Difference between revisions of "Image Frequencies"
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An image is a false signal received on a frequency that does not actually exist due to poor receiver design. | An image is a false signal received on a frequency that does not actually exist due to poor receiver design. | ||
| − | For a detailed description of how and why this occurs see the article at | + | For a detailed description of how and why this occurs see the article at Electronics-Notes.com linked at the bottom of this page. |
| − | Many people can receive control channels, repeater outputs, etc. in the upper end of the 700 MHz band around 790-800 | + | Many people can receive control channels, repeater outputs, etc. in the upper end of the 700 MHz band around 790-800 MHz. These are images of 800 MHz stations. Whistler and Radio Shack scanners designed and formerly manufactured by GRE are particularly susceptible to 700 MHz images. See the forum thread [https://forums.radioreference.com/general-scanning-discussion/294449-gre-scanner-spurious-calculator.html GRE Scanner Spurious Calculator] for more information. |
Many older scanners used a dual conversion receiver with a 10.7 or 10.8 MHz IF. With these types of receivers images can be received at 21.4 or 21.6 MHz higher than the actual frequency. | Many older scanners used a dual conversion receiver with a 10.7 or 10.8 MHz IF. With these types of receivers images can be received at 21.4 or 21.6 MHz higher than the actual frequency. | ||
== 700 MHz == | == 700 MHz == | ||
| − | The 700 MHz band is split into two 30 MHz wide sections. Mobiles use a +30 MHz offset. | + | The upper 700 MHz land mobile band is split into two 30 MHz wide sections. Mobiles use a +30 MHz offset. |
| − | + | * 746-776 MHz - Base (repeater outputs, mobile talk-around) | |
| − | + | * 776-806 MHz - Mobile (repeater inputs) | |
See [[700 MHz Public Safety Band Plan]] for the list of channels available for use by public safety trunked systems. | See [[700 MHz Public Safety Band Plan]] for the list of channels available for use by public safety trunked systems. | ||
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== Links == | == Links == | ||
| − | *[ | + | *[https://www.electronics-notes.com/articles/radio/radio-receiver-selectivity/image-rejection-response.php Radio receiver image response and image rejection] |
| + | |||
| + | |||
| + | [[Category:Amateur Radio FAQ]] | ||
| + | [[Category:Scanners FAQ]] | ||
| + | [[Category:Aviation FAQ]] | ||
| + | [[Category:Military FAQ]] | ||
[[Category:RR Glossary]] | [[Category:RR Glossary]] | ||
| − | [[Category: | + | [[Category:Amateur Radio Glossary]] |
| + | [[Category:Aviation Glossary]] | ||
| + | [[Category:HF Glossary]] | ||
| + | [[Category:Military Glossary]] | ||
| + | [[Category:Receivers Glossary]] | ||
| + | [[Category:Scanners Glossary]] | ||
| + | [[Category:Signal Analysis and Decoding Glossary]] | ||
Latest revision as of 13:52, 24 August 2020
Images
An image is a false signal received on a frequency that does not actually exist due to poor receiver design.
For a detailed description of how and why this occurs see the article at Electronics-Notes.com linked at the bottom of this page.
Many people can receive control channels, repeater outputs, etc. in the upper end of the 700 MHz band around 790-800 MHz. These are images of 800 MHz stations. Whistler and Radio Shack scanners designed and formerly manufactured by GRE are particularly susceptible to 700 MHz images. See the forum thread GRE Scanner Spurious Calculator for more information.
Many older scanners used a dual conversion receiver with a 10.7 or 10.8 MHz IF. With these types of receivers images can be received at 21.4 or 21.6 MHz higher than the actual frequency.
700 MHz
The upper 700 MHz land mobile band is split into two 30 MHz wide sections. Mobiles use a +30 MHz offset.
- 746-776 MHz - Base (repeater outputs, mobile talk-around)
- 776-806 MHz - Mobile (repeater inputs)
See 700 MHz Public Safety Band Plan for the list of channels available for use by public safety trunked systems.
If you are receiving control channel data or repeater outputs in the 776-806 MHz range (in the US or Canada) you are receiving images.