Delfi-C3 is the first Cubesat with a linear transponder. Unfortunately the transponder had failed after short period of operation. TU Delft was planned to fly a redundant transponder, but this was scrapped prior to launch.
Now we are waiting for another nanosatellite equipped with linear transponder i.e. TURKSAT-3USAT from ITU university .The good news is that the TURKSAT-3USAT have a redundancy for all subsystem.
The backup transponder onboard VU-SAT is a good example of successful to remember.
Beside linear transponder I've came across some other features of similarity and difference between Delfi-C3 and TURKSAT-3USAT.
Structure 3U cubesat .
Size of 10 cm x 10 cm x 34 cm and a mass of ≤ 3 kg
ADCS (Attitude Determination and Control Subsystem).
Both satellites with PMAS (Passive Magnetic Attitude Control System)
EPS (Electrical Power Subsystem):
No batteries used on Delfi-C3. Spacecraft is powerless during eclipse periods of its orbit.
TURKSAT-3USAT 2 EPS units are provided. The primary unit use Li-Polymer batteries in 2 series configuration. The secondary unit use super-capacitors.
There is a camera payload to take images of the Earth and Deorbiting System.
One Unit Cubesat:
FUNcube from AMSAT-UK ,It will carry a linear transponder too that features a 435 to 145 MHz ,
I think it will be the 1st 1-Unit CubeSat with a linear transponder !
FOX-1 from AMSAT-NA a 1-Unit CubeSats with an analog FM repeater !
The 1st Cube-sat with FM repeater!
The first link through the Delfi-C3 transponder
PE1RAH Ultra Small Linear Transponder for satellite, balloon or terrestrial use