Like fingernails on a chalkboard at + several dBm.

From the MOTOTRBO mailing list. Names omitted to protect the innocent.

While I understand the meaning of RSSI in the WiFi world, I am curious if  a LOW (i.e. -60 DBm) means a better signal being received from the  DMR repeater I am connect to, or is a -106 DBm a better signal.

While I think this might sound like a remedial question, I am trying to get clarification.

Appreciate any information you can provide

The first reply:

LOWER IS BETTER

And the light clicks on

-106 is lower than -60. Are you guys sure you’re explaining yourselves well?

Such is just basic number theory.

(Negative numbers) Weaker signal <- 0dBm -> Stronger signal (Positive)
The 0dBm point is the reference – one milliwatt. Numbers below or above are that many dB above or below one milliwatt. In the case of receivers, the signal strength is usually very well below one milliwatt. In the case of transmitter output power, it is often above. In either case a higher number is a better receive signal, and -60 is higher than -106.

It always just bothers me when I see this as someone who thinks a growing absolute value of a negative number in this field will be chasing their tail FOREVER trying to figure out reception problems. 😉

The Analyzer’s New Clothes

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This Tektronix 1705A L-band spectrum analyzer has temporarily borrowed a garment from an old waveform monitor.

Why?

Because as I had it on my bench powered up naked after running through a calibration on the CRT power supply, an operator comes walking in and rests his arm riiiiight here. Luckily I got him to move before any BANG occurred.

How do you even guard against awful human error like this?!

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Small naked wire and HV diode are on the input side of a voltage multiplier that puts out FU Kilovolts.

Now if you’ll excuse me— I need to make a sign for him. 😉

Bonus: The resistor the other tech never bothered to replace. Amazingly it still works, but I wasn’t gonna leave it like this!

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while we're on the subject of near crispy critters

Just Big and Lousy

Today’s— uh, victim— JBL LSR2325P active studio monitor. It’s a nice sounding biamplified monitor with an active crossover system and suspicious “Imagine” brand capacitors. Hmmmmm. 😉

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Our music producer came to me with this loudspeaker he uses to play his creations for our news director, among other things, because it was crackling and popping ferociously when the input gain knob was touched. I found the input gain knob loose on the rear panel and guessed I’d also find cracked solder joints. But where?

Input gain control is below the inverted plastic bathtub under that board. So how do you remove this plastic bathtub? Desolder the shitty thermoplastic power switch—- which will melt and eject its metal parts. WTF??!!

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You can see the switch on the panel here – it’s a snap in flange mount – the only way to get around doing this would be to cut away the plastic flange and back it out, I guess. The tub it’s in is sealed so this wouldn’t create an air leak. But still— AARGH!!! Also, WHY THERMOPLASTIC? I have a problem with this. See, if the switch starts warming up, the plastic will soften, removing pressure from the contacts, creating more heat. Eventually the fault will only clear when the switch either totally loses contact or the thermoplastic erupts into flames.

Proper electronic assemblies use thermoSETTING resins. Glass reinforced polyesters/epoxies are nice. These are resins that set either when two parts (a resin and a hardener) are mixed, or enough heat+pressure are applied to kick over a curing reaction. This reaction is a one way process and the resulting product WILL NOT MELT and soften. It may eventually be flammable, but most thermosetting resins, especially glass fibre filled ones, have a very good track record of self extinguishing.

Phenolics are very common in solderable connectors. You can always tell when you’re dealing with a phenolic resin because it will not soften and allow the connector to deform with extended heating during soldering. These resins are often colored teal blue/green, or a tan color on Amphenol products. Ever wondered what the name “Amphenol” is about? 😉

Wikipedia article on thermosetting polymers

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I don’t even want to think too hard about what that AC power inlet fixture is made of, all things considered.

The header pins leading to both the boards inside this tub were also graced with total shit-grade soldering and I reworked them. There’s one board below with the three jacks and one board above with the amplitude pad and the HF/LF trim filters. I resoldered the input pot and tightened the nut around it with some Loctite purple on it. In theory, I probably should have used blue, but I can’t find the blue, and red is right out of the question. Whatever works, right? I’ve had just as good luck with things like this using nail polish on them.

 

That’s the fate that befalls any nail polish I buy that looked GREAT in the store but when I put it upon my claws it turned out all watery looking or otherwise unsatisfying. (“NYC Color”, this means you. Well– some of their shades. Some of their newer ones are actually formulated with, well, color, in them.)

After this– I can’t wait for my assistant here to show up so I can run my fingers through his thermal insulation and hear him make silly happy squeaky meows.

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How to achieve silly smiles… 🐱

A post shared by #include <wonderland.h>; (@blueneon) on

PowerExtra VL003-170 LED light

Just a quick look at this after it arrived in the mail today– for under $20 shipped, I’m impressed. 170 white LEDs and a clever power system.

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You can use AA cells or any of a long list of camcorder batteries.

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Boost converter. When it’s running full bore I measured 13.8vdc across the led array. This from six aa NiMH cells…

The board at foreground is a push button LED battery fuel gauge. One to four lights indicate the voltage. When I crank the light on the NiMH cells, it drops to one or two immediately. This thing will really shine on lithium ion…

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A ventilated cover goes over that…

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Thermal issues? Not particularly. I ran the light full tilt a while and the board got barely bath water warm.

It includes two color matching filters and one diffuser. Hopefully it’ll get a test drive tonight.

I’m wondering if it will handle being hooked up to a 14.4v pack. Specs on their website say 7.2-12v but the TI switcher chip and caps are rated for enough… I guess there’s just one way to find out! Where’d I put those D-tap plugs?

The curious elements of Unobtanium and Expensivium

A module upon which the Unobtanium evaporated as the Magic Smoke was lost.

