Compare coax cable attenuation at the operating frequency and on the same length basis before choosing a cable size. For standard Times Microwave LMR-240, LMR-400, and LMR-600, the published typical attenuation at 900 MHz is 7.6, 3.9, and 2.5 dB per 100 ft, respectively. LMR-600 has the lowest cable loss of these three, but its larger diameter and bend-radius requirements can affect routing and termination choices.
The reference tables below identify the exact cable models, manufacturer-published attenuation, construction, and mechanical specifications. Use them to shortlist feeder cables, then calculate loss for the actual installed length and account for the other components between the equipment port and antenna connection.
Coax Cable Attenuation by Frequency
These values apply to standard 50-ohm LMR-240, LMR-400, and LMR-600 cable—not automatically to UltraFlex, plenum, 75-ohm, or other similarly named variants. The individual manufacturer data sheets label attenuation as typical, with VSWR = 1.0 and ambient temperature of +25°C (77°F). They are reference values under those conditions, not guaranteed maximum losses for a completed installation.
Each cell lists dB/100 ft followed by dB/100 m.
| Frequency, MHz | LMR-240, dB/100 ft / dB/100 m | LMR-400, dB/100 ft / dB/100 m | LMR-600, dB/100 ft / dB/100 m |
|---|---|---|---|
| 30 | 1.3 / 4.4 | 0.7 / 2.2 | 0.4 / 1.4 |
| 50 | 1.7 / 5.7 | 0.9 / 2.9 | 0.5 / 1.8 |
| 150 | 3.0 / 9.9 | 1.5 / 5.0 | 1.0 / 3.2 |
| 220 | 3.7 / 12.0 | 1.9 / 6.1 | 1.2 / 3.9 |
| 450 | 5.3 / 17.3 | 2.7 / 8.9 | 1.7 / 5.6 |
| 900 | 7.6 / 24.8 | 3.9 / 12.8 | 2.5 / 8.2 |
| 1,500 | 9.9 / 32.4 | 5.1 / 16.8 | 3.3 / 10.9 |
| 1,800 | 10.9 / 35.6 | 5.7 / 18.6 | 3.7 / 12.1 |
| 2,000 | 11.5 / 37.7 | 6.0 / 19.6 | 3.9 / 12.8 |
| 2,500 | 12.9 / 42.4 | 6.8 / 22.2 | 4.4 / 14.5 |
| 5,800 | 20.4 / 66.8 | 10.8 / 35.5 | 7.3 / 23.8 |
| 8,000 | 24.3 / 79.7 | 13.0 / 42.7 | 8.8 / 29.0 |
Sources: Times Microwave Systems LMR-240 data sheet, printed page 19; LMR-400 data sheet, printed page 25; and LMR-600 data sheet, printed page 33. Both unit columns reproduce the manufacturer’s published values rather than converting one rounded column into the other.
Choose the frequency before comparing cable sizes
Read across a frequency row to compare models. Read down a model column to see how its attenuation changes with frequency. In these published tables, attenuation increases with frequency, so a loss value taken at a lower frequency can understate the loss at the intended operating frequency.
For a frequency between table entries:
- Obtain the manufacturer’s frequency-specific calculation or attenuation curve for the exact model when the result is close to a loss limit.
- For preliminary screening within the tabulated range, the next higher listed frequency provides a higher typical attenuation value for these models. Label that choice as a screening assumption, not an exact-frequency result.
- Do not extrapolate beyond the published data or treat the last table entry as proof of the usable frequency range of every connector or completed cable assembly.
For example, the 2,500 MHz row can serve as a higher-frequency screening value for a 2,400 MHz application. It should not be relabeled as manufacturer data measured or calculated at 2,400 MHz.
