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

Gary DeBock

Hi Kevin,
Thanks for the interesting question about the performance of stock and modified Ultralight radios with large loops.
Many DXers have been puzzled why their sensitive AM portables (like the Sony ICF-S5W, ICF-EX5 or Panasonic RF-2200) don't receive much of a signal boost from their smaller tuned passive loops (Select-a-Tenna, Terk Advantage, Q-stick etc.) while their smaller Ultralight radios (like the SRF-59, DT-400W etc.) get a very serious signal enhancement from the same external antennas. Probably the best explanation is that the external loop's weak-signal reception capability must be much greater than that of the portable's stock loopstick, in order to make much of a difference in DXing performance.
The 7.5" loopstick-modified Ultralights ( "Amidon PL-380," Slider E100, Slider SWP, etc.) behave exactly like the most sensitive AM portables in this regard, receiving almost no signal boost from the smaller tuned passive loops. The stand-alone DXing performance of these modified Ultralights often equals or exceeds that of the stock model inductively coupled to the same loops, so that's probably no big surprise.
The DXing performance difference between stock and modified Ultralights (and the very sensitive AM portables) disappears as the loops get larger, however. From my experience, the tuned passive loops about 6' and larger (per side) provide the same huge signal enhancement to any portable brought within inductive coupling range, whether it is a stock PL-380, Amidon PL-380, ICF-S5W or even the 30" loopstick ICF-2010. All of these portables simply get "swamped" by the RF boost provided by the large loops, so there really is no difference in the strength of the DX signal received (although there is a big difference in how well the portables can handle the massive RF, depending upon their selectivity, and "crunch resistance").
After discovering this fact, I had a blast using one of the smallest Ultralights on the planet (the lighter-sized Sony SRF-S84) inductively coupled to the 9' PVC loop, and discovering it could easily receive multiple exotic TP's (as soon as I could figure out what frequency I was on :-)
73, Gary       

In a message dated 1/13/2010 7:00:04 A.M. Pacific Standard Time, satya@... writes:

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, 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@... ..>
> 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 _
> ( ) 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
> y

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