Re: Tuned loop antenna

Rick Robinson <w4dst@...>

Hi Nick,

If you are handy with a soldering iron, the PL-310 is very simple to modify for external antennas. See the group files section for the "Laurie" mod to the PL-310. The PL-380 mod is more involved but is a better radio due to its lack of extreme soft mute and AGC issues that the '310 has. I have modified my '310 and 2 '380s for use with external antennas. The Si4734 will tune any antenna in the 180uH to 400uH range with its built-in 500pf - 20pF varactor. No need to purchase bulky tuning capacitors, it's all in the radio. I used 1/8" stereo jacks on my PL-380s, and depending on the type of jack you use,you can keep the internal ferrite bar in place and usable when the external antenna is not being used.

I use a 24 inch spiral wound loop antenna with an inductance of 260uH with my ULRs. BTW, a spiral wound loop has much sharper peaks and nulls than ferrite bar and "box wound" loops and is much quieter than ferrite bar antennas. However it is somewhat more difficult to construct than a "box wound" loop and is not as easily transported as a ferrite bar.

I've been using these modified ULRs for almost a year with no problems at all. The Si4734 is a robust chip and does an excellent job of tuning external MW antennas without use of external capacitors.

Good DXing,

Rick W4DST

On 6/27/2011 6:47 PM, g4irx_uk wrote:

I've looked at some of the amazing ferrite rod antennas for ultralights.

Has anybody tried a tuned loop antenna in place of the ferrite rod, letting the si4734 do the tuning rather than a capacitor on the loop? I have a large hexagonal loop and I'm considering mounting the PL-380 on the loop frame itself, disconnecting the internal ferrite.


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