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G8MNY > TECH 24.08.20 16:52l 93 Lines 3669 Bytes #-1527 (0) @ WW
BID : 39351_N1URO
Read: DJ6UX DF7EAV GUEST DL9YCC OE7FMI
Subj: VHF Test Oscillator
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Sent: 200824/0707Z @:GB7CIP.#32.GBR.EURO #:2738 [Caterham Surrey GBR] $:2738_GB
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From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jan 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is the circuit of a VHF marker oscillator that was used for a club on the
evening construction contest. (by G4VTD)
ÚÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÂÄÄÄÂÄ100ÄÂÄÄÄÂÄÄÄÄÄÂÄÄÄÂÄo +9v
³ __ (6T ³ ³ ³ ³ ³ ³ ³
³ O/P __) (4mmí ³ ³ 10k 100k 100k 10k ³
³ ³ L ³ ³ ³ ³ ³ ³ ³u1
39k ÚÄÄÄÄÄÄ´ ³ ³ ³ ³ ³ ³ ===
³ ³/ 2SC ³ ³ 10n³ ÃÄ´ÃÄÄ´ ÃÄÄ´ÃÄ´ ³
ÃÄÄ´ 549 ³ ³ === ³ 10n \ / 10n ³ ³ 2SC549 &
³ ³\e 3p3 ³ === ³ ³ X ³ ³ 2SC540
³ T1 ÃÄÄ´ÃÄÄ´_ ³10n ³ \³ / \ ³/ ³ .-.
1n³ ³ ³/| ³ ³ T2 ÃÄÄÄÙ ÀÄÄÄ´ T3 ³ /...\
=== 100 === ³ ³ e/³ A F ³\e ³ ÀÄÄÄÙ
³ ³OSC /³1-10p³ ³ ³ ASTABLE ³ ³ e b c
ÀÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÁÄ< 0v
tube type
HOW IT WORKS
T1 is a ground base amp to form the VHF Colpitts Osc, with L tunned by the 2
current gain/tap caps 3p3 & 1-10pF, & putting part of the Collector output back
into the emitter. The 2x 10nF across the supply completes the high Q tunned
circuit RF path. Base current is from 39k & together with the emitter 100R
forms a stable osc bias.
Tone modulation is from the 1kHz 2 transistor (T2 & T3 2SC540) astable osc,
where T2 square wave collector current slightly varies the Osc supply via the
shared 100R. The 2x 10n & 2x 100Ks set the on-off ratio & the frequency.
TIN CAN
A flat piece of tin plate 3 x 4cm or PCB is used to attach all the components.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³_ C ³
Output³_). CÄÂ100ÂÄÄÄÂÄÄ´+³Power in
Coax³ ³ L C 10k ³ ³ 10k³
³ _)()))) ³ 100k 100k³ ³
³ /\ ³ ³ X ³ ³ ³
Trimmer³(0) T1 30kà C C ´ ³
³ C 100 T2 T3 ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
COMPONENT MOUNTING
All were standard small components as the design is ugly constructed & the lead
wires used to support all the components. All wire lengths kept at a minimum
in the "best VHF practice" in the oscillator stage.
TESTING
The oscillator runs between 120-160MHz with this coil, & the trimmer can be set
with a Rx, or a frequency counter from the nearby small coax pick up loop.
The square wave AF oscillator is about 1kHz & provides a 1% power rail change
to give AM/FM mod. Deviation is about 20kHz p-p of FSK. Output level around
-20dBm for single turn pick up, & haronics are all >-30dBc.
FINISHING OFF
If all goes well & you want to box the unit, try adding a tin top cover...
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³''''''''''''''''''''³
³ ³ DC
ÚÄÄÄÄÙúúúúúúúúúúúúúúúúúúúúÀÄuÄÄÄ¿
RFÀÄÄ¿ : : :³
CoaxÚÄÄÙ : : :³
³: : : :³
³: : : :³
³: : _ trim : :³
³: : (_)hole : :³
³: : : :³
ÀÄÄÄÄ¿úúúúúúúúúúúúúúúúúúúúÚÄÄÄÄÄÙ
³ ³
³....................³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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