ZHAOXIN HC-F2700L (Atten F2700C) Frequency Counter un-stable count - Page 1
Forum section: electronics / testgear

author: Gonzini
author_rank: Contributor
timestamp: March 19, 2013, 11:14:13 pm
content: Anyone got one of these?Picked one up but its all over the place and not stable across the range so useless.Not had a look inside yet but not a good start...Looks like more than calibration out to me, if it can be calibrated?Just cheap Chinese rubbish that doesn't work?

author: Thor-Arne
author_rank: Unknown
timestamp: March 19, 2013, 11:31:08 pm
content: Yes, I've got one....When I bought it I didn't expect much from it, at least the box would be usable.I was prepared that I'd have to make my own, and that might be the final result anyways.The counter functions ok, but I haven't bothered checking it's accuracy.Main issue I had was that the soldering washorriblein there, and even the oscillator on the back was broken off.Also, I suspect that it's built withused parts, the date codes doesn't match.Bottom line, these cheap things can be a experience in itself regarding what some are willing to do to save a couple of cents.

author: karlmag
author_rank: Contributor
timestamp: March 19, 2013, 11:35:40 pm
content: I got one.It didn't work in the 100MHz range at all. No output.IIRC some of the ICs had pins that where bent to outside the sockets too, but bending them back and resocket the ICs didn't help.I ended up swapped out all the (socketed 74-series) ICs and it started working after that, so I think the problem was at least one failed IC.It seems to work properly after that.Good thing all those ICs where in sockets, which made the swap easy.And as Thor-Arne pointed out, I have seen better soldering joints.Heck, even *I* solder better than much of that (and I'm the noob Thor-Arne is singing about).

author: Gonzini
author_rank: Contributor
timestamp: March 20, 2013, 12:26:26 am
content: Hi GuysI did wonder if it was going to be trouble, i only need it to check transmitter pack frequencies but its all over the place and can be a few 100KHz out. It doesn't seem to be out by a constant amount either.More broken stuff that i haven't got time to sort out. I think l'll pop the lid off and have a look though...Can these be calibrated some how?Found a manual for the Atten F2700C which looks like the same unit, is this a rip off of the same design or is it a re-badged Atten? Are they as crap as well?!CheersJust opened it up, its a turd all right. Metal case covers and no earth connection...No pins hanging out of sockets on this one, see what you mean about the soldering...The 13MHz reference seems to be bang on when measuring itself, with no drifting or jumping about.Hummmm....and.... as it reads on the back... To avoid electric shock protective ground connector must be connected to.... NOTHING

author: Thor-Arne
author_rank: Unknown
timestamp: March 20, 2013, 10:00:50 am
content: The only thing that can be calibrated in this unit is the reference frequency oscillator (under the metal shielding), the rest is just logic feeding the micro controller.It's probably not the oscillator causing the "jumping around", and if you start messing with that you need some way of re-calibrate the unit.I'm quite sure it's either one or more bad soldering joints or one or more defective logic chips.I'd start with fixing the solder joints, and hope that fixes it.

author: bingo600
author_rank: Super Contributor
timestamp: March 20, 2013, 03:14:37 pm
content: I have one of these (another name though) mine has an Atmel 8515 MCU in it ..I think it was , and the Xtal oven 13Mhz sucks big time (and it wouldn't adjust enough down , using the ferrite).I succeded in making a decent counter (actually quite decent) of it , by using this super nice 26Mhz OCXO and a 74AC74 as a /2 divider to get 13 mhz. 'bay # 130718871982.Adjust the ocxo controlvoltage with a 10K multiturn Pot.So ditch the canned xtal , and use this ocxo , and get a counter that is rather stable (measured with a 10Mhz Rubidium)Ohh ...I made a separate 5v for the ocxo + divider , by grabbing the 8v from the existing diodebridge , and using a mic2940-5v with 470uF before the MIC , and 10uF + 100nF after./Bingo

author: Thor-Arne
author_rank: Unknown
timestamp: March 20, 2013, 03:55:46 pm
content: Good idea to upgrade the oscillator.

