Ciro Baby Loop — Fault Finder

1 — Siting & Height

Loop mounted outdoors in clear open space? Critical

Indoors or near walls prevents the system finding a valid SWR.

Loop between 1.5 m and 2.5 m above ground? Important

Too low and ground losses prevent a valid SWR.

4–5 m clearance from all metal structures? Critical

Guttering, fire escapes, railings, fences. 3 m is often not enough.

All persons 3 m+ away during tuning & TX?

ICNIRP: minimum 2.4 m compliance distance. Standing closer causes SWR shift and may exceed safe RF exposure limits.

No other antennas or overhead cables nearby?

Any parallel conductor affects the loop's resonance.

2 — Feedline

Coax completely straight — no coils at all? Critical

Coiled coax corrupts the noise bridge SWR readings entirely. Even a loose bundle causes failure.

Good quality 50 ohm coax? Important

Poor quality coax introduces mismatch the system cannot compensate for.

Antenna connector clean, dry, and fully seated? Important

A poor connection gives a wildly varying or open impedance reading.

Feedline kept away from the loop conductor?

Coax running parallel to the loop causes coupling.

3 — Controller & ATU Setup

Manual operation confirmed working? Verify first

Press 9 to open, 3 to close on the ATU keypad. If this fails, go to the Advanced tab and carry out Test 0 and the Direct Motor Test before drawing any conclusions.

First turn-on Auto Detect completed correctly? Critical

Must be run on first power-up to learn motor polarity and travel range.

Full setup re-run after any firmware reinstall? Important

Reflashing wipes all calibration. Auto Detect must be re-run from scratch.

Operating frequency within 6.6–29.8 MHz?

Outside this range a valid SWR can never be found.

Motor cable correct gauge for run length?

Up to 20 m: 2×0.75 mm · 20–30 m: 2×1.5 mm · Over 30 m: 2×2.5 mm

ATU supply confirmed at stable 24V DC?

Undervoltage causes erratic PIC behaviour and spurious errors.

🔍

Tick the boxes in the Checklist tab and your diagnosis will appear here automatically.

Equipment available?

Radio receiver connected to feedline 50 ohm dummy load Oscilloscope & RF tap Multimeter

Test 0 — Manual operation check

Equipment: None required

Press 9 on the ATU keypad — the loop should open (capacitor extends). Press 3 — the loop should close (capacitor retracts). Both directions should operate smoothly through the full travel range and stop cleanly at each end stop.

✓ Both directions work

Motor driver IC confirmed good. Motor, actuator, end stops, and driver IC are all working correctly. The fault lies entirely within the RF sensing chain.

✗ One or both directions fail

Manual operation has failed. Do not assume a motor driver IC fault yet — the motor itself may have failed. Scroll down to the Direct Motor Test below to determine whether the fault is in the motor/actuator or the ATU motor driver IC before drawing any conclusion.

✓ Both directions work ✗ One or both fail

⚡ Direct Motor Test

⚠ This test bypasses the ATU electronics entirely and connects a power supply directly to the motor at the antenna. Read all steps before starting.

Equipment needed: 12V DC supply · 1A inline fuse · Two short test leads

1

Disconnect the motor cable from the ATU controller completely at the ATU end.

Do not disconnect at the antenna end. The motor wires are the two-core cable running from the ATU to the antenna mast — not the coax feedline.

2

Fit a 1 amp inline fuse in series with the positive lead of your 12V supply.

This protects against shorts. Do not omit the fuse. A standard automotive blade fuse holder works well.

3

Connect the 12V supply (via the fuse) directly to the two motor wires — Polarity 1: Red to +12V, Black to −12V.

The motor should run and the loop should move in one direction. If the loop is already at an end stop in this direction it will not move — this is normal, not a fault.

4

Reverse the polarity — Red to −12V, Black to +12V.

The motor should now run in the opposite direction. If the loop is at the opposite end stop it will not move — again, this is normal end stop behaviour.

5

Observe and record the result below.

✓ Motor runs in one or both directions

Motor and linear actuator are mechanically confirmed good. The fault lies in the ATU controller — specifically the motor driver IC or its wiring. The ATU should be returned to the supplier for service.