Unobtainium and Expensivium are very vital, curious, yet annoying elements. They are commonly used in parts for electronic devices, particularly those in the world of broadcast RF transmission.

Although no link between actual physical toxicity to humans or any other animals has been proven with Unobtanium or Expensivium, those involved in occupations where they have to procure and work with Unobtanium and/or Expensivium parts tend to suffer a greater number of headaches.

Misspent youth – the Yihua YH-305D

Boy, was I ever young and stupid. It was the summer of 2004 or so, and various Chinese electronics vendors were just starting to flood the US market with some really cool looking toys, and the quality hadn’t faded to zero on them yet either! Mostly….?

At the time I’d just gone through a big mess with most of my workshop having been left out in the rain for several days in my absence, so I didn’t have a power supply. I bought this Yihua YH-305D on eBay and thought it was pretty great for the price, even after it arrived with the instruction manual calling it a “DC POWRE SUPPY” and the plastic nuts on the front panel binding posts don’t actually… work. (I got around this using banana plug leads.)

Years later it finally occurred to me to be suspicious of the fact that the constant current regulation is sloppy as hell, and the cooling fan starts to run if you draw more than one amp off it continuously. At five amps steady draw, the Powre Suppy doesn’t get noticeably warm, but the fan continues to howl forever.

I opened it and realized just how misspent my youth truly was.

wp-1483573643309.jpgThis… beautiful… board greeted me right away. There are places where traces kinda got half etched over there on the side then subsequently, but incompletely, covered with solder to fix it. Ummmmmmmm yeeeeeaaaaah D-

wp-1483573603318.jpgThe underside of the regulator pass transistor assembly. That’s three *supposed* 2N3055 transistors, paralleled. Why would you need three 2N3055’s for five amps?? You can run 15 amps through ONE real 2N3055 if it’s heatsinked properly. Oh wait, I forgot the key word… real. Genuine. Official. Not Pure Unadulterated Chineseium. I couldn’t get a picture of the labels on these “2N3055” transistors that were SO GOOD that they had to put three in parallel to pass 5 amps, but I was able to get a peek at it and they were printed in a gray looking ink with a nonsense logo– it looked like the Marvell Semiconductors logo??!! Either way, this video details what I’m probably actually looking at and why they are… very… very… derated.

The heatsink they are bolted to also explains the fan behavior. It’s nothing more than a flat plate with very little mass and surface area.

wp-1483574274591.jpgThe fan sucks up air from right above it and exhausts it out the back when the thermal switch seen in the background snaps on. I’m not sure how hot it has to get to trigger that, but it sure gets there in no time.

wp-1483573638001.jpgThe main filter capacitor looks underwhelming and I have my doubts it’s actually a Rubycon as its clothing would suggest.

 

This is paired to, uhhh, the death capacitor, as I lovingly call it. If you are using a power supply like this as a limited current source and you lose connection to the load momentarily, and the voltage limit is significantly higher than the voltage the load pulls it down to, any capacitor on the output will be charged up to that level. Once connection is reestablished to the load, it is presented with very high available current at this higher voltage. I detonated some high efficiency white LEDs under test with a power supply like this years ago while trying to develop a boost converter based driver for solar lighting applications and was royally pissed. So, without further ado, the death cap…

wp-1483573631845.jpgand…. the… rubber cement disaster of the century. The entire front of the supply is just…… bespooged with this cement…. Another red cement is found splattered all over the place as well. At left in the above picture is the digital meter board which I am not even going to touch let alone try to calibrate the screwed up zero point on, FORGET THIS

 

wp-1483573620558.jpgThe board is supported only by one small bracket from the rear; if I drop this power supply it will experience the sweet release of death it so sorely longs for.

 

Yeah. I was young and stupid and I bought this.

 

There’s a great thread on EEVBlog’s forum about these, including the wonderful thing that happens when you switch one on and it goes wham, overshoot, boing, boing, boing, and either stops bouncing or… not…

 

Measure up: a beautiful vintage meter.

So a meter is a meter is a meter, right?

Bzzzzzzzzzz.

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This monster is nearly eight and a half inches wide.

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Neat scale.

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Spade tipped needle.

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The passive scale illumination: a ground glass band on top allows ambient light to light the dial.

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Connection post. This isn’t exactly a blazing sensitive meter– putting a digital multimeter set to ohms across it yields no visible deflection. (Some meters peg!) Setting the DMM to diode check, which usually applies 5mA or so, gave me about a 61. Please admire that rough carpentry. I love finding things like this!

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Better view of that nicely made wooden base. Unlike the edges of the connection post holes, the outside is immaculate.

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Dwarfing a Gossen Lunasix.

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Hand written serial number.

What was this made for? Judging by the lack of any visible brand name, wood tabletop base, and unusual scale with no units, I’m suspecting it was a classroom/lab piece. You’d calibrate with a known voltage reference and do the math yourself. You know, old school nonsense. 😉

The low sensitivity is curious too. I’ll have to test later and see just what scales out to a 100.

I did open the meter briefly because there was some loose material rattling around that I didn’t want damaging the movement. An old wire wound spool resistor is mounted inside in parallel with the movement, likely for damping. It looked similar to the spools in my Weston but covered in cloth tape instead of wax.

Crap Power Strips

This has significantly bothered me for a while.

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This is one of the most common power strips available now, as it’s the least expensive available out of China. Note what happens if you miss just a little plugging in a two prong plug. If you touched the prong here and any grounded object, hi diddly shockarino, neighbor!

But guess who doesn’t seem to have a problem with this.

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Genuine meaningless hologram.

This strip is available under a number of brand names including General Electric, Westinghouse, Belkin, Sunbeam, whoever the retailer licensed a brand name from that week. You should not buy it.

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