author: karlmag
author_rank: Contributor
timestamp: March 20, 2013, 04:27:16 pm
content: Quote from: bingo600 on March 20, 2013, 03:14:37 pmHi,You wouldn't mind posting the schematic for that, would you?Thanks--KarlMag

author: bingo600
author_rank: Super Contributor
timestamp: March 20, 2013, 05:45:10 pm
content: Quote from: karlmag on March 20, 2013, 04:27:16 pmEhh schematicI never made one ...I just flicked it together , and used the ocxo DS as "inspiration"http://pletronics.com/files/index.php/ohm4%205.0v.pdfI did put 220R to GND on the 26Mhz out , so give it some load./Bingo

author: karlmag
author_rank: Contributor
timestamp: March 20, 2013, 06:29:42 pm
content: Quote from: bingo600 on March 20, 2013, 05:45:10 pmOki,I guess I need the exercise of trying to puzzle it together by myself (being rather nooby).Thanks for the tip. :-)Have a nice day!--KarlMag

author: bingo600
author_rank: Super Contributor
timestamp: March 20, 2013, 07:34:14 pm
content: Flip-Flop divide by 2http://www.electronics-tutorials.ws/sequential/seq_4.htmlOhh and do use an AC74 , you toggle 26Mhz.The output from the FF (Clock + GND) should be connected to the freq "plug/pins" on the counter , using either a short coax or at least twisted pair.I used some twisted pair wire (a pair) from a stripped CAT5 network cable./Bingo

author: Gonzini
author_rank: Contributor
timestamp: March 20, 2013, 08:11:37 pm
content: Interesting with my unit if i feed the 13MHz reference into input 1 i get the 13 plus all the zeros and its completely stable.If i feed 13MHz from a Marconi 2022C the lower 2 digits drift all over the place.Even worse at higher frequencies, it can be a few 100 KHz out when using input 2.I might try feeding it another 13MHz source and see what it does.Also l'll blitz the board for dodgy joints.Looks like there's some adjustment under the input cans as well, i see 2 holes which look like adjustment access.Not much time at the moment to play with these things, i hoped to just get on and use the bloody thing.I'd use it for a door stop but its not heavy enough...Cheers for the encouragement for trying to get this going, it feels good to not be alone

author: Thor-Arne
author_rank: Unknown
timestamp: March 20, 2013, 08:30:40 pm
content: Perhaps there something going on with the input amplifier, if it triggers correctly from the 13MHz output on the back it should trigger from the Marconi to.How do you hook these up together?

