UHF RFID Calculation for Laundry: Zebra FX9600 + Brady XA20

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Laboratory · Read Range Calculation

Friis model calculation for laundry / textile environments. Three scenarios: dry fabric, wet fabric, dense stack. FCC limit compliance and 6 m cable loss included.

Reader

Zebra FX9600

US FCC · 31.5 dBm · 4-port

Antenna

Brady XA20

9 dBi · circular polarisation

Tag

GAORFID Laundry Tag

−18 dBm · IP68 · Textile

Standard

FCC Part 15

915 MHz · EIRP 4 W max

01 · Link Budget 

Input Parameters & FCC Limit

Parameter	Value	Notes
Frequency	915 MHz	FCC US band centre
Wavelength (λ)	0.328 m	λ = c / f
TX Power (Zebra FX9600)	31.5 dBm	Before FCC adjustment
Cable loss (6 m LMR-195)	−2.7 dB	@ 915 MHz
Power at antenna input	28.8 dBm	After cable
Antenna gain (Brady XA20)	9 dBi	Circular polarisation
Calculated EIRP	37.8 dBm	Exceeds FCC limit
FCC EIRP limit	36.0 dBm (4 W)	Part 15.247
TX Power (adjusted)	29.7 dBm	FCC compliant
Polarisation loss (CP→random)	3 dB	Circular→random tag orientation
Tag antenna gain	1 dBi	GAORFID Laundry Tag
Tag chip sensitivity	−18 dBm	GAORFID datasheet
Available link budget	34 dB	After all losses
Max allowable path loss	52 dB	To sensitivity threshold

⚠️ FCC LIMIT: calculated EIRP 37.8 dBm exceeds the 36.0 dBm limit. TX power reduced from 31.5 to 29.7 dBm.

02 · R_max Results 

Read Range — Three Scenarios

Scenario 1 · Dry Fabric

~4.6^m

Practical: ~2.9 m

Mismatch loss: 2 dB
Link budget: 50 dB

Scenario 2 · Wet Fabric

~1.5^m

Practical: ~0.9 m

Mismatch loss: 7 dB
Link budget: 40 dB

Scenario 3 · Dense Stack

~0.8^m

Practical: ~0.5 m

Mismatch loss: 12 dB
Link budget: 35 dB

⚡ Key finding: humidity is the primary enemy of RFID in laundry environments. Wet fabric losses (10–18 dB) far exceed cable losses (2.7 dB). The only reliable read point is after the dryer, BEFORE packaging.

Model limitationFriis equation does not account for multipath from metal drums (±15 dB), electromagnetic noise from washing machines (20–50 MHz), or non-uniform fabric moisture distribution. All values are theoretical upper bounds. Test with 1000+ real tags before deployment.

03 · Mismatch Loss 

Humidity & Substrate Effect

Fabric condition	ε_r	tan δ	Mismatch Loss	Resonance shift
Air (baseline)	1.0	0	0 dB	0 MHz
Dry fabric	1.5–2.0	0.05	2–3 dB	−15 MHz
Wet fabric	5–10	0.3–0.5	7–10 dB	−50 MHz
Soaking wet	15–25	0.6–0.8	12–18 dB	−100 MHz
Dense stack 50+ pcs	N/A	N/A	10–15 dB	N/A (shadowing)

04 · Cable vs Direct 

6 m LMR-195 Cable vs Direct Connection

Cable length	Loss @ 915 MHz	R_max (dry)	Coverage area loss
0 m (direct)	0 dB	4.85 m	baseline
3 m	−1.4 dB	4.57 m	−7%
6 m	−2.7 dB	4.57 m	−14%
10 m	−4.5 dB	3.85 m	−22%

05 · Laundry Conditions 

Laundry-Specific Critical Factors

Factor	Impact	Mitigation
Humidity (RH 60–90%)	+5–10 dB loss	Dry before reading
Temperature (60–90°C)	drift ±2 dB	Heat-resistant tags
Washing machine EM noise	20–50 MHz noise	Filtering, shielding
Metal drums	multipath ±15 dB	Antenna positioning
Water in fabric	+10–18 dB loss	Read AFTER drying
Detergent chemicals	tag degradation	IP68+ encapsulation
Mechanical stress	antenna damage	Flexible inlays

✓ Best practices for laundry:

✓ Read DRY linen — after dryer, before packaging
✓ Circular polarisation antenna for random tag orientation
✓ Cable no longer than 3 m (LMR-400 preferred over LMR-195)
✓ Antennas in zone with RH < 50%, T < 40°C
✓ Air-gap IP68 tags
✓ Test 1000+ tags in real conditions before go-live

✗ Avoid:

✗ Reading wet laundry — up to 90% signal loss
✗ Dense stacks > 30 cm without separation
✗ Cables > 10 m without amplifiers
✗ Antennas next to metal drums
✗ Tags without IP68 in wash zone

06 · Recommendation 

Engineering Summary

Metric	Value	Notes
R_max (dry, theoretical)	4.6 m	Ideal conditions
R_max (dry, practical)	2.9 m	With 8 dB reliability margin
R_max (wet, practical)	0.9 m	Only close to antenna
R_max (dense stack, practical)	0.5 m	Separation required
Cable loss (6 m)	2.7 dB	−14% coverage area
Humidity loss	7–18 dB	Critical factor
Expected read rate (dry)	95–98%	After dryer
Expected read rate (wet)	60–80%	Undesirable zone

Final recommendationDesign the read point BEFORE packaging (after dryer). Expected read rate: 95–98% dry, 60–80% wet. Use 2–4 antennas to cover the conveyor. Minimise cable length.

07 · FAQ

Frequently Asked Questions

Why should wet laundry not be read?

Water (ε_r ≈ 80) causes heavy dielectric loading on the tag antenna: resonance shifts from 915 MHz to 850–870 MHz, VSWR degrades from 1.5 to 3.0+, losses reach 10–18 dB. Practical range drops from 2.9 m to 0.9 m.

Why does a 6 m cable reduce performance?

LMR-195 cable at 6 m introduces 2.7 dB loss at 915 MHz. This reduces power headroom and shrinks coverage area by approximately 22%. When reading wet laundry, the system operates at the edge of sensitivity.

How should a read point be set up in a laundry?

Optimal location is after the dryer, before packaging. Humidity in the read zone should be below 50%. Cable length should not exceed 3 m. Use air-gap IP68 tags. Expected read rate: 95–98% for dry linen.

rfid.org.ua · Laboratory · 2026-02-27Model: Friis · FCC Part 15

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