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August 08, 2012

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.

james patterson

The Harmonic Chirping,Squashy sound is exactly what I have in my radio,and when I put my hand on the antenna it certainly amplifies it.As mentioned in a reveiw by Giorgio.Im takeing my PL660 back,but it seems from most reviews,they all have this problem.Everdently the 600 doesnt have this problem,I havent read any.But according to other reveiws,the 600 has other problems.So can we DXers win at all?The Tecsun Receivers are said to be amongst the best in portables,then why all the problems?Im hopeing to check all the stock of PL660s where mine came from,there must be a good one amongst them,because I found no probs with FM,AM broadcast came in very well at my location.So if I can find one with no loud harmonics up on HF,well I'll be happy.Note that the harmonic sounds are alot worse if the SSB mode is set to on,and you wouldnt want that sound over top of a favourite frequency that you often listen to.I listen to 8.86700,Sth Pacific HF Airways.Well the harmonic sound is there and it climbs either up or down the band on its own.If you tune higher or lower,you will find it there somewhere.

Tom Welch

I would very much like to purchase a new world band radio, however, every month an international broadcaster goes out business. The latest is Radio Australia. I thinking a PL 390 now!!!

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