Cable Dimensions, Construction, and Bend Radii
Lower attenuation is only one part of the comparison. Cable diameter and permitted bending affect cabinet entries, routing space, service loops, and the transition to equipment connectors.
| Specification | LMR-240 | LMR-400 | LMR-600 |
|---|---|---|---|
| Nominal impedance | 50 Ω | 50 Ω | 50 Ω |
| Outside diameter | 0.240 in. / 6.10 mm | 0.405 in. / 10.29 mm | 0.590 in. / 14.99 mm |
| Center conductor | Solid bare copper | Solid bare copper-clad aluminum | Solid bare copper-clad aluminum |
| Dielectric | Foam polyethylene | Foam polyethylene | Foam polyethylene |
| Outer conductor and braid | Aluminum tape and tinned-copper braid | Aluminum tape and tinned-copper braid | Aluminum tape and tinned-copper braid |
| Standard base-model jacket | Black polyethylene, outdoor | Black polyethylene, outdoor | Black polyethylene, outdoor |
| Installation bend radius | 0.75 in. / 19.1 mm | 1.00 in. / 25.4 mm | 1.50 in. / 38.1 mm |
| Repeated bend radius | 2.5 in. / 63.5 mm | 4.0 in. / 101.6 mm | 6.0 in. / 152.4 mm |
Sources: manufacturer construction, electrical, and mechanical specifications on printed pages 18, 24, and 32 of the respective data sheets. Jacket descriptions refer to the base part numbers LMR-240, LMR-400, and LMR-600.
The listed bending dimensions are radii, not loop diameters. Keep the manufacturer’s “installation” and “repeated” categories separate: the smaller installation value is not the repeated-bending allowance. Check the selected connector’s installation instructions and required clearance as well; cable bend radius alone does not establish the space needed behind an equipment port.
Match the complete part number
A cable family name does not identify every installation property. Times Microwave distinguishes standard outdoor polyethylene-jacket cable from watertight, fire-retardant, plenum, and UltraFlex constructions. Its brochure describes UltraFlex as using a stranded center conductor and thermoplastic rubber jacket. Do not transfer the construction, attenuation, or installation rating of one variant to another without its matching data sheet.
An outdoor jacket designation is not a plenum rating. Confirm the exact product listing required for the cable route rather than selecting from attenuation alone. For applications requiring low passive intermodulation, also note that Times Microwave explicitly states that standard LMR construction is not suitable for low-PIM applications.
Calculate Loss for the Installed Cable Length
Use the attenuation value at the selected frequency and multiply it by the installed cable length on the same unit basis:
where:
- (L_{\text{cable}}) is cable-only attenuation in dB.
- (\alpha_{100}) is attenuation in dB/100 ft or dB/100 m.
- (\ell) is cable length in feet or meters, matching the attenuation unit.
Use the cable length between terminations, including service loops and routing allowances—not just the straight-line distance between equipment and antenna. This calculation scales the manufacturer’s typical attenuation to length; it does not introduce an allowance for different temperatures, termination quality, damage, or mismatch.
If unit conversion is necessary:
=
\alpha_{\text{dB/100 ft}}\frac{100}{30.48}
The published feet and meter columns are rounded separately. For consistency, use one published column throughout a comparison instead of switching between a converted rounded value and a separately published value.
Add component loss without double counting
For a preliminary matched-system estimate, add the insertion losses of the components in the same signal path:
=
L_{\text{cable}}
+
\sum L_{\text{components}}
Here, (L_{\text{feed}}) is the estimated loss between the chosen equipment and antenna reference points. Component losses may include connectors, adapters, jumpers, and an RF surge protector. Use frequency-specific data for the actual parts.
Keep these boundaries explicit:
- If an assembly insertion-loss specification already includes its connectors, do not add those connector losses again.
- If a measured end-to-end insertion loss already includes the cable and accessories, do not add the cable-table estimate to it.
- Keep a planning margin separate from estimated physical loss.
- A scalar sum of insertion losses does not calculate the full behavior of a significantly mismatched system.
The manufacturer’s cable attenuation conditions specify VSWR = 1.0. Consequently, the tabulated cable loss is not a calculation of additional effects caused by mismatched equipment, connectors, or antennas.