author: wb0gaz
author_rank: Frequent Contributor
timestamp: April 13, 2014, 09:48:07 pm
content: I too encountered one of these instruments (?), and built the 26/2 MHz OCXO-based reference as Bingo600 first suggested. Bingo600's circuit definitely did the trick. I already had the OCXO module (bought on ebay a few years ago) and don't see them currently available, but if someone has the part in their junkbox and ends up with one of these counters, below is the hook-up I used (again, same as Bingo600 design). FYI 13 MHz is a common reference frequency for GSM cellular base station gear (which requires high accuracy timebase) so I suspect other 13 MHz (or multiple) oscillator would accomplish the same thing (and use of 13 MHz reference is why I selected this counter in the first place, expecting to use the OCXO on hand.)Schematic-in-words (check carefully against datasheets before building):First, I kept the existing reference module hooked up (but removed from the back panel) until the very last step, as the reference signal is evidently needed for the CPU to run at all (else display is unlit.) Once the new reference signal was built (as below) and verified, I switched the input from the old module to the replacement.OCXO and 74AC74 are powered from added 7805 regulator (hole in counter's existing heatsink used.) 0.1 uF bypass on output of 7805. OCXO and 74AC74N put on small perf board, powered by +5 on the second (new) regulator. Heatsink under the new load (250 mA peak, less when running) remains acceptable temperature.OCXO output (pin 8) connected to 220 ohms to ground as load, then to the 74AC74 as below. OCXO pin 7 = ground, pin 14 = +5 from new regulator (with 0.1 uF bypass to ground), pin 1 (control voltage with 0.1 uF bypass to ground) to wiper of 10K pot (adjust 0..5V, use new regulator's 5V as reference, didn't bother with a separate reference regulator). Due to the height/weight of the OCXO part, its thin leads, and my use of IC socket, I arranged a tie-wrap to hold the part in place. During operation, OCXO quickly becomes warm to touch, not hot.74AC74 (see datasheet for pinouts) tied pins 1,4,10,13 thru 10K to +5 (again using new regulator 5V source) - these 4 pins must be held high for the part to operate as intended. Pin 7 is ground. Pin 14 is VCC (with 0.1 uF bypass, to the new 5V regulator). Tie pin 3 and 11 (CLK in) to pin 8 of the OCXO (CLK out). Tie pin 2 to 6 (D to Q-), tie pin 8 to 12 (D to Q-), these two connections tell the 74AC74 to divide-by-two; as there are two separate D flip-flops in the part, I used one to drive the counter internally, other to drive the external reference output jack. 13 MHz now available on pins 5 and 9 (independent, identical signals.) I used pin 5 to feed the original ref input to the main board, and pin 9 to feed the BNC jack (re-installed after removing/discarding the original LO), both via RG174 mini coax.Lacking a primary reference I cannot quickly adjust the control voltage of the OCXO but the pin 1 input via pot gives the expected range.OCXO data sheet says 30 seconds warm-up time (much better than the non-oven 20 minute warm-up time the counter originally required.)By the way, I don't know what (kind of solder) they used for solder for the heavy wire connections and tinned sub-assemblies; it was difficult to remove and replace with tin/lead solder. I don't know if the same solder was used for PC board assembly (I can't imagine that would have been successful at all).I tried up to 2000 MHz using an old Weinschel sweep generator on CW; that's the highest frequency I can generate and the counter handled as expected. I didn't find any signs of instability during count tests after this change.

author: Vgkid
author_rank: Super Contributor
timestamp: April 13, 2014, 10:51:50 pm
content: That is a rather fast heating ocxo, I almost bought one several years ago.

author: wb0gaz
author_rank: Frequent Contributor
timestamp: June 01, 2014, 11:12:24 pm
content: Updating my original post on my adventure with Zhauxin HC-F2700L.After retrofitting the counter with a Pletronics 26 MHz OCXO (and divide-by-two), I went in search of a way to calibrate the counter. I ended up buying a Motorola ONCORE UT PLUS GPS module (circa 2000) and GPS antenna on ebay (total outlay under $20). The UT PLUS has a 1 pulse-per-second signal which is very accurate long-term but has a ~20 nS jitter spec from one pulse to the next. I made a small counter circuit that gated the 13 MHz reference output on the back of the counter into the BNC input on the front of the counter, and set the counter to totalize mode, so the 13 MHz signal would be present for 10 seconds, then absent for 10 seconds. I expected to see "30 000 000" on the display if everything worked (130,000,000 counts). Some struggles ensued as there were many missing counts, somewhat random.The problem turns out to be this - when the HC-F2700L overflows the 8-digital display in totalize mode, input pulses are ignored for a small, somewhat random period of time, presumably while the firmware deals with the overflow condition. I eventually worked around this by changing my pulse gate to pass a series of 1-second periods of 13 MHz alternating with 1-second periods of idle.Save for the totalize overflow problem (I guess I can't say its a bug, because the counter's totalize mode wasn't specified for this use), my very cheap chinese counter now has a real oven controlled reference oscillator that can be put on frequency to good accuracy with GPS signal, and total outlay is under $100.Although it would be possible to make a "GPS Disciplined Oscillator" at 13 MHz (so the GPS would be in use continuously rather than just for occasional calibration), this accomplished what I set out to do in the first place (which was enabled by the peculiar 13 MHz refernence oscillator used in the HC-2700L.)

