SDR TX test on 50MHz
by JA7TDO
It is difficult to get IQ Lo on 50MHz.Because 74AC74 can not work over
200MHz.This test TX is getting IQ Lo by 1.5 m patern on PCB. One signal
goes direct reaching 74HC4052.The other signal detours around 1.5m over
PCB.It become 1/4 wavelength delay.
right click for enlarge.
Crystal is 16.93MHz X 3 to 50.8MHz.
result
I can get USB and LSB using DG8SAQ SSB IQ Generator.
problem
There is little side band suppression. The cause is because an IQ
signal does not become 90 degrees precisely,I think.(I have forgotten
there is short ratio of wave length on PCB. Short ratio is about
0.56.) I am making
another PCB with adjustment for patern length.
conclusion
This method is good for transmitter ,but should not to use for
reciever.The patern for delay 1/4 length become small antenna! It round
it in a mixer.
comming soon.
I have made 90 degree phase shifter with another
method.Using inverter
and CR can make 90 degree shift on VHF easily.