[R-390] Felton Electronic redesign of R-390A
Bob Tetrault
[email protected]
Thu, 4 Dec 2003 23:00:30 -0800
James,
Don't forget the 10db decrease in bandwidth (3500 to 350Hz) which goes
directly to the bottom line. A zero noise figure receiver with a 1 Hertz
bandwidth would have a sensitivity of -174dBm. Make that 500Hz BW and the
sensitivity goes down by 27db (10*log500) to -147dBm. Add in the typical and
conservative noise figure of 5dB for a well adjusted 390 and you're
at -142dBm. That's MDS, mind you. Figure on 10db S/N and you have -132dBm.
With a coherent (product detector) system, this is very typical performance
figures for 390's but outstanding for modern communications receivers. Open
up the BW and the sensitivity is reduced accordingly. When you realize a
typical 20kHz two-tone IMD IP3 at 10dBm for the 390's you have a truly
remarkable rig. (easy there, Hank, we know, we know). The dBm-BW approach is
the method used by every coherent detection engineer in the world. When you
convert from dBm to microvolts the numbers are startlingly small, yet
nonetheless true. Mr. Johnson is still there, but his contribution has been
reduced by the reduction in bandwidth. I remember working on the early Bell
Labs specs for cell phones back in '82 and being unimpressed with a
sensitivity spec of -112dBm until I found the references for required
receiver BW to be many tens of kHz (inaudible control tones)... they all
reduce to the -174dBm/Hz baseline. Every time.
Bob
Portland, OR
-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of James A. (Andy) Moorer
Sent: Thursday, December 04, 2003 6:30 PM
To: [email protected]; [email protected]
Subject: Re: [R-390] Felton Electronic redesign of R-390A
I have no experience with his engineering work - I am sure the receivers are
remarkable devices, and I am sure his work is top-notch.
But his reported sensitivity figure of .012 microvolts across 50 ohms can't
possibly be true.
Please refer to my "noise and sensitivity" page at:
www.jamminpower.com/main/noise.jsp
The short version is that a 50 ohm resistor at room temperature will exhibit
a .0266 microvolt "thermal noise" voltage. This has been known for decades.
A sensitivity measurement reports the voltage that is 10 dB above the base
noise floor. The absolute minimum sensitivity possible with a 50-ohm load
would be 10 dB above .0266 microvolts, which is about .084 microvolts. That
is the theoretical limit - the actual sensitivity is probably much higher
than that.
James A. (Andy) Moorer
www.jamminpower.com
P.S. - even a receiver with a 100-200 microvolt input sensitivity is an
incredible receiver! No reason to inflate (deflate?) the numbers beyond
physical limits.
----- Original Message -----
> Good evening all:
>
> Does anyone have experience with the above mentioned company. He makes
some
> pretty impressive claims, but I haven't heard anyone ever mention him or
his
> work.
>
> http://www.feltondesign.com/
>
> Thanks for your input!
>
> Randy
>
_______________________________________________
R-390 mailing list
[email protected]
http://mailman.qth.net/mailman/listinfo/r-390