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Re: Re: T adapters and Elk Antennas for HTs?



Alan,
White noise -50 to -70 dBc +/-2% or more from the transmit frequency is not
to be confused with phase noise. It exists in the PA transistors and is a
function of device physics.It is present in crystal controlled equipment as
well as modern PLL rigs.
If you have ever done any repeater work you will find that the white noise
from a SS PA will require at least 1 BP cavity on the TX side to keep the
noise out of the receiver. The older tube rigs did not need this cavity and
many times after a repeater conversion to SS was done the trustee was forced
to add a cavity to prevent desense.

Art ,KC6UQH
----- Original Message -----
From: <alan_bloom@agilent.com>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, October 21, 2004 11:21 AM
Subject: RE: [amsat-bb] Re: T adapters and Elk Antennas for HTs?


> Actually tube transmitters do indeed have broadband noise.  It is true
that old tube-type transmitters tend to have less of a problem than modern
solid state rigs, but it has nothing to do with the use of tubes vs
transistors.
>
> The main noise source in many solid-state transmitters is the PLL
synthesizers.  Especially the first-generation synthesizers in older solid
state rigs had quite a bit of broadband phase noise.  But even if there is
no phase noise, there is amplitude (AM) noise.  Assume the oscillator runs
at 1 milliwatt and has a perfect 0 dB noise figure, meaning the noise level
is just the thermal noise of a 50-ohm resistor.  By the time you amplify the
signal up to 10 watts, the noise will be 40 dB above thermal, even with 0 dB
NF amplifiers.  With real amplifiers it is even worse.  That is true for
both tube and solid-state amplifiers.  However, tube transmitters almost
always have fairly narrow-band tuned circuits that remove most of the
out-of-band noise.  Solid-state amplifiers may or may not have such filters.
>
> Alan N1AL
>
>
> > -----Original Message-----
> > From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
> > Behalf Of KC6UQH
> > Sent: Wednesday, October 20, 2004 9:15 PM
> > To: Pieter Ibelings; amsat-bb@AMSAT.Org
> > Subject: Re: [amsat-bb] Re: T adapters and Elk Antennas for HTs?
> >
> >
> > Pieter,
> > Good thoughts, but for further amplification, white noise is prevalent
in
> > the output of any solid state Power Amplifier and the diplexer will
filter
> > that out as well. Note: The on redeeming feature of the vacuum tube is
> > VTamplifiers have no white noise.
> >
> > Art, KC6UQH
> > ----- Original Message -----
> > From: "Pieter Ibelings" <sietetrescincoprimo@hotmail.com>
> > To: <amsat-bb@AMSAT.Org>
> > Sent: Wednesday, October 20, 2004 2:05 PM
> > Subject: [amsat-bb] Re: T adapters and Elk Antennas for HTs?
> >
> >
> > > Using T adapters to connect the two sides of an arrow antenna is not
> > > recommended. For certain impedances and cable lengths, you
> > could have
> > > extremely bad SWRs. You could also end up having non
> > optimal patterns and
> > > polarization. The proper way of connecting two antennas of
> > different bands
> > > is using a diplex filter.
> > > There is a way that a diplex filter used with an arrow and
> > an HT can help
> > > your desense. Antennas can create distortions in their
> > metal to metal
> > > junctions (even at 5 watts). If you use a diplex filter to
> > combine both
> > > antennas in an arrow, the distortions created by the 145
> > MHz transmitter
> > > will not be able to get back to the radio through the low
> > pass side of the
> > > diplexer. It is true that the 435 side antenna will capture
> > some of that
> > > harmonic energy, but the fact that they are 90º spatially
> > will minimize
> > it.
> > >
> > > On the ELK antenna, any distortions produced in the antenna with be
> > "common
> > > path distortion" (CPD). There will be no way to filter
> > these because they
> > > occur in a common path to both the 145 and 435 sides.
> > >
> > > Pieter
> > > ----
> > > Sent via amsat-bb@amsat.org. Opinions expressed are those
> > of the author.
> > > Not an AMSAT member? Join now to support the amateur
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> > ----
> > Sent via amsat-bb@amsat.org. Opinions expressed are those of
> > the author.
> > Not an AMSAT member? Join now to support the amateur
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> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
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----
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