If you're willing to experiment, you'll find out that you can tune pretty much anything from a random spool of wire to an iron frame bed, and in this case custard. I've found that an inductively coupled sausage is a nice match on the VHF air band with a proper number of turns.
However, getting a nice 1:1 voltage standing wave ratio only means that the transmitter sees a proper 50 Ω load that does not reflect anything back. Most of the radiation probably happens in the feedline and the rest is absorbed as resistive losses. The whole setup only works because at lower "high" frequencies signal levels are relatively strong and receiver sensitivity is rarely a problem. Most HF transceivers actually have front panel knobs for attenuation and gain reduction.
Also, FT8 is a relatively new digital modulation that works at low SNR and is not feasible for transmitting any information apart from the callsigns of the communicating parties.
Exactly this. A dummy load (a 50-ohm resistor) will give you a perfect 1:1 SWR, but makes a rubbish antenna... an SWR match just means it's less likely to fry the transceiver's power stage.
You could transmit data over FT8, but you're right -- with identification requirements you'd be limited to maybe half a dozen characters per 15-second cycle. Slow as molasses but it'll be receivable even if the signal is down in the noise floor.
Can anyone simulate this light bulb setup in HFSS or another antenna simulation software? I'm always on the lookout for comparisons on weird cases like this for the simulation code I've written. If I can find material property data on custard as easily as for tungsten (watch the temperature dependence!) I might give that a shot next.
You really don’t need to simulate it. It will just be a electrically small magnetic loop with a large real resistance. Any antenna text book should have it, with gain proportional to frequency.
Of course the nonlinearity of the filament will change things slightly, but it will converge down to a fixed impedance.
I suppose a bit more context would be explanatory. My real interest is not the free-space performance of the antenna, but the eventual installed performance. In the video describing the setup he says "I talked with a couple of engineers, and some other guys, and we've come to the conclusion that if I put 100 watts into it, it might radiate a milliwatt. And not all that well." I'm not sure if they were thinking of it as a magnetic loop antenna the way you described or coming up with the numbers some other way. But then at the end mentions, "I'm gonna set it on the top part of that air conditioner and put it right in the window." How much of his success is a result of sticking the antenna on what may be effectively a (admittedly electrically small compared to 20m) metal box? That's what I think is interesting to simulate.
I've initially thought it was some sort of April fool's article. But I'm skeptical.
He didn't detail, but probably used a proper, non-irradiating cable, or no cable at all, when he experimented with the dummy load. If that was the case, he can't say he just swapped the dessert with the dummy load and, then, can't attribute the change in the results to that. So my guess is that the wires were in fact playing the role of an antenna there.
Besides, impedance matching doesn't mean much per se. As they say, even a dummy load can be tunned. The effectively irradiated power and the irradiation patterns are even more important than tunning in many situations.
In this configuration, yes, the wires are most likely doing quite a bit of the pickup.
The custard is more or less a dummy load - I didn’t intend it to radiate or really work as an antenna - I just wanted to try it to see what would happen.
I do want to see if I can make custard radiate though. It’ll probably be quite lossy but it’ll be fun to try!
Perhaps the custard is working as a resistive load of a kind of beverage antenna.
It's a valid experiment. I only think that is a bit misleading for those who read about it. People get impressed thinking that the custard was tunned to operate as an exotic antenna.
Without knowing anything about this, how much of it is the custard vs. the wires leading to the custard? Like, could you pull them out, and have them hanging in the air a few inches apart and get the same result? Or, I suppose, insert a resistance equivalent to the custard?
Indeed. But he didn't mention how he connected the dummy load to the radio. Dummy loads have usually a standard antenna connector and are meant to be attached directly to the radio or through an non-irradiating cable. So, my guess is that, by using the dummy load, he disconnected the actual antenna: the "dipole" made by the wires between the radio and the dessert
A few centimetres of unshielded wires are typically enough to receive some of the strongest signals on the amateur radio bands.
If you are using such a short and therefore highly inefficient antenna, both the noise and the desired signal decrease significantly, but the signal may still stay above the noise floor.
The statement in the article that the antenna tuner doesn't do much on receive is not correct.
On a related note, radio hams were previously successful in establishing transcontinental contacts in Morse code using all kind of unusual antennas, including bed springs :-)
> If you are using such a short and therefore highly inefficient antenna, both the noise and the desired signal decrease significantly, but the signal may still stay above the noise floor.
That doesn't apply to FT8 and some other digital modes. It uses signal processing techniques to receive signals below the noise floor.
My wording ("above the noise floor") was not well chosen. What I mean is simply this:
Your receiver will have a certain noise floor which you will see/receive even without an antenna connected to it (internally generated by imperfect components).
If you connect an antenna, this antenna has a certain "antenna factor" which describes how much of the field strength of a signal "in the air" will be converted an electrical signal at your antenna terminal.
For a very short antenna, this factor is small, for a "good" antenna this factor increases.
Assuming both your "bad" and "good" antennas are still good enough to pick up background noise and desired signals above your receiver noise floor (which is usually the case, even if you put your finger into the antenna terminal!), all you get is a difference in absolute signal levels while the SNR (ratio between the desired signal and the noise) will not change.
So this principle is universal, independently of the modulation scheme.
Isn't it possible to convince most antenna tuners to effectively match "into themself", and dissipate most of the power internally? I accidentally did that with a matching network I was trying to use to tune a weird inductively-coupled plasma setup.
Sounds like he made a weird partially-shorted dipole antenna, and needs a good VNA to answer the rest of his questions.
It is. In this case however I suppose the resistive component of the custard plays a significant role in the match and therefore power dissipation (but not radiation). The main components acting as an antenna here are indeed the wires.
The custard will present a certain impedance (resistance and reactance, normally represented as a complex number) at a frequency. A radio transceiver normally expects 50ohms (real) at the antenna port for maximum energy transfer (and smallest standing wave voltage ratio). Using a network of capacitors and inductors (the tuner) the custard's impedance can be transformed to 50 ohms. But it's still not an efficient antenna, in the sense that it won't radiate more.
You are using the ubiquitous jargon of radio engineering. But for those on this site who are not radio engineers: of course the impedance of the custard does not change. The impedance of the system including the custard and the antenna tuner is different – and better for the radio to work with — than the custard alone.
Not directly related to the post, but I remember back in the day we had a black-and-white TV which could receive only 3 basic channels in the country. I connected a co-ax cable to the output of a receiver and connected it to a dipole antenna. Now, after tuning the TV on the exact frequency of the antenna, I could play anything on the TV. It was a simple in-house broadcasting station. Of course, had to disassemble it due to concerns with electromagnetic waves.
However, getting a nice 1:1 voltage standing wave ratio only means that the transmitter sees a proper 50 Ω load that does not reflect anything back. Most of the radiation probably happens in the feedline and the rest is absorbed as resistive losses. The whole setup only works because at lower "high" frequencies signal levels are relatively strong and receiver sensitivity is rarely a problem. Most HF transceivers actually have front panel knobs for attenuation and gain reduction.
Also, FT8 is a relatively new digital modulation that works at low SNR and is not feasible for transmitting any information apart from the callsigns of the communicating parties.