RE: [amsat-bb] Re: T adapters and Elk Antennas for HTs?

[<alan_bloom@xxxxxxxxxxx>]

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
> > ----
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