Friday, December 30, 2011

R7000 Moves to Micro-Shack

Putting up the R7000 at the Micro-Shack took a bit of doing. I didn't want to leave any concrete monuments in the yard, so I had to look for something a bit more temporary. Fortunately, there's an outbuilding behind the house that appears to be made of salvaged lumber. This little shed has seen better days, but looked sturdy enough to support wall brackets. A few 2x4 reinforcements inside the framing received lag bolts for a couple of wall brackets I had on hand.

The hard question was -- what to do for a mast? The 1 1/2 inch rigid EMT I used worked ok for 15 years, but EMT isn't meant to be a mast product. Plus, it wasn't the right outside diameter to fit the mounting U-bolts for the antenna. A 12 to 15 foot piece of 2 inch galvanized, chrome-moly steel would have been ideal, but not easy to come by.

Top end of mast, showing R7000 attached. Notice the R7000
radials are not installed. They get in the way so it is easier
just to put them on just before raising the antenna.
I ended up using an different combination. First, a 10 foot piece of 1 1/4 inch steel pipe, a 1 1/4 to 1 1/2 inch adapter, then a 12-inch long 1 1/2 inch steel pipe nipple, and finally a pipe cap. Steel pipe is quite a bit thicker than rigid EMT, and a lot more expensive. A 10 foot 1 1/2 inch pipe would have been almost $40! The 1 1/4 inch pipe was just over $25, and the 1 1/2 inch nipple made it 11 feet total height. 

The 1 1/2 inch nipple fit the mounting U-bolts much better than the old rigid EMT did. Close, but not as perfect as a 2 inch mast would be.

It just took a warm afternoon to put up the brackets, assemble the antenna and raise the mast. Unfortunately, the antenna did not show the characteristic low SWR on the ham bands. Some work with an antenna analyzer showed relatively high SWR on every frequency from 7 to 26 MHz. Only on 10m did it show a slightly lower SWR of about 3:1. 

Uh-oh. Looks like this 15-year-old antenna needs a rebuild.

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