Wednesday, November 10, 2010

Tower Bonding & Repeaters




I recently helped a friend put up a Rhon 25 tower. We got into the discussion of what he might put on the tower. And proper grounding, etc.

This lucky guy got a hold of someone who had an attachment for a Hilti hammer drill to drive the 8 foot ground rods. (Notice the plural, as in two).

Years ago I wasn't able to find anyone with this so I did mine hard way.

Then I brought up the idea of relocating repeaters and such.

From the Hardware Noise section on repeaterbuilder.com:
Without the proper grounding and bonding you may constantly be looking for noise sources. Pay particular attention to any point where two conductors are in poor contact with each other.


Tower bonding is something I didn't find a whole lot on when I did a google search.

Every 10 feet you have a semi-conductor. Snow and water do get into those joints on your Rhon tower, and over time there is light rust in those joints. This is a recipe for degraded repeater performance.

I showed this on an un-bonded tower that we once had our tech club repeater on.

We'd notice that on windy days, the weaker guys on HT's and such would have excessive creaking and popping on their signals.

So I keyed the repeaters local mic and went out and shook the tower as a demo.

Degraded noise floor.

After installing Copper Clad/ Zinc Grounding Clamps above and below each joint of the tower (as shown) this went away.

It's important to note that we also ran some RTV silicone around those clamps to prevent yet another water / rust joint. And finally spay paint them, as copper clamps rust easily.

There is a whole lot more I could write on keeping a quiet noise floor in duplex environments. But most of it has been covered elsewhere.

Most people don't understand how important this all is. I think this is because their experience is only in simplex operations. When you have something transmitting at the same time it is receiving the whole tower becomes like a charged capacitor.

http://www.repeater-builder.com/antenna/cracking.html:
This situation happens when transmitter power is put into the antenna and the surrounding area is lit up with the RF energy - yours or someone elses. What happens is the RF then creates tiny arcs and sparks in the broken joint and the receiver is desensitized by the wide band RF created by the sparking.


And RF Grounding is different than surge or safety grounding.

In RF, the length of the ground runs has much more to do with the fraction of a wavelength at the frequency involved than the DC resistance of the wire.

Good RF grounding can add several S units to the receive signal and dramatically reduce noise on the signal. Think surface area, and creating as big as RF counterpoise outside at your ground system.

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