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VHF-Low Explorer

A low-cost NBFM receiver for 68-88 MHz

VHF-Low Explorer
This article, we hope, will have serious consequences. Not negative, mind you, because apart from enabling beginners to experience the thrill of picking up radio traffic in a generally neglected band, the arrival of this inexpensive 4-m receiver should help to get the IARU section of the 4-m band released to radio amateurs in countries all over the world in due course. known as ’70 MHz’, and the IARU-approved band plan shown in Figure 1 is on the wall in many a radio shack up and down the country. So far, only a few other countries including Ireland, Denmark and — quite recently — Croatia have followed suit by releasing the frequency range between 70.000 and 70.5000 MHz for use by licensed radio amateurs. Unfortunately, in many other countries the relevant frequency range is in use by government or military services which need to have a few arms twisted (pun intended) before they move out.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Resistors:
R1=100kOhm
R2=150kOhm
R3=100Ohm
R4=22kOhm
R5=330kOhm
P1=50kOhm logarithmic potentiometer
P2=50kOhm linear potentiometer
Capacitors:
C1=39pF
C2=27pF
C3,C6,C14=10nF
C4,C11,C13,C19,C23,C24,C25,C26,C29=100nF
C5,C12=1nF, lead pitch 5mm
C7=100nF, lead pitch 5mm
C8=220pF
C9,C18=330pF
C10=10pF
C15,C17=3nF3, lead pitch 5mm
C16=180pF
C20=22pF PTFE trimmer
C21=150pF
C22=100pF
C27=2nF2
C28=10µF 16V radial
C30,C31=100µF 16V radial
Inductors:
L1=100nH (brown, black, silver)
L2=330nH (orange, orange, silver)
L3=180nH (brown, grey, silver)
Semiconductors:
D1=BB911
T1=BF981
IC1=TDA7000
IC2=78L05
IC3=LM386 N4
Miscellaneous:
8 ohm, 1 watt miniature loudspeaker
Diecast case: e.g., Hammond type 1590B
9V battery (PP3 / 6F22) with clip-on leads
PCB, order code 020416-1
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