author: bingo600
author_rank: Super Contributor
timestamp: June 02, 2014, 03:56:29 am
content: Hi DaveSaw your post on t-nutsStrange that the counter can't handle a "wrap".How do you set it to count 7x 1Sec , manually (1pps pulse led counting?)/Bingo

author: wb0gaz
author_rank: Frequent Contributor
timestamp: June 18, 2014, 09:08:47 pm
content: Hello Bingo, thanks for the question!Yes, time-nuts has been totally invaluable resource; I am just scratching the surface of my learning there (which I joined initially to learn about GPSDO which would be used to calibrate this ^*#&$*&!! frequency counter.)I actually came back here to post an obsevation about the counter, now that I have put it in service.It appears the counter cannot resolve the least significant digit as expected (tested when counting up to 100 MHz signal) any closer than +/-6 counts. For example, if I seek to measure 99.000000 MHz (from a synthesizer), as I adjust the synthesizer up slowly (Hz by Hz), the counter first shows 99 000 000, then 99 000 006, then 99 000 013, then 999 000 020, etc. This is very undesirable behavior, because it says my "8 digit" counter is really 7 digits useful.As for the wrap problem (which is only seen in "totalizer" mode I use with the circuit described, for setting the reference oscillator), the reference to a 7 second gate is with purely external circuitry I built for the purpose of calibrating the thing. I use an old Motorola ONCORE UT+ GPS module which has 1 PPS output to drive a divide-by-7 circuit (74HC163 configured appropriately), then that output into a 74HC74 (half of) to get 7 seconds high, 7 seconds low. I then routed the 13 MHz reference oscillator (the 26 MHz OCXO module I installed, with 74HC74 dividing by 2 at the output to get 13 MHz) from the output of the counter back panel reference oscillator output jack, through an AND gate (74HC08) gated by the 7-second-hgh GPS-derived signal, into the counter's B channel (lower frequency) input. When the gate opens, the counter counts from 0 up to (ideally) 91 000 000 counts (13 MHz * 7 seconds), then stops counting for 7 seconds, then the cycle repeats. One of the counter's front panel buttons lets me reset the totalizer back to 0 (which I do during the 7 seconds between count-up periods). I adjusted the bias voltage on the 26 MHz OCXO module (divided by 2 inside the counter before going in where the original piece-of-junk reference oscillator existed) until I get 91 000 000 counts. This adjustment does appear to have 1 count resolution (unlike the frequency counting mode) so if the counter part worked as I expected, I'd have reasonable accuracy; as it stands the accuracy is ~6x worse than I expected.Where the "wrap" problem happens is this - I originally had set the gate period (of my external circuit that connects counter's refernce output to counter's totalizer input) to be longer - 10 seconds - in which case I expected to see 130 000 000 (10 seconds at 13 MHz), with the first digit absent (so I'd really see 30 000 000 if properly adjusted). I was very puzzled at first seeing a random variation of a few thousand after each cycle, which I initially attributed to using the wrong (trailing) edge of the GPS module's 1 PPS output (which I was). Once I fixed that, and continued to see the random variations, I eventually discovered that as the counter crosses from 99 999 999 to 00 000 000 (and does "overflow") in totalize mode, the microcontroller is evidently busy doing other things - perhaps lighting the overflow indicator - and misses several thousand counts. Given the large number of simple ICs (counters and otherwise) inside - although no schematic - I had expected (wrongly) that the microprocessor was just doing configuration and display management; as it turns out it is involved in the counting itself in some way. I have no plans to try to re-engineer it.Of course, this is a very low cost benchtop counter (I think I paid about $45 US for it, plus about $5 I have in the OCXO module bought a few years prior), and I can calibrate it (such as I have tried) with $13 invested in a GPS module and a few glue parts, so it's adequate, but not the home run I had hoped for in the first place. Given the newly discovered problem with least significant digit, I'd now dissuade anyone else thinking about buying this counter (which is still available on ebay).I certainly didn't take the most cost-effective route to a counter with use of GPS to adjust ref oscillator, but I've learned about GPS modules which I had no prior experience with, and in the end that makes the experience worthwhile.

