Class 1 licence, cross-border interference and the 2 m band
You hold an Austrian Class 1 (CEPT HAREC) licence and are operating a 2 m FM station from a hillside site near the Slovenian border. Power at the antenna is 50 W into a 3-element Yagi aimed east. A listener in Slovenia reports that your signal is blocking a local repeater on an adjacent channel, and a second station 40 km away in Austria says your audio is distorted only when you use the high-power setting. Your transmitter's harmonic output is not specified in the manual. You can reduce power, change antenna direction, or add a low-pass filter. The local repeater input frequency is close to your transmit frequency.
1. How should you decide the order in which to apply remedies, and what regulatory principle governs the cross-border complaint?
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First separate the two symptoms. Distorted audio only at high power suggests the transmitter is being overdriven or the power supply is sagging, not a propagation problem; the harmonic and intermodulation products rise faster than the fundamental when a stage saturates. That is the first thing to check, because a clean 50 W signal is both legal and less likely to cause adjacent-channel trouble than a dirty one.
Regulatorily, the governing principle is that you must not cause harmful interference to other services and must accept interference from stations you are not entitled to protect. Cross-border complaints are handled between administrations, but as the operator you are expected to take reasonable steps: reduce power, use the minimum power necessary, and if the complaint persists, change antenna direction or add filtering. You should log times, frequencies, power and the complainant's details, and report through your national society or regulator rather than negotiating directly.
Practical order: (1) verify power supply and drive level, (2) insert a low-pass filter and re-measure, (3) reduce power to the minimum that maintains the contact, (4) reorient the beam away from the border if the complaint is genuine and repeatable. Do not simply ignore a foreign complaint; document and act.
2. The listener's repeater input is close to your transmit frequency. Explain why this matters and whether a filter at your end can fix it.
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If the repeater input is close to your transmit frequency, the problem is not harmonic radiation but receiver desensitisation or blocking at the repeater site: your strong signal arrives in or near the passband the repeater is trying to listen on, and the repeater's front end is overloaded. A low-pass filter at your transmitter removes harmonics but cannot remove energy at your fundamental, which is exactly the energy causing the trouble.
The effective remedies are therefore geometric and power-based: reduce ERP, change antenna direction so the beam null points toward the repeater, increase separation, or use a narrower mode. You could also check whether the repeater's own filtering and receiver selectivity are adequate, though that is the repeater keeper's responsibility.
The key judgement is recognising that 'my signal is clean' does not settle the matter. A perfectly clean signal can still block a nearby receiver if it is strong enough. The exam expects you to distinguish spurious emission (your fault, filterable) from blocking and desensitisation (a system-level problem, fixed by power, distance and antenna pattern).
3. What measurements would you make to prove your station is compliant before responding to the regulator?
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You would measure, at the antenna port into a dummy load: carrier power, harmonic levels up to at least the third harmonic and ideally to 1 GHz, and any spurious products. A spectrum analyser with a suitable attenuator and a calibrated power meter is the tool; a receiver with an S-meter is not adequate for a compliance claim.
Record the measurement setup, attenuator values, analyser settings and the resulting dBc figures, plus the date and the station configuration. Compare against the limits in your licence: spurious and harmonic emissions must be attenuated by the prescribed amount below the fundamental, and the transmitter must stay within its permitted bandwidth.
Also measure the DC supply voltage and current at full power to check for sag, and listen to your own signal on a separate receiver with an attenuator to confirm the audio distortion. If the harmonic suppression is marginal, fit a commercial low-pass filter and repeat the measurement. A dated, reproducible record with the instrument identified is far more persuasive than an assertion that the rig is 'factory compliant'.