Antenna Guru

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

Tag Archives: PTCRB

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

Machine Wireless Interface

logo01

Machine

Wireless

Interface

LLC

I have been hard, hard at work these last weeks… working on the link between a really cool gizmo and the rest of the world.

After drilling down deep into the physics of microwave devices for a quarter century, it appears that I will be spreading out what I have learned.

Tonight my beloved Nurse Debi gave a name to this thing new born – Machine Wireless Interface©

Thank you, beloved…

Just Wail

You’ve got to learn your instrument. Then, you practice, practice, practice. And then, when you finally get up there on the bandstand, forget all that and just wail.

Charlie Parker

I was called in to help on a design project to marry a cell phone with a portable medical device. As it usually happens, almost everything about the project is pretty well set in stone and the mortar is drying fast. Trouble is, the equipment failed the approval testing that it needs to be legal. (Sort of like when you car won’t pass inspection, except the inspection costs $20,000 …)

There is no time to design a new antenna for the device. I fired off an email to a buddy of mine who works at the company who made the antenna, and his antenna expert said, “Make the housing bigger.” (Sort of like when the Wizard of Oz told Dorothy, “Go see the Wicked Witch and ask her for her broomstick.”) This is one of those cases where the left brain just ain’t gonna cut it… So I took a stroll through the imaginary door into the world of ideas. What I came back with sort of resembles the ignominious “coat hanger antenna,” but actually has some theory behind it – it’s called a “coiled coax balun.” It’s almost free, and it worked for this project.

Stay ‘tuned’.

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