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G8MNY > TECH 12.03.24 09:00l 183 Lines 8418 Bytes #999 (0) @ WW BID : 3122_GB7CIP Read: GUEST Subj: Dip Oscillator Path: ON0AR<OZ5BBS<CX2SA<PE1RRR<KA1VSC<GB7CIP Sent: 240312/0750Z @:GB7CIP.#32.GBR.EURO #:3122 [Caterham Surrey GBR] $:3122_GB From: G8MNY@GB7CIP.#32.GBR.EURO To : TECH@WW By G8MNY (New Nov 07) (8 Bit ASCII graphics use code page 437 or 850, Terminal Font) Here is the circuit of a 1 FET dip oscillator that was used for a club on the evening construction contest. (by G4VTD) The "Grid Dip Oscillators" were originally valve & the dip in the current indicated that some of the oscillator power is being "sucked away" by a nearby resonant circuit, aerials etc. thus indicating the correct resonance or not. It also works just as a simple signal source, but not too stable! It can even be use for testing Crystals as poor ones won't oscillate. This is the FET equivalent of the valve circuit. кФФ1KФФФТФФФ68RФФФФФФФФФТФФФФФФТФФo +9V Г Г Г Г 4mm n1 |Г|fb Г Г Г 0ФФФФФФТФФФФФДУФФФФФФФД === 5K6 Г Г Г_ Г 1nГ Г Г o = push in post Г 145pГ/| Small Г Г Г Г Plug ) === Ganged Г РФo RF to Г Г in ) /Г MW+VHF Г counter Г Г search ) кФФФФД_ Caps Г Zero Г .-. coils ) Г145pГ/| Г кФФФД1K кФСФП /...\ L Г Г === 2N3819Г Г pot Г1n Г РФФФй Г Г /Г n1 g УФйd Г Г === === d g s 0Ф)ФФФФСФДУФТФФФТФФ>УФПs _ Г _Г_ Г u1Г 2N3819 4mm Г Г Г Г 1n ft /~ ~\ Г D2\_/ РФТФй Г _Г_ 120K кФСФТФФФФФoДMeterУoФД _Г_2 x Г Г D1 /_\ Г Г Г ~Г~ -\_ _/+ Г D3\_/1N4 Г Г 1N4148Г Г === 1K Г ~ === Г 148 Г Г Г Г u1Г Г Г u1 Г Г Г РФФФФФФФФФСФФФСФФФСФФФСФФСФФФФФФФФФФФФСФФФФФСФФФФФФСФФ 0V HOW IT WORKS The split tuning caps with the search coil L gives 180ј phase reversal between the FET's Drain & Gate to from a Colpitts oscillator. As the gate is not a Valve grid, a diode D1 is needed to keep the gate voltages all negative. The source voltage follows the mean Gate voltage plus the FETs bias potential (~2V), & this appears across the source 1k resistor. The meter compares this voltage to zero pot preset voltage. Now if the tuned circuit gain "Q" is altered due to loss from a nearby tuned circuit, the oscillator power will change, reducing the mean -ve Gate voltage, so the source will go more positive & the meter will show this as you tune across the nearby circuits resonance. The frequency counter output is a small tapping of the drain output, set here at 50ъ Z with a 68R for 120mV output (60mV term), for 75ohm use 82R/100R for 200mV output (100mV term). The Ferrite Bead (fb) on the drain 1k gives a little bit more gain at VHF. TIN CAN CONSTRUCTION A pre punched U tin plate is used to house all components. fold fold кФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФП HolesГ ....... | m- + | .. Г for Г :O O: | ft>O O | ( ) Г Large dual Г : _ : | | ~~ Г Holes gang Г () (_) () | | 0<Pot Г for 4mm Cap Г : : | | hole .. Г Banana Г :O...O: | O O | ( ) Г Sockets Г | m+ rf | ~~ Г РФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФй holes for 3 through push in posts, 1 preset adjustment pot, 1 feed through cap. COMPONENT MOUNTING All were standard small components as the design are ugly mounted & the lead wires used to support the components on the available fixed points. The wire connection push in post use the