Re: [IRCA] TECSUN PL-300WT AM Sensitivity Variations
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Re: [IRCA] TECSUN PL-300WT AM Sensitivity Variations



Hi John,
 
The possibility of replacing a damaged PL-300WT loopstick with the E100's  
loopstick is interesting indeed. They are similar in shape and size, and 
both  have a single coil.
 
I'm sure that the E100's loopstick would work just fine in the PL-300WT, as 
 long as the coil could be set to match the DSP chip varactor's optimum  
inductance value. Since this could be anywhere from 180-450 uh, however, some 
of  the E100 loopstick coils could end up partially off of the bar at the 
180  uh value, and I'm not sure if the E100 coils can provide 450 uh, even at 
the  center of the bar. I guess we could keep the idea as a back-up plan, 
however, if  only to give us more confidence as we attempt AM alignments on 
the PL-300WT  :>)
 
73, Gary   
 
 
In a message dated 6/14/2009 6:37:33 P.M. Pacific Daylight Time,  
bjohnorcas@xxxxxxxxxxxxxx writes:

Gary  DeB:

What is the possibility of replacing the stock 300WT loopstick  with 
one removed from the E100???  Especially if someone tried to  align 
the 300WT and broke the bar or destroyed the coil, a "pulled" part  
from an E100 could resurrect the 300WT and might (with special  
dispensation) still be called a "barefoot" Ultralight???

I've got  seven (yes! seven) E100 ferrite antennas that I was going to 
leave here in  Oklahoma.  I think that I'll pack them after all :>) 
"Waste not,  want not" :>)

John B.





