[600MRG] Rx noise 630m

[Ed Cole]

Measuring noise floor is tricky so using a 500-ohm term probably yields 
more comparable results.  I never measured the SDR-IQ into 50-ohms. 
Something else to-do!

SDR-IQ is currently idle but operates off a SV1AFN 50-ohm splitter with 
my K3.  This is fed via SP5T sma relay from either 630m antenna or 
28-MHz IF of 144/28 or 1296/28 transverters; Two relay positions idle:
http://www.kl7uw.com/2023_Station.jpg

73, Ed - KL7UW

On 3/18/2023 1:08 PM, Dave Riley via 600MRG wrote:
> TNX, Tom for another look through your prism..
> 
> I just set the Cushman 24 up on 475kc.  With a shorted input it reads 
> -111 db ( not sure of cal )
> 
> Then I plug in the loop and it goes up to -5 on the Cushman or +6 db 
> over -111 noise.
> 
> I'd guess that the -111 is the noise floor on that meter.  It was on 3.1 kc
> 
> I tuned off to 460 and then 490 and the noise indicated -110 db on the 
> edges.
> 
> Tuned to 476 kc. and it was -5  ' fairly good loop Q '
> 
> Best I can do is 'relative'...  Think I should be using a 50 ohm load 
> instead of a short..
> 
> TNX summore de DaveR W1FRV
> 
> 
> 
> 
> On 3/18/2023 4:09 PM, Tom W8JI wrote:
>> Hi Dave,
>>
>> Relative performance or noise performance is very difficult to measure 
>> in a meaningful way.
>>
>> 8dB is meaningless. 8 dB is just a ratio, what is the 8dB ratio 
>> against and under what condition?
>>
>> The 13dB difference between a short and an antenna doesn't mean very 
>> much of anything either. It only means the antenna is picking up 13dB 
>> more noise than a short. That doesn't mean anything about ambient 
>> noise or antenna receiving performance. It only means is the antenna 
>> system has 13dB more background noise than a short in some test. It 
>> doesn't tell us anything about how well something is working, how 
>> poorly it is working, or what the ambient noise level is unless there 
>> is some good reference.
>>
>> Now if we have some reference signal it might mean something. My full 
>> size inverted L antenna in January was about -73 dBm in 3.1kHz 
>> bandwidth daytime at this time of day, and -70 dBm average on a quiet 
>> night just before sunrise.
>>
>> I just measured it now and it is -72 dBm in the same 3.1 kHz 
>> bandwidth. Some digital signal on right now is -86 dBm, 14 dB below 
>> the 3.1kHz noise floor.
>>
>> My guess is that is N4WLO, my level meter can't decode digital signals.
>>
>> Even this does not mean much.
>>
>> 73 Tom
>>
>>
>>
>>
>> On 3/18/2023 3:11 PM, Dave Riley via 600MRG wrote:
>>
>>> Saying good bye to seasonal DX..
>>>
>>> Think the bulk of QRN has been nulled out here but still, the 
>>> difference between antenna and a short is about 13db
>>>
>>> Not much difference in noise level with loop spun around either..
>>>
>>> Maybe there is 8 db ambient noise average, some say that is low..
>>>
>>> What you say??
>>>
>>> TNX Dave @ W1FRV
>>>
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