Hi
I also tried some simulations on Ltspice and multisim..but i didn't managed to make any succesful simulations..
Best check the datasheet for the LDO, it'll say in there whether there's special requirements for the output capacitor. .
Another thing I notice, is isn't there supposed to be a second 47K between base and ground? (not just the one 47K).
The other thing that's frustrating with transmitter circuits when you're inexperienced, is that you don't know if it's making much RF power or not. Or what frequency it's on even. Most hobby oscilloscopes won't even register 100 MHz.
A great piece and a very useful piece of RF test equipment is an RF sniffer. Get a moving coil microamp meter, and wire two small schottky diodes in series, connected between the meter's + and - pins. From the centre tap, you can either touch it on the circuit and see if there's RF present, or you can attach a piece of wire and make a field strength meter
You must have a ground on the LTspice circuit.!
EDIT:
Try this sim as a starter.
If you post a link to d/s, someone, or me can oblige.why don't you?<..> read a datasheet...
This transmitter design is very very old. I built one very very similar 30 years ago, and back then it was the same 2n2222 as well. Over the years I'd expect it to evolve a bit, but I wasn't expecting to see the base of the 2n2222 with only one resistor. This circuit used to have a 10K up and a 10K down from the base in the 1970's. Perhaps it was done that way back then because transistors used to have varying hFE and they are more stable nowdays.can you explain further? first of all my schematic it is based on Audioguru's design...most of the circuit it is taken from his design.
https://www.electro-tech-online.com/threads/help-with-rf-diode.34306/you mean something like that?
If you post a link to d/s, someone, or me can oblige.
But reading between the lines, if the output current is only a few mA (note there's 0.65 mA idle current), it probably goes unstable if the output capacitor is more than 10 uF, and if it's 'too good' a capacitor. Fix this by replacing any fancy tantalum with some crappy electrolytic instead, or if you can't find one put 0.1 Ohm in series.
I just looked at the ferrite data. Ferrite is magical stuff, solves lots of problems. It's under-rated.
Just wondering, why was AJ6 ferrite chosen? Any special reason?
the specific ferrites are what's left from an old project of mine...
47K biasing resistor at the oscillator transistor must be lower value or higher value when the regulated power supply is 3.3V?
the feedback capacitor at the oscillator transistor substracts or adds to the capacitance of the LC tank?
how can i accurately know the resonant frequency for my LC tank?
Measure and report the DC voltage on the emitter resistor, then I'll tell you. If there was 2 base resistors the circuit would behave better.
Easiest way I found of measuring the res frequency is 'dip-it'. By using a hand-held Grid-Dip Meter that sweeps through frequency until it hits the tank frequency. When the osc is powered it'll be a slightly higher frequency, because the transistor is a _Varicap_, with a voltage on it. A calibrated wavemeter is a good idea to have, they do not 'lie' like a radio can.
right now i got a 15K biasing resistor the regulated voltage for some reason dropped to 2.80V and after few minutes it went again 3.28V...the voltage to the emitter resistor is ~920mV
you mean a frequency meter? my english aren't that good... if you mean that...i had one Lutron LC-1200 available few days ago...
Maybe RF is reaching the reg and it's over-reacting to it? Just maybe. If so, a ferrite might save the day. Also, is the supply rails of the oscillator decoupled together, decoupled separately from the reg IC?
920 mV is reasonable. You can get more or less RF by changing this voltage by altering the 15K. You usually get as much RF as you can.
Try put ferrite just upstream of decoupled osc. supply rail.
yea! i know about the ground.. but it was a messy simulation anyway... i couldn't find the right components and the appropriate values...Ltspace can't find the LM317 so your simulation also can't work correct. can you help on that?
Place these files in the appropriate LTS folders.
where is the upstream?give me more details on how to arrange the ferrites and how to do a more careful decoupling..
i don't have problem re designing the PCB layout (since it helps me get improved) but atleast if i have to develop a new PCB it should work this time
btw i don't see any comments on my design...
Before add ferrites I think you ought to temporarily stop the oscillator and see if it's RF that's making the LDO malfunction.
I would put a ferrite in the power line feeding the oscillator. The ferrite to attenuate the RF reaching the LDO.
I'm puzzled why there's surface mount components used on your PCB? I am sure leaded components work just as well and they are easier to use.
You know I normally recommend people to do as much as they can to design an unfamiliar RF circuit first, before doing a PCB for it. If it's leaded components, you can even develop this circuit on 2 short lengths of tinned copper wire screwed to a peice of wood! Then when you're happy with the design, you can do a PCB. Some people I know prototype the PCB layout on blank sheet with tinned copper wire as though it is etched tracks.
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