive, while we sit here shivering, staring at our our dead computers and radios.

[bd139]

No they will die a couple of weeks after they get a serious infection and there is no medicine to treat them. Like the rest of us.

Anyway I’m not going to be sitting there shivering. I’m going to be eating fresh brains.

[A.Z.]

The only reason they end up in those places is they were fixed in those places last time 

would those folks fix a bird meter ?

just curious

They'd hit something with a hammer until it looks like one at least 

and then solder the stuff using that Jesus soldering iron; that one would be pretty good for SMD or to repair an HP scope

[xrunner]

The attenuator is supposed to be on the way from Amazon ... unless it suffers the same fate as a computer case I ordered last week and just decided to check on since I hadn't heard anything since I ordered it. 

[bd139]

Ah I get that occasionally. They always send out another one.

They did it with an SSD once and I ended up with a soggy wet one arrive a week later that I was never charged for 

[xrunner]

Tracking sez the PC case is in town, so it'll probably get here now.

Back to the issue at hand, the 10W 40 dB attenuator is out for delivery. I'm prepared for the worst in product design, so if it turns out to be OK I'll be pleasantly surprised.

[xrunner]

The attenuator has arrived!

Out of the box it appears made OK, but I want to take it apart and see what's inside. Of course the manufacturer's name and model number isn't printed on the thing - that I expected. Let's just see where they marked the power and dB attenuation for easy reference on the outside of the case ...

Oh stupid me they didn't mark that on the thing either. What a waste of ink that would be. 

Every penny counts these days. 

For reference I took a pic of it standing next to a Narda Microline 20W 10 dB attenuator. Do you think the little guy can take 10W and survive? Well that's what we're going to find out! 

[fourfathom]

My bet is it's good for 1W continuous.

[joeqsmith]

I thought you had already been down this path.

https://www.eevblog.com/forum/rf-microwave/inside-a-cheap-chinese-made-rf-attenuator/

https://www.teleworldrf.com/10w-coaxial-attenuator/10w-sma-attenuator.html

[xrunner]

I thought you had already been down this path.

Oh I forgot about that one. 

Your brain tends to want to erase terrible incidents in your life.

This site says -

https://www.teleworldrf.com/10w-coaxial-attenuator/10w-sma-attenuator.html

(if it's the same one I have) that it can withstand 125C. Heck my coffee cup warmer gets up to 98C. I bet it can't take it. I'm going to get a thermocouple attached to the atten. so we can see at what point it fails.

Here's a fresh plot of the 40 dB attenuator. The 10 to 40 dB atten. have a +/- 1 dB accuracy according to that website. Nope. I already have evidence enough to get my money back with that picture.

I suspect, as fourfathom does, that it won't be able to withstand 10W 100% duty cycle (which I will test with a DC power supply). I'll probably start gathering the return materials today so I'll be ready to go to the UPS store.

 

[bd139]

Do you have a mould available to pour that molten chinesium into to make it into something useful? 

[xrunner]

Do you have a mould available to pour that molten chinesium into to make it into something useful? 

No I don't have any moulds for liquid metal. You can bet it won't be laying on my workbench mat. It will be held with a metal vise.

[xrunner]

The spec sheet from the Amazon supplier is attached. As already observed, it barley meets in some ranges, and fails in others, the attenuation accuracy claim up to 1.5 GHz (+/- 1.2 dB for the 40 dB model).

I had other things to do today but I did lash up the attenuator (with a 50 ohm load) up to a DC supply. I was able to check the voltage drop across the attenuator and the load resistor, and verifying with the common formula 20log(vo/vin) that it was achieving a nominal 40 dB attenuation.

I applied up to 2W power and made a subjective measurement of the attenuator case temp (with my finger). I registered "hot" - at that point I turned it off to do other things. The specs state a max operating temp of 100 C. Should be interesting to see the results of 10W applied. I plan to attach a thermocouple to the case for that test.

[joeqsmith]

They have left you with the problem of sorting out how to keep it below 100C with 10W is all.   I wonder if it will still fail if you are able to draw the heat away. 

[xrunner]

They have left you with the problem of sorting out how to keep it below 100C with 10W is all. 

That's true, I can deal with it with forced air cooling. If it approaches 100 C I will shut the test down and, provided it still works, I may keep it. Well, another test would of course be to repeat the test using a fan for cooling. All this will be done for the entertainment of all who care to read this thread. 

It's pretty constant at about 38 dB attenuation so I can deal with that number just fine. It's just irritating that they put this stuff out with claims that are not being met.

I wonder if it will still fail if you are able to draw the heat away.

If I make this power meter to test up to a 10W transmitter, it wouldn't need to be keyed for more than a few seconds to check the power, or if adjusting - maybe less than a minute. I would have a fan on it and it would be OK. 

[xrunner]

Close-ups of the 40 dB attenuator construction. The resistive elements are on a ceramic substrate. Tried to extract it to no avail.

You might think the end contact point is a little dirty (and the opposite end as well) and may be a good thing to brighten it up. Maybe that's causing the attenuation to be off ... oh wait the attenuation is too low we're going in the wrong direction with that.

 

Can it take 10W? Place your bets.