The Poor Man's Antenna Analyser for Ham Radio Operators

VIDEO

Getting an antenna to resonate correctly doesn't require an expensive antenna analyser. With a bit of method and a simple VSWR meter you can tune dipoles, end-fed half-waves and many mobile whips to the part of the band you want to use. This guide explains a reliable, low-cost way to find the resonant point of an antenna and how to interpret what the meter tells you.

• A transceiver capable of producing a steady carrier (AM mode is convenient).
•  A VSWR meter (cross-needle types work well; budget meters such as the Moonrakaker SWR20 are perfectly adequate).
•  Coax and connectors in good condition.
•  A line isolator (ferrite choke) to reduce common-mode currents and improve measurement accuracy.
• Paper, pen and a simple graph to record VSWR versus frequency (or a spreadsheet if you prefer).

Cross-needle VSWR meters display forward power on one arc and reflected power on the other. The VSWR reading is indicated where the angled bars or needles cross. When you sweep frequency and note VSWR at each step, the resonant frequency is where the VSWR bottoms out (the minimum point).

1. Set up the radio. Switch to AM mode and select low power (around 4–5 watts is fine). Make sure the frequency is clear and produce a steady carrier.
2. Prepare your graph. Draw a horizontal axis for frequency (for example the 80 m band: 3.5, 3.6, 3.7, 3.8 MHz) and a vertical axis for VSWR (1:1, 1.5:1, 2:1, 3:1).
3. Take readings every step. Key the transmitter at each 100 kHz step (or suitable increments for the band) and write down the VSWR reading on your graph.
4. Plot and join the dots. Connect your points to reveal the VSWR curve. The lowest point is the resonant frequency.
5. Interpret the curve and adjust the antenna: 
   • If the minimum VSWR is to the left (lower frequency) of the desired operating range, the antenna is too long — shorten it.
   • If the minimum is to the right (higher frequency), the antenna is too short — lengthen it.
   • Make small changes and repeat the measurements; do not cut large amounts at once.

• Example 1: The VSWR curve falls steadily toward the lower frequencies. The resonant minimum is below the band edge, so the antenna is too long. Trim a little, re-measure and repeat.
• Example 2: After trimming, the curve now shows the minimum near the top of the band. That means the antenna was cut a little too short. The solution is to restore length if possible or adjust the feed/matching to shift resonance back to the desired spot. The key lesson: adjust in small increments and re-check.
• Example 3: If readings across the band are erratic and give no clear minimum — a jagged high VSWR curve — that is an indicator of a problem. Either the antenna is grossly wrong for the intended band or there is a mechanical/connector/coax fault. Always measure twice before cutting and check connectors and coax if the curve looks nonsensical.

• Works best for antennas with definite resonances: half-wave dipoles, end-fed half-waves and mono-band mobile whips.
• Mobile HF whips and helical mono-band whips tune well with this method, but remember they are often narrowband so expect a small tuning window.
• Does not work reliably with random wire antennas or other non-resonant configurations. Random wires rarely show a low, well-defined VSWR across a band.

•  Use a ferrite line isolator. Pass the coax through a ferrite core with several turns (five to eight turns is typical). This reduces common-mode currents that can distort VSWR readings.
•  Check connectors and coax. Dirty or loose connectors and damaged coax give misleading VSWR graphs. A messy curve often points to a connection or cable fault.
• Keep records. Save your graphs for each band and antenna. Over time they become a valuable reference and can help diagnose changes in performance.
•  Adjust slowly. Small incremental changes are safer than large cuts. You can always trim more but you cannot put back what you’ve cut.

A simple VSWR meter and a bit of patience will get you on frequency and make many antennas usable without expensive test equipment. An antenna analyser provides finer detail and faster diagnosis, but for newcomers or budget-conscious operators the VSWR-graphing technique gives clear, practical results. Use logic, measure carefully, and keep notes — you’ll be surprised how much you can learn about an antenna from a few plotted points.