Amatorki projekt


Posted on Feb 6, 2014

Add to our circuit despreading spectrum 2 identical branches more. Difference is only in phase of PN sequences given to each branch (to input of double-balanced mixer). In EARLY branch, phase of PN sequence is earlier about ½ byte. In LATE branch, phase of PN sequence is later about ½ byte than phase in ON-TIME branch. If frequency of PN generat


Amatorki projekt
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or in receiver becomes higher, we will have impulse in EARLY branch. If frequency of PN generator in receiver becomes lower, we will have impulse in LATE branch. Both impulses are used to adjust (decrease or increase) frequency of PN generator in receiver. If this generator is not connected to frequency adjusting circuit, we will have RSSI impulses appearing in EARLY, ON-TIME, LATE branches or reverse order. It depends on which PN generator (in transmitter or in receiver) has higher frequency. Incoming wideband signal 192MHz with spread spectrum from antenna goes to input amplifier. This amplifier must have bandwidth more than 8MHz. We can control gain of this amplifier by changing voltage on second gates of T1 and T2. Amplified signal is downconverted by mixer UL1042 (SO42P). Mixer is driven by first local oscillator 122MHz. The product of mixer we need is wideband first IF 70MHz (192-122). First IF has spread spectrum from about 66MHz to 74MHz. IF amplifier must have bandwidth more than 8MHz. Amplified first IF is split to 3 identical branches. In each sighal branch (EARLY, ON-TIME, LATE) signal with spread spectrum after buffer goes to double balanced mixer configured as biphase shift keyer. Mixers (DBM) in signal branches are driven by PN sequences (identical as in transmitter) shifted about ½ byte. (EARLY-PN, ON-TIME-PN, LATE-PN). If PN sequence has identical phase as PN sequence in transmitter (synchronism), spectrum...




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