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- เผยแพร่เมื่อ 22 ก.ค. 2020
- I got two of the wildly available PLJ-8LED frequency counter modules from Ebay. These are in fact clones of the real PLJ-8LED and one isn't working properly. As a little weekend project, I decided to put the good one in a little box and then show some of the problems you need to watch out for when using these modules.
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Thanks for the video, extremely helpful. I bought this counter to put in an FM radio I am building. When I was testing it with my function generator the numbers were going all over the shop. Your video was perfect as describing what's going on. Thanks!
many thanks for the very clear English info, I have purchased one of these units primarily for IF offsetting for use with old receivers, and the available data and info elsewhere seems to be very limited.
Your video has been extremely helpful especially with the practical mounting and set up.
Vielle dank fuer alles, gruss aus England. Chris
Excellent tutorial and dialog. Thanks much!
I appreciate your wonderful review.
I was able to understand the configuration of this module very well.
Fantastic video. Thank you for an honest, well thought out and well presented review of these cheap devices. I also love the reference to ElectroBOOM at 13:30!
This is a very useful video - thank you!
thx!
danke für den trick mit dem auftrennen der eingänge.
das hat mir sehr geholfen!
liebe Grüße, a
Thanks, very useful as mine came with zero instructions!
Thank you for a clear easy to follow discussion.
I just got one from China and will certainly do a couple of mod like separating the High & Low inputs.
Of course, I speak in the name of all the basic movements of the 21st Century. Again, DAMN Good!.
Hola TheHWcave. Muy buen vídeo explicativo de las características de este frecuencímetro. Te felicito. Me ha gustado mucho la investigación realizada sobre sus virtudes y defectos.
Un cordial saludo.
Ketk.
Many thanks / muchas gracias
Well done! Thank you
thanks for helping this old man settup and understand this counter. mine is installed in an old cable box and i have a bnc connector for connecting a scope probe. . my question instead of the probe sometimes i would like to use straight input wires with no isolation.
so when servicing tube equipment whats the max vdc on the signal input this counter can handle w/o burning it out ?
Its tricky to say. Hi and Lo inputs are wired together (but can be separated). They are AC coupled followed by two anti-parallel diodes of 1N4148 type. The volts rating of the caps is unknown. The impedance of the caps goes down with frequency, so the diodes will see an increasing AC current. Also the diode reverse voltage should be below 100V. Based on this 100Vpeak is the absolute max from the diodes but the caps may have a lower rating. And the higher the frequency the lower the max voltage (because of the current through the diodes). I think there is 1 nF cap in the LO input, at 1 MHz that's about 160 Ohm and with 0.2mA through very! hot diodes that's just 32V. In short very little headroom. You better add a 20dB (1/10) or 40 db (1/100) attenuator at the front
Damn, that's good!. Dunka.
Very complete analysis. Thank you for this. I bought two of these and managed to blow both of them out. I was measuring with my eico 124 as input and got reasonable results, but when I hooked to my feeltech FY3200, the counter started flashing and stopped working in about 10 secondsj. Im afraid my signal generator is introducing some extraneous voltage thats blowing these things out. Do you think there is any fix or what the most likely failure is? I have some surface mount parts.
have you looked at my videos on the Feeltech FY6600. I found that mine produced stray voltages because of the badly designed power supplies. if you earth the outside BNC shell of your Fy3200, does the problem go away?
@@TheHWcave I will check that. I had read about this but never had a problem with any of my other endeavors, so never bothered to check it.
Do you have an idea of what might have blown out?
I have a couple of these in the radio room and they actually work quite well sampling the RF output on the radios but this would not be the best choice for a bench frequency counter choice in the shop where you needed more diversity and the fact they didn't set up some kind of selector switch in the hi and lo front end doesn't make sense. They had to know that would be an issue.
yes, using them as a readout for an analog signal gen or a radio dial is a better use
@@TheHWcave Let me run something by you here. The frequency stability for these counters are 2.5 ppm so in the 10 to 12 meter bands this will deliver an accuracy within a 60 hz up to 70 hz window but you can pick up these oscillators all day long at Digikey and Mouser rated at .5 ppm literally for a few bucks which would technically take the accuracy window to around to around 13 hz to 14 hz accuracy. I have not looked at the oscillator module on this counter yet but I think this can be done. Any thoughts if it's worth a try?
@@flash001USA Yes, that should be possible if such accuracy is needed.
Thank you for great and usefull video! Is it possible to get manual or find it on internet? All manuals i found is for another model that look like this.
I am on the road and can't check my files, but I believe the ones I have were made (or are clones) of Sanjjian studios who came up with the original design. This may help: archive.org/details/plj8ledmanualtranslationen
If using this in an old signal generator, for AM and Shortwave 455Khz and 1600Khz for alignment to insure my alignment frequencys, can this be done........I dont need high megaherst for a transoceaninic
G500 radio, what i want is a way to have a frequency counter in my old EICO 324 signal generator for accurate radio alignment
Hi gene,
lovely bit of kit, the EICO 324 (I looked it up). I am afraid adding this counter isn't all that easy. The problem is that terrible input stage of the PLJ-8LED with the two anti-parallel diode limiters that will mess up the wave form of any signal coming out of your EICO. You need to make yourself a buffer circuit that presents a high impedance input to the EICO and can tolerate the signal butchery of the PLJ at the output. Since you are not looking at very high frequencies, normal (single-rail) opamp should work and you could feed that circuit from the low-volt DC supply you need for the PLJ anyway.
