Quick Reference SheetRF, Radar & Communications
RF Units and dB Conversion Cheat Sheet
A denser offline guide to dB, dBm, watts, power ratios, and the conversion habits that make RF budgeting less error-prone.
Printable PDFOpen download
Revision GuideRF, Radar & Communications
Free-Space Path Loss and Link Budget Revision Pack
A stronger revision pack for free-space path loss, received power, link accounting, and the practical dB habits that turn path numbers into usable RF planning decisions.
Filename: free-space-path-loss-and-link-budget-revision-pack.pdfFile size: 4 KB
Formula highlights
FSPL
FSPL(dB) = 20 log10(d) + 20 log10(f) + constant
Budget pattern
received power = transmit power + gains - losses
What this pack covers
This pack ties together free-space path loss, received power, fade margin, and hardware losses so the propagation and system sides of a link can be read as one story.
Core formulas
- FSPL(dB) = 32.44 + 20log10(dkm) + 20log10(fMHz)
- Pr = Pt + Gt + Gr - FSPL
- Received power = source terms + gains - all losses
- Fade margin = received power - receiver threshold
How to read the dB bookkeeping
- Path loss is a propagation term, not a cable term.
- Antenna gain, feeder loss, and connector loss should each stay visible as separate budget terms.
- A positive-looking budget is not the same thing as comfortable margin.
Worked example: first-pass path loss
A 2.4 GHz link over 5 km has free-space loss of roughly 114 dB. That is a normal RF-scale number and only becomes meaningful when combined with the rest of the system terms.
Worked example: budget and margin
A 20 dBm transmitter, 18 dBi antennas at each end, and 114 dB path loss give a first-pass received power near -58 to -60 dBm depending on the implementation losses included. Comparing that result against receiver threshold reveals the useful margin.
Common mistakes
- Mixing units and constants in the path-loss formula.
- Hiding cable or connector losses inside the propagation term.
- Comparing received power against the wrong threshold or data mode.
- Ignoring fade margin when deciding whether the link is robust.
Best offline use
Use this pack for quick RF planning, revision, and sanity checks before moving into detailed deployment assumptions or site-specific propagation modelling.
Related calculators
Use the formulas in live tools.
Free-Space Path Loss Calculator
Estimate the line-of-sight path loss between two points from the distance and frequency you enter.
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Coax Loss Calculator
Use the Coax Loss Calculator for quick coax loss estimates in RF, radar, and communications work.
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Link Budget Calculator
Combine transmitter power, antenna gains, path loss, and miscellaneous losses to estimate received power.
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Friis Received Power Calculator
Estimate received power from transmitter power, antenna gains, distance, and frequency using the free-space Friis relationship.
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More downloads
Continue the topic cluster.
Guide cluster
Related reading around the same topic.
RF, Radar & CommunicationsFlagship guide
Propagation and Path Loss
A practical guide to free-space path loss, wavelength-aware intuition, and feedline loss, built to explain what the loss figure really means before you roll it into a larger RF or microwave link budget.
Students, RF engineers, and communications practitioners who want path-loss numbers to mean something physically instead of living as isolated calculator outputs.Read guide
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Link Budgets and Received Power
A practical guide to RF link budgets and received power that treats every gain and loss term as an accounting decision, making it easier to see whether a link is viable and where the margin is being won or lost.
RF, microwave, and communications users who need link-budget calculations to support planning decisions rather than sitting as disconnected dB sums.Read guide