EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: p.larner on January 17, 2024, 06:32:27 pm
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can anyone explaine the role of L4 in this atu schematic?.
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To provide a minimum series inductance when all sections of L3 are shorted out by the switch.
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A designer can omit L4, and combine it into the winding construction of L3 with appropriate inductance. However, sometimes the physical component layout is impossible within a given chassis size dimensions, and so the inductor is split into two.
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read about someone talk about adding coil for the higher bands,any idea what thats about?,was in relation to a pi tank cct
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Generally if you need to add inductance this will be for a lower-frequency band, but it's all going to depend on the antenna, the cable length, etc. Any matching network (TEE, Pi, L, etc.) will need to cancel the antenna/cable reactance and transform the result to something near 50 Ohms to keep the transmitter happy.
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read about someone talk about adding coil for the higher bands,any idea what thats about?,was in relation to a pi tank cct
I have read about adding coils for "top band". Don't mix up the terminology "top band" with "higher" bands.
Top band refers to the 1.8MHz 160m band. Adding a coil is invariably required due to the large inductance required to achieve tuning for 1.8MHz.
The name is no longer correct insofar as dictionary definition and EM spectrum physics is concerned, nevertheless the name has stuck. The name comes from early radio days, where they once believed in an upper limit for practical radio frequency communication ("top of the radio band").