Transmitter and crystal oscillation

Status
Not open for further replies.
M

manve_13

Junior Member level 1
Joined
Mar 1, 2010
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,455
Hello,

I'm trying to design a transmitter thats going to work around 216Mhz. I have a crystal that's frequency is 72.025Mhz. So according to the this thread (https://www.edaboard.com/threads/137908/)
and this image . If I use 10pf capacitor, my inductor value should be .05uH. Thats true, right?

But when I connect the collector of the transistor to the oscilloscope, i see a signal like this "vV" little one's magnitude is 15mV, bigger one's is 25mV. As i know i need to see an oscillation with magnitude Vcc x2.

How can i make my crystal to oscillate?
 
Last edited:

.17uH with 10 pF will resonate at 1/[2*pi*sqrt(.17u*10p)] = 122 MHz

if you want a resonance at 216 MHz you'll need C=1/[(2*pi*216MHz)^2*0.17u) ≈ 3 pF

C is quite low and layout can be critical. Keep L//C close one each other.
 

Data sheet is for inductance of 680 nH, not 50 nH.
 

In addition, you hardly can acquire the oscillator output with a passive oscilloscope probe at the collector. It will completely de-tune the circuit, add a strong real load and most likely stop any oscillation (if the oscillator has been working before).

If the crystal isn't designed for overtone operation, it will possibly show very bad behavior at 216 MHz.
 
In the HF frequency range higher Q is a must for inductors as it represents less dissipative loss.
For the best results air core inductors are often silver plated, but also enamel covered copper wire will do the job as copper inductors has acceptable Q. Try to make your own 50nH inductor, see details
An introduction to the air cored coil
 
I dont think its possible to see 216Mhz oscillation with my oscilloscope(Discontinued Model 2120A, 2120 20 MHZ SCOPE WITH PROBES - DISCONTINUED - B&K Precision), Im going to buy a new one, can you suggest one around 400$? I'm thinking to buy this one (Amazon.com: Rigol DS1052E 50 MHz Digital Oscilloscope with 2 channels plus USB storage and connectivity and 1 GSa/sec sampling: Industrial & Scientific)

And about my circuit, I've found this circuit on web, but its not working.

This is going to be tracking transmitter, so for beeping rate I'm using R1 as 5.1M and C2 as 4.7 uF. R2 is 8.2k.

I have a 72.025Mhz designed for 3rd overtone crystal. C3 and L1 is for tuning oscillation around 216Mhz. I used 2.2pf and .247 uH.

I dont know exactly what's for R4 and C4 but i want to boost the range with that transistor.

How should I calculate the value L2?

If someone can help me about these circuit, i would be so appreciate.

Thank you.

 

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…