there is a major fault in the dro schematic.
somehow the schematic works and does
deliver very good video.
The NPN seems to be working as a diode.
I bought some 10 GHz lnb's in the past which where usable in the 10 GHz band.
Some of the lnb's are now turned into 10 GHz transmitters based on DRO modulation.
With the first experiments I used a simple amplifier with a single transistor.
The amplifier had poor amplification so I had to come up with a better amplifier.
After digging in some
old schematics I found a non inverting Video Amplifier.
After some work I turned
it into a good non-inverting DRO modulator with sufficient Video Signal.
you can see the final schematic.
Use R9 to set the desired DRO voltage.
But be carefull while setting the DRO voltage.
Some DRO's might get killed when they
endure to much voltage.
I experimented with a DRO in an echostar LNB type ILNBTBXXX.
These DRO's can withstand 8V for some time.
I have made a <document> with this schematic plus the print
and its layout.
But as a perfectionist i was, i still was not happy with the video quality.
I started to splitt the schematics and i used as little electronics as possible
inside the LNB.
The changed and better working DRO modulator can be seen below:
The potmeter R11 must be adjusted before soldering J3 to the DRO.
Adjust R11 to get 5V on J3.
With no doubt this modulator delivers good video.
The Baseband in needs a very low level video. Maybe about 200mV.
This depends on the sensitivity of the DRO.
If the RF output of the LNB delivers a vage or faulty video signal on a
sattelite receiver then the impedance of the RF paths can be wrong.
This is difficult to correct. that's way i use the echostar lnb's.
These are supurb in comparison to other lnb's. And there is enough space
inside too for alot of pcb's.
Baseband in means that the Video has undergone preemphasis and has
been given an audio carrier.
Below you can see a preemphasis schematic:
R15 can be 2 resistors parallel to create the 75 ohm value.
Audio can be plugged in "baseband out" with a very small capacitor
You can experiment with capacitor until there is no damage to the video quality.
My last advise is to use 2 cables for a transmitter lnb.
1 for baseband in.
1 for powersupply.
Video quality will always degrade if you try to combine supply and video.
Video Quality of my DRO based transmitters
My capture card and camera are not of the best quality so I better show a comparison.
A picture taken with my sony camera directly connected to the capture card:
A picture taken with the receiver connected to the capture card.
The camera signal goes in the basebandmodulator first as it goes into the DRO