The Good and the Bad on Bill's Second Tecsun PL-660

 

 

You know how when people disagree in review threads about whether or not The Object is any good, they so often end up getting vicious and personal about it? I was going to do a review like that with Past Bill and Future Bill ending up going to war over whether the Tecsun PL-660 was any good or not. I’ll spare you and say the replacement unit I got is far better than the original, although still flawed. 

The new PL-660 seems to be hot on SW and acceptable on MW. MW stations that are usable signals but less than perfect on my other radios come in acceptably on the new PL-660. It picks up the weak and unusable ones well enough to make out what they are. This is not top quality DXing performance but it’s good enough. 

The strong false signal on 980 KHz is still there on this one, but I guess I can do without one frequency. The false signal does not repeat itself up the shortwave spectrum as one fellow on You Tube reported.

There are still some annoyances. The radio definitely wants to be tuned one KHz high on MW (tuning to 1231 KHz sounds a lot better than tuning to 1230 for example). I did not notice this on SW. The radio has the feature, common to so many Chinese shortwave portables, that when you rest it on its back the telescoping antenna cannot be made to point straight up. This makes it more likely you’ll walk into the antenna and break it, or knock the radio off the table. They do include a plug in wire antenna; it might be good to use that, in this situation. 

The ergonomics and convenience features of the radio are nice, and I consider its sound to be better than my Sony ICF-7600gr. The sync seems to work better too. 

I don’t have any particular interest in the air band, but it’s cool that it’s there. 

One feature of the radio I haven’t seen mentioned is that there is a little wire bracket at the lower rear edge that pulls out, to make the radio stand more securely on its narrow lower side. That does allow you to extend the telescoping antenna directly upward, of course, at the price of balancing the radio on its narrow edge instead of the broad, stable back, but for something like a windowsill, where you’re not likely to bump into it from behind, that is useful. 

It has two alarms, many memories, a light you can turn on and keep on if you want, and the Automatic Tune System that scans the bands and puts signals into memory.

As for that automatic tuning system, I don’t find it quite as spiffy as that on the PL-390. The PL-660 seems to go by signal strength, so it picks up strong noise and remembers that, while failing to notice anything that isn’t particularly strong. Perhaps because the PL-390 is based on one of those digital signal processing radio chips, it seems to be able to tell what is strong noise, rejecting that, while recognizing weak signals and accepting them. Still, the automatic scan is very nice and will give you a few hours’ strong signals to listen to, no problem. I like it. 

The replacement PL-660 is a worthy radio. I’m going to keep it despite its imperfections. After all, compared to the old analog radios I started with, where you were lucky to be able to tell where you were within 40 or 50 KHz, being 1 KHz off is no big deal. 

Just don’t talk about my mother running out from under the porch to bite you because my particular example of this radio is not as good, or not as bad, as the one you got. Sample variation would seem to be a problem with this model, based on my experience. Getting a lemon doesn’t mean you’re a bad person! 

--bill

 

 

Comments

[Bill]

Details on automatic scans to find shortwave stations with the PL-390 vs. PL-660:

Side by side on my windowsill, the PL-390 scanned in up 21 good SW broadcast signals, although one of these was recorded as 5khz off its actual frequency. The PL-660 scanned in 32.

Each one scanned in one good station the other missed.

The PL-660 also scanned in as stations what seemed to be two spurious signals, 10 instances of electrical noise, and four "signals" which were actually spatter from strong signals the next frequency over; the PL-390 didn't log any of these.

What one radio could pick up the other could as well, as far as I could tell. Neither one was catching everything there was. I scanned the 49 meter band by hand and lost count of the number of stations; about 20 were coming in, I think. Any signal the 390 could hear, the 660 could also. The 660 had one that might have been a spurious signal. On the other hand, signals that were really too weak to make out sounded slightly less bad on the 660. It wasn't enough to make them listenable, but you could make out what was going on a little bit better.

I tried the sync to resolve some adjacent channel problems, and it works fine- if there is a strong interfering station on one side of the one you're trying to hear. Not if there are strong signals on both sides; in this case the sync made things worse.

All in all, an interesting mixed bag.

