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RE: Don't want to break my downconverter for AO-40



Mario,

It is all a matter of dB.  Look at your diplexer and see how many dB down 70
cm is from 2m.  Also look at your transmitter specifications and see how
many dB down the 70 cm harmonics are from 2m.  Then get out your calculator.

For example, if your 2m signal is 50 watts that is about +47 dBm.  If the
maximum you think you think your preamp can handle is 0.1 mW that is -10 dBm
so you need to be 57 dB down.  Add the diplexer drop in dB to the
transmitter filtering dB and if that is less than the 57 dB, then you need
more filtering.

My suggestion, don't transmit into the preamp output if there is any way to
avoid it.  Otherwise really, really pay attention to your filtering and also
put some sort of trap or crowbar on the preamp side.

Hope that is useful.

Ron, AG5RS

> -----Mensaje original-----
> De: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org]En nombre
> de ea4ckm@aeromodelismo.net
> Enviado el: lunes, 22 de abril de 2002 19:15
> Para: amsat-bb@amsat.org
> Asunto: [amsat-bb] Don't want to break my downconverter for AO-40
> Hello all.
>
> I have a Kenwood TS-2000, with separate 2m and 70cm connectors, but would
> like to have only one cable to the antennas.
>
> Is it possible to use a duplexer at the antenna side to separate the 144
> receive (the downconverter's output) and the 70cm transmit and
> have a single
> coaxial down to the RX/TX (with another duplexer)?
>
> Can the small energy that passes the 70cm power into the downconverter
> damage it?
>
> 73
>
> EA4CKM
> Mario El Kati

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