Kevin Explains How DSP Technology Results in Superior Radio Performance

Here's my take on DSP (Digital Signal Processing). The DSP is presumably in the intermediate frequency (IF) filter part of the receiver where, among other things, you try to isolate the signal of interest from adjacent interference.

Old-style filtering with simple LC circuitry (which is typically what you get on cheap receivers) produces a gentle attenuation/roll-off from the signal of interest, meaning that rejection of adjacent channels (say, rejecting 1280 khz while trying to listen to 1290) is not that good, maybe only 20-30 dB down. Ceramic and other filters (as with the Sony S5W) are even better, and have an even sharper attenuation - the adjacent slopper 10 khz might be 50-60 dB down. However, for a strong local, this will still let quite a bit of slop through from a strong adjacent station.

With DSP filtering, the slope of attenuation can be pretty much infinite, meaning that you can pretty much shut the door on adjacent interference, or to mix metaphors a bit, the attenuation curve looks like falling of a cliff. For instance, to listen to 1290, the filter would let absolutely nothing through outside the range of 1285-1295, allowing both sidebands of the target of interest through, but completely attenuate everything else. It's basically about as good as you can do, and as long as a strong local station doesn't slop too far out of its assigned band, an adjacent channel will be much more readable.

The little Degen/Kaito DE1123 has DSP, and the selectivity is outstanding. So, if the PL-300WT has DSP (likely included on the "radio-on-a-chip" IC used), plus a reasonable-sized ferrite, it could be a fairly hot DX machine.

Hope this helps - Kevin

Comments

[Kevin S]

Hi all:

Just posted to the Ultralight and IRCA boards is a review of the PL-300WT, and it's what many have hoped: excellent sensitivity (considering the size) and other-worldly selectivity from the DSP filtering. This was specifically for the Tecsun, not for the Grundig G8.

[c]

goodness,i had a 1123. it fell apart after about 6 weeks, and it was by far worst sounding unit ive ever heard

[Kevin S]

Sorry about the DE1123 - it's so small that the AM sensitivity is quite poor as well, so I've heard.

Check out:
http://bbs.tecsun.com.cn/0002.asp?open=110900
There are several DSP radios emerging out of China, including a DSP version of the CR-1100, reviewed here earlier. This could be a very good radio now, not that it was horrible before.

[Jeffrey McMahon]

Kevin, I have a CR-1100 unopened, still in the box, an exchange. I don't even know if it's DSP or not. Wait, it must be. It says so on the box. I think I'll open it and review it tomorrow. Thanks.

[Kevin S]

Do let us know! It may be super-sensitive on FM like the little PL-300WT, and with razor-sharp selectivity.