Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Nov Tue 24, 2020 2:34 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 21 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Strange problem with ALL these Chinese frequency counters.
PostPosted: Oct Sun 25, 2020 8:57 pm 
Member
User avatar

Joined: Nov Wed 08, 2017 11:52 pm
Posts: 326
Location: Phoenix AZ
So far I have built all (#1, 2, 3) of these cheap Chinese frequency counters kits including a 4th version on a prototype board. #1 and #2 are almost identical and they don't have any RF amplifiers so I built two different versions of amplifiers for them. #3 is also very similar to #1 and #2 except it has a built in RF amplifier. Now all 4 counters can measure "reliably" ~250mv P.P of signal all the way to ~70MHz. #4 (not a kit) is still on order and I believe it is also based on the same original PIC controller design just with a built in prescaler that can measure frequencies up to a couple of GHz.

All my 4 counters have his very strange behavior when measuring frequencies in the range of 2-4MHz (which I found by accident). Any other frequency in the range of 100KHz to 70MHz, all these counters measure perfectly. Below exactly 4MHz the displayed frequency is totally irrational to the actual input signal frequency. The displayed "frequency" in the 2-4MHz range is inconsistent, widely changes with input signal amplitude, totally not linear and is different from counter to counter and from different PIC controllers on the same counter board. The input signal to the PIC controller (pin 3) on all these counters looks perfect on a 100MHZ digital scope, proper amplitude, fast rise and fall times and displaying the correct frequency. All the rest pins on the PIC controller look fine as well.

Any ideas what the hell is going on and can some other people with any of these frequency counter including the #4 version which I don't have yet and verify this problem.


Attachments:
4 counters.jpg
4 counters.jpg [ 106.67 KiB | Viewed 737 times ]


Last edited by upsss on Oct Mon 26, 2020 4:07 am, edited 3 times in total.
Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Sun 25, 2020 9:35 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6082
Location: Minneapolis, MN USA
What are you generating the 2-4 MHz signal with ? And is it the same device used for the frequencies below and above ?


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Sun 25, 2020 10:15 pm 
Member

Joined: Jan Sat 25, 2020 5:23 am
Posts: 220
Location: Colorado Springs, CO 80917
The OP said:
"The input signal to the PIC controller (pin 3) on all these counters looks perfect on a 100MHZ digital scope, proper amplitude, fast rise and fall times and displaying the correct frequency."

If a good signal is going into the counters, what Kind of device generates the signal ought to be irrelevant. Otherwise, it kinda puts an unacceptable restriction on where or when you can use the things.


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Sun 25, 2020 10:52 pm 
Member

Joined: Nov Thu 22, 2007 11:31 pm
Posts: 959
Location: Johnston, Iowa
I'm working on a project with counter #4 and using a 3MHz signal the readings match my B&K1803B counter and are stable throughout most of the amplitude range of my B&K 2050 signal generator. Number 4 is stable at lower amplitude than my B&K 1803B. Not bad for a $12 counter.
Keith


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Sun 25, 2020 11:16 pm 
Member
User avatar

Joined: Nov Wed 08, 2017 11:52 pm
Posts: 326
Location: Phoenix AZ
Keith, can you tune your signal generator slowly from 3.5MHz to 4MHz with different signal levels and watch carefully the counter display?

BTW, I am not talking about a couple KHz discrepancy but anywhere from 250KHz to 1MHz in this 2-4MHz spectrum. This problem is most noticeable in the 3.5 to 4MHz range with none linear variation of up to 500KHz. In the spectrum of 2 to 3.5MHZ the discrepancies are not as consistence between the different counters, PIC controllers and signal amplitude and they can vary as much as 1MHz.

Just to make it clear, I am fully aware of these counters capabilities to program (add or subtract) a fixed offset frequency. That is NOT what I am talking about and such an offset would be linear and would apply to ANY input frequency.


Last edited by upsss on Oct Mon 26, 2020 3:20 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 2:42 am 
Member

Joined: Nov Thu 22, 2007 11:31 pm
Posts: 959
Location: Johnston, Iowa
I'll do the test tomorrow and get back.
Keith


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 4:03 am 
Member

Joined: Jun Sun 15, 2014 5:37 pm
Posts: 690
Location: Montreal, Quebec
You can get odd counting if the input signal isn't strong enough. That includes if the amplifier bandwidth isn't flat, so it tapers off below or above a certain frequency. If the frequency goes too high the logic may not be able to keep up. Odd waveforms, especially with mediocre strength input signals, may cause miscounts.

