can replacing FET in oscillator with DRO alter it frequency more than 1000 MHz?

Status
Not open for further replies.
T

Terminator3

Advanced Member level 3
Joined
Feb 25, 2012
Messages
802
Helped
71
Reputation
142
Reaction score
63
Trophy points
1,308
Activity points
9,027
What causes that? FET inside phase shift, FET biasing, or anything else?
 

The amount of tuning that can be obtained by any of methods can reach up to +-20% of the unperturbed value of f0, however, it is good practice to restrict this amount to below 5% in order to prevent degradations on both temperature coefficient and unloaded Qs.
 
In a good DRO oscillator, the dielectric resonator determines the free-running frequency. A rough tuning is done by a conductive or dielectric post on a screw on resonator axis. Varying the distance varies the frequency.

Replacing the transistor by the same type can move the oscillator frequency by less than 5%. There are other factors like DR coupling in the feedback loop, tuning varactor coupling, etc. You did not say what is the oscillator frequency. If it is 20 GHz, a 1 GHz change is possible.
 
I replaced transistor by other type. What can i do to restore original frequency? Glue some metal plate near DRO's top? or maybe some dielectric on feedback line?
Signal loss in band-pass filter after oscillator, welding copper line above filter gives good signal, but wrong frequency. I think band-pass filter is just for DC-blocking, maybe i can remove it without harm for new transistor?
 

you can use a tuning screw over the top to adjust the frequency slightly. You can put a few drops of epoxy on top of the puck to lower F, and grind away a little material off top to raise F.
 
at 10GHz. But i can't measure it. I think it is more than 1000MHz, because band pass filter blocks RF signal.
 

Does this mean that the oscillator does not oscillate, or you don't know if it does?
 
it oscillate, because when i shortened band-pass filter, it works (gives some readings according to antenna movement and direction).
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…