component leads as the connection wire. The feed through capacitor is soldered into the Tin Can. All wire lengths kept at a minimum in the best VHF practice. The tuning capacitor is only soldered in, when most of the smaller components are fitted, there are vertical wires needed on the outside of the tin can linking its VHF & MW sections. Finally the search coil sockets are mounted & wired up with the n1 capacitor leads to the tuning capacitor. LAYOUT There was no specific layout, but the finished item looked like this. Banana sockets .-. Г _____кХФФТФП ___/ \ Search Г___ =[_____ГГ Г Г<_ \ / Coil Д Г] nutРХФФСФй '-' Knob__ГMW+Г n1 Г ^tube Г__ГVHFГ Г Cap ГCapГ fet Гpot link Д___Г] Гhole verticalГ кСП кСПГ РФФФФФФХФХФХФХй ~Г~ ~Г~ External Connections TESTING With about 20cm of thick 1mm enamelled copper wire 8 turns 10mm dia as the search coil & ends prepared to make firm connections (bent into U), the oscillator ran between 24-70MHz with a frequency counter connected. The indicating dip meter can be any sensitive (100uA) VU type or a centre zero meter, or even a DVM. Once the preset Zero pot for a particular coil it should not need adjusting. Various coils can be made to get the desired кФФ((() frequency needed, or / кФФФй even just made up as <_____/ / Awkward needed for best size, / access access shape & <______/ search coil frequency range Turns Dia Wire Usable range _ _ _____ Single U 10mm 2mm 100-200MHz /~ ~\ /~ ~\ нБББББо 2t 10mm 2mm 68-170MHz Г Г Г\_ _/Г нБББББо 8t 10mm 1mm 24-72MHz Г Г Г ~ Г Г~~~~~Г 28t 10mm 0.8 8-24MHz Г Г Г Г Г Г 48t 10mm 0.4 3-19MHz U U U U U U 110t 10mm 0.2 2- 8MHz Heat glue melted on the coils (soldering iron) will help to keep the smaller coils stable. With more turns & thinner wire you need a paper former (sticky label inside out making a tube on a pen) wind the coil & again use heat glue to hold in place. Double up or use thicker wire for the in & out leads. Much lower frequencies can be obtained with a ferrite rod cored coil of needed for say 1.8MHz or 465kHz. If the coils are well made & stable, a frequency scale for the capacitor can be made for each coil. FINISHING OFF If all works well & you want to box all the bits, try adding a cross shape of Tin Can.... кФФФФФФФФФП /Г Г\ Г Г PP3 Г Г Г Г batt Г Гshort sides long Г Г Г Гenough for Г Г Г Гbattery & meter Г Г Г Г Г Г Г Г \Г Г/ кФФФФФФФФФФФФФФФФФФФФФФФФФФйњњњњњњњњњРФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФП /Г : : : Г Г Г : : : Г Г Г : : : top Г Г Г : bnc _ : : Г \Г : (_): : Г РФФФФФФФФФФФФФФФФФФФФФФФФФФПњњњњњњњњњкФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФФй /Г Г\ Г Г Г Г Г Г on Г Г Г Г off[] Г Г line sides long Г Г Г Г enough to reach Г Г meter Г Г the top of unit Г ГкФФФФФФФПГ Г Г ГРФФФФФФФйГ Г \Г Г/ РФФФФФФФФФй _____________________________ SearchГкФФФФФФФПГ __ Г Coil ГГ dial ГГ Г Г PP3 Battery Г ( )ГГ ( ) ГГ ГVUГ Г__ BNC to ГГDip OscГГ Г__Г [] on/off Г__Г Counter ГРФФФФФФФйГ Г ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In practice some of the tin plate is left off for battery access etc. Why Don't U send an interesting bul? 73 De John, G8MNY @ GB7CIP
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02.05.2024 06:39:35l

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