Between any two microwave radio antennas, there is one direct ray and multiple refractive/ reflective multi-path rays. In the eighth and last installment of our Radio Head Technology Series, Aviat Networks Principal Engineer and master storyteller, Dick Laine, relates how restrictive tower rules for San Francisco’s historic China Basin Building required fine adjustments of a horn antenna to resolve reflective rays from the surrounding bay.
As Dick tells it, to accommodate a Space Diversity arrangement, one horn antenna on the building had to be hung upside down. During the installation process, the alignment for the upside-down diversity antenna created a reflection point 3 miles out into the bay. Because of this installation, the performance was horrible, but at the time no one knew why. For example, when a little speedboat or anything larger went through the reflection point, there would be an outage as the signal was interrupted. There did not seem to be an obvious fix to the alignment issue. The horn antenna did not have a way to check the alignment on the horizontal with a bubble level.
To find out how Dick solved this antenna mystery, register for the Radio Head series (it’s free). Then to put it all in context, Dick goes over Huygens’ Principle as it applies to microwave signal diffraction. And if you ever wondered what happened to periscope antennas, Dick provides some key insight! Tune in to find out!
Ever wonder which antenna polarization is more susceptible to rain outage? Vertical? Horizontal? Which should you use for very long hops?
What would you do besides add extra fade margin to mitigate rain outage? Design a shorter path or use a lower frequency band?
Aviat Networks’ microwave radio guru, Principal Engineer Dick Laine, tackles these tricky questions and others in the latest episode of our Radio Head Technology Series of videos.
Dick also talks about rain outage—as calculated by ITU using a simple scientific calculator, or computer programs (Starlink) that use the Crane model. He goes through an ITU-R availability calculation in one example, noting specifically about rain attenuation calculation above and below 30 degrees latitude. Dick then proceeds into a deep dive on calculating outage when you know the fade margin, followed by a discussion on the Crane rain attenuation model.
Aviat Networks invites our readers to register to be added to our Radio Heads distribution list to get notified of new Radio Head Technology Series releases and links to replays.
Five-nines (99.999 percent) availability is a concept that is familiar in wireless engineering. Dick Laine, principal engineer of Aviat Networks, compares five-nines availability to 78-rpm records in our most recent episode of the Radio Head Technology Series.
As he relates, even with scratches and pops, a 78-rpm record still is able to transfer aural information so that you can hear it, i.e., its availability is intact, as it does not drop performance. Scratches and pops only represent degradation in the quality of communication. But when the record is broken, an outage occurs—no record, no communication.
The same goes for wireless communication systems. If a microwave link drops 315 or fewer seconds of microwave communications per year (in increments of up to 10 seconds at a time), it is maintaining five-nines availability. The microwave link is offering 99.999 percent availability for wireless backhaul. Only if the microwave link is unavailable for more than 10 seconds has an outage occurred, for the purposes of determining if microwave communications traffic has been dropped.
Dick goes on to explain about what happened in 1949 when 78-rpm records were superseded by 45-rpm records. Dick got a sneak peek at the top-secret 45-rpm record project when he visited the legendary RCA facility in Camden, New Jersey, which played a crucial role in the development of the modern music, radio and television businesses. Unfortunately, unlike a five-nines microwave link, 78-rpm and 45-rpm records are mostly unavailable nowadays.
As most radio engineers know, Vigants calculations, which are discussed in a broadly cited Bell System Technical Journal article, are widely used to determine reliability or error performance for microwave link design. In Video 2 of Aviat Networks’ popular Radio Head Technology Series, which is now available for viewing, Principal Engineer Dick Laine explains how he uses Vigants calculations in conjunction with the three completely separate ITU-R Fixed Wireless System (FWS) models for TDM.
Because of all these models, he likes to use Vigants calculations as a “sanity check” to see that he is close to the correct result for his path engineering plans. The free Aviat Networks’ Starlink wireless path engineering tool can be used to handle Vigants calculations for Aviat Networks’ and other vendors’ equipment.
Can’t wait to hear more of Dick’s experienced views on microwave radio transmission engineering? You can get ahead of the learning curve by registering for the series and get these videos sent to your inbox as soon as they are released.