[opendtv] Re: Noise Figure
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 25 Feb 2008 23:22:42 -0800
Bert wrote:
> If one specifies SNRin and SNRout, i.e. all the elements thereof,
> then one doesn't need to also specify the NF.
One could use such a calculation if SNR was known or specified. However NF
is the standard specification and is a constant.
> That's what I meant about liquid nitrogen cooling of the receiver.
I actually worked with cryogenically cooled receivers in past years. Older
high gain RF amplifiers designed to receive signals in the thermal noise
region were "super" cooled, at great cost, to limit self generated in-band
"noise" from masking the desired signal and therefore improving the NF.
These days a $200 solid state LNA/LNB will do the trick.
Fortunately, at the low frequencies and the relatively high signal levels
used in broadcasting, *very* inexpensive high performance low noise
amplifiers are readily available and would be of benefit at times.
Anyway, this discussion started when I speculated that perhaps Zenith and
others might use a better quality front end in the low cost coupon
receivers. It would be extremely damaging to 8VSB IP holders and others, if
those devices worked poorly so I assume they are highly motivated to assure
acceptable performance. We've had a couple of user reports recently
suggesting the possibility of such improved performance and long detailed
esoteric discussions, such as those above, tend to obfuscate the issue I
raised, whether it actually has merit or not....
Dale
> -----Original Message-----
> From: opendtv-bounce@xxxxxxxxxxxxx
> [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Manfredi, Albert E
> Sent: Monday, February 25, 2008 5:57 PM
> To: opendtv@xxxxxxxxxxxxx
> Subject: [opendtv] Noise Figure
>
>
> Those gremlins are hard at work.
>
> In short, the NF is defined as SNRin - SNRout. And the SNR is assumed at
> some temperature, typically 290 or 300 Kelvin.
>
> If one specifies SNRin and SNRout, i.e. all the elements thereof, then
> one doesn't need to also specify the NF. Matter of fact, if one does not
> specify the temperature, then in principle the NF can be allowed to
> vary, with no ill effect to the consumer. That's what I meant about
> liquid nitrogen cooling of the receiver.
>
> http://en.wikipedia.org/wiki/Noise_figure
>
> That said, obviously 15.5 dB of C/N and -83 dBm of sensitivity required
> from A/74 can be improved upon, as Samsung convincingly showed in the
> Gemini receiver it shipped to the CRC for testing.
>
> Bert
>
>
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