Re: New antenna, new loggings

jim_kr1s <jkearman@...>

--- In ultralightdx@..., Tony Germanotta wrote:
> Jim, I hope you feel better soon. At least with your new no-knobs antenna situation you can DX from the sickbed.
> Have you thought about building one with more turns and feeding it with 300-ohm TV antenna wire? Would you be able to eliminate the internal transformer that way? You could use a shunt to ground plug and be able to use both internal and external antennas that way.

Hi, Tony,

I think I have the aliens on the run. I've been sleeping almost constantly the last three days. I'll never catch up to Rob this way!

Because the tuning capacitor is in the radio, connecting an inductor directly places the feed line in parallel with the tuning capacitor. Three-hundred-ohm twin-lead has about 12-pF/meter capacitance. You probably could get away with one meter of it if you kept the inductance low, but it's stiff. The thin speaker wire I'm using is very flexible, and I was initially using a 12-foot length with no problems. That was longer than I needed so I used an eight-foot length for the final version.

The hoop loop is slim and lightweight. It spins nicely on my little 9-inch Copco turntable. With only three turns, the turns are spaced well for minimum self-capacitance. A larger loop wouldn't be as convenient. Transformer loss is insignificant. By the way, this system could be used with any radio, with the antenna remotely positioned but tuned at the operating position. I included a schematic on a RadioBoard  post.

There's another way to build something like this that didn't occur to me at the time. If you installed the jack in the top center of the case, you'd still have to remove the internal loopstick, but you won't miss it. That would shorten the ground wire by a couple of inches. Then you could mount small, shielded boxes holding the inductor of choice for LW or MW. A pair of spring-clip speaker terminals would make for easy connection of the matching loop (thanks to Chris Knight for that idea). As you need about 830 uH to tune down to 153 kHz, that coil almost has to go outside. A hint: You don't have to obtain the total inductance from a single coil; it could be spread out over 3 or 4. The -77 mix is better than -61 at LW, and requires fewer turns to get the needed inductance.  An FT114-77 core would be my choice for LW. I'm not into beacons, but it would be fun to receive LWBC from Europe on the PL-380.  Maintaining the same impedance ratios would take more turns on the antenna, but you'd want a physically larger antenna for LW anyway. 


Jim, KR1S 

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