Message-id: <FF4788B2DD3E4EB18AB0D44399ABF747@DR2>
From: "dave.riley3" <dave.riley3@verizon.net>
To: <rsgb_lf_group@blacksheep.org>
Cc: "600MRG" <shmrg@piobaire.mines.uidaho.edu>
References: <000a01c99a91$a54a1180$1402a8c0@e7010>
 <FA25C6BCA43E4B89B3C17DA7F30F45EE@DR2>
 <7.0.1.0.1.20090305091934.0181aca8@magma.ca>
 <AD7E12A9D7A74A95803E074AC91E48B7@DR2>
 <fc7eccec0903051131r31ffec17wb1bb4213b5c92813@mail.gmail.com>
Date: Thu, 05 Mar 2009 15:43:19 -0500
MIME-version: 1.0
Subject: Re: LF: Deep copy...
Content-type: text/plain; format=flowed; charset=iso-8859-1; reply-type=original
Content-transfer-encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


>What is the expected ambient noise say
> @ 600M one should expect??

> I then connected to the outside antenna with no external pre-amp or any 
> non
> linear device and saw -117 dbm of noise across 10 khz. with a few weak and
> floating predictable BB noises..

Like I say, just a look @ the neighboorhood in which we are engaged as 
stated above, there to see the DIFFERENCE between it and the outside 
noise...

In today's case was -17 dbm delta... Tonight it may be -27 dbm or so... 
Lotsa places for weak signals to hide, even without Turin's theorem...

It's not like I have to tweak the front end by aiming this loop at the sun, 
thence to a quiet place in the blue sky, and then @ the ground cuz I won't 
see 3 different relative noise levels like with the 2' dish @ 10ghz...

Am only interested in knowing the difference between the receiver and the 
outside noise, pick your own parameters, say at the bandwidth that you like 
as zero degree K won't matter...

Right now I can get away with a Darlington pair of point contact transistors 
biased high into class A and still have headroom to spare, as far as front 
end noise figure is concerned...
The P-P Western Eklectic 417As are wasted here...

But since the outside world is so appreciably more noisey then there must be 
a better treatment of the antenna farm short of a full blown Wullenwebber in 
order to ditch the noise...

Why should a guy have to run 100 milliwatts when 10 will do?? We don't have 
an endless supply of carbon credits here in the colonies you know...
For now the double balanced, biased 1N34s are fine...
Tried 1N23As, no big deal... Like giving strawberrys to a donkey on 600M...

TNX until the sound of

Dave @ /17









----- Original Message ----- 
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, March 05, 2009 2:31 PM
Subject: Re: LF: Deep copy...


It all depends on your resolution bandwith which you don't specify.
Pnoise = kTB

With my SDR-IQ set to 190kHz span and 131072 point FFT, resolution
bandwidth = 1.5Hz and Rx set to +10dB gain to get the best  noise
figure:
-145dBm with a 50R load.  With the Antenna connected this rises to
-115dBm (measured at 1920 UTC) with no obvious lines or peaks
contributing.

If you normalise to the standard 2.5kHz noise measurement bandwidth,
that equates to -112 (50R)  and -82dBm.(antenna) respectively

Thermal noise at reference temperature of 290K is -174dBm/Hz, so for
2.5kHz that gives -140dBm suggesting the noise figure of the SDR-IQ
could be 140 - 112 = 28dB.    It probably isn't this low as we're in
the quantisation noise with no input signal, but a NF of 15 - 20dB
would probably be a rough guesstimate.

Andy  G4JNT
www.g4jnt.com



2009/3/5 dave.riley3 <dave.riley3@verizon.net>:
> Thanks to ALL who responded with quick and cogent findings...
>
> It has seemed for a time that with the receiver AGC and NBs OFF that I
> generally can see a deeper signal, depending on conditions...
>
> The final audio filter assures that the program does not have to deal with
> noise outside of the passband of interest...
>
> TNX
>
>
> Here is today's gnawing question... What is the expected ambient noise say
> @ 600M one should expect??
> Rural, City, Country, remote battery operated, etc. combinations...
> Especially well away from AC neutral wires...
>
> Today I ran the input to the SDR-IQ into a 50 ohm load and set a long
> integrate ( 64+ ) and saw approx -134 dbm of baseband noise with NO
> signals...
>
> I then connected to the outside antenna with no external pre-amp or any 
> non
> linear device and saw -117 dbm of noise across 10 khz. with a few weak and
> floating predictable BB noises..
>
> At night it is sure to be up to near -100 dbm depending on conditions and
> noises present...
>
> What do YOU get for a noise difference between a terminated antenna input
> and your regular receive antenna??
>
> I'm about to place several e-probes about this place in order to mix and
> match phase and amplitudes in order to see what net gain can be made to 
> the
> SNR with the hope that the most offending noises will not be in the path 
> of
> a desired signal...
>
> TNX and ain't this fun???
>
> Dave @ WD2XSH/17
>
>
>
>
>
>
>
>
>
> ----- Original Message -----
> From: Bill de Carle
> To: rsgb_lf_group@blacksheep.org
> Sent: Thursday, March 05, 2009 9:58 AM
> Subject: Re: LF: Deep copy...
> At 09:25 PM 3/4/2009, you wrote:
>
> I seem to get best results while trying to pull signals out of the noise
> when the AGC of the receiver is OFF as well as the Noise Blanker and Noise
> reduction features being OFF...
>
> Do you concur??
>
> Also setting a good audio filter to the passband of interest seems to 
> bypass
> some heavy static hits as well...
>
> I've noticed that when doing HF frequency measurement tests (working to 
> the
> nearest milliHertz) - turning off the AGC under high static conditions 
> seems
> to improve the accuracy of the measurement, at least with the software I
> use. One plausible explanation is that AGC action necessarily introduces
> amplitude modulation (on all signals in the passband). When I process the
> AGC'd signal with what amounts to a very narrow DSP filter the added
> amplitude modulation shows up as apparent sidebands close-in on the signal
> I'm trying to measure. If the power in those sidebands is comparable to
> that of the signal whose frequency I'm looking for, the FFT algorithm 
> (which
> assumes the real signal has the largest amplitude) gets confused and comes
> up with an estimated frequency somewhere between the correct value and 
> that
> of a nearby sideband. The effect is small however because the AGC pumping
> action doesn't occur very fast so the added sidebands are seen to be only
> some milliHertz away from the signal. The sidebands occur on both sides of
> the "real" signal, so one might expect them to cancel out but in practice
> they don't because the amount of error depends on where the "real" signal
> falls with respect to the fixed frequency bins of the FFT. It should be
> possible to model the AGC action of a particular receiver and compensate 
> for
> it in the software. No doubt the phenomenon becomes less significant with
> smaller FFT's or shorter integration times. Changing the AGC setting
> between SLOW-FAST-OFF might help under some conditions. With QRSS-60
> signaling rates it can take a long time to find out which setting is
> optimum, especially when band conditions are changing or the QSB period is
> close to a bit time, hi!
>
> VE2IQ
>