Antenna Guru

RF is not 'black magic' – It's Synthesis, Optimization, Analysis and Realization.

Monthly Archives: January 2013

IIABDFI

dishwasher disassembly for repair/replacement ...

dishwasher disassembly for repair/replacement of chopper (Photo credit: Wikipedia)

If it ain’t broke, don’t fix it!

About eight years ago I bought a KitchenAid dishwasher. I had had good experience with them over the past quarter century or so, and I didn’t even think about a different brand. Today, I am very impressed with this latest model, but it did not start out that way, the way I had expected.

From the time I first brought it home, it never cleaned the dishes like I thought it was supposed to. It would leave soap in the dispenser if I didn’t arrange the dishes just right. Coffee grounds would stay in the bottoms of the tall cups I like to use if I left the dirty cup on the counter all day before rinsing it out like I like to do. So even though they were just little nagging issues, I was not happy with the appliance.

Right after I bought the thing I had called a repair guy and asked him to check it out. He came out, ran it through a cycle, made some perfunctory tests, and said, “Well, your water’s not hot enough, and you’re not using the recommended detergent. That’ll be eighty-nine bucks.”

I figured they’d sold out, cheapened the product; I figured the new ones weren’t as good anymore. But it still worked. So, if it ain’t broke, don’t fix it, right?

About a month ago we had a thunder storm come through that knocked out the power in such a way that the lights went off and on several times and dimmed and so on. The dishwasher had been running at the time, and the storm fried it — The blue LED’s would sort of dimly light on the control panel, but the buttons didn’t work. So, I ordered a control board. That didn’t fix it, so I sent it back and ordered a control panel. The new control panel let me turn the dishwasher on and cycle it, but it didn’t clean the dishes at all.

“Time for a new dishwasher,” I thought. “At least I can send back the panel, too.”

But being a little short of cash right now, my wife talked me into trying some more to fix the (eight year old) one we had. So I puzzled and I thought. I probed and I Googled. I went through that entire dishwasher, cleaning all the strainers and inspecting all the wash arms. Reluctantly, I ordered a circulation pump assembly. I wasn’t hopeful that this would fix it, because when the dishwasher cycled water sprayed… sort of. But I had looked at everything else.

The circulation pump arrived and I replaced it with the help of an online video and Debi’s thoughtful suggestions. (Her suggestions really helped: She studied the video, too, and saw important details that I had missed. Plus, she had encouraged me to press on instead of giving up in the first place.) When we started it up Debi said, “It seems louder to me,” and that was because…

The dishwasher now cleans better than it ever has in the last eight years!

There’s a metaphor in there somewhere, certainly.

What We Do (SOAR)

I am trying out some copy writing for our upcoming website. Here’s just a smidgen…

Synthesize

The most general meaning of the word is “combination of parts to form a whole”. In electrical engineering, the term strongly implies mapping from mathematical functions, e.g. Chebyshev polynomials, to some sort of network, e.g. a lumped element filter or an antenna array. We prefer the general meaning which includes the math-to-circuit idea but further conveys the thought that we bring our individual talents to bear on every problem (as necessary)– and our collective expertise spans a number of subject areas.

Optimize

Again, the general meaning of the word, “make something as functional and effective as possible,”  is what we intend to convey. We have a passion for making things and we are passionate about making them as functional and effective as possible.

Analyze

In synthesize the activity goes somewhat like this: If you give us a set of performance requirements we will try to come up with a combination of elements that performs as required. Analysis inverts that activity, like this: If you give us a combination of elements we will try to predict their performance. If synthesis involves “putting it all together”, analysis involves “breaking it down.” We often employ computational techniques to break a problem down, but we also apply philosophy and common sense.

Realize

“…bring into concrete existence …convert into actual money …be fully aware of …cause to happen …”  We have a machine shop so that we can build prototypes. We have a test lab so that we can measure them. We have project management experience because time is money. From beginning to end we like to “keep it real”.

The Internet of Things

Thingernet

The “internet of things” is already here — in the media, at least.

