Tecsun PL-680: SSB display inaccuracy

PL-680-Sync-Detector

SWLing Post reader, Olli Turunen, writes:

I thought you would like to know this. I bought PL-680 few days ago and I noticed that mine has the display about 1 khz off. I contact Anna on Anon-Co and got a quick reply:

“I have received a response from the supplier regarding the 1 kHz deviation issue of the PL-680 radio. Unfortunately they consider this to be within their tolerance standards for SW reception. Overall, their standard is set to be +/- 0.5 kHz, which translates to 1 kHz on the LCD display. They understand the effect it may especially have for SSB listening, which is why fine tuning has been added as a feature.

For MW/AM the situation is a bit different. According to the supplier this is an issue that both the PL-680 and PL-660 radios have and cannot be avoided. As they indicate, unfortunately only the PL-880 has a special function for MW frequency calibration.”

I just checked my PL-680 and did a zero-beat in SSB against WWV on 10 MHz. If the BFO adjustment is correct when in the middle position, I can confirm that mine is almost 1 kHz too high as well.

For AM listening, a 1 kHz deviation isn’t noticeable.  If you’re using ECSS, though, you’ll certainly have to fine tune the BFO accordingly.  If locating a CW or SSB signal (in the ham bands, for example), you’ll also need to adjust the BFO fine tune control in advance.

Most importantly–and fortunately–when you turn on the PL-680’s synchronous detection, the receiver is exactly on frequency (at least on my early model PL-680).

Many thanks, Olli, for sharing this information! I’ll note this negative in the PL-680 review.

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20 thoughts on “Tecsun PL-680: SSB display inaccuracy

  1. Mark

    Hi I’ve bought a PL 660 and the display reads 5KHz too low from Long Wave right up to 30 MHz. For example if tune to 558 kHz, I have to tune the radio until it reads 553 to get there. However with the narrow filter on, the frequency is correct. This is a faulty radio. I’ve not seen anything on the web that this is normal. (The FM band reads correctly)

    I think I should send it back. It was aliexpress. Has anyone else had this problem or advise what to do?

    Reply
    1. Gary

      This is exactly why I’m here today. I just got my 660 yesterday. 5Khz low on SW. WWV is 9995 or 4995. Radio Havana Cuba is 15135. FM is spot on. AM is spot on. Yes I understand about the days of the analog dial and not knowing where you are at but this isn’t 1970 either. Am I expecting too much?

      Reply
  2. robert k scorpio

    I am investigating a Tecsun Pro Version at $175 or so which has the AM Medium Wave Performance of 660 the improved sensitivity of 680 and Calibration of the 880 with line out and a few other features.
    Thinking at about $175. IF Tecsun knows there will be an initial Demand foe 1000 units…they will tweak the PL 660 /680 Into a Pro Version or PL 700 etc.

    Although I like the form factor of the PL 880 including Li-ion Battery…it will require complete redesign …not realistic to expect..
    BUT – tweaking and re calibrating Frequency…getting best version of PL680 with AM Sensitivity from PL660 and a better Calibration( 880) and Sync from 680 Should be possible …as a Premium 680 or best of 660 and 680 into one Unit at higher Price..
    Line Out; Display always on possible..AM Band from 660 and overall 680 Performance ?
    Possible ?

    Reply
  3. Vasily

    Has anyone figured out a way how to fix the 1 khz issue on the 680? Any “hidden menu” we should be aware of? Thanks.

    Reply
  4. Henry

    I have been using Alkaline cells, I’ll try rechargeable batteries later. I tried Duracell batteries but they seem to die rather quickly. I use the ICF-2010 as a reference, and perhaps I was “spoiled” by this radio; I don’t hear any “self noise” or hash. I solved the ICF-2010 memory problem by installing a 1.5 Farad capacitor. Its only remaining problem is its 100 Hz SSB tuning, I may try solving this if I can get my hands on another ICF-2010 sample. The PL-880 uses DSP so its filters should be perfect, but I don’t like using batteries I can’t buy at my local corner store. The PL-880 resembles a radio you would buy if you wanted Sony performance with great audio; the Grundig Satellit 700.

    Reply
    1. James Patterson

      The problem Ive found with some brands of Alkaline batteries is that they may be old stock,sitting on the shop shelf for many months.They do have a life.Ive bought batteries of good brands only to find some cells are only showing half voltage when tested.So I try to stick with re-chargables.I buy Energizer brand.Ive never had a problem with these.I now see on the market re- cycled re-conditioned batteries.Sold along side the new battery packs.I hope the world is not becoming a dumping ground for these re-cycled batteries.

      Reply
      1. James Patterson

        Also Duracells,Ive never had any Luck with these.They certainly dont last compared with Eveready or Energizer Alkaline batteries.

