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dual versus...

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Old 11-08-2005, 09:10 PM
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bil2
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Default dual versus...

1)What the heck is the diff between a dual conversion receiver and a single? 2) Is a single the same thing as a narrow band? 3)if not, what's the diff? 4)Which one do I need for just reg electric 3 or 4 channel electro-flight? Thank you very, very much. Bil
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Old 11-08-2005, 09:28 PM
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Default RE: dual versus...

dual conversion receivers take the transmitted frequency and convert into an intermediate frequency and finally into the final signal (simplistic view). this gives the receiver two chances to eliminate noise. Generally dual conversion is considered "better" than single conversion. However, many very good receivers are single conversion. most of the JR receivers are single conversion, but they use alternative technologies to reject interference. They are as good or better than many dual conversion receivers.

Narrow band refers to the receiver being to distinguish the signal within a narrow range (say 20 hHz). this can be accomplished with either dual or single. For your application, almost any standard narrow band receiver will work OK.
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Old 11-09-2005, 10:35 AM
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Default RE: dual versus...

Thank you. One less thing to think about!
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Old 11-09-2005, 03:19 PM
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Default RE: dual versus...

To be a little bit more accurate......

The main problems facing receivers are Co-Channel Interference, 3rd Order InterModulation, and Image rejection. Most of these can be minimised by careful front end design and expensive filtering. By compromising with decent design and cheaper filters the main problem is then Image rejection.

JR Single conversion receivers use a crystal running 455kHz below the channel frequency. This is fed to the amplified incoming RF and fed to a mixer. This mixer adds and subtracts the 2 frequencies and the resultant output is fed to a filter. This filter is centered at 455 kHz and passes this 455 KHz signal onwards for processing to the demodulator and decoder.

All well and good but if we get a situation where another transmitter is running at 2 x the IF ( 910 kHz ) this will also be accepted and ............... down goes your aircraft. ( Worse case scenario ! )


This is the image problem.



With Dual Conversion, an extra stage of frequency conversion is implemented. This time the crystal frequency is 10.7 MHz below the channel frequency. Again this is fed to a mixer and the resultant outputs are fed to a filter centered on 10.7 MHz. This is then mixed with a 11.155 MHz crystal, filtered at 455kHz and fed on to the demodulator and decoder.

This time the interference signal would need to be 21.4 MHz away which is going to be extremely unlikely.

This way, it resolves the image problem without costing too much extra over and above the Single conversion receiver.

I hope this explains the main difference between the 2 types, there are many websites that explain in greater detail.
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