Alternatively, you could try hooking up the PLJ temporarily to the EICO to set its frequency and then disconnect it when using it to align your IF stages and hope that the frequency doesn't drift too much.
Did I miss where you eventually mentioned the other 3 trimpots? Would be interested to know what they are for.
No its there starting at 23:25 or thereabouts
A useful analysis. A follow-up question: I have 2 counters - one gives an acceptable error of ~10Hz, and the other ~40Hz which is way too much. Do you know how to calibrate the counter? At least how to apply a systematic error correction?
I assume you have tried the trim pot to adjust the oscillator frequency for the time base? I have 2 modules and in one the range of the trim pot was not sufficient to remove the error. I managed to fix that by soldering in an additional resistor. The video is here: th-cam.com/video/MGNRo2G30xc/w-d-xo.html
@@TheHWcave Based on your video, I was able to adjust frequency to reasonable accuracy without an extra resistor. Thanks!
Did you find the temperature stability to be ok from cold on either or both of your modules ?
This is certainly a handy counter module, even with its problems....
I "burned-in" both modules by running them continuously for at least a week 24/7 before attempting to adjust the oscillator. The "green" LED module never got closer than 5Hz and that is already right at the end of its trim range. I adjusted the "blue" LED module about a month ago and have not touched the setting since. So far no drift. Its frequency trim pot is not "in the middle" but it isn't maxed out either. There is hardly any change after starting from cold. It is within 1Hz of a 10 MHz reference right from the start. It may show slightly more often the +1 count display in the first 15 minutes. One of the reasons may be that there is not much of temperature variation given the reduced 7.7V supply voltage and that the recycled power brick (which does get warm) is not in the enclosure.
You are right in that it is a useful counter to have, especially for the price but all I am using it for is as a short-term transfer standard to control calibration of my function generator against a GPSDO reference. With that I mean, I select the same frequency on the GPSDO and the function generator and then use the PLJ-8LED connected first to one, then the other verify and calibrate the function generator. This procedure means I always know the to be measured frequency and use well defined clean signal shapes. The PLJ-8LED is certainly well suited for this task.
@@TheHWcave To be within 1 Hz at 10MHz from cold and then stay there seems pretty amazing for the cost of these modules - don't you think ?
Your green module - I wonder if they have loaded a wrong value component around the osc. so that it won't pull in properly ? Could be a 2nd good module if so :o)
(I built a 10MHz standard locked to Radio 4 on 198kHz, which is a ref std, to perform the same function as your GPSDO, and my old '80s counter plainly drifts from -6 Hz to + 6 Hz then back to zero within 30 mins from cold - but is not too bad after that - but then its xtal osc is old - school !)
@@noakeswalkerTo answer your question on wrong component values, I spent the last 45 mins on comparing the oscillator circuits of the two counters. They do appear identical but I found that the whole circuit (TCXO and trim pot + separate resistors) are all fed from a tiny XC6206 3.3V regulator marked 662k. On the "blue" counter, that is producing 3.3V as it should but on the "green" one, its 3.6V. According to the XC6206 datasheet that is way out of tolerance, even for the non-high-accuracy version. So the problem may be a dodgy regulator. I just ordered a few from Ebay (10 for £1.90 including postage) to see if that solves the problem. If it does, I'll post a short follow-on video.
@@TheHWcave Good find ! That does seem a likely cause - let's hope it is.
Chips arrived and just before replacing, I decided to check voltage again.To my surprise its 3.315V , certainly within spec. I have no idea what went wrong when I measured a couple of days ago, but there is no point replacing a working regulator. The frequency is still off by 5 Hz on 10 MHz. So now the only alternative is to replace the TCXO but not sure if that's worth the effort.
спасибо было интересно
Спасибо пожалуйста
Does anybody know what is low side prescaler IC?
The only prescaler in this is a MB506 chip but that is on the high frequency input. As far as I know it is hard wired to /64
where on earth did you find the button extensions? ive searched high and low
Search eBay for "SWITCH CAP for Tactile Push Button Switch". They are still there.
I made mine by disassembling some salvaged tactile switches. The extensions are trapped between the plastic face and the circuit board by the rim that holds the button in the tact switch to begin with.
I'll never understand why people make a vidio of their project refuse to provide a parts list of the parts used, how much they cost and where they can be found!!!!
Parts are often what I found in my a spare parts bin of spare and recycled electronics and mechanical gear. occasionally a project may require an item that I don't have. If its a commodity item, I will generally buy, say 5 switches when the project only needs 1. That way I get discounts and meet free shipping threshold and build up a stock of items (the parts bin). Problem is of course that I often don't remember the details of the items and where I bought it from. I generally work under the assumption that most electronic hobbyists do the same, take the video as an idea and modify it to what they already have or can easily get in their country, and change the design in ways they prefer more. The one exception are safety critical components for which I generally specify vendor and part numbers. I normally don't add sources because they change too quickly .
th-cam.com/video/PgS0vDWRBFw/w-d-xo.htmlfeature=shared