Hunny, there are some gentlemen from the FCC at the front door saying there is a communications blackout for a 1/4 mile around our house. What did you do now!!! LOL

@joesmith-je3tq

2 ай бұрын

Hopefully our government has better things to do.

I’m also reminded that many early Tx’s were actually rotating machines wound to produce a fundamental carrier and then the field windings were modulated with an audio source.

Awesome video Joe! If you haven't already check out the book called "200 meters and down" it's a fun read about early radio. Thanks for sharing.

I remember reading in old QST's (late teens, early 1920's) talking about hams using a spark coil from a model A and a decent antenna maybe getting out a few blocks at most. Many early hams might get out a couple houses away. Not too worried about your baby spark gap transmitter causing problems. Love this series! Thanks for doing this!

@joesmith-je3tq

2 ай бұрын

I imagine back then the majority of hams didn't have access to much beyond the ignition coils. I could increase the output level of this transmitter by increasing the breakdown voltage of the spark gap. At the end of the video, there were a few slides. One showing the turning capacitor used in this transmitter breaking down. I think this was with 3kV on the gap which would get us 600mW.

Interesting experiment, nice variable capacitors, I’ve not seen any suppliers of such parts since the mid 80’s here in the UK. Spark-gap transmissions are illegal in the UK.

@MidlifeRenaissanceMan

2 ай бұрын

Ali Express has some C&C / 3D print variable capacitors for a _reasonable_ price. Haven’t ordered any just yet. I was looking for a dual gang version for a mag loop.

@joesmith-je3tq

2 ай бұрын

@@MidlifeRenaissanceMan Good to know. This particular part breaks down below 3kV. This is why the transmitter was limited to 1.6kV. Lots of margin. Looking for used, higher voltage, higher capacitance parts, didn't turn up a lot.

@MidlifeRenaissanceMan

2 ай бұрын

You’ve kind of got to make your own for that stuff. I’ve made all sorts of high voltage things for magnetic loop antennas out of coax, out of plates, out of series / parallel 6KV ceramics. If you try hard enough you can make flames :-) I’m keen to build a tight bandwidth spark transmitter and matching. Cohera receiver. That said, the Titanic had a regen receiver on board. The Cohera was the backup.

Great work, most enjoyable

Yes demonstrating that a good antenna and ground are important. Decent ground, long wire antenna and you probably could get some better range on that. At least along the terminator line and at night.

Good fist. All the best books on longwave seem to have been published before about 1930, back when people were still developing radios and antennas for those frequencies. I have a few of my owwn, and read others from the NIST library when working on my longwave antenna design. Nowadays there is very little in the way of comprehensive info published on the subject.

Looks similar to my homebuilt CB radio receiving crystal radio which tunes to 8 to 30 MHz

Here's a high voltage puzzle that I hope isn't too off topic: I have a grounded in-line PolyPhaser IS-50UX-C0 coaxial lightning protector (with internal discharge tube) installed in the feed line between a 17.5 foot tall 2m 3x5/8 vertical antenna (mounted 44 ft. at the tip) and an iCom V/U FM transceiver, with the protector unit located a few feet from the radio, inside my house. I was sitting only a few feet away a few nights ago when I heard a loud crack, like a high voltage discharge. I may have seen a flash too, but I was most impressed with the very loud crack, which was about 10 times louder than an outdoor bug zapper. My rig immediately shut down, apparently some kind of protection circuit, leaving it undamaged. But there was no lightning outside and I heard no thunder. The winds were calm and the sky clear except some thin streaks of wispy clouds. So where did this sudden high voltage discharge come from? (I say "sudden", because I assume any slow static charge would bleed off as the gas discharge tube is designed to do.)

@mikesradiorepair

2 ай бұрын

They do not bleed off charge. As voltage applied across the electrodes is increased it eventually reaches the "strike/breakdown voltage" and at this point the localized ionization of the gas initiates a avalanche process that spreads through the tube and it discharges. To eliminate the build up of charge the easiest thing to do is add a high value resistor between the center conductor and shield/ground. Most "cheap" two way radios did just that for decades on base station radios. If you looked inside the radio you would find a resistor from the center conductor to the chassis. It would not protect from a lightning strike but does protect from electrostatic fields building up on your antenna that causes ESD damage. I have only ever worked on one radio that was the victim of a lightning strike and you could tell by the rather charcoaled interior. On the other hand I have repaired dozens of transceivers and receivers that suffered from a ESD event. All it takes is dry air and the slightest breeze blowing across your antenna or snow.