It is not hard to find these types of articles nowadays. Whether or not you think connecting your cow to the www is a great idea, it certainly is a popular topic of conversation. I’m all for it. Here is why, as Linus Pauling famously said

If you want to have good ideas you must have many ideas. Most of them will be wrong, and what you have to learn is which ones to throw away.

But there is a problem with the populist application of internet-to-things that goes unmentioned by the tech writers. The cacophony of “information” that results from Farmer Brown giving Bessie her own cell phone potentially threatens our shared bandwidth. This is the reason we have the FCC and the PTCRB. We need to comply with their rules so we all can remain in polite conversation.

Spurious Emissions

The physics is no longer bewildering to me, as it was thirty years ago when I was thrust into the microwave business, but the rules and regulations can still be−

PTCRB

Let’s start with this five-letter acronym for “PCS-type Certification Review Board.” Nested within this acronym is another acronym for “Personal Communications Service.” Surfing over to their home page, “Welcome to PTCRB,” one is confronted by more acronymia. (By the way, ‘ptcrb’ is not found in acronymia.com’s dictionary at this writing.) I tried unsuccessfully to find out the rules for “obtaining PTCRB Certification on a mobile device” because I couldn’t provide the required company website on the Registration Page.

RSE

This TLA stands for “Radiated Spurious Emissions.” RSE are(is?) at the crux of the PTCRB certification. Finding their source(s) and mitigating them is exactly like the other stuff I love to do. Except finding out the rules, which is exactly like the stuff I hate.

CTIA

Originally dubbed the “Cellular Telephone Industries Association,” but now calling themselves, “CTIA – The Wireless Association,” lets you browse their website. I found a Test Plan for Wireless Device Over-the-Air Performance there, but no mention of allowed RSE levels.

Time to change tactics… I decided to look at websites of companies who operate the equipment.

The Horn reflector antenna at Bell Telephone Laboratories in Holmdel, New Jersey (Wikipedia)

AT&T

Sometimes I forget all the great engineering that came out of the old Bell Telephone Laboratories. So it was great to find this App Note: Antenna Fundamentals. (Maybe I liked it so much because it was like an advertisement for what I am good at doing!) I especially liked this quote:

A failure to meet FCC regulations or PTCRB radiated-spurious-emissions-conformance requirements due to a level of harmonic energy generated by the device is often blamed on the antenna. In truth, the antenna can often influence the level of the harmonics but does not generate these signals. An antenna almost never has gain at the harmonics of the intended band of operation. Provided the radio has acceptable harmonic performance, excessive harmonic generation is typically an interaction between the impedance of the antenna and the impedance of the final stage of the transmitter.

−ATT Antenna Fundamentals – Technical Brief, p.  34

Heck, yeah!

This is a great Tech Brief, especially because it doesn’t push one type or brand of antenna over another, and it isn’t written to scare anybody into becoming a customer …but I still didn’t have my RSE answer.

ECN

(I don’t remember what the letters stand for, but it’s been a trade magazine for a long time. I emailed the editor, so maybe he’ll get back to me on this.) Bleary-eyed, I clicked on a link to their article, Cellular Carrier Certification Requirements and scanned down the page… Bingo!

Note that PTCRB limits follow ETSI limits, not FCC limits.

ETSI

(European Telecommunications Standards Institute) After all that, I really appreciated their website: The first link on their homepage was Standards. It still took a while to get to the right document, but at last I believed I had found it:

ETSI standard ETSI EN 301 502 V10.1.1 (2012-01)

Table 4.2.5-1: Spurious Emissions Measurements outside the transmit band

Band

Frequency offset outside

relevant transmit band

Maximum power limit

Multicarrier BTS

9 kHz to 1 GHz

≥ 2 MHz

≥ 5 MHz

≥ 10 MHz

-25 dBm

-20-4,2*(Δf-5) dBm

-36 dBm

1 GHz to 12,75 GHz

≥ 2 MHz

≥ 5 MHz

≥ 10 MHz

-25 dBm

-20-3*(Δf-5) dBm

-30 dBm

Crying in the Wilderness

So they said to him, “Who are you? We need an answer! What do you have to say for yourself?”

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