QRP T/R Switch


From: rohrwerk@holonet.net
Date: Sat Mar 04 1995 - 02:05:58 EST

On 02-28-95 mmarmor@pluto.njcc.com wrote to qrp-l@netcom.com:

> I am building W1FB's QSK QRP T/R switch and have a question about what
> transistor to use in the circuit. The circuit is on page 141 of the
> _QRP Notebook_. "Q1 may be any PNP transistor that can safely pass
> 300mA or greater DC current." The circuit shows a 2N2801 but I can't
> find this transistor in the Mouser catalog. I have access to some
> device data-books and would like to find a transistor that can "pass
> 300mA or greater DC current" but I don't know what column to look at
> in the books!

Look right below the 2N2801 and you'll see another number, TIP-30, which is
MUCH more common and easy to find!

Advice: You do not need two pairs of diodes as found in this circuit. I have
used only the lower pair, even without the protection diodes back to back, and
got less than 1 volt p-p into the RX at 5 watts output.

Other tips:

Use 1000 uH chokes if you want to work as low as 160 meters.

You can eliminate the RF chokes and blocking caps at either end, IF your
circuit provides a DC return to ground via a transformer. This is often true
in the transmitter, and in the RX if you have a link coupled input circuit.

I can provide schematics in PostScript and more details of one that has a
switching transistor added so you can just ground a key line to put the switch
in transmit mode. Also an approach that Ten Tec used in the Argosy, using
1N4007 diodes, power diodes which incidentally have a PIN structure. You have
to back bias these with a little rectifier/filter circuit from the transmitted
RF. This is good to 50 watts.

: John Seboldt rohrwerk@holonet.net / "Should I go
: Amateur radio K0JD... / left or right?"
: Church of the Annunciation, / "No... go deeper."
: Minneapolis /

 -> Alice4Mac 2.3 E QWK Eval:05Mar94

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