Re: Comparing ferrite loopsticks a box loop on longwave

Kevin Schanilec

Hi Peter/all:

My understanding is that the Tecsuns use a varactor (variable capacitance) to tune the internal ferrite to the desired frequency. This tuning process occurs every time you adjust the tuning knob, in which case the receiver valiantly hunts for the optimum varactor setting. This is a neat trick, allowing for enhanced sensitivity. This means that it wants the ferrite to be tuned to where it wants it tuned. If a modest external antenna (e.g., a Q Stick) is brought nearby, the Tecsun will resist being de-tuned or otherwise influenced, even if the external antenna just wants to help at the exact same frequency.

However, if you have a larger antenna nearby (box loop, monster stick, amplified smaller loopstick) with a higher "output", this will overwhelm/swamp the Tecsun's front end (ferrite/varactor/etc.) and dictate the frequency. The Tecsun can no longer ignore it! The Q Stick cannot do this, but the Quantum Loop (essentially a Q Stick that has been amplified) has enough output to get over the threshold and take over the front end. The monster stick and big box loop can take over "barefoot".

With the Sony 7600GR and other receivers, the front ends are broadband: they do not tune their internal ferrites to a specific frequency. Rather, the receiver's front end passively extracts the frequency it is looking for. If even a small external antenna supplies a little more energy at the frequency of interest, it is happily accepted by the 7600GR's front end. That's why I used the 7600GR in my evaluation, since it is a good indication of the relative "output" of each passive antenna, without the antenna needing to get over a certain threshold to make a difference.

Hope this helps - Kevin

--- In ultralightdx@..., Peter Laws <plaws0@...> wrote:

On Tue, Feb 8, 2011 at 23:22, dhsatyadhana <dhsatyadhana@...> wrote:

I note that I used a Sony 7600GR for these tests, because the Q Stick is not powerful enough to couple with the tuned front ends on the Tecsun DSP Ultralights (it does fine with the 7600GR).  Had I used a PL-310, for example, the Q Stick would have delivered minimal improvement, if any.  The amplified output of the Quantum Loop is able to couple just fine with the Tecsuns.

Can you expand on this? What makes the 7600GR so different from the
Tecsuns that it can make use of the Stick while the others cannot?

Peter Laws | N5UWY | plaws plaws net | Travel by Train!

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