[Giorgio]

All PL660 that I know of have the 980 kHz spurious carrier. It seems to be produced by an internal DC/DC converter.
The worst feature of the PL660 is a sort of squelch that cuts the highs of low signals. It makes fading AM stations almost incomprehensible. This feature can be removed by modifying the radio. I did it with success. See youtube to find how.
Another "new" weakness is that the case of the tuning encoder is not connected to electrical ground; this makes tuning noisier sometimes. Again I corrected this easily.
I bought the PL660 to substitute my older PL600. After the above touchups (TECSUN !! read this) I can say that the PL660 is much better than the PL600 in every respect.
TECSUN, Please connect the microprocessor to the DC/DC converter and shift its frequency when the radio is tuned near 980 kHz and its harmonics. Thank you.

[Bill]

Thank you, Giorgio. It's good to know the problem with my 660 is not unique. It gives me some reassurance that the radio might not be about to die on me.

Strange that nobody mentioned this problem in the reviews I saw. I've seen too many product reviews that were matters of religion; true believers insisting The Product is perfect, worshipers of other brands saying it is a Crawling Abomination from Hell. It's almost as bad as operating system wars. I wish people would tell the truth in reviews, including the good and the bad. But if you did that, people looking to buy would be put off and tend to buy things about which the truth had NOT been told.

I was not able to find any instructions for modifying my PL-660 on the page you mentioned. It is in Russian and I don't read Russian. I used the Google translation but if there are any instructions in there they are nonsense to me. Of course I've never modified a radio, so it is likely I simply can't reconstruct what's being said. In any case, do you know of any idiot level instructions, including pictures, of what would need to be done?

Also, my sole electronics modification experience is soldering up custom RS-232 cables back in the day. This required some soldering in small spaces but nothing fancy. Is the modification required within such basic abilities?

Thanks.

---bill

[Giorgio]

Instructions for defeating the dynamic audio low pass filter of Tecsun PL660. (that I made on a rev.2 radio)

To illustrate the activity I link pictures and a video that are not mine. They are not under my control.
This picture shows the two tracks that must be shorted to disable the dynamic low pass filter (dynamic squelch):
http://s019.radikal.ru/i601/1204/34/252b4d832084.jpg

To go there you need a good skill and be quite careless about any warranty, just think that you can do it:

0)A good solder station and a set of screwdrivers are required. Always pay great attention not to touch the plastic with the soldering iron.

1)Remove batteries, remove 4 screws on the back e and 2 screws in the battery compartment.
2)Pull out the 3 knobs.
3)Separate bottom and front shells. The electronics is now attached to the bottom shell. Do not touch LCD and the transparent window.
4)Look at the electronics. Look at the strap location. Write down the revision number of your radio that you can read on the PCB....
5)Remove the screw at the lower right corner as shown in the video.
6)Uplift the electronics, starting from the "knobs" side. Shift right and separate from the bottom shell.
7)On the back of the electronics there is the "big" shield. It has 4 solder points and 2 alignment small fin/slots. Remember where it is soldered. Remove the shield starting from the solder points that are far from the fin/slots.
8)Do the short by soldering a hair-thin copper wire taken from a common electrical bicycle wire.
9)Resolder the shield by first inserting the small fins in the slots.
10)Reassemble.

Video:
http://www.youtube.com/watch?v=PKpWED2ppgE
time 0:16 "big" shield removed to access the two tracks that must be shorted.
time 0:35 shows the only screw that must be removed to uplift the PCB frame.

It is possible to convert the tone switch to a switch that enables and disables this modification.
http://s019.radikal.ru/i638/1204/10/a2e2866ba201.jpg
http://s019.radikal.ru/i609/1204/2c/ba350c59c553.jpg
http://s15.radikal.ru/i188/1204/9a/eb171f52fd8d.jpg
http://s018.radikal.ru/i501/1204/7a/82963e83a7ee.jpg

Instead I kept the tone switch and defeated the dynamic filter in a permanent way with the thin wire.

[Giorgio]

Oops, keep track of the U shaped foot while "openig" this box. Maybe keep it in position with some tape.

[Bill]

Thanks! I'll look at this and see if I think it's something I could do. It doesn't sound too horrible.

[Giorgio]

This youtube video shows a strange non-fading carrier at 4820:
http://www.youtube.com/watch?v=Qu79uA4RRFU
Because of the beat frequency of about 2kHz with a station, the strange carrier is not on channel.
The anomaly is not recognized as such.

[Giorgio]

In the above video a "chirping" carrier can be heard at 4800 kHz. The operator tries to cancel it with sync detection. By the sound, I can recognize this as a harmonics of the ~980 kHz spur.
I still don't know if all PL660 have this feature.
More comments are needed.
It is radiated by the radio circuitry and enters through the antenna. Because of that I believe that additional shielding of the supposed source DC/DC converter may solve the problem.