GAAS FET Preamp Component Question
I'm planning to build the GAAS FET Preamp for 430 MHZ that's in the 2008 ARRL Handbook on page 14.37. One of the components on the drain of Q1 looks like a ferrite bead. I've never used these in construction before and the parts list doesn't specify any particular value or rating. Does anyone know what value/rating should be used? Any info would be greatly appreciated.
Thanks, Gene (KB3ONA)
Hi Gene,
I don't have read the scematic yet (I will do later in the morning), but I suppose your schematic is a common source LNA.
If it's so, the ferrite on the drain it's a choke, used as a bias tee to isolate the RF portion of the circuit (the GaAs FET) from the power supply.
For this purpose, you can use any ferrite bead that has an equivament impedance in the range of the kOhms in the band of interest. As an alternative, you can use a big inductance, that should do the trick.
Cheers
Simone - IW1FYV
Il giorno 27 febbraio 2012 03:41, Eugene Crist ejcristjr@gmail.com ha scritto:
I'm planning to build the GAAS FET Preamp for 430 MHZ that's in the 2008 ARRL Handbook on page 14.37. One of the components on the drain of Q1 looks like a ferrite bead. I've never used these in construction before and the parts list doesn't specify any particular value or rating. Does anyone know what value/rating should be used? Any info would be greatly appreciated.
Thanks, Gene (KB3ONA) _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Hi Gene, KB3ONA
As described into your Handbook at page 10.30 Chapter 10, the ferrite bead is slipped over the drain lid of a GaAsFET to prevent a possible autooscillation of your MGF-1402 and in your case a ferrite bead of Fair-Rite no.43 material is expecially suitable for this purpose.
BTW any ferrite bead of 3 mm in diameter is suitable provided that the ohmic resistance of material as measured with an ohmmeter across the ends of the single hole is around 30 K
Take care when handling a GaAsFET as it is very sensitive to static charges on your hands so that all working tools and as well your body must be grounded in order do not destroy the device.
In addition if your solder iron is not a low voltage 12 volt AC statically insulated from the AC line for solder GaAsFET's and active devices it is recommended to solder the GaAsFET at the end of the job using the solder iron sufficiently hoth but disconnected from the AC line supply.
Have fun.
73" de
i8CVS Domenico
----- Original Message ----- From: "Eugene Crist" ejcristjr@gmail.com To: amsat-bb@amsat.org Sent: Monday, February 27, 2012 3:41 AM Subject: [amsat-bb] GAAS FET Preamp Component Question
I'm planning to build the GAAS FET Preamp for 430 MHZ that's in the 2008 ARRL Handbook on page 14.37. One of the components on the drain of Q1 looks like a ferrite bead. I've never used these in construction before
and the
parts list doesn't specify any particular value or rating. Does anyone know what value/rating should be used? Any info would be greatly appreciated.
Thanks, Gene (KB3ONA) _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
participants (3)
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Eugene Crist -
i8cvs -
Simone