author: Bored@Work
author_rank: Super Contributor
timestamp: June 18, 2014, 09:33:14 pm
content: Quote from: wb0gaz on June 18, 2014, 09:08:47 pmI am to tired at the moment to do the math, so take the following as pure speculation. I think this could be because of the 13 MHz oscillator. The display displays in fractions of 10th, the measurement is gated in multiples of 1/13 MHz. I.e. you see rounding.

author: wb0gaz
author_rank: Frequent Contributor
timestamp: June 18, 2014, 10:34:04 pm
content: I was thinking the same thing - I had hoped (obviously incorrect!) that they'd just divide ref osc by 13 first, then by powers-of-10 as needed to drive the counting function, but it appears more along the lines you were suggesting.Oh well, I guess it will be a pretty accurate 7-digit counter, for whatever that's worth!

author: saturation
author_rank: Super Contributor
timestamp: June 21, 2014, 12:13:24 pm
content: A commendable amount of work, but if you need a true accurate counter, it may be futile to upgrade/repair and build on the questionable quality of this device. Even if the counter did work correctly, holding its cal remains unknown, until after more testing. For the time and labor involved, it may be more fruitful to put effort into a pedigreed counter like the HP 5335a or Racal Dana 199x series and repair them. The probability suggests your labors will be better rewarded.

author: wb0gaz
author_rank: Frequent Contributor
timestamp: June 21, 2014, 12:42:51 pm
content: Saturation - totally agreed - this project did degenerat into a science project!

author: saturation
author_rank: Super Contributor
timestamp: June 21, 2014, 04:29:37 pm
content: I found this years ago, they are made for spot checking radios and have limited functions, resolution to 0.1Hz :http://www.amazon.com/Frequency-Counter-RSR-2-5-GHz/dp/B0007Z49ZU/ref=sr_1_23?ie=UTF8&qid=1403367666&sr=8-23&keywords=frequency+counter+GhzIts OEM I think is from Taiwan. OEM sells for $160-200 for 1.5-3 GHz models, and if its a brand name of the same model its $300-400.This isn't available in the USA but likely in the EU:http://uk.farnell.com/aim-tti-instruments/pfm3000/frequency-counter-3hz-3ghz-8-5dig/dp/1601132Again, just note the resolution and accuracy they are not OXCO.

author: orin
author_rank: Frequent Contributor
timestamp: February 05, 2015, 10:49:43 pm
content: I too have one of these counters (badged MADELL) and it had been going goofy after a few minutes of warmup.The problem appears to be due to the buffer board mounted on the reference output BNC socket. If I disconnect this board, all is normal. Leave it connected and the frequency displayed starts jumping around, eventually becoming garbage. When just jumping around a little, I found that just touching the ground at the 13MHz BNC output would stabilize it! So there is obviously something going on with the buffer board. There's just a 74HC04 on the board so it shouldn't be difficult to find out what's going on.So, if you have one of these and it starts acting goofy, try unplugging the reference output... fortunately it's on a .1" header on my unit and easy to disconnect.

author: wb0gaz
author_rank: Frequent Contributor
timestamp: February 05, 2015, 11:13:29 pm
content: Thanks very much for the alternate suggestion. I am seeking a replacement as after all of the effort to fit OCXO, the math used in the microprocess of the counter is very poorly done so in fact rather than 8-digit resolution, the least significant digit moves only in steps of 6. For example, yesterday measuring 144 MHz signal, expected resolution would be 10 Hz, actual resolution was 60 Hz, which is very poor.

