I am trying to make a short distance transmitter and receiver using logic gates , 555 timers , Capacitors , OpAmps and Crystal Resonators . I know how to make a transmitter with 555 timer (square wave) it transmits Morse code at a frequency of around 24kHz but I can't make a proper receiver of my own . Any idea for a circuit? I really don't know what to do ...

 

Interesting nickname.

 

Is this over the air or over wire.
How does the 555 send the Morse Code?
How is the 24kHz modulated?

 

Google "vlf amateur radio", tons of stuff out there
on VLF.

Regards, Dana.

 

Well I googled it but found nothing for more that 9kHz . For the transmitter I used a 32.768kHz crystal to generate the carrier wave . I have 2 of these crystals . Can I use the second one to make a low pass filter for the receive and then lead the signal to an amplifier ?

Also can I use an NE555 timer chip to filter out all the other frequencies from the receiver?

 

Hello,

Again, how is the morse code modulated on the carrier?

Here is a schematic of a VLF receiver:
http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/ar/1989/12/page10/index.html

Bertus

 

I just added a 4 pin push button , one pole is connected to the antenna and the other pole is connected to ground through a resistor . Amplitude is reduced significantly when I press the button but the oscillation's frequency remains stable

 

The 9 Khz VLF information is pertinent to VLF antenna construction,
and receiver design. You would scale the design for the particular
frequency of interest. Principles and issues same across this band region.

The ARRL has several books on VLF design.

http://www.qsl.net/on7yd/136lit.htm other info.

https://pe2bz.philpem.me.uk/Comm/- ARRL/VLF/vlf.html



Regards, Dana.

 

Here are a few more references for your VLF receiver:
http://www.burningimage.net/clock/2007/10/23/sensitive-60khz-receiver/
http://www.qsl.net/dl4yhf/speclab/vlf_rcvr.htm
Austria Microsystems: AS3933 and AS3931 Low Frequency Wakeup Receivers

The input FET (2N3819), which can be hard to find, may not be necessary depending you your signal strength/antenna. The rest is basically op-amps and filters.

 

So you say that I can't make a band pass filter out of crystal oscillators . For a 32.768kHz signal what is the length of the wire (antenna) in meters . The width of the wire is 22mm

 

Here are the designs. I followed the FEBO design and used 100 ft of shielded coax:
http://www.stormwise.com/page28-VLF.htm
Here's the antenna I made: https://www.febo.com/time-freq/wwvb/antenna/


Here's my receiver schematic w/ antenna:


My antenna:


And the tuner/match box:


I was an air core variable capacitor to get close, then used mica fixed capacitors for the final tuning. Mine was tuned to 6o kHz (WWVB), but you can tune to any VLF.

 

This is the transmiter circuit : http://tinyurl.com/y8wur7md
analog out == antenna
P.S. frequency is 32.768 kHz not 400Hz
Can't I use just one wire (long or short I dont really care) to receive the signal ove a distance of around 10 - 15 meters ?

 

P.S. frequency is 32.768 kHz not 400Hz

So far as I know, you can use a coat hanger. 32768 Hz is about 9155 meters in air; shorter in water based on the refractive index. Anything practical will be "short" in radio theory.

Where did the "400 Hz" come from? Your original post mentioned 24 kHz, now 32 kHz. My experience is at 60 kHz, which is close enough for comparison. I have also listened to the Soviet/US? submarine bands on SDR at lower than 24 kHz as I recall.

 

Where did the "400 Hz" come from?

I used this frequency for demonstration purposes . I increased the 555 timer oscillation square wave frequency at 53.something kHz . Now what is the length of the wire needed ? if I use it to transmit under sea water how shorter does the wire become??

 

Look up "refractive index." It is wavelength dependent. Since your antenna(s) will be a small fraction of the wavelength in any case, you decide how long a wire you want or can use and design around that. You have been given several links on point.

Edit: Here's a link that might help: https://en.wikipedia.org/wiki/Wavelength