06 September 2012

degen de321 dsp portable receiver review

A number of new portable radio products are being designed around a DSP chip. The Tecsun PL-300wt was one of the earlier DSP-based radios that caught my attention. Enthusiasts of so-called ultralight radios were impressed with its AM broadcast band and shortwave reception. So this is a category of products I want to follow.

A popular radio near the $25 price point, the Tecsun R-911 / Kaito WRX911, seems set to be replaced by the physically similar, DSP-based Degen DE321 / Kaito KA321. In October 2011, I purchased a Degen DE321 for a total of $21 from an eBay seller in China. As I already have a WRX911, that radio will be used for comparison in this review. My trusty Eton E5 will be used as a reference to confirm broadcast frequencies.

I powered the DE321 with alkaline batteries and went to work in my somewhat radio-hostile apartment in San Francisco. Here's what I found.

Degen DE321.


The basics

Both the DE321 and the older WRX911 measure approximately 4.75 x 3 inches on the front, but the WRX911 is 1 inch thick and the DE321 is 0.75 inches thick. The new radio feels sturdy, but it gives an impression of being less sturdy than its predecessor.

The DE321 lacks the DC adapter port that the WRX911 has. That doesn't affect me, since I never got an adapter for my WRX911 and I prefer to power my radios with batteries. As you might expect, the battery compartment door is very thin.

The telescopic antenna is approximately 1.5 inches shorter on the new radio.

The tuning dial provides just the right amount of resistance, making tuning easy. On contrast, I find that the volume dial is very touchy. It's challenging to dial in the right volume level, and it's startling when the volume changes dramatically.

Block diagram of the Silicon Labs Si4831 / Si4835. Source: silabs.com

The audio

The DE321's built-in speaker is fine for news/talk/sports, but not a good performer for music. When I turned the volume up to room-filling level, the output began to distort. The volume is there, but the radio and the speaker aren't really capable of delivering it.

With an old pair of iPod earphones, I spent some time listening to a baseball game on KNBR 680. It was difficult to plug in the headphones. Hopefully the headphone jack does not stay this tight over time.

At zero volume, there is a persistent hiss noticeable in the earphones. I have experienced this same problem on other pocket-sized radios, but I'm always disappointed when each new radio I get has the same problem. This hiss was also noticeable in my Sennheiser headphones.

When I tried to unplug the white earbuds for the first time, I had a problem. This is one stubborn, incredibly snug headphone jack. And these old earphones don't have much of a plug to hold onto, either. I twisted, I pulled, I pinched, and didn't make any progress until I resorted to a pair of needle-nose pliers. Headphones forcibly unplugged, and headphone jack appears intact.

Mediumwave

It's a pleasure to find stations on mediumwave, because the tuning is precise and the audio lacks distortion from imprecise tuning. I did not observe any problems finding local stations.

I am satisfied with the bandwidth and clarity of strong local station receptions on the DE321. This radio delivered the 2012 MLB all-star game to me (from KNBR 680).

Tuning to local flamethrower KCBS 740 shows the tuning needle right on the 800 in the mediumwave band.

I ended up hearing a bit of music on mediumwave, as "Is this love" by Whitesnake was used as bumper music on Coast to Coast (KKSF 910).

Naturally, I came across infomercials on mediumwave. One ad promoted a pill that promised to combat stress and pain, and keep your heart beating. It used a doctor-on-the-phone with easily-impressed-host format. I didn't feel compelled to pull out my credit card to place an order, despite the free offer to the first 100 callers.

If you're used to tuning slightly off frequency to emphasize the treble portion of the audio tone, you will be disappointed here. I don't know the exact specs, but the AM bandwidth is limited, and tuning off the frequency means that the signal is lost. The reduced treble for AM stations is another noticeable difference between this radio and the WRX911.

Shortwave

The WRX911 has a 60-meter band (including 5000 kHz for WWV and WWVH), and the DE321 does not.

Radio Taiwan International on 9680 kHz from Okeechobee turned out to be my first shortwave reception test. I had a relatively strong signal on my Eton E5 for reference, and found the broadcast on the DE321 pretty quickly. However, the reception was covered with noise, and momentarily muted at times.

Voice of Russia was coming in decently on my reference radio, on 15425 kHz from eastern Russia. I found this broadcast on the DE321 easily, with the needle just above the "15.40" label on the tuning scale. (The shortwave bands are labeled with megahertz frequencies, but I prefer to write frequencies in kilohertz). This broadcast was difficult to listen to, though I think that Voice of Russia's audio production could be improved.

WWV on 10000 kHz came in loud and clear from Fort Collins, Colorado. The tuning needle is right on the "10.00" label, indicating good calibration.

Radio Nacional Amazonia is a regular catch for me on 11780 kHz (broadcasting Portuguese to South America). While the signal sounded fine on the E5, I tuned all the way through the SW4 band (covering the 25-meter band) multiple times on the DE321, but only heard what sounded like distorted FM radio stations covering a wide span of frequencies.

