jim_kr1s <jkearman@...>

--- In ultralightdx@..., "wa8lcz" wrote:

> is the balun xfrm much improvement over direction connection ?
Direct connection to what?

The PL-380 requires an inductor that resonates with the varactor on whatever band you choose. For MW, the data sheet says 180-450 uH, assuming minimal stray capacitance on the board and interconnecting wires. I ended up with 240 uH (see below). Now I needed to match the impedance of my loop antenna to the impedance of that inductor. I've just now finished tweaking the winding that goes to the antenna, which netted me another 12 dB of signal strength from 530-1700 kHz (I have stations on both frequencies close enough to be steady in daytime. Radio Enciclopedia - 530, some 300 miles away, is showing 47-25 on the meters in broad daylight. Fidel didn't scrimp when he built that station.).

Impedance matching is important, as you know. The impedance of the antenna determines the necessary turns ratio. For more turns on the antenna, you'll need more turns on the transformer primary (the one connected to the antenna).

An easier way to do this for your TS-450S is to find a suitable -61 core and wind a coil that will resonate with a 365-pF variable. Then put on a primary that goes to your loop. Now you can resonate the antenna remotely through twisted-pair and not have to use that huge variable. The antenna could likely be tuned from 12-15 feet away.

> do you twist the 8 ft leads from the loop to the radio to prevent computer noise pickup ?

I haven't, but I don't have a PC near the radio. Bunching up the wire, wrapping it around a ferrite rod and generally tossing it around the table doesn't noticeably affect signal strength. Neither does the length of the cable, in the range of 3-8 feet, which is a bonus. I might twist the wire some night when the band is dead, but it hasn't been necessary yet.

> also, you use pretty small wire, 28 ga, for the toroid, wouldnt 20 or 22 ga and a larger toroid be more efficient ? less resistance and losses ? larger skin area for the RF.

Hee-hee. I had a deuce of a time getting 240 uH on an FT50-61 core with #28! I wanted to use a few more turns but ran out of space. I was shooting for 63 turns, stopped at 60 and wished I had some #30 wire. OTOH, #28 is about as small as I can see these days.

For anyone contemplating doing this to a PL-380, consider hanging the toroid outside the radio. That would let you use a larger core, too. To jam in a 1/8" jack I ended up milling out most of the plastic framework in the area above the headphone jack, removing the whip antenna and taking out the ferrite rod, which wasn't hooked up anymore anyway. The toroid now sits in the hole where the rod used to go. I never used the radio on FM and SW anyway, and Joyce could probably find me another one if I need it.


Jim, KR1S 

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