Gate 2 is controlled with a constant voltage extracted through the divider R1/R2. ![]() Input is applied to gate 1, via a 2nd tapping, and R3 using the by-pass capacitor C2 delivers biasing to the source terminal. This kind of antenna may have lower directivlty therefore does not need to be adjusted, and could be elevated over a light-weight post or mast.įor receiving 144-146 MHz signal, L1 is permanently adjusted to approximately 145 MHz by means of T1. This is often of rigid wire, which could be around 38½in long overall, with the connecting cable climbing down through the middle. However, an initial attempt could be to start with a simple dipole antenna design. A raised up antenna may normally improve the reception range. In a few conditions a small straight aerial or cord could be employed for getting ample signal power. This 144 MHz preamplifier can be applied to any 2 metre receiver gadget, or used just before the 144 MHz stage converter explained above.Īerial input is applied to an intermediate tapping on inductor L1, which can be usually through a co-axial feeder. L4 consists of four turns, wound over the 元 coil close to the earthed (positive line) end of 元. 元 is wound using fifteen turns of 26 swg enamelled copper wire over a 7mm former equipped with an adjustable core. The distance between the turns are adjusted such that turns the total length of the cols are ½in or about 12 mm long. Both the coils are built using five turns of 18 swg wire, self supporting, accomplished by making the coils over a 7mm diameter former. L1 and L2 are identical with their winding specs, except that L1 consists of a tapping on one turn from its grounded end. It is additionally feasible to select some other transmission bands and output frequencies, if coils L1, L2 and 元 are apprpriately customized. ![]() The oscillator may basically be adjusted over or under the converter's antenna circuit frequency, since it is the converter's difference between the signal input and oscillator frequencies that decides the output frequency of the converter. 元 is approximately adjusted to this band, and L4 connects the signal to the short wave receiver. ![]() Consequently, 144- 146 MHz could be covered by adjusting the receiver from 28 MHz to 30 MHz. In the same way, when the oscillator is fixed at 116 MHz, supplying an input with 146 MHz to gate G1 provides an output of 30 MHz. Therefore when the signal at G1 is 144 MHz, and TR2 is adjusted to oscillate at frequency of 116 MHz, the output is set at 144 MHz - 116 MHz = 28 MHz. The output frequency from the TR1 drain which forms the mixer stage causes the difference between frequencies of G1 and G2. Oscillator function is implemented via C3 on the gate 2 of FET TR1. TR2 works like the local oscillator, and the functioning frequency in this design is fixed through the inductor L2 and trimmer T2. L1 is roughly tuned to the desired frequency band through T1, to enable the signal input to reach the gate 1 of FET TR1.
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