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diy qfh antenna (self.amateur_radio)

submitted 5 days ago by evasync to c/[email protected]

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hello,

i want to make this antenna (check link) to get sat weather images sata with my sdr.

will it make a dofference if I replace.the plastic parts with wooden?

also is any other type of antenna more suitable for this purpose? (I want it to be as compact as possible because the only space i have available is on my flat's window)

https://www.instructables.com/Building-a-QFH-Antenna-and-How-I-Did-It/

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[–] [email protected] 2 points 2 days ago (1 children)

wood is fine but make sure to waterproof it if used outside. use as little as practical, performance can change with weather unlike with plastic. no metal fasteners either as this will have weird effects

do you want it to be compact when deployed or compact when stored? you can also make crossed dipole yagi, you probably want it to be rather nondirectional so one director, driven element and reflector would be fine. that antenna is much longer but i think you get the idea https://www.qsl.net/dk7zb/Cross-Yagi/crossyagi.htm you can also make bifiliar helical antenna but this one again gets a bit directional. you can probably make it shorter than these 5 turns and change pitch too to decrease directionality https://secwww.jhuapl.edu/techdigest/content/techdigest/pdf/V12-N01/12-01-Stilwell.pdf you can also make unifilar helical antenna but it needs a big reflector baseplate so it won't be as compact, it looks like this https://www.ab9il.net/wlan-projects/wifi3A.html

[–] [email protected] 2 points 2 days ago* (last edited 2 days ago) (1 children)

wait, do you want to use it at 140-ish MHz? these antennas will be quite sizable no matter what you do. you can make cross-dipole yagi but with loops instead of straight elements to make it a bit more compact. again, one director will be fine, hell you can even skip it too and just use driven element + reflector. take reflector + driven element from there https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1990/01/page24/index.html and first director from there https://www.iw5edi.com/ham-radio/2425/directional-antennas-cubical-quad this will get you antenna looking roughly like 60x60x70cm box, 60x60x40cm for two-element version. you can get away with using ferrite beads instead of these bespoke sleeve baluns, it's done this way because it's made for high power. i don't think you can get much more compact. you will have to resize it for your frequency. closest band is 144MHz

really you can use any calculator for cubical quad yagi like this one https://www.qsl.net/yt1vp/CUBICAL%20QUAD%20ANTENNA%20CALCULATOR.htm, just with this modification that instead of one feed you need two feeds geometrically 90 degrees apart, that are electrically also 90 degrees apart. this means you can use feed system like this one for 435MHz:

just scaled up for your frequency. also replace these sleeve baluns with a couple of ferrite beads and you're good to go. mechanically, you can make elements from thick copper wire and you can make it all hold up partially on tension of that wire. remember to factor in velocity factors of your cables

[–] [email protected] 1 points 21 hours ago

now that i'm thinking, you can make loop antenna with circular polarization and mesh reflector with closer spacing that would be even more compact and that would have more of one sided donut shaped radiation pattern, which would be probably more suitable for your application, but it's guaranteed to have different impedance and so would require simulation

[–] gofsckyourself 3 points 5 days ago (1 children)

I know nothing about this, but I am wondering why you want to use wood instead of plastic?

[–] evasync 2 points 4 days ago

i despise plastic and i want to minimize it where possible.

in this particular case the components will be exposed to the sun and that will degrade the plastic over time, and that is something that wont happen to wood :)