One of the best shortwave catches on the DE321 was Radio Japan on 5960 kHz, from Sackville, broadcasting Japanese to Latin America. Strong signal, low noise. However, I noticed a lot of momentary muting. This could just be the usual signal fading, but the effect seems more dramatic on the DE321 than other radios. It seems like the DE321 takes longer to recover and bring the volume level back up. I put my head between the two radios at one point, and the DE321 was muting the signal while the E5 still had an audible broadcast. Interestingly, the muted moments on the DE321 were directly correlated with what sounded like increased static on the E5. My ears and my mind can filter out the static, but I can't simply imagine a signal that's not there, so the DE321 is not performing up to my expectations here.

University Network on 6090 kHz (English from Anguilla) came in fine on the E5, but was weak, distorted, and frequently muted on the DE321.

Voice of Croatia on 9925 kHz from Germany (English to North America) performed a bit better than average. I heard frequent muting, but in this case, each instance of muting was very short. So although the audio level was jumping all over the place, the aggregate signal was understandable. It would be fatiguing to listen to something like that for longer than a couple minutes.

China Radio International was loud and clear on 9690 kHz on the E5, coming from Spain. This signal came up easily on the DE321 and was one of the better receptions there.

FM

I spent some time tuning through local FM stations. As expected, I had no problems clarifying the stations or isolating adjacent stations. The internal speaker showed itself as inadequate for music. It was easy, however, to tune slightly off-frequency from an FM station and hear a distorted broadcast.

I came across a classic rock station (K-FOX 102.1) and listened to a few songs: "I can't get no satisfaction" by the Rolling Stones, "Hitch a ride" by Boston, "Even the losers" by Tom Petty and the Heartbreakers, and "Always with me, always with you" by Joe Satriani. To my ears, with the internal speaker, cymbals often detracted from the audio quality. I'd speculate that the higher-frequency audio signals cause the speaker to distort. The electric guitars sounded great, though. There may or may not have been a few moments of air guitar. But, this experience shows that the internal speaker is a poor choice for listening to music.

A community radio station (KPOO 89.5) was playing jazz both times I came across it, and I enjoyed listening to this the most on FM. Brass instruments, including trumpet and saxophone, really sounded great. This station is in San Francisco, broadcasting with 270 watts. For this station, the tuning needle was just about centered on "90" for the FM1 band.

While listening to my local NPR station (KQED 88.5), I heard a clear signal, but the signal was somewhat distorted with crackling, and sibilance sounded poor through the speaker. The sibilance distortion was not heard in my Sennheiser headphones. "Electric counterpoint (movement 3)" by Steve Reich was used as bumper music at the end of "To the best of our knowledge".


Kaito WRX911 and Degen DE321.


Conclusion

So, is this a good $20 radio? Would this radio be a good way to introduce someone to shortwave?

This DSP-based radio with analog-style tuning display is an interesting product, but ultimately, I do not recommend it.

I always prefer a digital frequency readout to know what frequency I'm receiving. I consider this especially important for shortwave where the challenge tends to be "where's 7490", as opposed to "where's something I can listen to" for local broadcast bands. But the slide-rule tuning display keeps component costs down, and the tuning scale is as accurate as it can be for its size. The tuning knob offers the right amount of resistance.

I didn't like how this radio performed on shortwave. With weak signals, the radio was very noisy, and the signal muted at times of high static or low signal strength, or some combination of both. For me, that makes the radio less usable, since I have no chance of knowing what was missed. I've learned that the muting behavior is a design feature of radio receiver DSP chips. It's a good concept, but it's happening far too often during my usage of the radio.

The volume control is loose and touchy, quickly and dramatically altering the volume. The headphone jack proved problematic as I needed a tool to unplug my iPod-style earphones. The combination of the audio circuit, its filtering, and the built-in speaker result in a product that by itself is not good for music. Using high-quality headphones remedies this.

So, what does DSP do for this radio? Tuning accuracy was excellent, but complete and accurate delivery of the desired audio content was lacking. I decided not to open the DE321, but it would be interesting to compare the circuitry inside the WRX911 and the DE321. I'd expect the DE321 to use many fewer components and have a smaller size. With a DSP chip at the center of the design, radio manufacturers could consider making much smaller radios. By excluding a built-in speaker and telescopic antenna, and using a thinner rechargeable battery for power, portable radios could become something quite different from the typical black rectangles.

When reviewing a product like this, there's always the chance of receiving a bad iteration, whether due to a quality control issue, or a problem that is subsequently fixed for later production runs. As always, I'd be pleased to learn how my experience compares with yours on this product.

1 comment:

Heinz H said...

By far the best review for the Ka321 that I have seen. I agree on all points! As result, I have deleted my own review of the KA321 on Amazon. Suggest you should put your's there. Heinz H