AVOIDING IMAGE FREQUENCIES

You might discover one of your regular stations on another frequency that is not listed. It might be what is known as an image frequency. For example, you might find a service that regularly uses a frequency of 431.875 also on 474.675.

To see if it is an image, do a little math.

 

Note the new frequency.

474.675

Double the intermediate frequency of 21.4 MHz

 

(42.8)

 

and subtract it from the new frequency.

–42.8

If the answer is the regular frequency,

431.875

then you have tuned to an image.

 

Occasionally you might get interference on a weak or distant channel from a strong broadcast 42.8 MHz below the tuned frequency. This is rare, and the image signal is usually cleared whenever there is a broadcast on the actual frequency.

FREQUENCY CONVERSION

The tuning location of a station can be expressed in frequency (kHz or MHz) or in wavelength (meters). The following information can help you make the necessary conversions.

1 MHz (million) = 1,000 kHz (thousand)

To convert MHz to kHz, multiply by 1,000:

9.62MHz × 1000 = 9620 kHz

To convert from kHz to MHz, divide by 1,000.

2780 kHz ÷ 1000 = 2.780 MHz

To convert MHz to meters, divide 300 by the number of megahertz.

300 ÷ 7.1 MHz = 42.25 meters

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Radio Shack Pro-71 owner manual Avoiding Image Frequencies, Frequency Conversion
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Pro-71 specifications

The Radio Shack Pro-71 is a compact and versatile handheld scanner that remains a favored choice for enthusiasts of radio communication. Designed for ease of use, the Pro-71 offers a variety of features that cater to both casual listeners and dedicated hobbyists. One of its standout characteristics is its impressive frequency coverage. The radio can receive a wide range of frequencies, from VHF and UHF bands to public safety channels, aircraft communications, and even some amateur radio bands. This extensive range adds to the versatility of the device, allowing users to explore countless transmissions.

Equipped with 300 memory channels, the Pro-71 enables users to store and quickly access their favorite frequencies. This feature greatly enhances convenience, particularly for those who frequently monitor specific channels. Additionally, the scanner includes a priority channel option, enabling users to monitor a specific channel while scanning through others. This ensures that important communications do not go unnoticed, especially during critical monitoring sessions.

One significant technology featured in the Pro-71 is its autofrequency search capability. This allows users to scan through the radio waves automatically, quickly identifying active frequencies without the need for manual input. The ease of operation is complemented by a backlit display, which ensures visibility of information even in low-light environments. This thoughtful design allows users to adjust to their scanning needs regardless of the conditions.

Furthermore, the Pro-71 offers a range of scanning modes, including single, memory, and auto store scan modes. This flexibility enhances the listening experience, as users can select the mode that best suits their monitoring requirements. The built-in keypad allows for intuitive operation, and the robust speaker delivers clear audio, ensuring that users can easily discern communication.

Durability plays a significant role in the design of the Pro-71, making it suitable for both indoor and outdoor use. Its compact size and lightweight construction enable easy transport, making it an ideal companion for travel, outdoor events, or emergency preparedness.

Overall, the Radio Shack Pro-71 delivers a powerful combination of features, technologies, and characteristics appealing to both novice and seasoned users. Its flexibility, wide frequency coverage, and user-friendly design continue to make it a trusted tool in the world of radio monitoring.
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