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" <[email protected]>
Sent: Sunday, August 16, 2015 7:38 PM
To: <[email protected]>
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" <[email protected]>
Sent: Saturday, August 15, 2015 9:50 PM
To: <[email protected]>
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" <[email protected]>
Sent: Saturday, August 15, 2015 6:18 PM
To: <[email protected]>
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
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