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G8MNY > TECH 21.07.03 11:56l 33 Lines 1471 Bytes #999 (0) @ WW
BID : 6537_GB7CIP
Read: GUEST DB0FHN OE7FMI
Subj: QRP SWR Bridge
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<7M3TJZ<IK1ZNW<IK6IHL<SV1AAW<LZ0FBB<
GB7CRV<GB7CIP
Sent: 030721/0841Z @:GB7CIP.#32.GBR.EU #:6537 [Caterham] $:6537_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
For QRP work a resistive (lossy -6dB) type that you switch out after use is the
best. However I don't think these are made commercially! You sometimes see the
simple circuit with QRP rigs & I suggest you get a local to build it, possibly
a novice!
The circuit uses a double pole changeover switch (measure operate), a SWR C/O
switch Forward & Reverse, 3 50ê Rs rated at 1/4 RF power, 1 RF diode (OA81),
2 caps, series meter calibration variable R (10K) & a meter(100uA).
It is best to make it from an old CB meter as you get the Box, Meter SWR scale,
sockets and switches. Sensitivity is down to about 0.2V of RF at the detector
which is about 0.8mW. Depending on the layout and components used the meter
could be accurate to VHF.
OPERATE
TX Socket o------.-->o----------------------o<--.------o Load Socket
MEASURE o--------50R-----------o MEASURE
! !
50R Diode 1n !
!----!>!----!!---.-->o SWR
! ! o CAL
50R Cal Pot !
! ! !
! !---- !
! Meter ! !
! ! === 1n !
! ! ! !
Gnd------------------------------------------Gnd
/QSL
73 De John, G8MNY @ GB7CIP
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