Custard Antenna
michaelcullen.name
michaelcullen.name
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.
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.
Slow as custard, surely.
https://www.youtube.com/watch?v=XSy271C07b4
FT8 is really something. I built a cobweb antenna and got Japan from Massachusetts on my new IC-7300:
https://photos.app.goo.gl/ciefcobDkiTrawsB9
So here's a funny thing: FT8 was written by a Nobel laureate in Fortran!
Of course the nonlinearity of the filament will change things slightly, but it will converge down to a fixed impedance.
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.
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!
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.
For example, what are the merits of using a fresh, organic or powdered custard. Would Madigascan vanilla increase reception?
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 :-)
That doesn't apply to FT8 and some other digital modes. It uses signal processing techniques to receive signals below the noise floor.
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.
Sounds like he made a weird partially-shorted dipole antenna, and needs a good VNA to answer the rest of his questions.
I mean i don't understand it. He puts some wire into custard and then a device is 'tuning' and then the reception is better after?
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.