        Reply
  5. Henry

    I forgot to mention how you must turn the radio on for a while before adjusting it. I find the PL-660 is too noisy, and activating SSB makes it even more noisy. This is where Sony had the advantage with very few models being noisy. Sangean is also quiet but usually less sensitive than Sony. Passport pointed this out years ago, their tests indicated Sangean models were excellent with an external antenna. Sangean models are also known for high battery consumption. A good thing about the PL-660 is that its BFO is less “touchy” than I expected; but is also “battery hungry.” I might try modifying a Sony ICF-SW7600GR for a less sensitive or “touchy” SSB fine tuning. It seems my best bet for a top small portable is to modify an ICF-SW7600GR with a “slowed down” SSB fine tuning.

    Reply
    1. James Patterson

      In reply,Ive found that both my PL660,and Sangean 909x flag ship model are very good on batteries.I use rechargables 2000mah.But I dont recharge them in the radios,I have a seperate charger for them.Yes the PL660 is very loud on Static,hash as we call it,but the Sangean 909x is very quite,even with a long antenna.But not quite on receiving Short Wave,AM or FM.Stations just boom in,Ive had Sony,national Panasonic portables and others,but both the PL660 and 909X certainly by far are better all round.Mind you,I still fire up my 45 year old National Panasonic DR 49.You cant beat that for sensitivity and no “hash” at all !!.

      Reply
  6. Henry

    I have the PL-660, I opened it and calibrated it so that the BFO center produced zero beat. Activating SSB with WWV didn’t produce any beat frequencies, you wouldn’t even know the BFO was active unless you looked. I tried the same on the AM band with identical results. I believe the problem is inexpensive IF filters; if you look at ceramic filter datasheets, you may see what I call “asymmetrical response.” You may see the filter’s response is “slanted” and one side is wider or narrower than the other. This will be more noticeable with narrower filters. This is a reason why I like “old fashion” IF cans; I can tune them for maximum selectivity or less selectivity with better audio. The display is surprisingly accurate but its ceramic filters could be better.

    Reply
    1. James Patterson

      Yes as I have commented in the past,SSB will most likely always be off top dead center.Many factors can cause this,and like Ive found,if I re-tune the BFO filters to top dead center,then reassemble the radio,turn it back on,Ive found that it is back off center again.So when I buy new portable receivers,I always check a few first and find one that is as close to top daed center as possible.Now here are the factors that I have found.Operateing in a hot climate,or very cold conditions can alter the BFO.What I do,is when switching over to SSB,even without a BFO trimmer,I put the offical HF frequency into it.It will most likely be a little off,and sound way out of tune.So I correct the tuning,or BFO trimmer.Then wait about 60 seconds then retune the frequency,or Trimmer to where it should be,and I always find that it has settled at Top Dead Center,or near enough to it.So I feel that ,the BFO circuit takes a little time to stabilize,or warm up.I dont have a problem with my PL 660.Out of many that I first tried untill I found one that I was happy with.I found that many I tried out,had very noisey internal harmonics,(Birdies) more so when tuned to SSB over all HF frequencies.So the one I finaly bought,had little or none of the birdie sound problem.That harmonic sound,was terrible if it came up on a HF frequency that I was listening on.It drowned it out completly.So the PL660 I have settles down very well on SSB once it has been on for arround 60 secs,and there is no drift at all.Also Ive noticed with the 660 that the “White noise” it creates is very loud,and when receiving a distant station,it is sometimes difficult to hear over it.Also it is so sensitive that it will pick up all outside electrical noise.The “Rain” static can be very loud.Yet my flag ship ATS 909X Sangean has very little white noise infact really none at all.If worked properly,and according to the type of outside antenna that is connected to the antenna input,it performs as good as the PL 660,and without that white noise problem.So I have two really great portable receivers.I like to DX the PL 660,then put the stations I find into the ATS 909X,and lable them with the Alfa numerics.

      Reply
  7. Dan Robinson

    There is still a lot of confusion about this issue. We’re talking about how a radio performs or is set to perform, as it leaves the factory, and about how to clarify the signal for EXACT ZERO BEAT. Yes, it’s correct to observe that portable receivers should not be held to as high a standard as communications receivers. But as someone else observed, it would seem to many of us that companies have the capability to ensure that you don’t have to turn the SSB adjust knob too far left or right of center to achieve exact zero beat whether in LSB or USB. I inquired of ANON-CO about this issue when I got my 660 about a year ago. The response was similar — that Tecsun reported that they PURPOSELY have the fine tune wheel zero beat off the center detent position, because obviously if it were AT the center position, which is a physical detent, it would not stay there, but automatically move off to a degree left or right of center. But one wonders why they would not just do what Panasonic engineers did many deades ago with the wonderful RF-B65 portable, which was that EXACT zero beat was set for the exact mid-point of that wheel, which did NOT have a physical detent. Also — I think the issue of drift is not the point here. Sure, every radio will drift a bit, but the real issue here is the original design out of factory…

