Description

When designing or tuning RF LNA or more broadly RF receiving chain, it is essential to be able to “evaluate” the noise insertion of the system under test (DUT). For this, all the major equipment manufacturers of measuring tools provide equipment called Panfi (Precision Automatic Noise Figure Indicator) such as HP8970 or Eaton 2075. The problem with these tools is that they are hard to find on the market of used equipment at reasonable prices and it often takes about 1000euros to acquire one with postage and customs.

During CJ2015, the German team of DF9IC Wolf-Henning, DL8AAU Alexander and DL2ALF Frank introduced a freeware called CANFI (Cheap Automatic Noise Figure Indicator) using a single DVB-T dongle based on the IC RTL2832 for performing measurements Noise Figure cheaply. Here is the link to the website where this freeware is downloadable: http://www.canfi.eu/. I have not participated to the development of this freeware (only to find operating bugs that have been fixed since) so thank you to contact the autors of this freeware directly for any questions inherent in its use.

The assembly described here is a synthesis of hardware developed by these three German ham radio (described here: http://www.canfi.eu/downloads/mmrt14_CANFI.pdf) and all the optimizations that can be found on Internet to improve the sensitivity of receiving DVB-T dongles RTL2832.

Here is the list of optimizations embedded in this design :

The source files Cadsoft Eagle was drawn using version 5.

Modification dongle DVB-T R820T

For integration in the assembly presented here, some modifications have to be done on a DVB-T R820T dongle (some mods are tricky : be sure you know what you do) :

  1. Remove USB connector, the LED, the IR sensor, the inductor L7 (4R7), the transil diode D6, the crystal Y2 and its 2 capacitors, the regulator U4 (3,3V),
  2. Cut the track from pin 27 of  the RTL2832 and connect that pin27 to ground,
  3. Add 10nF + 22uF on 1,2V in place of L7 and inject 1,2V from JP6 of the PCB,
  4. Add 47uF close to C1,
  5. Add 10nF + 22uF on the track just before L4,
  6. Add 10nF on the track just before L5,
  7. Add 47uF + 10nF close to C2,
  8. Add 47uF in place of U4 and inject 3,3V from JP5 of the PCB,
  9. Inject the output of the LNA from JP3 using a small coaxial in JP2 of the dongle,
  10. Inject USB signals from the PCB in place of the USB connector of the dongle,
  11. Add the following circuit to inject the 28,8Mhz in the tuner R820T :

TCXO_R820T

The PCB is designed so that JP4 (28.8 MHz), and JP1 (USB) fall in front the R820T dongle pads. The easiest way is to solder some resistors’ legs on the three points of the PCB and then set up the dongle into the shielding box by ensuring that the resistors’ legs fit directly into the corresponding pads of the dongle. It is therefore recommended to make all other mods before. Once in place, it only remains to solder the ground plane of the dongle to the shielding case on two edges.

R820T_mods

Here are the caractistics of the LNA after building the prototype (S11 at the input of the LNA using a 50ohms load at the output in place of the dongle) :LNA S11(sur charge en sortie) + S21

The S11 parameter is almost the same when replacing the load used for the measurement by the DVB-T dongle.

Usage as SDR

This assembly may also be used with any SDR software compliant RTL2832. The interest in this case is to take advantage of the optimizations of the dongle for a better reception quality (less spurs mainly, the reception gain in addition, frequency stability, noise floor slightly better).

If this arrangement is made just for this purpose, in this case, it is not necessary to wire the entire 28V supply portion to the noise source.

Some pictures of the prototype

Please note, the photos presented here are those of my prototype so there are elements that may be different from the version of PCB proposed here.

_IGP0008 _IGP0003
_IGP0004 _IGP0005

WARNING !!!!

There is high voltage in this assembly that can therefore be dangerous to handle on. I CAN IN ANYWAY BE RESPONSABLE FOR THE USE THAT WILL BE DONE OF THE ASSEMBLY : THE READER HAS TO TAKE ALL NECESSARY PRECAUTIONS FOR ITS OWN SECURITY.

For information on my prototype I protected all the high voltage section with KAPTON and I made sure to cut the components’ legs enough to prevent the KAPTON to be torn.

Cadsoft EAGLE Files

Hardware_CANFI_V1_Eagle
Title: Hardware_CANFI_V1_Eagle (948 clicks)
Caption:
Filename: hardware_canfi_v1_eagle.rar
Size: 101 KB

