On 7/14/2010 5:52 PM, dhsatyadhana wrote:

Excellent points, Rick. Correct me if I'm wrong, but that is what happens with the PL-310/360-380 when I plug in or inductively couple a broadband antenna like the Wellbrook FLR-100 or LF Engineering H-900 whip - complete overload here in urban Seattle.

Absolutely right Kevin. The Si4734 based receivers are very sensitive but are very overload susceptible, especially in urban locations. Nice antennas BTW. I use a Wellbrook AP-100 preamp/splitter with my external antenna system. I'm fortunate to live in a rural area of the Blue Ridge Mtns. without any bad MW RF problems or the preamp might cause me problems. LF Engineering antennas are highly regarded by LW non-directional beacon DXers.

However, if I put a simple tuned preamp like the MFJ 1020C in between, all is well, and no doubt a simple coil and varicap would do the same thing.

The "front end" of your preamp is an excellent cure for your problem, as you discovered. A cap and coil will also work well by making the radio more selective to the frequencies being applied to the antenna and attenuating off frequency signals.

What about putting a potentiometer, or a fixed resistor of the appropriate value, in-between the broadband antenna and Si4734 receiver to simply cut down on the RF energy being pumped into the front end?

That's exactly what the "DX/Local" swiches on some radios, like my Grundig G5, are. They are voltage dividing resistor circuits to cut down on the RF signal level. Some communication receivers have non-switchable MW attenuators installed in their front ends. The Icom R75 and Yaesu FRG-100 are 2 examples of receivers with these attenuators. There are mods available for removing them to increase MW sensitivity.

Best ULRing,

Rick