Re: [TenTec] Re: Orion rf gain and inherent noise

[tongaloa <tongaloa@alltel.net>]

Gery-

No schema or code to look at for Orion.
However, I suspect they are dithering the ADC
clock to  reduce quantization noise. With no input,
the dither would appear as noise.

Proof of the radio is in how well it hears relative to others
under the same conditions. Until I can afford Orion or
7800, Buzz Reeves old TR7/R7 combo with Sherwood 7SP
is my 'top of the line' radio. It will be getting ADC and
linrad added soon.

-Bob
ah7i, ah7i/w4
Gary Hoffman wrote:

> Many thanks to all those who responded to my question about a cold front
> end.  Looks like it would not be terribly helpful at HF.
>
> So, I guess I will turn my attention to active cooling of the heatsink for
> the finals.  Could be fun.
>
> 73 de Gary, AA2IZ
>
>
> ----- Original Message ----- 
> From: "Ken Brown" <ken.d.brown@verizon.net>
> To: <tentec@contesting.com>
> Sent: Tuesday, June 10, 2003 3:58 AM
> Subject: Re: [TenTec] Re: Orion rf gain and inherent noise
>
>
>  
>
> > > > does COLD help cut the noise down ?
> > > >
> > > >        
> > Yes, but at HF the noise from other sources (as long as you have an
> > antenna connected, and a decent receiver) should be so much higher that
> > it will not matter whether the first stage of your receiver is at 300 K
> > (approximately room temperature) or cooled to cryogenic temperatures. At
> > higher frequencies, where terrestrial noise is lower, the temperature of
> > the front end of the receiver does matter.
> >
> >    
> >
> > > Radio astronomers cool LNAs to VERY low temperatures (around
> > > 20 Kelvin or about -425 deg F) to achieve very low noise
> > > temperatures.  A bit chilly compared to the typical home freezer :-)
> > >
> > >      
> > The receivers I maintain use a SIS (superconductor, insulator,
> > superconductor) mixer as the first stage, because there are no LNAs for
> > their frequency of operation, which is about 211 GHz and up. The mixer
> > is cooled to liquid helium temperature, around 3.6 K. Then after
> > downconverting to the first IF (4 GHz) the first stage of amplification
> > is called a HEMT (high electron mobility transistor) amplifier, which is
> > cooled to around 10 or 20 K.
> >
> >    
> >
> > > In the HF range, I don't see a need to resort to the ice machine.
> > > Standard design techniques and modern components can get you
> > > NF performance much better than band noise will let you reasonably
> > > make use of.
> > >
> > >
> > >      
> > This is absolutely true, including if by modern you mean in the last 50
> > years or so.
> >
> > Check this out.
> >
> >
> > http://www.jach.hawaii.edu/JACpublic/JCMT/Heterodyne_observing/heterodyne_o
> >    
> bserving.html
>  
>
> > >      
> > DE N6KB
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
> >    
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
>