[600MRG] RSSI Versa's Noise reports

[Edward R Cole]

Its specifically referenced to a bw of 2.5 KHz.  A -18 dB signal 
(SNR= -18dB) is at the threshold of hearing for CW.  Typically the 
threshold for decoding it -28 dB, but that can vary a couple dB 
depending on receiver MDS and local noise levels.  -18 dB on WSJT or 
WSPR is the same as -11 dB using the std of 500-Hz for measuring 
MDS.  10Log(500/2500) = -7 dB; or -1 dB if you use a bw=50 Hz (which 
is the typical ability of human hearing): 10Log(50/2500) = 17 dB.

My SDR-IQ has an MDS of -132 dBm with no antenna and sees from -110 
to -120 dBm with antenna connected.  I think this fairly typical for 
470-500 KHz conditions.  The one time I copied Rudy's CW his signal 
displayed about -98 dBm.  Display bw with Spectravue is different 
than audio bw which is sw adjustable with the SDR-IQ.

WSJT and WSPR use the 2.5 KHz reference for signal level display 
(which is SNR in dB).

73, Ed - KL7UW

At 03:48 PM 10/5/2016, Brian Pease wrote:
>These negative s/n numbers for digital modes are the signal to noise 
>ratio, in dB, of the received signal in the SSB noise bandwidth of a 
>typical receiver, 2.5 or 2.7kHz.  This give a more or less standard 
>way to report s/n.
>
>Since most modes are much narrower BW, they may actually have a 
>positive s/n in dB if measured and reported in a noise BW closer to 
>the signal BW.
>
>
>On 10/5/2016 6:14 PM, Alan Cooper wrote:
>>
>>
>>
>>
>>I like Rudy's dose of common sense of averaging many readings. In the
>>commercial field of
>>
>>telecommunications I run into a fair number of highly educated "engineer's"
>>who will tell one
>>
>>that on a certain street corner at the intersection of chaos and discipline,
>>the RSSI will always be
>>
>>a negative blah blah db without exception or variation. When I hear that I
>>always think to myself
>>
>>here we go again!  It however makes a valid point that most all of the guys
>>on this 600MRG reflector
>>
>>have a better practical understanding of propagation than they do! Not all
>>of those engineers mind
>>
>>you (there are some who are really sharp and are way under appreciated for
>>the skills they have).
>>
>>
>>
>>There is one thing I am not getting a good grasp of in these discussions
>>however that I hope someone
>>
>>can help me with..
>>
>>What are the points of reference that these S/N logarithmic readings revolve
>>around?
>>
>>In the telecommunications field the noise floor (with some manmade noise
>>thrown in) is considered
>>
>>To be between -125db down to -140db with normal loss of a call in progress
>>happening near -117db
>>
>>To -120db. A RSSI of a -45 to a -70db is considered to be a very HOT signal
>>level range. This of course
>>
>>takes place at freq.'s that range from 700 MHz up to 1.9 GHz.
>>
>>
>>
>>the reports here on the 600MRG of -30db then as compared to all of that (if
>>one could remove the noise factor)
>>
>>is a very good signal level so I feel that my points of reference are all
>>messed up in terms of 475Khz RSSI measurements.
>>
>>Can anyone please shed some light on this?
>>
>>
>>
>>Thanks
>>
>>
>>
>>Alan Cooper
>>
>>w7aln at netzero.com
>>
>>Bandon, Oregon
>>
>>
>>
>>
>>
>>Morse Code Forever! the original digital that started it all
>>
>>                                             AKA CW (circa 1880's)
>>
>>
>>
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73, Ed - KL7UW
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