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" <[email protected]>
To: <[email protected]>
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" <[email protected]>
To: <[email protected]>
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.
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