Cubical Quad Antenna
Xiaomi Mi Thermometer 2
Nagoya REVEX NA-660S Gooseneck UHF 400-470MHz SMA-Female Tactical Antenna
You were not clickbaited it is official name on Aliexpress 🙂
If you wondered how this antenna performs how is its SWR or what is hidden inside fiber-glass tube check the pictures below. Teardown of antenna is irreversible process beacuse everyting is glued together.
I dont know how manufacturer measures the antenna or if this design is one of that “dualband” because the resonance frequency is somewhere between VHF and UHF band but it looks like 300 MHz is a sweetpot.
Inside the antenna there is very interesting combination of sleeve monopole (counterweight) with normal mode helix as radiator. Further investigation of antenna will follow next time.
There is antenna specification from seller on Aliexpress:
Brand:REVEX (Nagoya)
Connector Type: SMA-Female
Frequency: 400-470MHz (400-470MHz will be better signal)
Gain: 3.5dBi
Max Power: 20Watts.
V.S.W.R: Less than 1.5.
Impedance: 50ohm.
Antenna length:330mm
Let it burn
Meander dipole antenna
It took some time from my first design on meander dipole antenna, but last weeks I made further progress. Meander dipole is electricaly same length as dipole antenna but meanders make it physically shorter and they are able shift impedance to the sweetpot of Smith´s diagram.
Big advantages of meander dipole antenna is near-perfect impedance match to power line and smaller size than physical. But of course there is disadvantage in lower radiation efficiency.
It looses about 8-12 % of efficiency which can be 0.7 – 1.2 dB which looks horribly but it certainly nulls the loss on full dipole because of impedance mismatch 73 + 43j Ohms to 50 + 0j Ohms.
Further development was made on implementation of SMD baluns. Previous experiments with various types of ferrite rings were not successful. I discovered cheap wideband SMD made by MACOM [4] which is rated to 250 mW only. But if you dont mind over saturation of core it can work up to 4 W without heating HI.
Model was made in AntennaDesigner toolbox from MATLAB. You can see that simulation of Impedance in Fig. 3 is nearly perfect antenna.
- https://www.mathworks.com/help/antenna/ref/dipolemeander.html
- https://www.qsl.net/kk4obi/Meander%20Dipole.html
- https://apps.dtic.mil/sti/pdfs/ADA617035.pdf
- MACOM / MABA-001759-000000
PV – battery
It has been a while I made some progress on PV system. So here I designed small holder for DIY BMS v4 on Samsung SDI 64 Ah cell from BMW i3.
Hamshack #2
There is short update on building my hamshack. I was working on walls and last night I laid the floor. Before weekend I’d like to finish all flooring and start placing furniture.
Hamshack #1
This room has been cleaned up many times last year and filled with stuff after. I hope this is last time and I can start jobs on new hamshack!
WireGuard & rinetd
Protože opakovaně připojuji další dislokované pracoviště a opakovaně hledám ty samé postupy ve svých poznámkách, odložím si zde komplexnější postup a podělím se o svou praxi, která by mohla někoho inspirovat.
WireGuard patří mezí nejprogresivnější a nejpoužitelnější VPN – ten kdo v korporátním prostředí řešil třeba IPSec nebo ještě staré PPTP, případně nějaké obskurní vendorlockované řešení, tak ví jaký je problém aby vše fungovalo všude. WireGuard je velmi jednoduchý na konfiguraci a širokou podporu platforem. Klient existuje jak pro macOS, tak pro Windows, Android i iOS.
rinetd je síťový nástroj na přesměrování TCP a v nové verzi 0.70 i UDP spojení. Používám to místo portforwardingu. V kombinaci s WireGuardem tedy není nutné vystrkovat porty na veřejnou IP adresu, ale stačí se v rámci VPN dotazovat jednoho zařízení, které pak v daném segmentu větší sítě přesměrovává místně dotazy.
Doporučuji zajímavý seriál Petra na root.cz – https://www.root.cz/serialy/wireguard-pro-jednoduchou-linuxovou-vpn/
Konkrétní usecase (třeba): Mám od poskytovatele Internetu zpřístupněné SNMP na WiFi zařízení, kterým jsem připojený skrz jeho síť MAN připojen do Internetu. Směrem z LAN se na zařízení v MAN dostanu, ale z Internetu už nikoliv. Ve virtuálním serveru v Internetu mi běží SNMP monitoring, kterým bych zařízení v MAN síti rád dohledoval.
Příště ukážu svojí konfiguraci rinetd.
3D printable replica of SATCOM / MILSAT antenna AV 2040
In spring 2019 I was asked to build an antenna which should be similar to equipment which is used by US Army and what more it should work.
After some research through sources of US military contracts and pictures there was a hot candidate for MILSAT or SATCOM antenna build: AV 2040 UHF Satellite Communication (SATCOM) Antenna from ULTRALife corporation [1]
There are STL [2] and OBJ [3] files for anyone who would like to print own atenna. The design is for 449,550 MHz but by adjusting lengths of active parts of the antenna it can be tunder in wide range, see below on Fig. 5
There are three formulas considering f as frequency in Hz need to be calculated to get three dimensions which are mandatory for best results:
red = (299792458 / f / 2) * 0.92 [meters]
blue = red * 1.05 [meters]
green = 299792458 / f * 0.225 [meters]
