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R:190804/1802Z @:GB7CIP.#32.GBR.EURO #:14750 [Caterham Surrey GBR]

From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW

By G8MNY (New May 05)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

This device is used to peaking up or "seeing RF" around your Tx aerial.

Here is a reverse engineered diagram of one I picked up the other day.

┌──────────────────────────────────┬───────┬───────────────┬────────┐
│ ┌───────)───────)──┬1k2─┬──┐ |) 390k
│ VHF \│/ │ │ METER│ │ _│_ |) L3 │
o┤ o 8p2 │ 10k 1M │ │ │ /_\ │ │
┌o──> │OFF<──o┬───┤├───o ┌─>FREQ │ BF547│ │ 10n│ │D3 ├───┤├───┤ _│_ o┤ o ) L1 39p │ POT │ T1│/ _│_ === │ |) 10n │
▄ 9V │ │UHF ├──┬───────┤├──)───)────┬──)─┤>├─┤ /_\' │ │ |) L4 │ _│_ │ │ │ │ 1n │ │ │ │ D2 │\e │24V │ ├────┤ │
▄ === │ ) ├──┤├─┬─12k─┤ PRESET │ │ │ │Z1 │ │ \│BF547 │
│ 10n│ │ L2 ) │/\ _│_ │ 22k │ SET │ │ │ │ T2 ├──┬───┤
│ │ │ ) === ───D1 === │ └─┤ZERO │ │ │ === e/│ 39k _│_
│ │ │ │/ │Ct /_\ 10n│ │ 4M │ │ │ │n22 │ │ /_\
└─────┴──┴────┴──┴─────┴─────┴───┴───────┴───────┴──┴────┴──┴────┴────┴───┘D4
TUNED CIRCUITS DETECTOR AMP DC INVERTER

L1 = 2T 23mm dia, L2 = 4T 7mm dia, L3 & L4 1mH ?

HOW IT WORKS
When switched to VHF/UHF the DC interter T2 D4 & D3 is powered. It
oscillates to provide >24V, which is fed to the 24V zener Z1 to make the maximum varicap D1 tuning voltage.

In VHF mode at max tuning voltage L2 & Ct set the highest frequency of 200MHz. The lowest frequency of 120MHz is determined by the voltage set by the preset.

On UHF mode L1 is placed across L2 to raise the frequency between 195 to 450MHz, & the slight inductance of the ground track gives the low Z aerial coupling needed @ UHF.

The RF detector diode D2 feeds the base of T1 to current amplify the signal for the meter. The 4M pot sets the bias level to set meter zero so that D2 & T1
are at the point of conduction.


Also look at my TECH buls on "Piston Absorption Wavemeter", "BURNS's MF-UHF Wavemeter TC-101", & "RF Field Indicatopr FL-30AH".


Why Don't U send an interesting bul?

73 de John G8MNY @ GB7CIP






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