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Re: Preamps, NF and Bandwith, the dilemma..

"Jens H. Jensen" wrote:

> I'm about to buy or build this all-important preamp, but there is a choice
> to be made:
> Narrowband or Wideband.
> I would like to use my wideband receiver, an AR5000, as the downlink from
> AO-40.
> But then again, this receiver is capable of a lot more than that (10Khz to
> 2.6Ghz), so the thought springs to mind that i might buy a wideband preamp,
> to be able to listen to other interesting signals above 30Mhz.
> My question:
> How much, if any, degradation is my reception of 2401Mhz likely to suffer,
> if i choose this wideband preamp, rather than a narrowband one.
> This of course assumes that specs of the two candidates are roughly the
> same, that means NF and Gain.
> I know that local conditions are hard to guess about, but are there any
> fundamental rules regarding this that i should be aware of?
> I can get a narrowband DB6NT for 248DM, but the wideband brother of it
> would increase the utility of the RX immensely :-)

My thought would be to go with the narrow band pre-amp.  Remember that although
you may well use the AR5000 receiver for things other than AO-40, you are
likely not going to be using the same antenna for all bands.  If I were going
to do it, I would use a narrow band preamp for 2.4 GHz and then a different
antenna (a discone maybe) for omnidirectional use below 1 GHz and maybe even a
couple more antennas for specific uses.  Then use an antenna switch at the
receiver to select the antenna.  Now to answer one thought that several of you
will come up with, is how well will an antenna switch work with a 2.4 GHz
signal.  Assuming that you use a switch rated up to 1.3 GHz (Alpha Delta has
these), it will be far from perfect at 2.4 GHz, but since many of us are having
to add a attenuator before the receiver, I don't see this as being a big

Jim Walls - K6CCC
626-302-8515    FAX  626-302-7501
AMSAT member 32537 / WSWSS member 395

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