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



I've also found the Q-stick+ difficult to use with the Tecsun radios (and often with my ICF-SW7600GR which doesn't have a good tuning indicator). In my opinion, there are three reasons for this.

Number one is that coupling to the Tecsun loopstick is very poor, so positioning of the Q-stick+ is very sensitive. Some of my recent experiments indicate that the loopstick in my PL-300 has very low Q, on the order of 15-20.

A second problem is the slow update of the digital RSSI meter. A fast analog meter is much easier to adjust by. This is not so much a limitation of the radio chip, but simply a practical tradeoff in radio design. For general usage, the slow update saves battery power and minimizes digital interference. I think the radio's main controller "sleeps" for most of the time between updates. I just tried an experiment where I connected to my PL-300 via USB and "grabbed" RSSI updates at 5 per second. This made adjustment of the Q-stick+ fairly easy, achieving an 8-10 dB boost on a strong station.

On my other radios, I tend to adjust the Q-stick+ aurally by dithering the knob rapidily in small motions about the peak. Quick motions make the audio change more obvious because the AGC can't keep up and smooth them out. On the Tecsuns, the AGC is generally very effective and makes even this dithering technique hard to hear.

Your suggestion of using another radio to pre-peak the Q-stick+ is a good one. I would add that one should experiment carefully with Q-stick+ positioning. The loopstick winding on the Tecsuns is toward the left-end of the radio and moving the Q-Stick+ more to the left improves coupling dramatically. I've found that having the knob-end of the Q-stick aligned with the right edge of the PL-300 is a good alignment for my radio (and my Tecsun's coil is slid rightward of the stock position!). Also, I am seeing that coupling is better near the back of the radio than at the top. Hooking the flip-stand of the radio over the Q-Stick+ works well.


--- 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

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

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 _
( ) 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

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

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

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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