I think we have to disentangle a few things, sorry!
Thought I'd try out my Tecsun PL660 on HF once I get out in open country.
Don't want to be stringing out the included long wire each time I stop.
So was wondering if a small active loop may be any better than the onboard telescopic.
I'm not sure I understood this - do you think unwinding a few meters of wire and plugging the 3.5mm phone plug into the radio is more hassle than fastening one SMA connector to the bias-T unit, then one of the feed line SMAs to the bias-T unit and the other end to the loop, then connecting the power source to the bias-T unit, finding a place for the loop and connecting it to the radio with an SMA or BNC->3.5mm adapter?
OK, you may have to wire up the whole shebang only once but you still need to find some suspension place for either the loop or the wire and then there's the power supply for the preamp to figure out...just to get basically the same results a stretch of wire would give you for free!
Speaking of the benefit - there is no easy answer. I take it that by "open country" you mean you are stopping in the middle of nowhere (RV?) - then QRM is really not an issue (you may have some sources in your car or RV though, unless all the onboard electronics go to sleep!). That means that it doesn't get much better than that for any radio - it can utilize all sensitivity it has and you can get very satisfying results with just the whip. Here's where it gets a little complicated: From all I know about the PL-660 the sensitivity can be pretty much all over the place, my example is the least sensitive radio I own. Still, the real benefit of no local noise is SNR and depending on what you're planning to hear with the radio the SNR may always be brilliant - only if you plan on weak signal (shortwave!) DX, a (good) active antenna (doesn't have to be a loop at all) may be really beneficial out there, in that it can lift very weak signals over the radio's sensitivity threshold.
Personally I'd stay away from loop amps that don't have a gain control. Putting it on a PL660 would introduce the possibility of overloading.
The PL-660 has a 3-position sensitivity switch, switching it from 'DX' to 'Normal' bypasses the RF input transistor and makes it swallow pretty substantial voltages. I inductively coupled a 30' steel flagpole at the beach to the 660 (wrapping the supplied wire antenna around the pole a few times, great way to use the Eiffel tower for an antenna!) - that worked really well with the PL-660 in the "Normal" setting.
That being said, strong out-of-band signals in the neighborhood of AM and FM transmitters are always a problem for most consumer-grade radios (or LNAs for that matter), so YMMV as per usual.
If you're a tinkerer and have the parts, you can build your own YouLoop and add an amp.
DIY is more fun for $ure but in this particular scenario with no QRM (assumedly) for the YouLoop to play it's main joker card - noise shielding - and the relatively underwhelming performance of the YL on shortwave I'd say it isn't exactly the best antenna for that job. Where the YL is pretty good is MW, and that's also the only place where it could cause overloading with a preamp, but the PL-660 doesn't use the external antenna input on MW.
In any case, there' an issue with the raw gain coming out of the amp. It might be too much for a little Tecsun portable to handle.
In my (limited, I only own an ML-200 and never tried one of the Chinese knockoffs) personal experience active SMLs may not have
that much output. This is particularly true for the YouLoop, which is still not like the other SMLs when you add a (typically 20dB) preamp, that's barely enough to compensate for the hefty losses on the higher portions of SW.
Here's a video showing how it receives a weak station without and with a preamp indoors. The surprising takeaway is that an LNA can be beneficial even indoors in some noise, which is for the most part due to said particular inefficiency on the upper shortwave.
Here's another one, showing how much the
passive YouLoop depends on the radio's sensitivity/gain reserves. As you can see (and not hear), the impedance mismatch with the Belka's high impedance input is enough to render it useless and the other radios just confirm the "high sensitivity receiver" disclaimer that comes with the YouLoop.
