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Follow up
Difficult to get a range for the dongle in DS
mode , the main gain is based in the
e4000 mixer , some 40 db, needed for its
intended wide band modes ,but direct to the
A/D produces a trace at 0.1 uV PD (gen set
to PD), both plots in USB , dial set 503 ,
With 60 dB dynamic range after processing
, compared to 120 + dB (no rf pre-amp) for
the Racal , the D/S option is not a serious
reception system , but , with a selective pre-amp
and what . say zero to 20 db
of gain , would make a good system ,
The D/S mode removes the need for
a mixer and second oscillator , but perhaps
requires a pre-amp and depending on
qth , some pre-selection , though reception
is possible directly , HF at night is quite
reasonable , but for $10 not bad !
NB - I have connected directly to pin 1
of the A/D for these tests , without access
to the chip architecture , its not possible to
state this is the ideal situation , some
arrangements use transformer coupling ,
one point that stands out , is that the out-put of
the e4000 remains in cct and could
shunt the Rf to ground , as there is a
coupling capacitor e4 >< A/D I
injected via a 0.1 cap .
There are some posts around removing
the cap from the board , to improve
D/S performance , by isolating the e4 , this
should/ could improve the sensitivity but at the
'loss' of the vhf/uhf function, but then again at
this price range , is that a problem ?
73 -G..
This plot is 1uV PD 504 KHz to
pin '1' of the A/D , 'Direct
sampling' input
This plot 0.1 uV PD at 504
KHz
For comparison
Racal RA6790GM ., with LF front end , no rf
pre-amp at 0.1 uV PD , USB ,
gain = full agc = on -med
easy CW copy from the Speaker at
0.1 uV , [short signal , gen set AM -on]
Sent: Thursday, April 04, 2013 2:01 PM
Subject: LF: £10 Dongel-SDR Direct sample on 504 KHz
All
£10 Dongel-SDR Direct sample on 504 KHz
The latest window drives for the
ultra-cheap sdr dongle project ,
now have the 'direct sample' option
all that is needed is a wire to
pin '1' of the AD chip , [ ie use the decoupling
cap as a terminal post]
select I/Q , and you have a HF rx , which
tunes down to zero (ish)
This is the 504 carrier from my main Ae via
tuner , showing qsb
navtex from the south coast last night 518
,100% copy , so not bad ..
73 -G..
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