Fly swatter ham radio transmitter

[joeqsmith]

Output winding.  Second harmonic is present.   

[joeqsmith]

The flyswatter ran from 2 X AAA batteries.  I had damaged the transistor while running it from an external power supply.   Swapped out the dead part for a beefier part.  Added a GDT to the output to prevent it from over voltage (future experiments) and doped it up.   With 3XAAAs, it runs cold.

[joeqsmith]

Coil with antenna and flyswatter.   Looking at the signal with the SA, it's fairly broadband compared with other stations as expected.    Also shown is my TECSUN PL-990 receiver.   It's not a bad general purpose radio.   Encoders have been flawless. 

Using this dead spot of the band, I can receive the signal almost on the other side of the house.

[joeqsmith]

ARRL article starts out talking about a car's ignition system.

https://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/Kennedy%20N4GG.pdf

If we grounded the car’s chassis, connected an antenna directly to the ignition coil’s HV output and added a telegraph key in series with the ignition coil primary, we would have a complete 1900 spark gap transmitter along with 21st century “comfort features” like a leather operating seat and a sun roof. What could we do with this lash-up? We could transmit Morse code to a range of about 10 miles, with the emission occupying a huge amount of spectrum, centered on a frequency determined by the L-C resonance of the antenna’s series inductance and parallel capacitance to ground.

With the modern resistive plugs and COP, I doubt it.  Even in the case where I used an ignition coil to drive mine with an antenna attached, I made it to the neighbors house.  A long way off from 10 miles.   My dipole is cut for the 40M band but I never measured it.   Consider I was transmitting closer to 25MHz, that certainly wasn't helping.   The FCC would have to be parked in front of my house to pick it up.       I wonder back in the early days how far the typical hams were actually able to communicate.  Consider the receiver I was using is a lot more sensitive than anything they had at the time.     

This last attempt will operate down to  6MHzish and should handle higher voltages once I replace that tiny tuning cap.     

[joeqsmith]

So far for all of my testing I have used DC voltage charging the cap at what ever rate, or in the case of the car ignition coil, driving it with my function generator.  I am thinking about making some sort of auto keyer for it. 

http://www.trainelectronics.com/MorseCode/
(I like their yard train set)

The plan is to have a programmable 1Hz to 1Khz with a fixed one-shot to drive the ignition coil.  I would mount everything,  including the battery.  The coil driver and would be on the same board.   Problem with increasing the voltage is it can create a fair bit of noise which could impact the circuit.   I thought about using CMOS gates to generate the timing and hard coding the identifier in diode logic.  Basically run it off a higher voltage to improve its margins.   It's not like we are dealing with anything fast.   

Micro would make more sense.   Just a DIP switch with a couple of bits for the modulation frequency (1,100,500 & 1k), 1bit for 5 or 10 WPM,  1bit for auto or manual, and a couple of bits to select an ID message.   

Idea would be to make it easier for the FCC (really me) to identify the source of the noise.   Right now, I am listening for a "click" sound which makes it difficult to tell if I am just hearing noise or the actual transmitter.   

[joeqsmith]

Shown with new tuning cap.  Running 5kV to the primary will cause it to breakdown but it easily handles 2kV. 

[joeqsmith]

Taken from the above article:

The beauty of this program is the way that it stores the information for each Morse code character.  It uses the  first 5 bits of an 8 bit binary number (made up of 1’s and 0’s) to store the dot / dash information for each character and the last 3 bits to store how many dots and dashes there are.  For example the letter “L” is “._..” .  0100 would represent dot/dash/dot/dot with zero (0) for a dot and one (1) for a dash.  Since the Morse code representation of the letter is four characters long the end of its binary representation would be 100 which is binary for four.  Finally, put it together: “0100” + an extra filler zero + “100” gives us 0100 0 100 (01000100) in binary which is 68 in decimal.  The letter “R” would be 01000011, or 67 in decimal.  The easiest way to decode 010000011 is to take the last three digits, “011” which equals three, and use that number as the number of characters to take from the “front” of the number.  That gives us “010” as the code which is dot / dash / dot. 

I think the basic idea is fine but punctuation characters are 6 places.   Looking at the last three bits,  I am thinking anything over five, is a six place character.  110 would be 6 places with the 6th (LSB) set low (dot).  111 would be 6 places with the 6th place set high (dash).  For example a '.' which is dot,dash,dot,dash,dot,dash  would be represented with 01010111.    A '?' would be 00110110.   

[joeqsmith]

I was thinking about adding a small amount of C in parallel with the spark gap.  Idea being I could apply more energy to the gap itself than what is available in the tank.  In turn it would further ionize the gas and reduce the impedance of the gap.   Of course, you would take longer for the current to fall off enough to clear the gap.  Not a good idea for a transmitter....

Article discussing several of Tesla's patents.   
https://waveguide.blog/tag/spark-gaps/

[joeqsmith]

Assembled and running with flyswatter.   

[joeqsmith]

Article on early detectors.  I've never heard of most of these. 
https://earlyradiohistory.us/1917de.htm

[joeqsmith]

Homemade detector from a glass fuse, two brass inserts and a slurry of metal.  The grill starter will trigger it from across the lab with no antenna but my transmitter, with a clip lead attached, sitting next to it, will not trigger it. 

[joeqsmith]

Housing for the aerial current and reflected power meters.   

[joeqsmith]

Left is a supply from an old air filter.  Takes DC in and outputs about 6kVDC.  The rectifier is internal to the white blob.   

Center one of those low cost HV transformers and MOSFET to drive it from and external signal generator.  The problem with this is the output power is very limited.   

Right is the flyswatter power supply.  Was 2kV DC.  Transformer is a kV with doubler.  Output cap removed and replaced transistor to allow operation at higher voltages.  Very limited power available and I want to drive the spark gap with a variable frequency. 

Leaning towards the car ignition coil.   Idea again is not to produce lots of noise and wipe out all of my neighbor's AM broadcast reception.   Maybe a small motorcycle coil would be a better choice.   

[joeqsmith]

Using a car ignition coil to power the latest transmitter.  Using my new Tecsun PL-990 portable receiver to determine how far we are transmitting.   Also shown is a demonstration of the home made cohere.   



Old movie showing using an X-ray machine as a transmitter to signal for help.  In the movies, it messes with every radio broadcast.  It's Hollywood..