Another Giant Antenna System - The “Russian Woodpecker” in Chernobyl (cold-war era stuff, no more operational)
An Array of “Cage Dipoles” working as “Over the Horizon” Radar.
Official name “Duga”, Nick Name “Russian Woodpecker”
At some point in 1976, a new and powerful radio signal was detected simultaneously worldwide, and quickly dubbed ‘the Woodpecker’ by Amatuer Radio operators.Transmission power on some Woodpecker transmitters was estimated to be as high as 10 MW equivalent isotropically radiated power.
The bane of hams around the world. It made HF operation a real hassle.
Essentially, it tore up any HF signal to the point of being uncopyable.
Aptly named, as it sounded very much like the bird it was nick-named after.
abcd567 & xlr99 - Thanks for the information. I grabbed a Progresso soup can out of my pantry and it’s about 85 mm diameter by 110 mm high. Using the calculator links and assuming that the TE11 & TM01 frequencies define the bandwidth, my vegetable soup is not looking like a good antenna for ADSB at 1090 MHz. I need a can of around 200 mm diameter and 99 mm length for the 3/4 wavelength, and more likely 263.8 mm to go with xlr99’s observation regarding 2 wavelengths. Fortunately, an 8" duct might be just about right so it looks like I’ve got a trip to the hardware store in the near future.
A lower cutoff of 990 Mhz is more desireable to get rid of both the GSM-800 and EGSM-950 Mobile/Cell signals - A directional antenna + a cavity filter - buy one get one free
The problem there is that he would need a somewhat smaller cylinder and that might not be readily available. (a waveguide diameter of 6.96 inches (177 mm) would give him a lower cutoff of 992 MHz.
So if he can find suitable metallic tubing with a diameter of 7 inches, he should be good to go)
But, if he builds it multiple waveguide-lengths long, as he indicated he might do, that will make the antenna
beamwidth narrower which will eliminate any signals his antenna isn’t aimed at. If the signals are not in the antenna pattern main lobe, but are very strong, they will be attenuated considerably.
If the interfering signal is in-line with the desired signal, then an inline filter might be required. The rolloff
of the antenna will help knock down the interference, but the skirts of the antenna response curve aren’t as steep as those of a cavity filter, hence the possible need for a filter at the antenna feedpoint.
The downside to a longer waveguide and thus narrower beamwidth, is aiming the antenna. The narrower
the beamwidth is, the more precise one must be when aiming the antenna at the signal source.
Raspi2B, blue Flightaware with integrated 1090-filter usb stick, el-chiepo ebay PCB antenna.
USB cable from raspi is extended few metres to mast, where quality Belkin USB hub powers the Flightaware USB RTL stick. Found this is the best combination, with best SNR on received ADS-B data.
Radio amateur background, I would really recommend attaching antenna directly to RTL stick, without any antenna cables. Every joint is bad, every metre of decent antenna cable is even worse.
RTL-stick will benefit from ACTIVE USB extension cable, due average 200mA consumption and bad noise generation on USB power lines. My setup has Belkin USB hub with RTL stick in it, so there are enough power delivery filters near the RTL stick.
power consumption measured:
RTL stick 200mA
USB-hub 250mA
USB active extension cable (no-name brand) ~3m 200mA
all powered from Raspi2B normal port.
Flightaware Raspi image running, with Dump1090-fa shared to Flightaware24 & Radarbox from dump1090-fa 127.0.0.1:30005
