What are they?

I activated W7Y/PA-222 yesterday. The views were spectacular and the Wyoming winds fierce. The wind was expected…the snow flurries were not.

My XYL still smiling while supplying extra support against the wind

Near the towers of folded dipole, microwave, and end fed antennas were these two parallel plates. I couldn’t see any wires going to them. What are they?

Dueling Drive-ins

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Those look like passive microwave repeaters/reflectors. Aim a dish at them and they bounce the signal down into the neighboring valley or over to the next ridge.



I agree, they look like passive reflectors for microwave signals.

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Has someone stolen the hoops from the basket ball court?

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Here are some passive reflectors used by the BBC. The UHF TV transmitter at Eitshal in the Outer Hebrides is fed from the Rosemarkie transmitter 160km away on a combination of active and passive repeaters on 7GHz. Due to the remote locations in the far North of Scotland there are 2 passive sites to save on the huge costs of running electricity to them and also building and maintaining relay stations.

This passive reflector is at Glenmarksie, 3.6m x 4.8m in size.

These back to back dishes are at Sgurr Marcasaidh and are 3.6m diameter. They linked with waveguide, no active electronics.

The link was built in mid-70s and went active in 1976. 45 years ago this was some serious RF linking!

Pictures © 1977 BBC Engineering.


Hi all,
I think the reason they are not in wide usage is an inherent 30 dB loss. Two Yagis can make up half of this and the resultant signal is still sufficient in the valley. Dish antennas have more gain which helps but the usable footprint is small.
Drive in theatre size billboards are good but their exposed location requires extreme strength. They reflect backwards so only feasible if on the far side of a deep valley on a higher ridge.

Active repeaters do a much better job which is why people go to the trouble of installing them.



I thought it was a double screen drive in movie!
Great information, I have never seen those before.


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You’re spot on. This example was from 1976 when a pair of 7GHz RX/TX would have need a 2x 6ftx19in racks and a building and power and telemetry. I’m not sure if there were any viable solid state PAs then but now you can make a 7 or 13GHz RX/TX with a few watts out and 0.5db NF that will be smaller than an 817 and can be run from solar / wind power.

Some context, here’s a view of the back to back dishes showing the kind of country they’re located in. Also they’re about 500m ASL and about 150km North of Moscow so you can imagine what the WX is like here in Winter :slight_smile:

© Geograph 2014

This link provided sufficient bandwidth to provide 4x PAL colour TV channels and many audio carriers. I don’t know if it still is used especially with the move to digital TV in the last 15 years. Considering where those dishes are located, they’re a damn fine advert for the durability of the products Andrew Corp make along with the engineers who installed them 45years back!

That’s a really big capacitor!!!

de Joe KE9AJ

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Ya need that cap for your next 2M amp ! That spacing ought to handle the plate voltage ~!
John, K6YK

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Passive reflectors - for a microwave link.

While we are considering odd installations. This one, just below the summit of Beinn an Turic, intrigued me. In particular the small unit (TRX+antenna?) which seems to be pointing up at the summit. Ideas?

Looks like a cctv camera on a pan and tilt mount, currently pointing downwards…?

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Ahh - yes I think you are right. Somehow that never occured to me! Too fixated on radio things… I wonder what the installation is/does?

You will know shortly if it is the security services… :slight_smile:

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Only if they can recognise me from my boots!

Gerald and I saw an almost identical enclosure complete with ground-observing CCTV camera on one of the other SS’s surrounded by a windfarm - might have been Common Hill SS-174, I’m sure Gerald will know for sure…

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Indeed it was - excellent memory Gungadin! I just caught part of it in one of my photos… I recall the feeling we were being watched, probably quite rightly on account of the nature of the site.

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Interesting. I activated Common Hill on the way up and it did not look anything like that! Clearly they have made changes. 360 view