So the Tx must be similar to a square wave modulation and therefore have an infinite number of harmonics at odd frequency spacing. If there are any apparent sub-harmonics then that suggests an AM type of modulation or even FM. Fascinating.

@joesmith-je3tq

2 ай бұрын

Sorry but you lost me as soon as you mentioned square waves.

@G6EJD

2 ай бұрын

Well before the spark-gap is triggered there is no current flow, then when it does, current t flows, it repeats at the resonant frequency, and so the waveform is effectively a square wave as there can be no modulation and the only current shaping will come from the inductance, either way it’s a very crude on-off energisation of the tuned circuit, hence the huge number of harmonics being produced rather than the single fundamental more normally expected. 73 Dave

@joesmith-je3tq

2 ай бұрын

@@G6EJD Of course there is current flowing before the spark gap triggers. The trigger time is not controlled by any resonant frequency, rather by how fast I trigger the coil. I showed the output waveform which was hardly a squarewave. Instead it is a dampened sinewave with a log shape. The resonance of the tank sets the output frequency (MHz), but has nothing to do with the spark rate (Hz). About the only thing we could consider a possibly a squarewave was my cycling the power to the transmitter with a 2 second period and 50% duty cycle.

@G6EJD

2 ай бұрын

@@joesmith-je3tq I’m confused as to how a current can flow through a spark gap until the gas has broken down to ionise a path that allows conduction, plus the parallel tuned circuit must severely attenuate any current flow either side of its resonance, so the tuned circuit must be a dominant controlling factor of the oscillation frequency.

@joesmith-je3tq

2 ай бұрын

@@G6EJD Your original statement was "before the spark-gap is triggered there is no current flow", which is not correct. As far as current through the gap prior to triggering, there would still be some some small amount but we can ignore that. Correct, as I stated previously, the resonance of the tank sets the output's dampened oscillation frequency. Nothing square wave about any of it. If you checkout the following link, I have the transmitter tuned for 6MHz and look at the output up to 20MHz. The step is caused by the SA. www.eevblog.com/forum/rf-microwave/fly-swatter-ham-radio-transmitter/msg5433917/#msg5433917

I still can't get over the fact that we can communicate from one end of the world to the other with such a simple device. This is astonishing. I am designing a spark transmitter that can operate in Hellschreiber mode using the Chaffee gap, in addition to microphone modulation. May the delicate vacuum tubes and cheap transistors can go to hell.

@joesmith-je3tq

Ай бұрын

Look at old photos of Marconi's station in Kahuku Oahu to get an idea of what it took to reach the end of the world. It's amazing how far mankind developed this technology in a such a short time span. Also how so many other areas of technology fed into that, like space flight for example. I posted some screen shots showing a gap cycle time of 40kHz using this ignition coil. That was the fastest I was able to achieve.

@AlexBurtonMusic

Ай бұрын

@@joesmith-je3tq Yes. Very large antennas are required. However, the Chaffee gap consists of trains of damped waves that meet each other in the correct phase in the 2nd or 3rd cycle. Practically they are very close to the continuous wave. They can also operate up to 15 MHz. Maybe you know. Even a small improvement like Telefunken's multi-plate discharge gap provided a huge increase in range and allowed for sharper tuning. Proper grounding and inductive coupling also serve these purposes. Given the quality and accessibility of today's materials and the advances that have been made in physics, I am hopeful that an acceptable transmitter can emerge, based on this technology.

@joesmith-je3tq

Ай бұрын

@@AlexBurtonMusic If you decide to post about it, provide a link. Or, feel free to use the one I provided on the EEVBLOG.

@AlexBurtonMusic

Ай бұрын

@@joesmith-je3tq Of course. I would love to share it when I complete my project. Thanks.

At 15:41 the LED started to glow before you triggered the grill starter.

@joesmith-je3tq

Ай бұрын

You may have noticed it also started glow right after resetting.

How are you measuring the signal strength to the antenna?

@joesmith-je3tq

Ай бұрын

Are you asking about the aerial current?

@joesmith-je3tq

Ай бұрын

Which is a old meter marked "Signal Strength"

@alphaindustries5775

Ай бұрын

@@joesmith-je3tq yeah

@joesmith-je3tq

Ай бұрын

@@alphaindustries5775 Transformer coupled, diode to rectify the signal, cap for filtering, trim pot to set the sensitivity and a meter. Because I am really only looking for a relative measurement in a very narrow range, the circuit can be pretty crude.