Message-ID: <B6CB04DF2A4F4E689F98BAE674619C2C@gnat>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <CAHAQVWP9OQ-dZ0q7hEp2tjuvZzghQGi+oDVBtbwL=xUHCYZi9g@mail.gmail.com> <CAHAQVWPuCx+WeejbnDgLMmQRWonYSM4eB8yhs8kRSWe15yhDzA@mail.gmail.com> <c6200e98-35eb-bb7a-1a39-75f306816ff0@btinternet.com> <CA20351BC5E841289F19B4E51BA463FC@gnat> <7553d9d1-2639-3846-feb9-7bffc4585597@btinternet.com>
Date: Mon, 22 Jan 2018 23:55:43 -0000
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Subject: Re: LF: 136kHz - this is how badmy system is!
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Hi Martin I think Andy has answered the question for me so I wont confuse 
your with further facts :-))

In the days when I used to pontificate daily on propagation I tried hard to 
ensure the sensitivity of the rx system was reasonably constant and I did 
not have too much external noise. We had problems but Brian CT1DRP had a 
line on his waterfall we never located but was external and very constant. 
It provided a very good confidence boost and I believe did show Brian when 
his earth connection corroded and fell off. The general opinion for the 
source of the signal was a harmonic from a digital comms line (I think it 
was a harmonic of 8kHz) I came across a couple of ceramic 'bookends' the 
other day which I never used :-))

Happy LFing
Alan
G3NYK


----- Original Message ----- 
From: "Martin Evans" <gw3ucj@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Monday, January 22, 2018 8:06 PM
Subject: Re: LF: 136kHz - this is how badmy system is!


>
> Alan - thanks for this.
> Being a bear of very little brain ( I wouldn't recognise a Newton if I 
> tripped over one!) much of your explanation goes over my head, but I 
> understand well enough your conclusion that "that is not bad".
>
> One thing that I don't understand is the relevance of bandwidth to an SDR 
> receiver.
>
> If I short my receiver input, my baseline stands at -140dB ( that's the 
> lowest that the spectrum display goes); connect my antenna and my 
> background noise level around 137kHz is around -120dB; DCF30 is 
> around -70dB at the moment, and if I increase my scan width, R4 on 198kHz 
> is -40dB. All these measurements are taken from the spectrum display in 
> the Elad software.
>
> I don't see where bandwidth comes into the picture(!!)
>
> No doubt one of these days some of this will begin to make sense....
>
> Thanks again,
>
> Martin GW3UCJ.
>
> ********************
>> Hi Martin, I would estimate the field strength from DCF39 in your area is 
>> about 0.5mV/m (from measurements done by PA0SE in the UK) and from your 
>> data that gives about 1.5uV at the RX input as the level of the noise. If 
>> that is in an SSB bandwidth that is not bad. I remember the noise plotted 
>> on my CFH measurements in around 2002 was in this area but in a 300Hz bw, 
>> on the AOR7030 (Remembering WSPR s/n is related to a 2.3kHz bw if I 
>> remember right)
>> My minimum signal detection using a waterfall on the audio was 5nV (rx bw 
>> not relevant) but 0.3Hz bin size using a good sig-gen. I guess this was 
>> little more than 1 to 1.5dB above the noise. I think it was probably 
>> quieter here in East Anglia 15 years ago than it i now.
>>
>> I hope that helps (saves you ripping your station apart :-)) )
>> Alan
>> G3NYK
>>
>> ----- Original Message ----- From: "Martin Evans" <gw3ucj@btinternet.com>
>> To: <rsgb_lf_group@blacksheep.org>
>> Sent: Monday, January 22, 2018 4:51 PM
>> Subject: Re: LF: 136kHz - this is how badmy system is!
>>
>>
>>>
>>> Watching Roger's adventures on 136kHz, I thought I'd go take a look and 
>>> I wondered -
>>>
>>> DCF39 is about 50dB above the noise at 16:44UTC.
>>>
>>> I'm using a 150ft inverted L, untuned, stuffed directly into an Elad 
>>> FDM-S2 SDR.
>>>
>>> Decoded G3XIZ, G4FTC, G8HUH & G4GIR between 16:12 and 16:44.
>>>
>>> What does this say about my setup?
>>>
>>> Is it deaf/average/ok?
>>>
>>> How far above the noise is DCF39 in an optimised "good" setup?
>>>
>>> Anyone tell me?
>>>
>>> Martin GW3UCJ Swansea.
>>>
>>
>>
>
>