Kenwood TS-480 manual FM circuit, FM modulation block diagram

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FM circuit

There were two approaches used for the FM circuit of the conventional all-mode transceiver. Either there was a dedicated modulation circuit using a 10.695MHz crystal, or the modulation was performed by the VCO on the 2nd OSC. The latter was not an option for the TS-480, and since the whole transceiver had to be compact, we did not adopt the former approach. How then is FM handled by the TS-480?

What we have employed for the TS-480 is something that is rarely seen these days in ham radios: the reactance modulation approach, which does not have the modulation applied directly to the oscillating circuit. This type of circuit was widely used in the days when a crystal was used to change channels in FM car transceivers, but it dropped from sight when PLL became the norm. It is not a new circuit, but it has excellent characteristics. In the TS-480, this reactance modulation circuit is connected to the output of the DDS, which serves as the source for the PLL reference frequency, so effectively it is modulating the 1st OSC.

This approach offers several advantages:

Since frequency modulation is not conducted in the TX signal circuitry, even if the TX RF signal is passed through a roofing filter, it will not suffer from any delay distortion caused by the filter; Since there is no need for an oscillator to perform modulation, “one-shot“ frequency management is permitted when transmitting on FM with the same precision as SSB;

This approach saves on space and cost.

Fig. 6: FM modulation block diagram

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Contents Page TS-480HX TS-480SAT Determination to create a unique transceiver Design ObjectivesBack to basics The appeal of HF lies in DX’ing Focus on basic performance Standalone control panel200W challenge Overview of the TS-480 Series Adding appeal to fixed station operationsTS-480 concept began with development of the TS-570? Development Objectives for the TS-480 SeriesAchieving 200W output in a compact transceiver Focusing on HF TX circuits 200W final section CircuitryTX IMD output 200W SPS schematic diagram SPS separate power sources TS-480HX only100W final section Failsafe device some TS-480HX versions onlyAntenna tuner TS-480SAT 200W final section FM circuit FM modulation block diagramRX 1st mixer RX circuitry Front endRX dynamic range RX sensitivity Jumpers for joy Comparison of optional CW filters 500Hz Circuitry after the roofing filterOption installation unit Features useful for 50MHz operations Auxiliary FeaturesFeatures useful for mobile operations Full compatibility with digital modes data modesNew 5MHz band DSP circuit Features of the Built-in DSPIdeal for mobile operations DNL Demonstrates how ignition noise is reduced by the DNL Noise reductionNR OFF BC OFF Beat cancelRX DSP filters Switching Width During CW operations CW auto tune RX equalizer & TX equalizerTS-480 menus TipsDSP Useful if you want to go on to tune FSK APO Functions that can be assigned to PF keys Assigned Use Split Quick menu Making menus easier to use Menu switchingInternal structure of the main unit Structural FeaturesCooling Cooling diagramUpper side Temperature rise around final transistors Page Design concept Constant recording function New Option Voice Guide & Storage Unit VGS-1Message recording/playback function Configuration mode for TX output, etc ResetMenu settings Split mode Voice GuideVFO mode, direct frequency entry Other featuresMemory channel Variable Voice Guide speedKNS added Main functionsButton layout & basic operation CW keying Changing memory and registered detailsReading and writing files Compatibility with KNS Kenwood Network Command SystemAccidental continuous TX Setting up KNS on the Arcp sidePage Using a broadband router New Option ARHP-10 Amateur Radio Host Program Freeware Checking LAN settingsUser setup Adjust PC volumePage Network & Operations Problem Solution TroubleshootingCannot get KNS to work Sound Problem Solution Connect a microphone to the computer and bring up TS-480 In-Depth Manual