But I can't see how any of this would cause problems for a segment of the spectrum.

Maybe the input amplifier is oscillating in an odd way?


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 4:12 am 
Member

Joined: Jan Tue 10, 2012 8:39 am
Posts: 1797
I have a similar unit and it changes ranges automatically as the input frequency changes. I forget the changeover frequency.

There are some unanswered questions regarding the operation of this unit. It has a socket for a programmer or something.

But for my purposes it's fine, to measure stuff too fast for my HP counter, which goes up to a few hundred megahertz; it goes to 2.4 GHz.


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 11:19 am 
Member
User avatar

Joined: Oct Sun 15, 2006 12:57 pm
Posts: 7288
Location: Liberty, Missouri
I have a few of the counters that look like your #4, and have seen no odd behavior in the 3-4MC area, I have one in my modulation meter so I can monitor the frequency of several of my old VFO transmitters.

Image

_________________
Pics, Bold & underlined text, are usually links.

https://mikeharrison.smugmug.com/

Mike


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 11:36 am 
Moderator
User avatar

Joined: Feb Sun 01, 2009 2:56 pm
Posts: 11568
Location: Victoria, Australia
While there is no indication of using modulated signal, it is pertinent to note that most counters do not like it and miss count. There is also a question of shielding, & decoupling, and dirty DC form a switch mode wall wart, albeit there needs to be more feedback from those with them. Perhaps leaving out the pigment in the case was not a good idea & it should not have been Perspex?

The only thing I could suggest for external influences other than power, would be to see what happens if you wrap earthed metal foil around the bulk of it. Naturally in such a fashion it wont short. Do not connect the foil to the PSU.

Marc


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 2:41 pm 
Member

Joined: Nov Wed 30, 2016 7:35 pm
Posts: 8459
Location: Sunbury, Ohio 43074
In the realm of the KISS thinking model .... is it possible your test cables are causing a notch, or peak, at certain frequencies? Long shot, but certainly possible. Also possible is someone gave you a phantom signal generator, buried it under your shop floor, and it's set to annoy you at the least expected times ........

I suppose if you can verify the signal purity at the input to the counter, that would eliminate any external forces.

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 3:21 pm 
Moderator
User avatar

Joined: Feb Sun 01, 2009 2:56 pm
Posts: 11568
Location: Victoria, Australia
The dirty DC hypothesis is the easy one to sort: Just use a battery. Ferrite beads are a way of reducing RF & the failure to decouple supply by having a Non-polarised cap across supply to decouple RF can bring one unstuck.

Obviously there is some thing with this one, that perhaps the others had, that this one doesn't, aside from a different circuit. What was used to generate signal? Sometimes the generator will have band problems, as they use the same parts as radios. Also check soldering (magnifier) some of those boards are dipped and resist marks on the board (contaminant) can cause a point not to solder. properly, if at all.

Marc


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 4:24 pm 
Member

Joined: Nov Thu 22, 2007 11:31 pm
Posts: 959
Location: Johnston, Iowa
I believe the #4 counter is a PLJ-8led and you should watch this video if you haven't seen ithttps://www.youtube.com/watch?v=WWy0821JLUQ . Apparently not all of these are identical with some being low quality clones. I just realized that I'm using the similar PLJ-6led but I reran the test and it's working perfectly.
Keith


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 9:26 pm 
Member
User avatar

Joined: Nov Wed 08, 2017 11:52 pm
Posts: 326
Location: Phoenix AZ
As I said, I don't have yet the #4 frequency counter so my problem doesn't apply to this counter at this time. I hope that someone with counters #1, 2 or 3 can verify or disprove this problem.

Just to repeat, the problem exist only in the spectrum of ~2 to 4MHz on ALL my 4 counters tested with the same Eico 324 generator. 150KHz to 2MHz and 4MHz to 75MHz with all 4 counters work without any problems! Again, all 4 counters have obviously different layouts and different RF input amplifiers and all PIC input signal look proper as you can see below.

Top 2 pictures, input signal is 4MHz when the counter works properly.
Trace 1 is the input to the PIC controller (pin 3).
Trace 2 is the input to the RF amplifier (S.G output).

