Re: Tecsun PL-310/380 Inductive Coupling to External Antennas


dhsatyadhana <satya@...>
 

Hi Gary/all:

Thanks for giving us the blow-by-blow on this! This is a good guide to the procedure.

This is similar to what I did when I was out at the beach with my little active-passive loop, the tuning of which is very precise and so it's easy to miss where I am actually trying to be. Using the Sony 7600GR and its fairly useless tuning LCD indicator as a spotter, I would set it to SSB in order to get a het on a TP/TA, then tune the loop aurally to the het - this actually works pretty well since the het really jumps out, and is about as tough to miss as the Christmas tree lights on the 2010 :-). I would then do as Gary suggests - move the spotter aside and put the Ultralight in its place (or simply retune the Ultralight if coupling it to the loop with a little ferrite coupler, which is more convenient and provides better signal transfer).

Gary - with a large loop, do you notice any difference in the resultant signal strength between a stock PL-380 and an Amidon PL-380? It seems that if the loop is big enough, it would more or less completely dictate the signal level, making the stock PL-380 viable as a TA/TP receiver if one has a big loop in the mix.

Kevin S
Bainbridge Island, WA

--- In ultralightdx@..., D1028Gary@... wrote:

Hello All,

Ralph Pollock asked a very interesting question about peaking external
antennas for use with the Tecsun DSP models-- a subject which has also
interested me from the beginning, due to my use of the radios with large tuned
passive loops during DXpeditions. The correspondence below may be of interest
to those with similar questions.

73, Gary

From: d1028gary@... <d1028gary@...>
To: Pollock,Raphael E
Sent: Tue Jan 12 20:10:10 2010
Subject: Re: LTG450GW Filter Modification to the SRF-M37V/W Models

Hello Ralph,

Thanks for your comments on the PL-310/380 experimentation, which are
appreciated.

Since these Tecsun DSP models have a somewhat delayed response to sudden
boosts in RF signal power from external antennnas, they typically don't have
the sharp audio peaks normally found on radios like the ICF-2010, E5 and G6
when external antennas are peaked on their tuned frequency. The digital
signal strength readings on the PL-310/380 displays are also of little help,
since both models use an averaging system which causes a delay in changes
to the digital display reading. For this reason, even I have found it
counter-productive to try peaking external antennas by listening to the
PL-310/380 audio, or watching the RSSI or S/N readings change on the digital
display.

After receiving your email, I did attempt to use a Q-stick+ for peaking a
PL-380, and while inconvenient, it did provide a significant signal boost
according to the S/N digital display reading (after a wait of about 5
seconds). The problem is that the PL-380 has no immediate response (either audio
or visual) to the peaking of the external Q-stick on its tuned frequency,
making it tough to determine when you have hit the peak. You need to wait
about 5 seconds to find out.

After developing a series of huge loop antennas (with the related
technical article linked at _http://www.mediafire.com/?igw1zjwfzmw_
(http://www.mediafire.com/?igw1zjwfzmw) ) and using them exclusively during DXpeditions
with the Tecsun models, I have found that the best way to adjust these
monster loops to the PL-310/380's tuned frequency is to first use the ICF-2010's
red LED display to peak the loops, then simply bring the PL-310/380's into
the inductive coupling field of the loops. The ICF-2010 is ideal for this
purpose, especially on dark ocean beaches where the LED signal strength
display will light up like a Christmas tree when the loops are matched in
frequency.

For the external antenna systems you have described, Ralph, they actually
will give a fairly decent boost to the Tecsun models' AM reception once the
frequencies are peaked, as described above. I wish I could build you a
booster bar that would give you an immediate peaking response from the Tecsun
models, but this is probably one congenital quirk that we will need to live
with.

73 and Good DX, Gary





In a message dated 1/12/2010 8:55:23 A.M. Pacific Standard Time,
rpollock@... writes:

Dear Gary: I have been following your experiemnts with the 310/380 radios
with keen interest. I am wondering if the 81 turn Amidon 7.5" ferrite
could be adapted as an inductively connected booster for these radios. If that
design would not work i am wondering if you would have any suggestions for
such an external devise. My Selectatenna, a Q-Stick +, a homebrew 27"
Stormwise ferrite antenna (40 turns of Schmarder Litz; tunable w/ varicap), and
a tunable 2' x 2' home brew box loop do not seem to add any improvement in
S/N over the entire varicap tuning range; however, all of these work well
inductively with my E5, Sony 2010, or Grundig G6--the big ferrite in
particular.

I would like to make an outboard inductively coupled booster for these
little 310/380 wonders but am not sure how to proceed. A Spring trip to the
Pacific Coast of Costa Rica is planned--would like to do some TP dxing from
there, and like all the rest of us radio nuts, I'm a little greedy for more
RF!!! Any thoughts you might be able to share would be deeply appreciated!



Raph Pollock



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