2024-04-22 RF Electronics
Introduction
RFC is being rushed due to the incoming of competition. Might never be merged officially but will be used for competition airframe. Done by @Daniel Puratich and reviewed by @Nathan Green . Started on evening of 5/11/2024 to get orders in just before competition but we’ll see time wise if I can swing it.
Table of Contents
- 1 Introduction
- 2 Information
- 2.1 RF Filters
- 2.1.1 Why
- 2.1.2 Filtering Required RF Devices
- 2.1.3 No Filtering Required RF Devices
- 2.1.4 Adapters
- 2.1.5 Filter Options
- 2.2 SDR Setup
- 2.3 Drone Antenna Locations
- 2.4 Ground Antenna Locations
- 2.5 Battery Information
- 2.6 Wiring Information
- 2.1 RF Filters
Information
RF Filters
Why
Everything needs a filter for competition as an attempt to filter out strong out of band signals to prevent ADC overload causing RF desense to our intended signals.
we experienced this at last competition likely due to airport radar operating above a kW
possible causes listed below but I will be SDRing on Friday at competition to validate this assumption.
https://en.wikipedia.org/wiki/Airport_surveillance_radar
2.6 to 2.9 ghz over a kW
https://tc.canada.ca/sites/default/files/2021-09/AIM-2021-2_COM-E.pdf
Air Voice (VHF AM) 118 to 137 MHz ← most likely an intermittent problem area, airport has a pretty strong TX generally but I can’t really find specs online, guessing above 200 W, when I lived near an airport this is what I heard lol
TSR, 1.25 to 1.35GHz ← most likely our problem area if the airport has one of these lol
PAR, 9GHz to 9.18GHz ← possible?
ASDE, 16GHz ← likely are antennas really aren’t resonant way up here
SSR (ADS-B), 1.03GHz and 1.09GHz ← low amplitude no worries
Filtering Required RF Devices
ELRS drone side bidir
MPN: EP1 TCXO Dual
HappyModel ExpressLRS TCXO EP1 Dual RX
Type: ISM2.4GHz
ESP32 PICO D4, dual SX1280(SX1281)
Antenna connector: IPEX MHF 1/U.FL
RF Frequency: 2.4GHz (2400~2480MHz)
Telemetry power: >19dbm
80mW
Receiver protocol: CRSF
over UART
Input voltage: +5V DC @ “+” pad
PCB size: 19mm x 14mm
Weight: 1gram exclude antenna
Built-in a TCXO (temperature-compensated crystal oscillator)
Gemini bidir
SX1261
https://www.mouser.com/datasheet/2/761/DS_SX1261-2_V1.1-1307803.pdf
lora module used? see schem
Tracking ant bidir
EP1 (not dual) ELRS
controller bidir
TX16 build in transciever
Video Tower VRX
rmrc 900/1.3 video receiver
Video Goggles RX
5.8ghz
transmitter is rush fpv something
No Filtering Required RF Devices
TX Only
Drone VTX:
No filtering required, transmit only
9CH (1080,1120,1160,1200,1240,1280,1320,1360,1258MHz)
ITU Regions
Bandwidth
20MHz for analog video, centered on these CH frequencies?
Guide: 1.2GHz -1.3GHz FPV Video System - Oscar Liang
“Based on reports from the community, a 400mW VTX is capable of doing 15 miles or more.”
“High power VTX could [cause ADC overload on] your radio receiver, causing [system] range issues long before your video gives up. “
https://s.click.aliexpress.com/e/_DmMRUKl TBS notch for 900MHz band (pass 1.3)
https://s.click.aliexpress.com/e/_DC313lr low pass (pass 1.3)
same as FCC table for region 2
960 - 1 164 MHz
1 215 - 1 240 MHz
1 240 - 1 300 MHz
Amateur 5.282 5.331 5.332 5.335 5.335A
1 300 - 1 350 MHz
1 350 - 1 390 MHz
RF power output: 0.1mw(0, pit mode), 25mw(1), 200mw(2), 800mw(3)
800mW peak
Button control and LED indicators
Built-in AGC microphone
7-26V DC IN (2-6S LiPo)
Power Consumption: 40mA(0.1mw), 110mA(25mw), 150mA(200mw), 250mA(800mw) @12V IN
250mA @ 12V = 3W => 26% Eff, 2.2 W heat in the sink
Video format: NTSC or PAL
Audio Subcarrier: 6.5 MHz & 6.0MHz, onboard microphone on 6.5MHz
RF Connector: MMCX
Weight: 12.2g
Size: board 35*35mm
Video Tower VTX
Tx only, no worries
Not Practical to Filter
Phone Telemetry bidir
internal to phone, should be properly designed antennas in there
not possible to filter easily
GPS receiver
gps denied should be anticipated tho hopefully antenna gain helps us
not possible to filter easily
vtx and usb are both scary
Adapters
https://cdn.everythingrf.com/live/sma_rpsma-male-female_636715630002666648.jpg
Filter Options
https://www.nooelec.com/store/ham-filter-bank.html
meant for amateur radio, cheap
more expensive
cheaper if not waterproofed
expensive
cheaper if not waterproofed
https://www.aliexpress.com/item/1005004674064653.html
out of shipping time for ali express lol
What Is Cavity Rf Filter and Why Is It Important? | TEKTELIC
for 900mhz lora
1.3ghz pass (low pass)
Challenge
i think i waitted too long to ali express cheap shit for airside. ground side idk if we wanna drop a hundred on a nice cavity filter. shipping just too late to do anything besides amazon and it's hecked. like running filters is not common at all for these systems, most filters are built for way more power than we need or are rlly shitty aliexpress ones or are cost optimized and somewhat reasonable provided u bring your own pcb which we outta time on. building our own cavity filter is a legitament option but we dont have a vna i trust above 500mhz.
Build our own?
SDR Setup
Two Yagi’s
Dipoles total length is a halfwave
Two support 900MHz band, one is meant for 2.4GHz
Normal antennas
will just use simple antennas for analysis at FT and prep for competition
Drone Antenna Locations
Hardware locations physically on drone
general
Viewing the flight paths from conops
asked people
competition:
above diagram shows intended flight for task 1 and task 2
comp info:
task 2 is far riskier so antennas should all go on right side of drone
components
elrs
vtx
right side to optimize for task 2 approach
mounted with gromets because it matches the 30x30mm mounting pattern ontop of drone!
mech people will likely improve accordingly, i did my best lol
should have null pointed toward GPS antennas to avoid interference, nearby bands
gps
spread out on top, already mounted, no change
putting the antennas on a VNA in person will be nice to verify assumptions
Ground Antenna Locations
Separate tower for video receiver and elrs
Battery Information
We are running four batteries (and not six)
this was proven preferable from flight tests
If the four arms are corners, then one battery per side
this has negligible impact on flight characteristics
Wiring Information
there's a few blanks to fill in currently in the doc but I (@Daniel Puratich ) do not have time before competition, hopefully onsite EEs are available for fun
if someone wants to fill in, plz do!
probably not, sadge