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Telegraph transmitter

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NE555

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hy folks...im new guy here on the forum and i'm really looking forward discussing 'bout electronics with you...so there's something i've been trying to do and i need some help...i'm trying to build a telegraph transmitter...i have an old book with a schematic in it and the circuit uses a germanium PNP transistor...since you can't find them nowadays...i wanna replace it with some other transistor or design a circuit myself...

thanks

NE555
 

NTE100 is a germanium PNP transistor suitable for high frequency oscillation, you might be able to drop this into your circuit with little or no change. A cw transmitter is simply an oscillator operating at the desired frequency power is increased using amplifier stages.

SiGiNT
 
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sigint said:
NTE100 is a germanium PNP transistor suitable for high frequency oscillation, you might be able to drop this into your circuit with little or no change. A cw transmitter is simply an oscillator operating at the desired frequency power is increased using amplifier stages.

SiGiNT
Click to expand...

Hy and thanks for reply...i think you didn't understand what i mean...that circuit already uses PNP transistor and it's AF261. Since you can't find it anymore...is there any that can replace AF261...is there any simillar or even same?
 

I think you missed the point of my post, germanium transistors did not vary wildly in requirements, things were simple back in those days - the NTE100 is a general purpose replacement and may be a replacement for your transistor, but my recommendation just for educational purposes is to find a silicon version similar in purpose, (high frequency oscillation), and check out the datasheet in may have a circuit suitable for your experimentation.

SiGiNT
 
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oh...now i see...thanks!



and btw...schematic is here

L1 is 90 turns, extract at 45. turn on ferrite core
 
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It looks as though your transmitter is for the AM broadcast band, (about 1 Mhz), the NTE replacement should work with no problem, you might want to make the 465 pfd variable or put a 100 Pfd variable in series with a 365 Pfd fixed or what ever the available closest is - it will allow you to change frequency over a decent range - after all it is about experimenting and learning :wink:.

SiGiNT
 

well the transmitting frequency is around 600kHz with this capacitor value...and transmitter range is about 100 meters...

---------- Post added at 09:25 ---------- Previous post was at 08:42 ----------

i found this schematic

**broken link removed**

but i don't understand one thing:
On what frequency is it transmitting (wich band AM/FM)???
 

CW is continuous wave with no modulation, so AM and FM do not apply it is simply a no sound quiet spot when listened to on a receiver, it only makes a sound when you have a BFO, (beat frequency oscillator), a built in feature on most shortwave receivers that adds a tone to it - exactly like one signal interferes with another, determining frequency is by calculating the L/C frequency of the components used in the oscillator, determining your frequency was hit or miss due to the unknown of the ferrite rod.

SiGiNT
 

NE555 said:
oh...now i see...thanks!



and btw...schematic is here

L1 is 90 turns, extract at 45. turn on ferrite core
Click to expand...

I want to ask, 90 turns of what gauge of wire usually?

What difference does it make if it's on ferrite?
 

sigint said:
CW is continuous wave with no modulation, so AM and FM do not apply it is simply a no sound quiet spot when listened to on a receiver, it only makes a sound when you have a BFO, (beat frequency oscillator), a built in feature on most shortwave receivers that adds a tone to it - exactly like one signal interferes with another, determining frequency is by calculating the L/C frequency of the components used in the oscillator, determining your frequency was hit or miss due to the unknown of the ferrite rod.

SiGiNT
Click to expand...


1. What is an BFO?
2. Should I connect a receiver somewhere because I already seen some other guys on internet are connecting small receievers to transmitters

---------- Post added at 08:55 ---------- Previous post was at 08:54 ----------
Zanderist said:
I want to ask, 90 turns of what gauge of wire usually?

What difference does it make if it's on ferrite?
Click to expand...

It's 22 Gauge...and I don't know about ferrite...that's what it says in the book where i got my schematic from...
 

NE555 said:
1. What is an BFO?
2. Should I connect a receiver somewhere because I already seen some other guys on internet are connecting small receievers to transmitters

---------- Post added at 08:55 ---------- Previous post was at 08:54 ----------



It's 22 Gauge...and I don't know about ferrite...that's what it says in the book where i got my schematic from...
Click to expand...

Okay I just read this last night about why ferrite:
Ferromagnetic core materials,such as iron and steel, offer considerably less opposition to the flux than do non magnetic materials such as air,copper,and aluminum...
Click to expand...
 

hey i have one more question. I often see somebody write "80m transmitter...or 40 m transmitter".
QUESTION:
1. Is that transmitter range? if not, what is it...?
2. I see people put 3.5 MHz or 7 MHz crystal...is it than a frequency of transmitting or what...can i anyway hear that signal on regular reciever...(AM/FM)?
 

80m and 40m is a wavelength specification , another word for 3.5 respectively 7 MHz licensed amateur radio band.

As already explained, you can't hear CW in a standard radio receiver. It's only producing a light "plop" or variation of background noise.
 
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80 meters refers to the wavelength of the frequency - for instance a 1 wavelength antenna would be 80 meters long, this is the 3.5-4.0 amateur radio band - an excellent resource would be the ARRL Handbook - you can buy it or search for it somewhere else.

SiGiNT
 
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only as a quiet spot, a BFO is an oscillator built into the radio, found only on shortwave radios it operates at a slightly different frequency than the IF and is usually adjustable to create the desired tone when the CW transmitter is keyed this creates the beep beep sound you've heard in movies, an external version can be built you should be able to find schematics and instructions, alternatively you could capacitively couple an audio tone to the base of your oscillator, this is an example of amplitude modulation.

SiGiNT
 
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