Message-ID: <08B4603A596D4233A7376DF32DF26E65@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <69624027609740299A8700F6BD23175F@AGB> <55CF747D.6040909@posteo.de> <C0B005B43382419EA510890EC2452941@AGB> <55CFA62B.5010301@posteo.de> <524DB27F17C843798472D2E9E7BA820B@AGB> <55D0D89A.3080400@posteo.de>
In-Reply-To: <55D0D89A.3080400@posteo.de>
Date: Sun, 16 Aug 2015 20:19:50 +0100
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Subject: Re: LF: Some LF again
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Status: O

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
>>>>>
>>>>
>>>
>>
>