HFTRANSCEIVERProfYofPINHASI

更新时间:2023-06-22 10:08:09 阅读: 评论:0

HF TRANSCEIVER Prof. Yof PINHASI
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The transceiver prented in this article is designed to operate in the radio amateur bands of the HF frequencies (3-30MHz). It was constructed on four printed circuit boards:
•Receiver and audio amplifier
巧克力英文•Intermediate frequency (IF) modulator and product detector
•Up-converter mixer and radio frequency (RF) power amplifier
•Transmit / Receive (T-R) relay and RF low pass filter.
A block diagram of the transceiver is illustrated in Figure 1. In order to avoid mutual electromagnetic interferences, the receiver and IF ctions are parated from the RF power stage. This requires transferring three signals between the two units; IF double-side band (DSB) modulated signal, local oscillator and the RF antenna signal.  Much effort has been directed to keep the design simple and compact by utilizing integrated circuits and direct couplings. Each of the four single-sided PCBs has i
ts own power supply, including a voltage regulation circuitry. In its prent version, the transceiver is operating in the 20m amateur band, covering 14.000-14.350MHz. The receiver can detect AM, FM and SS
apexB signals, while the transmitter operates in a DSB mode.
新东方小语种RECEIVER
TRANSMITTER RF 455KHz IF
BALANCED MODULATOR & PRODUCT DETECTOR Figure 1: Block diagram of the HF transceiver.
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I.THE RECEIVER
Figure 2 is the electronic scheme of the receiving module. The front-end of the receiver consisted of a 4.7µH inductor in ries with a 27pF capacitor, constituting a resonant circuit at 14.128MHz. The two diodes at the input protect from excessive signals by clipping spikes and large amplitudes that may damage the receiver front-end. The ries resonant filter it is followed by an impedance matching network
北京英语口语transferring the aerial 50Ω impedance into 4.5KΩ input impedance of the SA605 RF stage. The matching network is shown in Figure 3.a and its transmission characteristics of the matching network are shown in Figure 3.b.
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Figure 2: The receiver and product detector.
(a) (b)
Figure 3: Front-end impedance matching network: a) scheme, b) power transmission.
The main receiving chain is bad on the Philips SA605 mixer and IF system [1]. This integrated circuit (previously manufactured by Signetics with the number NE605) is a super-heterodyne receiver composing of an internal balanced mixer, local oscillator and intermediate frequency amplifiers. The 6.2V regulated supply voltage required at leg 7 is achieved by employing a zener diode.
The local oscillator (L.O.) of the SA605 is bad on a varactor-tuned variable frequency oscillator (VFO). The L.O. frequency should be 455KHz below the receiving frequency, i.e. 13.545-13.895MHz. In this Colpitts configuration, the frequency is determined by the coil L 3, the varactor C V and the two parallel capacitors C 3a  and C 3b , as shown in Figure 4.a. The oscillation frequency of the L.O. is following the expression:
()()
+⋅++=
21213321
C C C C C V C L V f V LO π
While using the BB109, I found out that the coil inductance should be L 3=0.577µH (12 turns on a T-50-6 iron powder toroid yellow core). The capacitor is approximately C 3=150pF made of a C 3a =120pF capacitor in parallel with a C 3b =50pF trimmer (e Figure 4.a). In that ca, the receiving frequency as a function of the voltage introduced to the varactor is shown in Figure 4.b. Note that besides the main 14.000-14.350MHz band (455KHz above the L.O. frequency), also image frequencies of 13.09-13.440MHz (455KHz below the L.O.) are expected to be detected as a result of a super-heterodyne configuration.
(a)      (b)
`Figure 4: The VFO: a) Resonant circuit, b) Receiving frequency as a function of theallegiance
儿童英文歌voltage in the 20m bands. The image frequencies are also shown.

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