Bill of Materials

Parts Value Qty Package Manufacturer Description FARNELL RS MOUSER
R1 16.5k 1 0603     2059425   754-RR0816P-1652D22C
R2 56k 1 0603     2447399    
R3 12k 1 0603     9238611    
R4 100k 1 0603     2447226    
R5 4.7k 1 0603     2447385    
R6 84.5 1 0603     2303053    
R7 1.8k 1 0603     2447283    
R8, R9 0.05 2 2512     1100065   756-LRMAM2512R05FT4
R10 49.9k 1 0603     2447380    
R11 71.5 1 0603     1170672   667-ERJ-3EKF71R5V
R12, R13 97.6 2 0603     2326678   667-ERJ-3EKF97R6V
R15 6.8k 1 0603     2447427    
R16 470 1 0603     2447374    
C1, C4, C8, C13, C23, C24, C25, C30, C33, C35, C37, C42, C44, C46, C53, C55, C56, C58 10nF 18 0603     1759102   77-VJ0603Y103KXACBC
C2, C21, C39 100nF 3 0603     432210    
C3, C5, C26 22uF 3 0805   10V CAPACITOR 2346921    
C6, C15, C16, C17, C19, C20, C27, C28, C29, C40, C41, C43, C45, C47, C54, C57 47uF 16 1210   16V CAPACITOR 1828819   81-GRM32ER61C476KE5L
C7 330uF 1 E5-13   100V POLARIZED CAPACITOR 1907145    
C9 680uF 1 E5-10.5   35V POLARIZED CAPACITOR 1800669    
C12, C14 2200uF 2 E5-10.5   16V POLARIZED CAPACITOR 2346569    
C22, C34, C36 100pF 3 0603     1759066    
C31, C32, C38 1uF 3 0603     1907343    
C48 12pF 1 0603     1759054    
C49 15pF 1 0603     1759055    
C50 220pF 1 0603     1759070    
C51 270pF 1 0603     1759072    
C52 120pF 1 0603     2496885    
F2, F3, F4, F5 NFE61PT102E1H9L 4   MURATA EMI Filter 9528202   81-NFE61PT102E1H9L
L1 744232090 1 1206 WURTH   1636474 500-3032  
L2, L3 820nH 2 0805 COILCRAFT 0805CS-821XJLB 2286433   994-0805CS-821XJLB
L4 MMZ1608B301C 1 0603 TDK EMI Suppression Ferrite Beads 1669686    
L5 270nH 1 1210 COILCRAFT 1008CS-271XGLC 2286664   994-1008CS-271XGLB
L6 470nH 1 1210 COILCRAFT 1008CS-471XJLB 2286707   994-1008CS-471XJLB
L7 680nH 1 1210 COILCRAFT 1008CS-681XGLB 2286670   994-1008CS-681XGLB
IC1, IC6 MGA-30889-BLKG 2 SOT89 AVAGO   1865178   630-MGA-30889-BLKG
IC2 TL783CKCSE 1 TO-220 TEXAS   1703396    
IC3, IC4, IC5, IC7 LT3042MSE 4 MSOP10 LINEAR Ultra low noise positive regulator 2475652    
T1 ZVP4424G 1 SOT-223 DIODES INC. Transistor P-Channel 9526757    
T2 2N2222 1 TO92   NPN Transistror 1611371    
B1 MB6S 1     Bridge Rectifier 1861519    
B2 DBS102G 1     Bridge Rectifier 1A 1861404   583-DB103S-T
TR1 44229 1 EI42-1 MYRRA Transformer 6V 5VA 1689079 732-0540  
TR2 44166 1 EI30-2 MYRRA Transformer 2x15v 2.8VA 1214590 173-9816  
QG1   1 XO-14   TCXO 28,8MHz 0,5ppm (EBAY)      
J1 FN9226-1-02 1   SCHAFFNER IEC Filter 1A 2449537   631-FN9226-1-02
J2   1   FCI USB Connector type B 1097897    
J3 5747844-5 1   TE / AMP SUB-D 9 1653995    
J4 B6252HA-NPP3G-50 1   AMPHENOL BNC right angle
1076293    
J5 73251-2200 1     FEMALE SMA CONNECTOR 2293854 800-6936  
SH1 403.16 1   OKW     237-2751  
SH2 MS355-10 1         826-6807  
SH3   1   HAMMOND   4272900   546-1455N1201

Schematic

Hardware_CANFI_V1_schematic
Title: Hardware_CANFI_V1_schematic (2026 clicks)
Caption:
Filename: hardware_canfi_v1_schematic.pdf
Size: 61 KB

PCB

Hardware_CANFI_V1_implant_BOTTOM
Title: Hardware_CANFI_V1_implant_BOTTOM (945 clicks)
Caption:
Filename: hardware_canfi_v1_implant_bottom.pdf
Size: 25 KB
Hardware_CANFI_V1_implant_TOP
Title: Hardware_CANFI_V1_implant_TOP (913 clicks)
Caption:
Filename: hardware_canfi_v1_implant_top.pdf
Size: 22 KB
Hardware_CANFI_V1_PCB_BOTTOM
Title: Hardware_CANFI_V1_PCB_BOTTOM (984 clicks)
Caption:
Filename: hardware_canfi_v1_pcb_bottom.pdf
Size: 139 KB
Hardware_CANFI_V1_PCB_TOP
Title: Hardware_CANFI_V1_PCB_TOP (1029 clicks)
Caption:
Filename: hardware_canfi_v1_pcb_top.pdf
Size: 119 KB