Re: LF: Some LF again

[Andy Talbot <andy.g4jnt@gmail.com>]

6dB per bit

'jnt

On 16 August 2015 at 20:19, Graham <g8fzk@g8fzk.fsnet.co.uk> wrote:

That's one  of those urban things  :)

Sure the  abs range  is  3 dB per  bit + 3

But the reference  point is  floating ,  or  else how to measure uV  changes , that's under the  control  of the   software , which puts the  devices  on the  'that's handy list' , there  is a  myth that  dB are directly linked to $$

Some  conditioning ,  B/W and  gain , may be  10 dB  should  render the device  quite  usable ,  noting  you  loose  one mixer and  oscillator , in the  process : ) what's  the  gain  compression  in the  mixer ? all  my Hf Rx have  high wattage  drive  to the  first mixer , switching  fet ring , something  like   5<>7 watts , with  100  + range

If it  works , then something  more  exotic  could be  connected  to the out put of the  conditioning  amp, the  air-spy   group  have  'hinted that direct  access  to the  a/d  is  provided ,  while  at the  same  time marketing  a  up convertor ...  at least there  being  honest .. but that is   24 bit ,  72 + 3 = 75 dB , still  30 dB  well  short of the   racal mixer , dating  from  1972 , but  with the  right software , will   do  much better

73-G,



--------------------------------------------------
From: "DK7FC" <selberdenken@posteo.de>
Sent: Sunday, August 16, 2015 7:38 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Some LF again

Hello G,

As far as i know, the dynamic range of these dongles is not suitable. 60 dB may be nice for playing arround but if you want to have a real RX for weak signal detection, something serious which is running 24/7, like Gary's grabber, you better spend the time and a bit of money and build something with 100 dB dynamic range. Or, if you don't like building your own stuff, buy some ready to use equipment, which is however just half of the hobby, in my opinion ;-)
But designs covering a whole band (VLF/LF/MF) are up to date i find. Not the SSB and dial stuff.

73, Stefan

Am 16.08.2015 18:48, schrieb Graham:

Thanks  Stefan,

Gary  sent a copy  of his   cct ,   Im wondering  what  one  of the  usb dongles  would  make of it ,  pre-amp  and  band pass filters  ...

73-G,

--------------------------------------------------
From: "DK7FC" <selberdenken@posteo.de>
Sent: Saturday, August 15, 2015 9:50 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Some LF again

Hi G,

No, i've made to many modifications from time to time. There is no up to date schematic.
But, it is a typical design. A suitable band pass filter, impedance converter matching to a SBL-3 mixer. The LO is 125 kHz, down-divided by a CMOS 4060 and a 4 MHz xtal. Then an IF-LPF. That's all. You may need an additional amp stage, depending on the incoming signal level...

73, Stefan

Am 15.08.2015 21:16, schrieb Graham:

Hi Stefan
Do you  have  a  link  to  the  CCT  for  the  soundcard  Rx ?

Tnx-G

http://myweb.tiscali.co.uk/wgtaylor/136SCRX.jpg

--------------------------------------------------
From: "DK7FC" <selberdenken@posteo.de>
Sent: Saturday, August 15, 2015 6:18 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: LF: Some LF again

Hi LF,

I'm back there is WSPR-15 for some time. The power is reduced by 4 dB, unfortunately.

Maybe someone can catch a trace anyway :-)

73, Stefan/DK7FC