FlightAware Discussions

Cheap ebay antenna outperforms FA antenna?


#140

Imagine this in your back yard… (Largest steerable dish in the world at Jodrell Bank, UK)
640px-Lovell_Telescope

Then there’s (what was, until 2016) the Granddaddy of 'em all
The_Arecibo_Observatory
The observatory has four radar transmitters, with effective isotropic radiated power of 20TW (continuous) at 2380 MHz, 2.5 TW (peak) at 430 MHz, 300 MW at 47 MHz, and 6 MW at 8 MHz.


#141

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.

View From a distance

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Close-up #1

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Close-up #2

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#142

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.


#143

OFF TOPIC AGAIN

A nifty bit of parking…

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#144

whelp, I see the four wave-guides, but whats all that other stuff for ?


#145

The Australian Over The Horizon Radar system which is still in operation.

JORN - Jindalee Operational Radar Network


#146

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.


Waveguide type directional antenna
#147

YVW,S!

8 inch duct will give you a lower cutoff of 865 MHz and an upper of 1130 MHz. Should work like a champ.


#148

Great.
Keep us informed of your progress and outcome.


#149

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 :slight_smile:


#150

Which is definitely a good thing.

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.


#151

For about last half of this thread, we are completely off the topic which is “Cheap ebay antenna outperforms FA antenna?”

Where is the OP? :slight_smile:


#152

Split those posts to a new topic?


#153

This can only done by admin.
It is better to post in a new topic like “directional waveguide antenna”

There are several existing directional antenna threads:

Directional antenna for ADS-B?

Directional antennas

Directional antenna

yagi - do you have experience with directional-antennas?


#154

@xlr99
@GDoggRaspberry

Ok, created following new thread:

Waveguide type directional antenna

Could not move relevant posts from here to there as I dont have admin power, but copied all relevant posts from here to there.


#155

Much cheaper to build an antenna arrays. But harder to tune.


#156

Easy to tune, harder to steer. :wink:


#157

You can steer it only if it starts. The truck seems to be from a scrap-yard :wink:


#158

That’s only if it’s got power steering. :wink:
Otherwise you could steer it, but you won’t get too far.

Yep. The old gal looks pretty tired! :smile:

The truck looks like it belongs in a scrap yard!


#159

In the same note, the show “Mysteries of the Abandoned” is very fascinating, at least for a technical-oriented mind. What people build, was state-of-the-art, and become obsolete and abandoned: