Try another channel; the problem may be due to a transmission fault. Ensure that the antenna is installed correctly (away from high buildings or other (metal) obstacles) and is providing a good signal level and a good quality signal. Picture quality may be temporarily affected by bad weather (heavy rain, snow).
Check the signal level coming from your antenna. If you have poor signal strength you should consult your installer as you may need to repair or upgrade your system to gain a stronger signal. You should ask your installer to check the antenna for damage as moisture inside it will affect signal strength and quality.
Check that the antenna input cables are connected properly. We always recommend that your consult a professional installation engineer for any issues connected with antenna system set-up.
Please see the CM-7500 FAQ, 'How do I check the Signal Strength/Signal Quality on my CM-7500 DVR+'.
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