Eddie guidesA field team faces an unresolved physical question: How much of the 23 dB basement fix came from the antenna? They must answer it before changing external gain on the real device. Predict the direction first.
See the relationship before changing it
The figure reads from left to right. The blue card is external gain. The middle card applies this page's relationship. The green card is 900 mhz wavelength. Walk the arrows once: set the input, apply the rule, then read the result with its unit.
The retained audit below checks several chapter fixtures. This added model holds every other chapter fixture fixed, so the numeric fixture does not switch without explanation.
Derive the baseline in four named moves
- 1
Name the input. The chapter baseline for external gain is 5.
- 2
Name the relationship. λ900 = 300,000,000 / 900,000,000 = 0.3333 m A0dBi = λ² / 4π = 0.008842 m² G5dBi = 10^(5 / 10) = 3.1623 A5dBi = 3.1623 x 0.008842 = 0.02796 m² -100 - (-123) = 23 dB measured 23 - 5 = 18 dB siting remainder = 78.26%
- 3
Substitute the chapter fixture. Set external gain to 5. The page ledger gives 900 mhz wavelength as 0.333 m.
- 4
Read the result. Keep m beside the value. Use it only inside the technical boundary on this page.
Predict, then change external gain
Try Predict the direction of 900 mhz wavelength. Move one control, calculate, then check your prediction.
Observe dBi enters a link budget directly. Any extra measured improvement must come from another changed variable, such as obstruction, cable, orientation, or local fading. Reset the control to 5 and compare 900 mhz wavelength.
Explain Only external gain moves here. The other chapter fixtures remain fixed.
Check yourself
What should you do before trusting a moved-control result?
What does this small model leave out?
1. Start with the physical story
An external antenna can change two things at once. Its gain can concentrate reception toward the cell, and its new position can escape a pit, metal riser, or wall. A measured improvement contains both effects unless the test controls one of them.
2. Name every algebra move
Find wavelengthDivide wave speed by 900 MHz.
Undo dBiRaise ten to gain divided by ten to get linear gain.
Find apertureMultiply linear gain by wavelength squared, then divide by 4π.
Measure the totalSubtract −123 dBm from −100 dBm to get 23 dB.
Find the remainderSubtract the 5 dB antenna change from the 23 dB measurement.
3. Reproduce the chapter case
A0dBi = λ² / 4π = 0.008842 m²
G5dBi = 10^(5 / 10) = 3.1623
A5dBi = 3.1623 × 0.008842 = 0.02796 m²
−100 − (−123) = 23 dB measured
23 − 5 = 18 dB siting remainder = 78.26%
The antenna model can explain 5 dB. The larger 18 dB remainder needs a siting and obstruction explanation, followed by a controlled retest.
4. Try one real input
TryMove external antenna gain above and below 5 dBi. Watch the bounded antenna contribution change while the 23 dB field measurement stays fixed.
ObserveAt 5 dBi, aperture is 3.16 times the 0 dBi reference, but 18 of the measured 23 dB remain outside the antenna spec.
ExplaindBi enters a link budget directly. Any extra measured improvement must come from another changed variable, such as obstruction, cable, orientation, or local fading.
This is an attribution ledger, not proof that siting caused exactly 18 dB.
- Antenna
- 0 and 5 dBi are representative values; the installed pattern, efficiency, cable, matching, and orientation must be measured.
- Site
- The remainder can include obstruction clearance, multipath, time variation, network changes, and measurement uncertainty.
- Metric
- A stronger received signal does not by itself prove delivery, latency, energy, or recovery performance.
Correct, not complete: this ledger does not certify the antenna or explain the remainder without a controlled test.
5. Use the result in the design
Retest with the same antenna at both positions, then with both antennas at one position. That pair of comparisons separates siting from antenna choice more honestly than one combined swap.
6. Record the evidence state
Record antenna model and pattern, cable, mounting position, orientation, band, time, network state, signal metric, delivery and retry results, controlled variables, uncertainty, and the retest trigger.
7. Check yourself
Why can 5 dBi explain only 5 dB of the link change?
Does 18 dB prove that position alone caused the remainder?
Why record delivery and retries as well as signal?
This is an attribution ledger, not proof that siting caused exactly 18 dB.
- Antenna
- 0 and 5 dBi are representative values; the installed pattern, efficiency, cable, matching, and orientation must be measured.
- Site
- The remainder can include obstruction clearance, multipath, time variation, network changes, and measurement uncertainty.
- Metric
- A stronger received signal does not by itself prove delivery, latency, energy, or recovery performance.
Correct, not complete: this ledger does not certify the antenna or explain the remainder without a controlled test.