At 08:45 PM 6/14/2009  -0400, you wrote:
>Hi Pete,
>
>Thanks for your generous  comments.
>
>Regarding the AM sensitivity variations in the new  Tecsun PL-300WT, an
>investigation of the issue has been made by myself  and Steve 
>Ratzlaff, and we
>have a pretty clear idea of how this  happened, and the solution for the
>problem.  The details of the  investigation have been  vjvbgjshared with 
the
>Ultralightdx  Yahoo  group, but those without access to the 
>Ultralightdx Yahoo  messages
>probably  don't know the full  details.
>
>Silicon Labs (the designers of the PL-300WT's internal  DSP chip) intended
>for the DSP chip to provide good AM and FM  sensitivity without the need 
for
>any  alignment system. This was  an innovative concept, and they  certainly
>succeeded in  accomplishing this in the FM section of the  PL-300WT. In 
the  AM
>section, however, the chip designers' original "no  alignment"  intention
>was greatly compromised by Tecsun's PL-300WT  manufacturing  process--
>specifically, by Tecsun's habit of  placing the loopstick coil 
>at  the far left side
>of the  ferrite bar, without making any effort to match  the  inductance
>needed by the DSP chip's internal varactor to provide   optimal AM 
>sensitivity.
>The varactor in the DSP chip requires a  certain fixed  inductance to 
provide
>maximum AM sensitivity in the  PL-300WT, and this  inductance can be 
anywhere
>from 180-450  microhenries. The only way to ensure  maximum AM sensitivity 
 in
>the PL-300WT is to align the loopstick coil to provide  the  fixed
>inductance necessary to optimize the match with the DSP  
>chip's  varactor component.
>Unfortunately, this alignment  process is not as routine as  most AM
>alignments, due to the  construction of the PL-300WT loopstick.
>
>To my knowledge, three  such AM alignments have been performed so far on 
the
>  PL-300WT--  two by me, and one by Steve. In Steve's case, he was able  to
>remove  the stock loopstick by disassembly, and was able to  peak AM
>sensitivity by  obtaining a final coil position providing  a 205 uh 
>inductance, to
>match the  value needed by the DSP  chip's internal varactor. 
>Unfortunately, that
>coil   position was partially off the ferrite bar, so Steve needed to cut
>away  some of  the left plastic mounting bracket to reinstall the  
loopstick.
>
>In my two alignments, being reluctant to remove the  loopsticks because of
>an apparent overload of glue holding down the  ferrite bars on both 
models, I
>  attempted to shift the single  coil by scraping away all wax along the 
coil
>  borders, and  patiently probing the coil sides until the coils finally
>started  to  shift along the bar. Both of them finally did, but the  
processes
>were like  marathons, and the risk of breaking the Litz  wire seemed high. 
For
>maximum  AM sensitivity, my first model's  coil ended up not too far away 
from
>the  original position, at  1/8" to the right of the left mounting bracket
>(compared to an original  position pushed completely up against the left
>bracket,  which is  apparently Tecsun's standard PL-300WT loopstick coil
>position).  This  was my original PL-300WT model, which had good AM  
>sensitivity
>out-of-the-box (as reported to the group in the  original post). 
>The  inductance
>at this position was 282  uh. Since that model's stock loopstick was  
removed
>in favor of a  7.5" loopstick transplant, I did have the chance to test
>whether the  glue holding down the stock ferrite bar would indeed  prevent
>removal  of the bar. In fact, the glue was so excessive  that it made 
>the stock
>ferrite bar break into four pieces, when  the bar was removed.
>
>My second PL-300WT model was received a  week ago, and had AM sensitivity
>noticeably worse than the first unit.  I reluctantly did the loopstick
>alignment procedure again, which was  another marathon of wax 
>scraping,  probing
>and pushing.  The coil finally did move (without any Litz wire breaking),  
 and
>ended up peaking AM sensitivity at a position a half inch to the  right of
>the original position-- at an inductance of 343  uh.
>
>For those DXers with a new PL-300WT providing less than  optimum AM
>sensitivity, the alignment option (despite its tricky  nature) is the 
>only  way to
>ensure correction of the  issue. Because of the variable nature of the
>varactor components in the  DSP chips, some units are going out with 
>fairly good
>AM  sensitivity, and others are going out with less than optimal  
sensitivity.
>Tecsun apparently thought that the "no alignment" feature  of the DSP chip
>meant  that the loopstick coil could always be  pinned against the left
>bracket, to cut manufacturing costs. This is  not the case, and we are now
>dealing with the consequences of their  decision.
>
>I hope to upload a pictorial for a Tecsun PL-300WT AM  alignment procedure
>soon, for those hobbyists willing to align their  models for peak AM
>sensitivity.  A fully aligned PL-300WT should  have AM sensitivity 
>fairly close to
>that of an  aligned  DT-400W, C.Crane SWP or SRF-T615. If your model does 
not,
>it  could  probably use an AM alignment, which unfortunately is a  trickier
>procedure than  the standard AM alignment. Hobbyists  should proceed with 
due
>caution.
>
>73, Gary  DeBock
>
>
>
>
>
>
>In a message  dated 6/14/2009 4:41:51 P.M. Pacific Daylight Time,
>ptdx@xxxxxxxxxxx  writes:
>
>Gary,  thanks for your exhaustive and continuing  research in the world
>of  mini-radios. We all, and the hobby, have  benefited immensely.
>Having  said that, it looks to me like we  might have some quality
>control  issues; perhaps it is between  factories or vendors. George
>Sherman  has just reported results  similar to mine. If you are getting
>hot  ones, it would be of  value to me to meet with you and compare
>mine  with one of yours.  I think we all agree that the selectivity is
>very  good but we do  seem to have variances in sensitivity not only
>between different radios  but also, at least in my case, between
>adjacent frequencies. There are  some quirky things going on...
>
>I  finally figured out how  to get it on LW (it doesn't work every
>time)  but the preset 9kHz  tuning doesn't always coincide with local
>outlets. The FM is quite good  and I haven't even bothered trying  SW.
>
>Onward! In the  meantime, thanks again for all your work on  this.
>
>Pete  Taylor
>Tacoma, WA
>12225w 4719n
>HQ180 + Kiwa air   core loop
>ICF2010 + "     "    "   "
>DX398; Palomar loop
>SRF-59 &  -M37V
>Eton   E100
>
>
>
>
>
>
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