Re: PL-310 external MW/LW antenna connection

Gary DeBock

Hello Laurie (and Byron),
Congratulations on your simple and highly effective modification of rewiring the PL-310's external antenna plug-in jack, to allow highly sensitive MW and LW antennas of all types to be used in boosting the PL-310's performance, Laurie. That's one of the best ULR modification ideas I've seen recently, and certainly one that should prove extremely popular!
Because most of my own LW and MW 7.5" loopstick experimentation has been concentrated on the PL-380 model, I had no option but to design a similar plug-in "docking port" for the top of the PL-380 cabinet, which would accept the 7.5" plug-in MW loopsticks already sent out to 22 DXers using the PL-360 model. This is certainly a more involved process than rewiring an existing plug-in jack, as in your PL-310 modification. For those DXers wishing to use the PL-310 with any type of external LW or MW plug-in antenna, your modification is certainly the way to go!
Regarding the avoidance of high AM-band varactor lockup (in the Si4734 chip) when transplanting loopsticks, I did run extensive tests with various coil inductances and orientations in the 7.5" loopstick PL-380 model, using a signal generator under controlled conditions. The results may be of interest to you in your PL-310 loopstick experimentation, Laurie, and are posted at . Thanks again for sharing the details of your highly effective modification, and we all appreciate your experimental success in transforming the PL-310 into a very effective DX receiver.
73 and Best Wishes,
Gary DeBock (in Puyallup, WA, USA)  
In a message dated 8/14/2010 9:32:05 A.M. Pacific Daylight Time, lmann98@... writes:


Hello All,
My apologies if this mod has already appeared in the forum.

I recently purchased the PL-310 and, eager to try out some of Gary DeBock's ferrite loopstick ideas, I popped the back off and I noticed, happily, that the 3.5 mm socket for the ext SW/FM antenna is actually a stereo switched socket and that the SW-FM switched connection for the whip antenna is directed to go to the tip of a 3.5 mm stereo plug. The other pair of switched terminals in the socket are for the ring connection to a stereo plug and are conveniently left unconnected on the PCB. Hence I routed the internal loop stick hot connection through these unused terminals so that with no plug in the socket the internal ferrite rod is connected as normal and, when a 3.5 mm stereo plug is connected, the internal ferrite rod is disconnected and the MW/LW input circuit of the radio is available on the ring connection of the plug. The only thing to watch for is potential shorts between the whip antenna base and these pads on the PCB as they are almost coincident with one anoth er when the back of the radio is in place; I put insulating tape over the base of the whip where it overlaps these pads and there has been no shorting problems thus far.

Via this plug connection made with a short length (few inches) of RG-174 coax, I tried large external loop sticks around 2,000 uH and they work very well on LW being tuned by the radio's internal cap up to about 400 kHz. For an external MW ferrite rod it is necessary to avoid too much stray capacitance for the upper end of the band if you want the radio's internal cap to tune the ferrite coil, or else optimise with a lower coil inductance than you might otherwise use. A switched inductance coil on the external ferrite rod will doubtlessly be the way to go but the stray C in the interconnect to the radio will be an issue and I may end up going with short open leads to the 3.5 mm plug to allow minimum stray capacitance.

The mod also allows for the direct connection of external tuned loops and my external amplified tuned MW/LW ferrite rods work very well through this interface.

Regards from Perth, Western Australia
Laurie Mann

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