[Lowfer] DDS 50 ohms buffer!

[Gilles Auger]

Hi Stewart.

The rule for the Hifer band have change from the present 10,000 =B5V/m at 30=
=20
meters, to 15,848 =B5V/m at 30 meters
this means 7.53mW EIRP or 4.52mW applied to the input of a halfwave dipole=
=20
in free space, or a quarterwave
vertical over an ideal groundplane.

The output specification at 14 Mhz for a 300 ohms load with a 50 pf is -6=20
db from the 1.35 volt max or something like .7 V p-p  for about 1.25 mw,=20
and i have not take into account the filter lost !

I will feel better with something that have some gain, 8 db will be good ..=
=20
I am not an electrical engineer and it's for what i need some help :)

Thanks for your help.

73

Gilles VE2DRW


>I believe that a simple emitter follower should be adequate.
>If the output swing is 1 V p-p, that's 2.5 mW into 50 ohms.
>
>With a PNP transistor, you shouldn't need any biasing parts.
>Hook the base to Iout (along with the usual 300 ohms to ground).
>Ground the collector, and use ~100 ohms from emitter to +5 V.
>Capacitively couple to your 50 ohm load.
>
>73,
>
>Stewart KK7KA
>
>----- Original Message -----
>From: "Gilles Auger" <augergilles@videotron.ca>
>To: <Lowfer@mailman.qth.net>
>Sent: Sunday, February 22, 2004 9:36 PM
>Subject: [Lowfer] DDS 50 ohms buffer!
>
>
> > Hi.
> >
> > I try to figure out what can be the amplifier that can match the AD9835=
=20
> 300
> > ohms output impedance to 50
> >
> > ohms with a gain of about 8 db at 13.5 Mhz.
> >
> > Is this can be done with a simple transistor or a monolithic amplifier ?
> >
> > I have take look on the net and they always use it unbuffered !
> >
> > Thanks in advance for any information.
> >
> > Gilles Auger  VE2DRW
>
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