|
Minto
Quick test at 0.1 uV pd as before
, dongle agc = off , gain = max
Good tone from the speaker at this
level , the drift 433 MHz is possibly
the xtal oven in the sig-gen warming up as
well as the dongle
low trace at 999 MHz , needed
about 0.3 0.4 uV for 'tone' but
I would not be 100% sure the dongle was looking
at the indicated level from the gen , also
the coax is still attached , but 0.1
uV to give these plots at vhf is reasonable
?
73 -G,
....................................433...........145.......70.........MHz
Sent: Sunday, April 07, 2013 1:00 AM
Subject: Re: LF: Re: £10 Dongel-SDR Direct sample on 504 KHz - S/N
TEST
Ok...Minto,
- silly question , you have the gain slider
set max in the driver set-up panel ? Then agen , my
ft897 could be u/s !
I will shorten the min coax I have soldered
to the device , and see what happens on
VHF with the gen on Sunday
with the same levels , ive emailed you
a recording of ssb station on 4
meters , using the dongle and indoor Ae
73 -G,.
Sent: Saturday, April 06, 2013 11:16 PM
Subject: LF: Re: £10 Dongel-SDR Direct sample on 504 KHz - S/N TEST
Hi Graham,
So maybe I should order another (type) of RTL2832 dongle. The one I
have certainly is wayyy less sensitive than my ft897 on 2 and 70. Probably the
type of tuner is different.
Well for the direct sampling test it is
irrelevant. I will have to filter 472, but that is no problem as I already have
such a filter (ft817 will overload from AM@675 without the filter).
I also have a 1.8 MHz
higpass. And as you say, at EUR 10 for a dongle there is not much to
complain about. It is fascinating that it works so well as it
does.
73’s Minto pa3bca
--------------------------------------------------------------------------
Ceterum
censeo Carthaginem delendam esse
Sent: Saturday, April 06, 2013 23:58
Subject: Re: LF: Re: £10 Dongel-SDR Direct sample on 504 KHz - S/N
TEST
Ok Minto
Yes this is the Q not Q or what ever
connection to the A/d
As to improvement's , ive no idea ! , but you
note the coupling C are both removed ,
the gain from the mini-whip my well be
enough to 'tip the balance' but s/n
for data is more important than 'peak signal
level' so gain (lots) may not be the
holy grail , I did copy nav text at 100% from the
south of Uk , audio level was very low , but
at a good s/n.
[ Gary's point , yes could switch , but I have the
impression , more could be gained by using
the balanced feed as in the link above , you
can run 2 dongles in the same pc
as the usb location seems to be part
of the driver addressing
There is 'no' gain in the A/D , to day
, the racal ra6790 produced a S3 / 4
cw copy from 0.1 uV , as can be seen from
the s-lab shot , but a low noise pre-amp would
solve the problem and with no additional
mixer , IMD should be much reduced , night
time HF was quite reasonable , left it
on 14,103 with the 40ft vertical, returned
after dinner and had missed Iceland
with -8dB signal .. typical !
The mixer in the dongle cannot
have much dynamic range , compared to one
designed for 'HF , eg the ra1769
first mixer is fed with 5 to 7 watts
of RF to ensure minimal transit times and
over 120 dB dynamic range , this could
be a contributing factor to any 'strange patterns
, which must be aggravated by having
two mixers in the rf path - one may
be 'good' but the e4000 may not
be , where as the a/d seems to be
quite clean
You have the same item I have hacked for MF ,
showing in the driver list as generic , the
other is the original ezeycap as per the first
posts ... When you say the vhf/uhf is
'low' that's odd as I would say this
one (ezy) is as good as the ft897d on
2/70 and on 4 meters , its better than the
spectrum trans V , using HDSDR
But the main thing is , it put's a
reasonable set-up in a very affordable price
, will be interesting to see the
performance ,D/S linked to the mini-whip , may be
the only way round the large carrier
problem will be filtering , or a move
to a better a/d , at least any
pre-amps and filters are transferable ,
should a better A/D be used at a
future data ?
73 -G.
Sent: Saturday, April 06, 2013 10:15 PM
Subject: LF: Re: £10 Dongel-SDR Direct sample on 504 KHz - S/N TEST
I have been experimenting too with an RTL-SDR dongle now for a few
weeks. I currently use a transverter to listen to lf/mf/hf. This transverter
upshifts the spectrum with 100 MHz.
Although the RTL-DSR is rather deaf when
used on 2m or 70 cm (compared to my ham equipment) when used for HF it is
sensitive enough with a pa0rdt active antenna.
I can also use it on 472. But
there I have to use my 472 KHz narrow band filter to keep out mf, especially
Radio Mario @ 675 Khz. And although the dynamic range is not stellar, as far as
I can determine reception on 472 is
very comparable to my ft817..
Grahams pointer to the direct sampling option
got me interested. Time to let the nice people from dealextreme send me another
on for EUR 10 so I can ‘experiment’ with it.
Some
interesting websites/video’s about the direct sampling
implementation:
http://ttrftech.tumblr.com/post/36283680013/rtl2832u-dongle-mods-for-7mhz-reception-with-gqrx
and
http://mikikg.wordpress.com/2012/08/22/prepravka-dvb-t-usb-prijemnika-sa-rtl2832u-za-hf-0-28mhz/
First site is in Japanese, second in Croatian, but Google
(translate) is your friend.
It is very nice to get an instant overview of 2 MHz of spectrum. I
have been plagued by ever increasing QRM here, which forced me to place a
magnetic loop antenna in my backyard to get any reception at all. QRM now is
S9+10 dB form 100 KHz to nearly 50 MHz. I have not been able to find out what
causes this (not generated in my house). See attached screenshot for a part of
the spectrum around 80 meters. This
wavy pattern can be seen everywhere from nearly DC to 50 MHz, with some
clean area’s in between. Sometimes the QRM stops waving – straight lines for
several seconds and then the waving restarts.
I am very jealous of other hams showing waterfall patters where
everything between real signals is dark blue... :-(
Anybody ANY idea what might cause this kind of QRM?
73’s Minto pa3bca
--------------------------------------------------------------------------
Ceterum
censeo Carthaginem delendam esse
Sent: Saturday, April 06, 2013 19:55
Subject: Re: LF: £10 Dongel-SDR Direct sample on 504 KHz - S/N TEST
Graham,
Maybe then....if the PCB was installed in a small
aluminium box the capacitor could be removed & a switch fitted to select the
original (VHF) arrangement or the HF/LF method. Possibly fit a pre-amp
also.
73, Gary - G4WGT.
|
