The AA2TX parasitic lindenblad, which was published in Feb 2010 QST (and has been available online for some time), is proving to be an enjoyable project. I have modified some components because I could not find them here in Atlantic Canada. The #8 aluminum wire for the passive elements is not in our big box stores (different wiring regulations?), and the PVC ferrules require a special order, at least at this point in the year, when no sane person would be installing eavestroughing. So I made do with what I had, and the results are encouraging.
I used 1/2" wood dowling for the horizontal members and #12 copper wire for the parasitic elements. I used exactly the same measurements as in the published project. I'm sealing the wood to ensure that it survives the weather, and I fixed the elements in their holes in the wood using a glue gun.
I'm getting about a 1.5 SWR at 435-436 MHz, which I consider acceptable. Moreover, the SWR drops as I tune higher. I believe this is a good situation, since ice and rain tends to drop the resonant fequency of an antenna.
One tip for anyone who is testing this as they build. Before you take any SWR measurements, make asbolutely sure that the feedline is tightly affixed to the vertical element and has its ferrites properly placed. With the feedline hanging loosely and about 1/2" away from the vertical element, I got very different results. Moreover, in my experience, the vertical element without the 'hub' will produce an extremely low SWR over a large part of 70cm. If you aren't getting that, don't fiddle with the hub; look into if your cable is correctly attached to the elements and if the coax is properly choked at the bottom of the lower element.
I will finish this version by using the Marine Goop recommended by Tony to seal and glue. I expect the doweling will survive nicely, even when affixed to the PVC hub with hot glue or epoxy: there just isn't much force on them.
DARK SIDE TO THE MAX: WA7HRG's Android Tablet SDR (with a question) - Jim's experience with the Android tablet SDR was very similar to mine. But he used a "Ham It Up" up converter ahead of the RTL-SDR while I used an RTL-SDR...
2 days ago