I have been bouncing back and forth to Schaumburg, since Motorola contracts require particular training for servicing and upgrading PSAPs. It’s a great place to spend the summer as it’s just a short trip down to the Loop, which is improving. If you get out early enough check out the Sears Tower Skydeck. I took an FRS walkie talkie and ham radio walkie talkie with me–50 km range is no problem due to line of site. You can make your own radio “pile-up” with so many people calling for you on the ham radio or FRS from Sears Tower.
Ham radio maximum distance reached from Sears Tower Skydeck
It’s been known for a few decades, particularly since the Sears Tower was built that one can see the tallest bits of the Chicago skyline from the bluffs south of St. Joseph, MI. Constricting myself to HT-HT DX (no yagis, repeaters, mobiles), just 5 watt walkie-talkies between the Sears Towers and them. Assuming Warren Dunes State Park has a bluff 240 meters AMSL, and the Sears Tower Skydeck is 412 meters AMSL, is communication possible? Yes, even with standard 4⁄3 refraction. Under conditions where one can see a mirage of Sears Tower, the RF connection is even more likely.
Using Radio Mobile Deluxe, I predict on 2 meters (144 MHz) a signal strength of -87 dBm with 70% spot reliability. 70 cm (440 MHz) is predicted to be -94 dBm. In pure free space (outer space) we expect a tripling of frequency to increase path loss by
20*log10(3) = 9.5 [dB]
Yet here we see only a 7 dB penalty for tripling frequency. This is because the Longley-Rice model inside Radio Mobile Deluxe takes into account that (for this path) at 144 MHz the Fresnel zone clearance is only 0.2 and at 440 MHz the Fresnel zone clearance is 0.3. Fresnel zone clearance relates to Huygens’ principle: at each point in space, we may imagine secondary reradiators. Thus for a wave front encountering an obstacle, we can model the “bending” around an object into a “shadow”. This is how we have radio coverage in urban areas, and why for mobile radios, high gain antennas are worse than low gain antennas in urban areas!
Motorola headquarters tour
I saw several interesting things in the Motorola Museum, including an old Centracom console (complete with OOPS code), and old handsets and dual TX-RX units from WWII era or thereabouts.
We saw an RF development lab where they test radios in real world conditions. They had a spectrum analyzer hooked to a broadband (discone?) antenna–when I looked through the 100-1000 MHz range, the quietest spectral locations were the amateur radio bands, they looked as if there’d been notch filters inserted in line! Of course that wasn’t the case, it was the relative daytime quiet of the VHF/UHF ham bands in Chicago compared to the immense commercial and government radio traffic. Yes, military aviation UHF was also a bit quiet.
We also saw a CAD lab where the engineers had quad monitors–wow, that would have been fantastically expensive just a few years ago when LCD monitors were $3000 each. Even still, with perhaps $1200 in two dual-monitor video cards and $1000 per monitor, and probably a $2000 desktop PC otherwise, that’s about $8400 per workstation in computing hardware. Obviously the productivity gains are compensating for that initial expense.
We also saw the dispatch center where Motorola handles field support calls from contracted end users and support staff. This might include Motient, large cities and government agencies. There is a backup center with undisclosed location and different employees as it would be vital in the case of a big crisis. The wall of the two story room was a giant screen, like one sees for NASA Mission Control, viewable from any of the perhaps three dozen workstations facing it.
In the end I collected over a dozen business cards from other students and I encourage them to call me for tricky RF system design problems.