
Custard Antenna - maxerickson
https://michaelcullen.name/2019/04/custard-antenna/
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anilakar
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.

~~~
philpem
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.

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nominatronic
> Slow as molasses

Slow as custard, surely.

~~~
philpem
Depends how thick the custard is. Is it thick enough to classify as a non-
Newtonian fluid?

~~~
thfuran
That isn't a label for particularly viscous fluids but for fluids where the
viscosity is dependent on applied force.

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jhallenworld
W6LG made a lightbulb dipole and got 750 miles with FT8:

[https://www.youtube.com/watch?v=XSy271C07b4](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](https://photos.app.goo.gl/ciefcobDkiTrawsB9)

So here's a funny thing: FT8 was written by a Nobel laureate in Fortran!

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mindviews
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.

~~~
madengr
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.

~~~
mindviews
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.

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pizza
You think that's cool, check out this antenna made from a jet of seawater:
[https://www.youtube.com/watch?v=9tIZUhu21sQ](https://www.youtube.com/watch?v=9tIZUhu21sQ)

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bobowzki
This is much cooler because it's actually an antenna that works.

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mich181189
I plan to make a working custard antenna. This was explicitly attempting to
tune a bowl of custard, not so much radiate

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myth2018
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.

~~~
mich181189
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!

~~~
myth2018
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.

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mothsonasloth
Great post, I would have liked a bit more deep diving into the custard.

For example, what are the merits of using a fresh, organic or powdered
custard. Would Madigascan vanilla increase reception?

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mikepurvis
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?

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brian-armstrong
The post mentions that he tried that and was not able to receive anything
using a dummy resistive load.

~~~
myth2018
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

~~~
anilakar
The custard probably mostly acts as a resistive load and mechanical support.
Actual radiation happens in the wires.

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msds
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.

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curiousfab
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.

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sigi45
What is he actually 'tuning'?

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?

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bobowzki
There's nothing surprising here.

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.

~~~
brians
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.

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Aloha
"Because I can" has produced some odd results over the years. This however is
among the oddest.

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behnamoh
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.

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bayesian_horse
Can it tune fish fingers, too?

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newaccoutnas
You can tune a piano but you can't tune a fish (finger). Allegedly.

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jfk13
But everyone knows you can tuna fish. (In either oil or water, according to
taste.)

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bayesian_horse
Just my kind of humor!

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IIAOPSW
Ok but can he tune a fish?

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skoopie
Looney tune

