Ham Shack

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12:14 AM

@NicHartley "Drill a hole and stick an antenna through it" is exactly how the simplest of antennas for this scenario works.

More precisely: There's a rigid or flexible wire (antenna element) entirely on the outside, about one-quarter wavelength long. On the inside, you run coax from your transceiver module's antenna port to the hole and connect inside and outside to the wire and the enclosure metal respectively.

This is called a "monopole" or "ground plane" antenna depending on the situation and which part you're focusing on.

Kevin Reid AG6YO

1:08 AM

I think it's fine to chat about general introduction stuff

you don't know what you don't know, and a little discussion helps clarify terminology

to address the things in order — "amateur radio" in the sense of our site name is specifically about transmitting under the legal status of an amateur, using the bands set aside for the purpose

Amateur radio

Amateur radio, also known as ham radio, is the use of radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communication. The term "amateur" is used to specify "a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest;" (either direct monetary or other similar reward) and to differentiate it from commercial broadcasting, public safety (such as police and fire), or professional two-way radio services (such as maritime...

but we also cover radio technology in general because amateur radio as a hobby and under the legal definition, is very much about learning and experimenting with radio technology

and also because there's overlap between formally amateur radio and other things, like what you're doing, unusual wifi setups, etc etc

do feel free to ask a question; I'm just saying don't feel the need to not say something in any given place

re "If I just slap a coax port on the outer wall, connect the radio module to the inside of the port with coax, and attach the antenna to the port instead of directly to the module" — that is the idea of how coax works

the caveat is that if you use a monopole antenna, that's not actually a complete antenna, and so it depends on how much 'ground' is adjacent to it

you have probably learned that "current flows in loops" — even if radio antennas look like open circuits, this is actually true of them too

there's always an "out" and a "back", and one part is the monopole and the other part is the ground that's attached to the coax or antenna port

many PCB-attached antennas work against the ground plane of the PCB (if there is one)

there are also more symmetrical, balanced, setups with two equivalent conductors, but anything using coax is unbalanced

if you use an antenna that is complete-in-itself in that it has two opposing elements instead of one, it doesn't need a ground plane but conversely you do need to get it away from your metal

so, if you are using a metal box already, a monopole antenna is the best choice and also easy to make

link?

Kevin Reid AG6YO

2:03 AM

Okay, that's an antenna intended to work without an associated ground plane

You can tell because a single-band monopole antenna is always about 1/4 wavelength, and this one's much longer. Also because those wifi-node-style antennas are known to be designed as coaxial dipoles

you're probably fine using it but it would be best to keep it away from the box as much as possible, e.g. mount it on the corner of one of the sides

@NicHartley (was distracted)

in order to extend it out of the box you would either mount the module sticking out (not the best for mechanical robustness) or get a bulkhead + coax pigtail like this (except shorter) amazon.com/bestkong-SMA-Female-Bulkhead-Pigtail/dp/B01E59CRJS

it's a piece of coax with a male SMA on one end and a female 'bulkhead' SMA on the other

bulkhead is connector-speak for "goes through a panel and fastened to it" especially when there's a connector on both ends as opposed to wire terminals for soldering

yeah, same idea

block water, block RF — both done with large mostly continuous pieces of metal :)

and you want to have proper seals at each point

if you're trying to make an RF-tight enclosure you need to not just not have large holes in it, but not have large slots in it (e.g. where two sheets meet at an edge of the box)

that's why on some equipment you see springy-fingered sheet metal or shiny foam pads at the edge of the openable part, it's to make sure there's contact all along the length of the gap

for homemade stuff, on the sides you're not going to want to get back in to, you can use copper adhesive tape, or solder, to close up gaps

ah, wasn't sure

no need to worry about that then

the thing you do want to make sure about is that everything between the rf module and the antenna is properly-made coaxial cable/connectors

any deviations mean you get less signal in/out, esp. at 2.4 GHz

sure, I've got a project that is still a breadboard inside a nice aluminum box :)

well the general rule is that both for physics reasons and legal reasons, the more bandwidth you need the higher the frequency (proportionally)

and secondarily you want to pick a frequency that's legal for you to use

for example, the 2.4 GHz ISM band is unlicensed, which is why WiFi is on it, which is why lots of other stuff is on it

'unlicensed' here meaning you do not need a license to operate a transmitter

the transmitter still has to meet rules about maximum power and harmonics and so on

Q: What are the (US) rules about unlicensed low-power transmissions?

It is common wisdom that transmissions of any sort (perhaps unidentified, encrypted, in the FM broadcast band, etc.) are permitted if they are sufficiently low power. Where are the FCC regulations which permit this, or where can I find a well-accepted interpretation of said rules? People say the...