✗ Motor does not run in either direction

Check the motor cable for continuity first. If the cable is confirmed good and the motor still does not respond to a direct 12V supply, the motor unit has failed. Remove the motor from the antenna at its hinge points and return the motor unit only to the supplier for service or replacement — the antenna itself does not need to be returned.

✓ Motor runs on direct supply ✗ Motor does not run

ML&S Martin Lynch & Sons — UK & Ireland Sole Distributor

ML&S are the sole UK and Ireland distributors for Ciro Mazzoni Loop antennas. All sales, support, and warranty returns for UK customers go through ML&S.

Baby Loop — Buy / Product Page

hamradio.co.uk — current pricing, options and ordering

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Midi Loop — Buy / Product Page

hamradio.co.uk — current pricing, options and ordering

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All Ciro Mazzoni Products

Full range — loops, cables, accessories and spare parts

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CI-1 Cable — Icom CI-V

Icom CI-V remote control cable for ATU 2.0 — 1.2 metres

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CI-3 Cable — Kenwood / Yaesu

RS-232 remote control cable for ATU 2.0

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CI-4 Cable — Elecraft KX2/KX3

USB data port remote control cable for ATU 2.0

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CI-5 Cable — FlexRadio

FlexRadio remote control cable for ATU 2.0

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Useful References

Ciro Mazzoni — Manufacturer

Official website and manual downloads

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ATU 2.0 Instruction Manual

ManualsLib — full Baby Loop manual

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In-depth User Review

Dr Scott Baker — detailed practical review

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Technical Test Report

WIMO / 5B4AIY — engineering analysis

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Community Reviews

eHam.net — operator experience reports

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Real-world Performance Notes

AJ Rushton — practical assessment

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DX Engineering — Product Page

Full specifications and replacement parts

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RSGB Band Plans 2026

Official UK amateur radio band plan — rsgb.org

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Install as App

To install this tool on your iPhone home screen:

1. Tap the Share button (box with arrow) in Safari
2. Scroll down and tap Add to Home Screen
3. Tap Add

The app will then work offline and open full screen like a native app.

Step 1 — Select your radio

Select your transceiver to see the exact cable, ATU mode, and radio menu settings required.

Yaesu — Modern

Icom

Kenwood

Yaesu — Legacy

Elecraft

FlexRadio

ELAD & Ten-Tec

ATU Keypad Frequency Reference

Full UK amateur band allocation per RSGB 2025 band plan. Green bands are covered by the Ciro Baby Loop (6.6–29.8 MHz). Tap a band to expand. Copy button enters the frequency directly onto your ATU keypad.

How to tune the ATU manually

1

Press / on the ATU keypad to enter manual mode.

The display will prompt you to enter a frequency.

2

Type the frequency using the numeric keypad.

Enter all digits as shown — e.g. 14200 for 14.200 MHz on 20m. Press ENTER to confirm.

3

The display will show the SWR reading.

The ATU is now ready for manual motor control.

4

Use the keypad to move the motor and tune the loop.

Fast movement: 9 open (fast) | 3 close (fast)
Slow movement: 8 open (slow) | 2 close (slow)
Inching: 7 open (inch) | 1 close (inch)

5

Tune for lowest SWR reading on the display before transmitting.

A correctly tuned Baby Loop should show 1.1:1 or better. Use inching (7/1) for fine adjustment near the minimum.

Auto tune mode

1

Hold down * on the ATU keypad to enter auto tune mode.

The display will prompt you to enter a frequency in kHz.

2

Type the desired frequency in kHz and press ENTER.

e.g. enter 14200 for 14.200 MHz. The ATU will begin automatic tuning immediately.

3

Wait for the ATU to complete tuning before transmitting.

The loop will move automatically until the best SWR is found. Do not transmit until tuning is complete and the SWR reading is stable.

⚠ Important safety warnings

🚫 Do not transmit while the ATU controller is tuning. Transmitting during a tuning cycle will damage the ATU and may damage the radio.

🚫 Maximum 200 watts through the ATU controller. Exceeding 200W will damage the controller. Always confirm the ATU has finished tuning before applying any power.