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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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