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28-Jun-2012

HF Antennas are back up and I'm back on HF after a couple years!

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The Homebrew Buddipole (Yet Another Field Ant)

I'm starting to feel like "Everyday is Field Day" in my backyard...and this time it's a homebrew Buddipole. I have my niece, Elisa, and her fiancee', John, to thank for starting me on this since they gave me a gift certificate to Elecraft. Wasn't sure how best to spend it, but I bought two of the 66" telescoping buddipole whips, and 6 coil taps. I probably should have skipped the taps and bought 4 whips so I'd have a couple spares, but oh well.

I'll start with the bits, unassembled and lying on the ground...first a wide shot to capture the collapsed, three section, 23' painters pole (~8 ft. collapsed).

Next a little closer. The base is a patio umbrella stand...very heavy. Even still, it was a bit breazy the day that I was testing the 17m/15m coils so I cut three lenths of black 1/8" dacron for guy lines. Of course the ground is still frozen, so the plastic pegs are out...instead, I used three old screwdrivers!

Ok, now for the fun stuff...the antenna itself. The center is a 3/4" PVC cross...with a 3/4" to 1/2" reducer cemented into each opening -- three are 1/2" slip fittings while, the bottom is a 1/2" threaded fitting which mounts (with adapter) onto the painters pole. The thinking for using the cross in place of a tee is two-fold... first, it gives me the option of mounting a vertical, and, second, I was thinking I could rig a support for the arms (if needed).

The two inner arms (24" x 1/2" PVC) have a banana jack on the end that slips into the center cross/tee and a 1/2" slip-slip coupling cemented on the outer end. One conducter of the #20 speaker wire runs from the jack on one end and escapes through a small hole in the coupling on the other end with a short pig tail terminated in a banana plug.

Now for 10m and 12m, there are no coils and the whip assemblies would insert directly into the inner arms and the mating banana plug/jack connected. The whip assemblies are similar to the inner arm assemblies with a couple changes...they are only 9" PVC sections and the PVC coupler is a slip-thread PVC coupler. I used brass adapters to reduce the 1/2" pipe thread to a 1/8" pip thread which is pretty close to a 3/8-24 thread...especially after chasing it with a 3/8-24 tap! The only tricky part was figuring out how to attach the speaker wire to the brass adapter. I considered soldering it, but decided to drill and tap for a 4-40 stainless screw.

For 17m and 15m, loading coils are required...through a calculation to get in the ballpark and a bit of trial and error, I found that 9 turns on the red side and 10 turns on the black side allowed me to tune on 17m with the whips almost fully extended. Note that this antenna design seems to get the best tune when set up as an off-center fed dipole, so everythings color coded...red stuff on one side connects to the center conductor of the coax, while black stuff on the other side connects to the shield of the coax. The coils again are simlar to the inner arms, but much shorter (3" long PVC) and with the #20 speaker wire escaping the pipe to make the turns and then going back in before reemerging as a banana plug terminated pig tail.

Ok, enough of the bits, here are some shots of the assembled and deployed antenna...

One thing to note is that I don't have the painters pole fully extended...without additional guying, it's just too flimsey. For this initial setup, the pole is at just over 15 ft. tall.

Here are a couple shots taken from a window on the second floor of my house...where I'm about at the same level as the antenna


The base is heavy enough to support the antenna without guys...even with the bit of a breeze that was going this day...I just didn't want to take any chances, especially since I have no spare whips!

The right tool for the right job? Not really, but the screwdrivers did the trick!

Finally, here's a shot showing the banana plug termination on the feedline as well as the bulge from two ferrites over the coax to prevent current on the outer shield.

Once set up, I went into the shack and made a quick QSO with Mike, G1MYA/mobile in the UK and was given a signal report of 57. Not bad for the 15w K2! Next on the adgenda is to wind loading coils for the 20m band. I'm also considering picking up a couple of the 10' whips to see if I can get this thing going on 40m as well.

All in all, yet another worthey addition to my collection of backyard/field antennas!