Zane has a Sherwood sync unit with his Palstar and might offer some user experience. I've heard some of Zane's off-air recordings comparing reception with/without and the sync detector does help. So does the sync detector on my Sony ICF-2010. Ditto the online web-controlled Drake R8-series I've compared with and without AM sync.
Does it help $695 worth? Not on my budget. I'd need a quieter location and good outdoor antenna to make it worth that little extra bit of advantage.
For that kind of money I'd look for a receiver that already has a sync detector built in: Sony ICF-2010 (which is also overvalued now on the used market); some of the high end Grundig portables; Drake R8-series tabletops; some JRC NRD-series; Lowe HF-150 and 225. The Icom R-75's sync detector reportedly didn't work well so study some user reports before buying that one for the sync detection.
And I'm satisfied enough with my Palstar R-30C as-is. For weak AM signals switching to sideband and the narrow filter works about as well as the Sony 2010 with AM sync.
Incidentally, that's the main advantage I've found with sync detection - picking out weak AM signals. Passport to World Band Radio
and other reviews often talked about "distortion." Eh... to me, DXing always sounds distorted - fadey, scratchy, etc. That particular characteristic seemed to be overemphasized. Most diehard DXers have built-in brain filters that help us ignore distortion and noise. Any sane person would have given up the hobby after a week.
The real advantages to AM sync detection are:
- Ferreting out weak AM signals and making them just audible enough to get an ID.
- Sorting out competing signals on the 49m band where stations are only 5 kHz apart.
Even the stock Sony ICF-2010 handles those challenges well enough. Several times when I've been unable to ID an AM pirate with the Palstar R30-C on an indoor loop, I've switched to the Sony 2010 with just the whip by a window and snagged just enough of the carrier to get a station ID.
For $695, I'd look for a good used Drake R8-series, or Lowe HF-150 (which offered an unusually flexible AM sync detection), if I wanted a conventional receiver with sync detection. I've tried some online web-controlled Drake R8's on various AM signals - weak and/or in crowded bands - and it really does make a difference.
If you'd like to test drive one, there's an online web controlled Drake R8
in Virginia - probably the oldest continuously available shortwave receiver. It's limited by an indoor attic loop so reception is comparable to mine at home. And rather than a continuous audio stream you can choose only 10 or 60 seconds worth of audio sampling. But it's very handy for comparing the benefit of AM sync against non-sync AM, or sideband tuning - and the disadvantages, as tuning is a little fussy with AM sync. You'll often need to adjust the tuning up or down a bit to get it to lock. Meanwhile, it'll whine as it struggles to lock on. An excellent challenge is WBCQ on 5110, which is only nominally on 5110 and kinda-sorta AM. Depending on day and moon phase, it's center freq is somewhere between 5109-5111, and it's AM/USB only. Lately, with my ordinary AM receivers, 5110 is almost unlistenable - with heavy selective fading it sounds like trying to tune a sideband signal with an AM receiver. Switching to USB helps. But it's best with the Sony 2010 in AM sync, with the tuner set to around 5110.1 to ensure it locks onto the upper sideband. So WBCQ's Area 51 block on 5110 is the single best challenge to test driving a receiver's AM sync detection mode.
But as Chris pointed out, a good SDR offers huge advantages to a dedicated DXer. Even in my area, an RFI-plagued suburban neighborhood, an SDR would offer certain advantages in flexible notch filters and noise reduction. And being able to record a wide swath of a band at once - pretty cool if you're seriously into pirates, numbers or mysterious DXing.