DVB-T2 Front End

[swarg_eu 43]

Selfmade RF frontend for Video signal (Analog, DVB-T, DVB-T2, CATV) amplification in a 75 Ohm system.

 

The RF frontend contains the following building blocks:

4-Way Wilkinson power combiner - combines the signal from 4 antennas (~6dB gain)

bandpass filter - eliminates the interfering radio signals (FM...)

low noise amplifier with a voltage regulator - for sensitivity improvement (~21dB gain, NF~1dB )

 

Interconnections: 

4    F type connector 75 Ohm inputs (antenna) 

1    F type connector 75 Ohm output (receiver side), requires a bias voltage in the range of 6-20 VDC and ~60 mA (for example: ZS300 antenna power injector )

 

Technical data:

Frequency range  from ~460 to ~880 MHz

Noise figure >2,5 dB (including insertion losses)

Gain <25 dB (including insertion losses and combiner gain)

P1dB ~19dBm

Max Pin 17dBm

Size ~250x120x25 mm

 

The use of this RF frontend is recommended in one of the following scenarios:

the picture is pixelated but you are already using a high gain antenna and amplifier

you are in a high power RF environment, Amateur Radio, FM radio is attenuated by more than 80dB ...

you want to combine the signal from multiple directions to a single cable (signal quality will/can be reduced)

 

Basic knowledge in antenna (phase) arrays is recommended to exploit the benefits of the RF frontend. 

Protective housing not included.

Antennas not included.

Power injector not included.

Coax cable not included.

 

Test results (scenario with a pixelated picture and high power RF environment)

 

DVB-T2 Transmitter side cordinates  45,89938 N; 15,94786 E;

DVB-T2 Reciever side coordinates  44,47105 N; 17,97297 E;

Link distance ~225 km, no line of sight.

 

Receiver side 2x2 antenna array with Triplex Loga Iskra P-47N (without an amplifier, marked on radio tower picture), connected with ~1m RG-6/U coax cable (length variation between antennas <1cm) to RF frontend.

Received signal strength (SNR) above the threshold including fading effects (SNR range 29-37 dB).

Successful elimination of interfering radio signals (see measured transmission response) on the receiver side (4 FM station with 400 W  ....)

 

Free worldwide shipping with DHL.

[swarg_eu 43]

Update,

Today I replaced an old front end and got additional 1.5~2 dB.

The old one had an improvised shielding 

[clanon 246]

How are the signals COMBINED...?

it's some kind of diversity or just added Gain...(like a Single antenna with 6dbi more...or so...)

Edited August 13, 2020 by clanon

[swarg_eu 43]

Combined via 3 x wilkinson splitter

2x antenna on wilkinson

2x wilkinson on wilkinson 

Its just added 6dBi gain by combining the 4 antennas to a 2x2 array

 

[Admin 2545]

,,, for the frequencies of 1.7 --- 2.7 GHz a splitter can be built...???

[swarg_eu 43]

Yes the length of the transmission line needs to adjusted  

https://www.microwaves101.com/encyclopedias/wilkinson-power-splitters

The simulation results for the DVB-T2 splitter 

[Admin 2545]

,,,swarg_eu ,you can post the hfss* file with a splitter on the frequencies 1.7-2.7GHz...???

[swarg_eu 43]

75 or 50 ohm system?

2 or 4 way splitter?

Is FR4 1.6 mm ok?

[Admin 2545]

,,yes ...!!!

-50 Ohm system--4 way splitter---FR4 1,5 mm

[swarg_eu 43]

finally got the time for the splitter

 

version 1 - a combination of Wilkinson and  impedance transformer

isolation >10 dB between the 4-antenna ports

 

version 2 - Wilkinson (the 50 Ohm line between the splitters is long and introduces some side effects in S33)

isolation > 20dB between the 4-antenna ports

 

for both versions, the GND VIA connection is modeled as a solid in the substrate (faster simulation), port 1 antenna input port 3 combiner output 

4-way_v1_TOP.dxf

4-way_v1_VIA.dxf

4-way_v2_TOP.dxf

4-way_v2_VIA.dxf

[Admin 2545]

,,,thanks Swarg_eu...!!!

,, so V2, is better ... ???

 

[swarg_eu 43]

yes, I would choose v2

[Admin 2545]

,,,hi buddy...!!!

,,,you can also make a 4-way Wilkinson with an impedance of 75 Ohm...???

[swarg_eu 43]

that no problem 

waths the frequency range?

[Admin 2545]

,,,the same...1.7-2.7 GHz

[swarg_eu 43]

finally got the time

 

4-way_TOP_75.dxf

[Admin 2545]

,,,thanks swarg_eu,can you put these dimensions, please ... !!!

[swarg_eu 43]

on the 75 ohm line, the radius is 7 mm, 3 mm from the end of the PCB

6 mm long line with a cut in the middle of  0,4 mm  to solder the 150 Ohm resistors

 

All 3 splitters have the same dimensions:

the radius on the transformer lines is 2,5 mm and the axial distance before the bending (from 75 Ohm line) is also 2,5 mm

the axial distance in the Wilkins splitter is 11,28 mm between the centers of the two radius bends 

the axial distance of the transformer lines is 2,88 mm (near the 150 Ohm resistor)

 

The horizontal distance between the two spitters is 25 mm 

75 Omh line 1,2 mm

transformer line 0,48 mm

[Admin 2545]

,, please if you can tell me if you can make a splitter for 4 batwing or 4 patches antenna with 75(100) ohms each...

[swarg_eu 43]

draw me a basic schematic of what you are planig

antenna impedance, source impedance ...

[Admin 2545]

,,, about these can be the dimensions...

Guanella transformers...

[Admin 2545]

,,, another way to adapt with the Guanella transformer....

[swarg_eu 43]

for this type of antenna, a simple power splitter is not a solution (no phase shift between ports)

the patches need to be driven with a 180 deg phase shift, otherwise, there will be no main lobe in the radiation pattern (in its place will be a zero)

Therefore it uses a transformer (wire loop) that transforms the single-ended (asymmetric) to differential (symmetric, 180 deg phase shift) port

the rest of the PCB traces (GND below) ensures a proper impedance match 

[clanon 246]

Losses...?

(besides Dielectric , tan loss)

[swarg_eu 43]

On 27. 10. 2020. at 6:11 PM, clanon said:

Losses...?

(besides Dielectric , tan loss)

for what?