My not-so-supercharged PL-380


gary_thorburn <gwt@...>
 

Thanks, Gary, for confirming that the PL-380 design has changed in a way that now makes it less suitable for supercharging. Something I suspected.  Fortunately, the PL-380 is still a nice FM machine!   I have a CC Skywave original model, which I like very much as is, so I'll probably keep it stock.


Max Italy
 

Hi Gary, thanks for the reply. I was just curious to know what is the advantage on having an higher inductance because i suspected that 430 uH was closed to the high limit.

Also, it would be interesting to have the specifications of length, diameter and geometry of the original ferrite bars on these radios to see if it can be just slided out and replaced with a longer one for those that do not want to get involved in winding a new coil. I wouldn't mind drilling a small hole on the top of the radio to follow a short path instead of entering with the wires from an exisiting hole.


Gary DeBock
 

I'm not sure who you are asking, Max, but the inductance of the PL-380 stock loopstick is about 280 uH, and the "Supercharged" loopstick version is about 350 uH. The internal Si4734 DSP chip is designed to accept any antenna inductance from 180-450 uH.

Gary


Max Italy
 

Hi, what is the inductance of the stock antenna and why making it different ?


Gary DeBock
 

Gary,

Since the original PL-380's were introduced in 2009 the Tecsun company has attempted to increase profits by significantly reducing the DSP chip shielding in all post 2011-models, resulting in the digital whine issue when the display is grasped. Knowing the Tecsun company as I do (I have performed about 25 "Supercharging" transplants on their models), I wouldn't be at all surprised if they reduce component quality even further in an attempt to increase profits. Because of this issue, I have personally stopped doing loopstick transplants on all recent-model Tecsun PL-380's. The only PL-380 models that I will "Supercharge" are the ones that I can confirm were manufactured between 2009 and 2011, with the fully grounded shield surrounding the Si4734 DSP chip. Of course, Tecsun's decision to reduce quality in order to increase profits is personally disappointing to me, especially after the time and effort that I spent to write out the 22-page "Supercharging the Tecsun PL-380" article.

As for your current project, I'm sorry that there are no quick solutions for the digital noise issue. Many recent Ultralight radio models have good internal shielding and no digital whine, such as the CC Skywave models (both the basic and SSB versions), the new Radiwow R-108 and the non-Ultralight XHDATA D-808. Of these four portables the Skywave models would be somewhat of a nightmare for beginners to "Supercharge," but the R-108 is reasonable, and the XHDATA D-808 is fairly easy (with the full procedure posted in another major article at  http://www.mediafire.com/file/t2989hg61vbkb5h/Supercharging_the_XHDATA_D_-808-FinalMWLW.doc/file

73, Gary DeBock (in Puyallup, WA, USA)

 


gary_thorburn <gwt@...>
 

Having some trouble 'supercharging' my Tecsun PL-380.  Opened it up, disconnected its internal ferrite antenna and connected a new one I wound on an 8-inch R40C1 ferrite rod from Ming Mak.  The signal strength was greatly improved over the internal antenna.  However, it is picking up noise which I believe is produced by the LCD display and its associated circuitry.  The lead connecting to AN1, which I think is the 'hot' lead, seems to be the one picking up the noise.  I played with the routing and the length of these leads, but could only slightly improve the situation.  Even tried a short piece of litz headphone cable for the internal routing.  Though not truly shielded, with this cable the AN2 lead closely hugs the AN1 lead.

The noise is an audible whine.  On a stock PL-380, as with some other radios, this can be heard on a weak MW station by grasping the top of the radio, apparently conducting the noise to the ferrite antenna.  Furthermore, I believe this noise confuses the Si4734 AGC, worsening the 'pumping' audio level which I find to be a common annoyance in DSP radios.  I was hoping the stronger signal would actually alleviate this. 

For now, I've reconnected the internal ferrite.  I wonder why the stock coil and its leads do not pick up the noise as much?  Maybe because of its lower impedance? 

Any ideas/comments are welcome!    A few more details below, for those interested:

  • Coil wound with 10/44 Litz.  Not ideal, I know, but its what I had on hand to experiment with, and has worked nicely on passive ferrite antennas I've made. 
  • About 120 turns, spread over about 60% of the 8-inch ferrite length.  Lots of turns, since R40C1 has lower permeability than Amidon 61.  My coil was checked by an RF engineer on an HP induction analyzer that cost way more than my car.  At 1MHz:  430 microhenries, Q=400. 
  • My coil is wound in the same direction as the stock coil, though I don't know if this is called a left-hand or right-hand helix, or if that would affect noise pickup anyway.
  • PL-380 purchased late 2018, SN: 36920181006731
Gary Thorburn