Low level AM Transmitter Circuit and little description.

[goldsmith]

Hi again
A suggestion , will reflect better result, see below , please : ( when an oscillator , is working in these low frequencies ( such as MW band ) , value of capacitor shouldn't be low ! if we increase it and decrease value of inductor , thus , FM effect , will be lower ! )


Good luck
Goldsmith

 

[Eshal]

Hmmm...
Thank you both of you.

It helped me.

 

[zsolt1]

Hi,
I checked the circuit, the only mistake i made in the drawing last days is that the last tranzistor (from the rf amp) is not c548, I used BF459 :smile:
**broken link removed**
here is a picture of the transmiter
**broken link removed**
I used multiple coil pairs and a switch so that multiple wave length bands are covered

 

[Eshal]

Hi zsolt1!

How are you?

Sorry, your attachments no more. I think moderators deleted them. Kindly upload it again.

 

[zsolt1]

hi,
I'm fine, thanks.


best regards,
z1

 

[Eshal]

So zsolt1 can you tell me how much it output power?

By the way, how much output power needed to transmit a signal over the range of 50m? And what should be output frequency then?

 

[goldsmith]

By the way, how much output power needed to transmit a signal over the range of 50m?

Hi Eshal
It depends on area and material ! for example , distance that your signal can go through , will be lower if buildings are tall ( and with much iron skeleton ) . if you test it in a desert , it will be at maximum distance !
It also depends of sensitivity of your receiver . with pretty powerful and proper receivers you can receive just 10 watt from distances more than 100000Km . easily ! but price of those transmitters are very high .
So , before trying to answer your question you should think about your situation and your receiver .
Good luck
Goldsmith

 

[Eshal]

Oh.. I see.

So why our teacher said to design the transmitter over the range of 30m? Doesn't he know that we these parameter depend on range?
If his receiver has not high sensitivity then obviously he would not be able to measure our signal to 30m. Are you getting my point? What I mean to say?

BTW: in university, there are not tall buildings, just 2 or 3 story buildings, not more tall than these buildings.

 

[goldsmith]

BTW: in university, there are not tall buildings, just 2 or 3 story buildings, not more tall than these buildings.

I know it , but the problem is that you don't have an standard antenna ( with standard distance and with standard connectors and standard cables ) in your university to test ! so , prediction is a bit hard with these problems .
For measuring radiations a radiation meter needed , and i don't think that your teacher has one of them ?

Are you getting my point? What I mean to say?

Perhaps he can use a simple radio receiver and walk until 30 meter ? ha ha ! a funny event ! :grin:
THis project isn't standard , of course ( with this situation that you have ) but as you have to do it , you can increase out put power , up to 2 or higher watts , thus you can be sure about it's distance .

 

[Eshal]

OK then you are going to help me in increasing output power for my project upto 2 or higher watts bro. Are you?

 

[goldsmith]

OK then you are going to help me in increasing output power for my project upto 2 or higher watts bro. Are you?

Yes , it is pretty simple ! just a current driver should be added and supply voltage should be increased , as an example , it can be ok too ( but it is around 1 W ) see below , please :

You can easily increase it's power up to some hundred watts .

 

[Eshal]

But one thing just come in my mind now, If we increase power, will this transmitter still categorized as low level AM Transmitter, as our teacher said to design, huh?

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You can easily increase it's power up to some hundred watts .

Of course I can, but according to the requirement of project, will it be under the category of low level or it would be call high level AM transmitter?

 

[goldsmith]

But one thing just come in my mind now, If we increase power, will this transmitter still categorized as low level AM Transmitter, as our teacher said to design, huh?

Yes , i told you some watts , is low , too !

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Of course I can, but according to the requirement of project, will it be under the category of low level or it would be call high level AM transmitter?

After some hundred watts no !

 

[zsolt1]

hi,
I can't provide numerical values since i do not have special rf instruments, the tx i presented to you covers for shore 50 m. I would suggest to use the 3.5 MHz frequency

 

[goldsmith]

Hi Zsolt

I can't provide numerical values since i do not have special rf instruments

But it is bot important to have RF instruments as start ! when i have started RF , design , i didn't have many of the required instruments , and during each project i bought them , one by one !
So , what equipment you need at first ? i have some incredible solutions for peoples that don't have them . for example , i think if you have a simple LCR meter , 50 percent of problems of your design will be solved ( because it is a low power ) .

I would suggest to use the 3.5 MHz frequency

It seems good idea !
By the way , is the picture in your avatar , your picture ? :grin:
Best Regards
Goldsmith

 

[zsolt1]

hi,
I referred to rf power meter (since Eshal asked about the radiated rf power) ,reflecto-meter, grid-dipp meter, ... and so. Thanks for offering solutins, i do have commonly used laboratory instruments, but i think you should post the offered solutions you mentioned , in order to help all of us (more ideas more progress...)
yes, that's me in the middle :-D

 

[goldsmith]

yes, that's me in the middle

Ha ha ! well ! a Gentleman ! ;-)

I have many solutions about PWR meter and SWR meter and radiation meter and Z meter . at starting days of my RF design , some old friends of mine , told me these ways , and after long time i could buy perfect of those equipments . but for peoples , that haven't access to perfect equipments , can be good , chance ! now i'm going out of my home for an special aim . but at nigh , i will be in my home , and then i can draw them , and i will attach them here .
With my best Wishes
Goldsmith

 

[Eshal]

I would suggest to use the 3.5 MHz frequency

You mean if RF frequency is 3.5MHz then, range could be ~50m. Is that are you trying to say zsolt1?

 

[zsolt1]

hi,
no it has nothing to do with distance, 3.5 Mhz is "free to use" :grin:

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if you use a arbitrary frequencys you may interfer with other transceivers or transmitters. For example 0.5 ........1.6 MHz is for AM broadcasting, If you got a local radio station that uses 1.114 Mhz and you transmit on the same frequency, it is not ok (hehe... i had trouble with a retired radioamator from the army for reasons like that)
I belive that range has to do with power and propagation issues .. (some radio amators could establish intercontinental links in special conditions with only 10 W transceivers -and special antennas- ).

 

[Eshal]

I still not understand which frequency are you refering to 3.5MHz.
What is 3.5MHz frequency? 3.5MHz is the frequency of which part in the transmitter?

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I don't know anything, but if you know then kindly you should help me, because you have knowledge and I am on your mercy.