    Reply
  8. James Patterson

    You should never have to turn the BFO all the way counterclockwise to bring in a LSB station.Remember it’s Clockwise for USB and counter clockwise ( Anti clockwise) for LSB.Have you checked that you have the correct frequency that you are looking for?Offical frequencies such as 13.261 mgs HF Air Craft, and so on are all on USB.Ham radio,on 3.5000mgs and 7.000mgs is LSB.Hams on 14.000mgs up wards are on USB.You need to know the difference.If you are trying for a Ham radio station on LSB,just turn your BFO anti clockwise slightly past the center notch.It will be slightly past that notch.It can never be top dead center on the notch,because you are tuning LSB.For USB,your tuning will be slightly clockwise past that notch.So with having the BFO in the correct position,try tuning the station you are looking for,or DXing.Maybe the reason why you have turned the BFO all the way anti clockwise just to try and tune in a station,is because you are not aware of where the station should be or what the true frequency is.You will get a station “Bang on” if you have the BFO turned only slightly past the center notch.The BFO is variable,but not as much as having to turn it all the way round.

    Reply
  9. Cornelius

    My PL-680 has the same quirk. With the BFO knob on the detent, it’s on frequency, within 200 Hz or so, but on any signal with even a hint of carrier, it sounds TERRIBLE. With the BFO turned all the way counter-clockwise, it’ll read 1 KHz high, but it sounds far better. I think I can pretty easily overlook that issue. I love heading outside on my lunch break for a brief SWL. The inclusion of LW is a nice perk as well.

    Reply
  10. Rob Wagner VK3BVW

    Isn’t it funny how we’ve become so fussy about a 1kHz discrepancy in readout on a cheap little portable radio! Years ago, the analog dial with the thick needle hauled around on a stringed pulley was the accepted norm.

    Having said that, Tecsun should be able to get a better result from their circuitry than a +/- 0.5kHz tolerance. That’s actually quite a wide range in today’s terms. Interesting!

    Reply
  11. pu3hag

    If memory serves well, the venerable Kenwood R1000 also had this little odd behavior. When in USB, you had to move the VFO around 1KHz up and 1KHz down in LSB to have phone transmission sound natural. After a few stations, one would get used.

    Reply
  12. James Patterson

    I have the PL 660,and Ive never had a problem with frequencies being off on the AM/MW band.As far as SSB on HF goes,nearly every radio with a BFO will be slightly out,it’s all to do with how the radio was tested and set at the factory,as well as “Room”temperture.Ive found that different room tempertures can acturly effect the SSB not being top dead center.Also Ive found on most radios,that when turned on,and the SSB mode switch is turned on,and you have tuned to an offical station/frequency,or one in your memory,the BFO will need to be re-adjusted after a few minutes.I think that part of the circuit needs to be warmed up to it’s operating temperture,befor it will show either top dead center,or slightly to the right for USB,and slightly to the left for LSB.I had a Sony SW 55,it had a “Re-Cal”feature,because sometimes it needed to be recalabrated on a SSB frequency.Sony was good enough to think about this when designing that radio.Anyway,this has always been my finding on most radios.For some radios that dont have a variable BFO knob,and they rely on slow,and small tuning steps to get the SSB correct,either the tuning steps are too wide,or the radio SSB circuit has not been correctly set at the factory,or you have a very poor quality radio,like the Digitec AR 1945,of which I do happen to own,but only through my paitence,am I able to acturly tune in SSB at all!!.So as far as your PL 680 goes,I wouldnt worry too much over that small problem,let it warm up for a few minutes,and see if it will correct to where it should be.Remember,Anticlockwise for LSB,Clockwise for USB.You should only need to turn it slightly past the notch,either way.Otherwise you may not have it tuned to the offical Side Band station properly.Eg,8.867mgs is an offical HF Air frequency used over the Pacific ocean.This is USB.13.306mgs is a Military Air frequency.You need to acturly know the offical frequencies,otherwise you could be tuneing off the frequency,and blameing it on the BFO setting…Happy listening from Down Under New Zealand.

    Reply
  13. Ernest Stagnetto

    Have had a PL680 for more than a year now and it has very sensitive reception which I put to convenient use with the telescopic antenna to check the bands from my bed thus saving myself a trip to the radio room and firing up all the equipment for nothing. For it`s price and considering the inclusion of a fine tuning facility, 1kz should not be an issue. If you think back to analogue receivers costing ten times the price one can hardly criticize the display accuracy. I suppose the PL880 is an improved version at extra cost. The only thing I am surprised at is the high battery consumption of the PL680.

    Reply
  14. Pingback: A review of the Tecsun PL-680 with reader survey results | The SWLing Post

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