Anritsu Site Master
Understanding the Anritsu Site Master
If you climb to the top of a 200-foot cell tower to install a new 5G antenna, you must physically screw a heavy, corrugated coaxial cable into the back of the antenna. If you don't tighten it enough, or if water gets inside the connector, the massive 100-Watt transmitter at the bottom of the tower will fire its RF pulse, the pulse will hit the bad connector, and a massive reflection will bounce violently backward down the cable, instantly melting the amplifier. To prevent this catastrophic failure, technicians rely on the Anritsu Site Master.
Invented in 1995, the Site Master created the entire category of handheld Cable and Antenna Analyzers. It is essentially a ruggedized, battery-powered, 1-port Vector Network Analyzer designed specifically for people wearing hard hats. Before turning on the high-power tower transmitter, the technician connects the Site Master to the base of the cable. The instrument fires a low-power sweep up the tower and instantly graphs the exact Return Loss (VSWR) of the entire installation, proving whether the cable is safe to use.
The Magic of Distance-to-Fault (DTF)
If the Site Master says the cable has a terrible VSWR (e.g., 2.0:1), the technician has a problem: the cable is 200 feet long. Where is the damage? Did a bird chew it at 50 feet, or is the top connector bad at 200 feet? The Site Master utilizes a mathematical algorithm called an Inverse Fast Fourier Transform (IFFT) to perform a Distance-To-Fault (DTF) sweep. It converts the frequency data into the time domain, displaying a physical map on the screen that clearly shows a massive spike in reflection exactly at "142 feet," telling the technician exactly where to climb to fix the cable.
Distance = ( c × Vf × Δt ) / 2
Where:
c = Speed of light.
Vf = Velocity Factor of the cable (e.g., 0.88 for foam dielectric).
The formula divides by 2 because the RF pulse must travel all the way up the cable to the fault, and bounce all the way back down to the instrument.
Comparison
| Measurement Mode | What the Screen Shows | What it tells the Technician |
|---|---|---|
| Return Loss (dB) | A graph of dB vs Frequency | Overall system health. Must be better than -15 dB to pass. |
| VSWR | A graph of Ratio vs Frequency | Same as Return loss, just displayed as a ratio (e.g., 1.2:1). |
| Distance-To-Fault (DTF) | A graph of dB vs PHYSICAL FEET | Pinpoints the exact inch where the cable is broken or crushed. |
| Cable Loss | A flat line of dB vs Frequency | How much power the cable naturally absorbs. |
Frequently Asked Questions
Why does the technician have to input the 'Velocity Factor'?
Because RF energy does not travel at the speed of light inside a coaxial cable. The plastic Teflon or foam dielectric slows the wave down. A typical cell tower cable has a Velocity Factor of 0.88 (meaning the wave travels at 88% the speed of light). If the technician forgets to type '0.88' into the Site Master and leaves it at '1.0', the math will fail, and the DTF sweep will tell them the fault is at 100 feet when it is actually at 88 feet.
Can a Site Master measure insertion loss?
A standard 1-port Site Master cannot directly measure S21 (Transmission) because you would need a cable running from the top of the tower back down to a second port. However, it can measure '1-Port Cable Loss'. The technician climbs the tower, places a permanent Short circuit on the top of the cable, climbs down, and measures the reflection. Because the energy went up the cable and came back down, the total measured loss divided by two is the exact Insertion Loss of the cable.