Worked Comparison: A 30-Meter Feeder at 2,500 MHz
Assume the following planning inputs:
| Input | Value and basis |
|---|---|
| Frequency | 2,500 MHz, a published table frequency |
| Installed cable length | 30 m, assumed for this example |
| Combined accessory insertion loss | 0.60 dB, illustrative assumption |
| Additional planning margin | 0.50 dB, illustrative assumption |
| Allowed loss allocation, including margin | 6.00 dB, illustrative project requirement |
| Cable attenuation basis | Manufacturer’s typical dB/100 m values at +25°C and VSWR = 1.0 |
The accessory allowance is not a manufacturer specification or a recommended universal value. Replace it with data for the selected connectors, adapters, jumpers, and protective devices. The cable rates are 42.4, 22.2, and 14.5 dB/100 m for LMR-240, LMR-400, and LMR-600, respectively.
For LMR-400:
Applying the same method to all three models gives:
| Cable | Cable-only loss | Estimated feed loss, including accessories | Screening total, including margin | Comparison with 6.00 dB allocation |
|---|---|---|---|---|
| LMR-240 | 12.72 dB | 13.32 dB | 13.82 dB | Above allocation |
| LMR-400 | 6.66 dB | 7.26 dB | 7.76 dB | Above allocation |
| LMR-600 | 4.35 dB | 4.95 dB | 5.45 dB | Below allocation under stated assumptions |
LMR-600 is the only one of these three candidates below the assumed allocation. Its calculated headroom is 0.55 dB after the illustrative margin. Because the calculation uses typical cable attenuation and assumed accessory losses, it supports a preliminary shortlist—not a guaranteed installed loss limit.
Convert loss to transmitted power
For the same matched-system estimate:
=
10^{-L_{\text{feed}}/10}
The LMR-600 example has an estimated physical feed loss of 4.95 dB:
Approximately 32% of the input power reaches the output reference point under the stated assumptions. Do not include the separate 0.50 dB planning margin in this physical power-transfer calculation: it is reserved headroom, not an identified dissipative component.
Estimate the Length Allowed by a Loss Budget
The same model can screen the maximum cable length:
=
100\frac{B-C-M}{\alpha_{100}}
where:
- (B) is the allowed loss allocation in dB.
- (C) is the estimated combined accessory loss in dB.
- (M) is the separately reserved margin in dB.
- (\alpha_{100}) is cable attenuation in dB per 100 length units.
- (\ell_{\max}) is in the corresponding length unit.
The numerator must be positive. If (B-C-M\leq0), the accessories and reserved margin leave no positive cable-loss allowance.
Using the preceding 2,500 MHz assumptions leaves:
The calculated screening lengths are approximately 11.6 m for LMR-240, 22.1 m for LMR-400, and 33.8 m for LMR-600. These are mathematical planning limits based on the published typical attenuation—not guaranteed allowable installed lengths. A proposed run near one of these values needs better-defined cable performance and accessory data rather than a pass decision based on rounded results.
Specifications to Check Before Ordering
After screening by attenuation and length, resolve the requirements that the loss table cannot determine:
- Route and handling: Check outside diameter, the applicable bend radius, connector clearance, and whether the cable will experience repeated movement.
- Environment and jacket: Select the exact construction and listing required by the outdoor, indoor, wet, riser, or plenum route.
- Connectors and assemblies: Confirm cable compatibility, interface, frequency performance, and whether quoted insertion loss includes the terminations.
- RF power: Check the manufacturer’s power rating at the operating frequency and under the applicable thermal conditions. The cited data sheets use different conditions for average-power ratings than for attenuation: +40°C ambient, 100°C inner conductor, sea level, dry air, atmospheric pressure, no solar loading, and VSWR = 1.0. The +25°C attenuation table alone does not establish power-handling suitability.
- PIM requirements: Use a construction specifically supported for the required application rather than inferring low-PIM performance from low attenuation.
For procurement, record the complete manufacturer part number, frequency, installed length, attenuation basis, accessory loss, and reserved margin together. That makes the shortlist traceable without treating a nominal cable size as a complete specification.