| |
G8MNY > TECH 03.12.03 08:12l 38 Lines 1701 Bytes #999 (0) @ WW
BID : 28615_GB7CIP
Read: DB0FHN DL1NGL GUEST OE7FMI
Subj: QRP SWR Bridge
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<7M3TJZ<ZL2TZE<GB7YFS<GB7CIP
Sent: 031203/0002Z @:GB7CIP.#32.GBR.EU #:28615 [Caterham] $:28615_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
simplist type. However I don't think these are made commercially! You sometimes
see the simple circuit with QRP rigs. If you run QRP & can't build one yourself
I suggest you get a local to build it, possibly a novice!
The circuit uses a double pole changeover switch (measure operate), another
single pole C/O switch for SWR Forward & Reverse, 3x 50ê Rs rated at ¬ of the
RF power (& each can be made from a 47ê, or 2x 100ê, or 3x 150ê for better
power rating), 1 RF diode (OA81), 2 caps, series meter calibration variable R
(10Kê) & a meter (100uA).
OPERATE OPERATE
TX Socket oÄÄoÄÄ>oÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄo<ÄÄoÄÄÄÄo Load Socket
oÄÂÄÄÄÄÄÄÄÄ50êÄÄÄÄÄÄÄÂÄo (eg aerial/ATU)
MEASURE ³ ³ MEASURE
50ê Diode 1n ³
ÃÄÄij>³ÄÂij³ÄÄÄoÄÄ>o SWR
³ ³ o CAL
50ê Cal R ³
³ ÃÄÄÄÄÄ¿1n ³
³ Meter === ³
GndÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄGnd
It is best to make it from an old CB meter as you get the Box, Meter with an
SWR scale, sockets, switches & pot. 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.
In MEASURE mode the Tx only sees 6.25% of the load reflected power, so this is
always a good SWR match on tuning up. Also the tuning up Load power is only 25%
of Tx power reducing Band QRM.
/QSL
73 De John, G8MNY @ GB7CIP
Read previous mail | Read next mail
| |
