[TenTec] Re: Orion rf gain and inherent noise

[Ken Brown]

>>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_observing.html
>
>  
>
DE N6KB