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Re: LF: Re: £10 Dongel-SDR Direct sample on 504 KHz - S/N TEST

To: <[email protected]>
Subject: Re: LF: Re: £10 Dongel-SDR Direct sample on 504 KHz - S/N TEST
From: "Graham" <[email protected]>
Date: Sun, 7 Apr 2013 14:53:56 +0100
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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
 
 
 
 

From: Graham
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

 
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Ceterum censeo Carthaginem delendam esse
 
From: Graham
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

 
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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.
 
 
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