author: orin
author_rank: Frequent Contributor
timestamp: February 07, 2015, 08:45:07 pm
content: I investigated the buffer board further. The 13MHz from the main board goes through two 74HC04 inverters in series, then through the remaining four in parallel. Three of the outputs are connected in parallel to a 51 ohm resistor. The other end of the resistor goes to the BNC on the rear. The final inverter output is unconnected. So, at least there are no floating inputs. FWIW, there is an unpopulated SOIC14 on the main board (surprising, the rest of the board is through hole) which almost does the same thing, apart from one input being unconnected.The buffer board is clearly designed for something else. The 13MHz goes all over the place.I put the scope on the buffer and as expected, the ringing is bad, partly due to the scope probe of course. To start with, here is the trace of the 13MHz clock on the main board with the buffer board disconnected, then the clock on the buffer board, then after the first inverter on the buffer board (yuck!) and finally, the output of the buffer board.I do not know what that drop is before the falling edge of the clock on the main board.

author: orin
author_rank: Frequent Contributor
timestamp: February 10, 2015, 05:39:18 am
content: Well, that ringing was so horrible that I got out the HP 1120A 500MHz active probe. Result for the signal on the main board is attached. The buffer board is in purgatory and I couldn't be bothered to go get it.Yes, that drop before the falling edge is real. But I was pretty sure of that anyway as previously I'd seen a similar glitch on the rising edge at the BNC output (there are three inversions in line on the buffer board, so the glitch appears on the rising edge).The rising edge on the main board is good, but after the glitch, it looks like an RC decay. Do I really want to follow this through further or should I just but the top back on and forget about it?Edit: I used a 100X tip on the probe so as not to overload it.

author: amyk
author_rank: Super Contributor
timestamp: February 10, 2015, 12:45:40 pm
content: I would suspect the last active component that signal came from; it looks like a defective pulldown transistor is causing the signal to go down at first when it turns on, then somehow it turns off (while the pullup is still half-on) making it shoot back up, and then decay slowly as the pull-up transistor turns off and the remaining charge leaks out.

author: orin
author_rank: Frequent Contributor
timestamp: February 11, 2015, 08:41:06 am
content: Quote from: amyk on February 10, 2015, 12:45:40 pmYes, sure looks like the failure of a pull down transistor.What we know is the TCXO is known to fail so this might be one of its failure modes. There is a mixture of LS TTL and HC CMOS chips on the main board. I'd guess the TCXO output is CMOS and it wouldn't surprise me if they are driving too many LS TTL loads resulting in the death of the TCXO output.

author: kt6ln
author_rank: Newbie
timestamp: April 05, 2020, 01:22:12 am
content: I was looking for some information on HC-F2700L, I came across this page. Although I have been reading through the eevblog forums for several years, this will be the first time I write.I recently got one of these freq counters. When I plugged in, I noticed exactly the same symptoms as mentioned in this thread. I know this thread is a bit dated but F2700L seems to be the same. I was going to open the case by taking out four screws on the back frame, I noticed that AC input is for 220V +/-10%. I am in US, here the power is 120V. Luckily, I have a 120V/240V transformer. When I plugged it to that, viola everything worked perfectly.Not knowing if the units that folks in this thread had also required 220V, I wanted to put my comments that it looks this is a good unit. I went ahead and opened the case to look what I could do. Out of pure luck, I found a similar sized 120V transformer in my scrap box. It has about the same output voltage also. Replacing the transformer was not difficult at all. Now, the counter is operating with 120Vac in. It's very stable but like all crystal oscillators, it will drift I am sure. So, I would think installing a better 13MHz reference is a necessity.Just to let everyone know.