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UHF AM Transmitter

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Jeg

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Hallo everyone and happy new year :)

I would like to make an AM transmitter for sending low freqs from 20 - 50 Hz.
The band i would like to use is between 300 - 900MHZ (More or less).
Is it possible to manage it by the use of transistors? Do u have a schematic or something with an LC tank and transistors (for these freqs)?
Power supply not over 9V.
Do u think it is easier by the use of a chip? If yes, is it possible to propose me some types?

Best Regards
Yannis G.
 
Jeg said:
Hallo everyone and happy new year :)

I would like to make an AM transmitter for sending low freqs from 20 - 50 Hz.
The band i would like to use is between 300 - 900MHZ (More or less).
Is it possible to manage it by the use of transistors? Do u have a schematic or something with an LC tank and transistors (for these freqs)?
Power supply not over 9V.
Do u think it is easier by the use of a chip? If yes, is it possible to propose me some types?

Best Regards
Yannis G.

Did you search the forum for "300MHZ"
 
Why do you want to do this?

Is it for a control system or are you sending data?

Does it need to be linear or is it alright to send pulses?

What reciever are you using?

You haven't supplied enough information regarding the modulation, SSB, DSB?

It's probably better to buy a pre-made transmitter unit rather than attempting to build your own.
 
Thanks for replying guys,
Mramos1 i didn't find anything that fits my requirements! But i haven't checked all the posts yet.

Hero999
It is for sending sinus continuous signals. DSB fits my requirements, and i prefer it to be linear. Its not for control, its for education purposes. I haven't thought of the receiver at the moment, because i haven't yet decided if it is going to be with transistors, chip or with a pre-made module as you said. I will build it in the same philosophy as the transmitter. I would like it to be portable with a small helical directional antenna that i have already in my mind. I have some drawings of transmitters up to 120 MHz, but the dimensions of the antenna make it too difficult to carry! :confused: ;)
 
I still didn't find anything on internet!!!
At least does anyone know a chip that i could use ? If the problem is the linear thing, then it's ok for me to build a none linear tansmitter!

Thanks in advance:) :) :)
 
Jeg said:
its for education purposes.
Right, so this is college work then.

We don't mind helping you but we won't do all the work for you.

Perhaps you should check out this page for inspiration.


There are still other factors to condier like frequency drift, power output and whether this transmitter is actually legal in your area.
 
Does anyone even use AM at those frequencies? FM would probably be easier to implement.
 
Thanks for the replies my friends!
I'll check your links shax! ;)

Hero you almost got me!:D
Can you pls explain to me about the freq drifting?

Thanks in advance
 
Until now i managed to take an output of about 101MHz. (Even the tank circuit is tuned to 120MHz!!!) Where did 20MHz go? I made many combinations of C1 R1, but the result was not so hopeful. :confused:

**broken link removed**

Anyway when i tune the tank at higher freqs, the transistor is dramatically slow!
Can a circuit like this generate high and steady Carrier Freqs? Do u think that i can not reach high output because of this specific type of transistor?

Do U think its simpler to make use of chips like MC44BS373CA ?
(Technical Data:
https://www.electro-tech-online.com/custompdfs/2007/01/MC44BS373CA.pdf)

:)
 
Last edited:
At the risk of repeating myself (as I've said in the dozens of similar threads!), you can't calculate the frequency because you don't know the values - stray capacitance and stray inductance will completely change your calculated values. Layout is also very critical, and gets more so as you go higher!.

If you want a radio link, use licence free radio modules, which will be legal to use - your homemade almost certainly won't be legal!.
 
The frequency is lower than you calculate due to the capacitance of the transistor and C1. I think you have not actually built this because the Ft of up to 2gHz will allow it to oscillate at frequencies that you can't measure unless the layout is very good. It would be better to buy a crystal controlled unit unless you want the experience of building it yourself. Check out QKITS ( https://store.qkits.com)
 
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