[TenTec] Re: Orion rf gain and inherent noise

[Gary Hoffman]

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 at verizon.net>
To: <tentec at 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
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