The next 2 pictures, input signal is 3.9MHz, the wave forms looks perfect and the counter display is all over the place anywhere between 3-3.5MHz depends on the input signal amplitude. As you can see, the input signal to the PIC still swing perfectly between 0-5V and the only difference is slight change in the rise and fall times and for some reason that causes the PIC controller NOT to trigger properly. Outside this strange 2-4MHz spectrum, all input signals looks similar on all of my 4 counters and the counters displays all frequencies without any problems.

The last picture shows my RF amplifier on the back of the counter which consist of a VHF JFET as a source follower and a VHF NPN transistor feeding pin 3 of the PIC. This is pretty much what you need to be able to measure frequencies up to 75MHz with these counters.


Attachments:
4MHz.jpg
4MHz.jpg [ 126.49 KiB | Viewed 461 times ]
4MHz in.jpg
4MHz in.jpg [ 128.15 KiB | Viewed 461 times ]
3.9MHz.jpg
3.9MHz.jpg [ 256.52 KiB | Viewed 461 times ]
3.9MHz in.jpg
3.9MHz in.jpg [ 230.61 KiB | Viewed 461 times ]
Back.jpg
Back.jpg [ 269.1 KiB | Viewed 461 times ]


Last edited by upsss on Oct Tue 27, 2020 6:13 pm, edited 1 time in total.
Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 10:44 pm 
Member
User avatar

Joined: May Sun 10, 2020 2:55 pm
Posts: 528
Location: Bridgman, MI
upsss wrote:
As I said, I don't have yet the #4 frequency counter so my problem doesn't apply to this counter at this time. I hope that someone with counters #1, 2 or 3 can verify or disprove this problem.

Just to repeat, the problem exist only in the spectrum of ~2 to 4MHz on ALL my 4 counters tested with the same Eico 324 generator. 150KHz to 2MHz and 4MHz to 75MHz with all 4 counters work without any problems! Again, all 4 counters have obviously different layouts and different RF input amplifiers and all PIC input signal look proper as you can see below.

Top 2 pictures, input signal is 4MHz when the counter works properly.
Trace 1 is the input to the PIC controller (pin 3).
Trace 2 is the input to the RF amplifier (S.G output).

The next 2 pictures, input signal is 3.9MHz, the wave forms looks perfect and the counter display is all over the place anywhere between 3-3.5MHz depends on the input signal amplitude. As you can see, the input signal to the PIC still swing perfectly between 0-5V and the only difference is slight change in the rise and fall times and for some reason that causes the PIC controller NOT to triggering properly. Outside this strange 2-4MHz spectrum, all input signals looks similar on all of my 4 counters and the counters displays all frequencies without any problems.

The last picture shows my RF amplifier on the back of the counter which consist of a VHF JFET as a source follower and a VHF NPN transistor feeding pin 3 of the PIC. This is pretty much what you need to be able to measure frequencies up to 75MHz with these counters.


this is diff question... you have your probes compensated?

_________________
only the dead fish go with the flow


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 11:25 pm 
Member
User avatar

Joined: Nov Wed 08, 2017 11:52 pm
Posts: 326
Location: Phoenix AZ
ttx450cap wrote:
this is diff question... you have your probes compensated?

What is the question... and what does "probes compensation" have to do with the problem I clearly outlined?


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Mon 26, 2020 11:36 pm 
Member
User avatar

Joined: May Sun 10, 2020 2:55 pm
Posts: 528
Location: Bridgman, MI
upsss wrote:
ttx450cap wrote:
this is diff question... you have your probes compensated?

What is the question... and what does "probes compensation" have to do with the problem I clearly outlined?

just wondering if they are comp? not sure how you are getting those waves?


this site dose not like a charter ? added in file name.. p,s. thats my own rambling trying to upload a pict...


Attachments:
uncomp.jpg
uncomp.jpg [ 171.37 KiB | Viewed 419 times ]

_________________
only the dead fish go with the flow
Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Tue 27, 2020 12:24 am 
Member

Joined: Jun Sat 09, 2007 8:14 am
Posts: 4308
Location: Florida
That change in rise time may be a clue. If the controller input circuitry lacks enough hysteresis it may trigger multiple times before settling. Slower transition times are more likely to cause this kind of problem.

Changes in power drain when things change state may also cause problems. It wouldn't hurt to try some bypass caps right at the chip's power pins.

RRM


Last edited by Retired Radio Man on Oct Tue 27, 2020 12:34 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Tue 27, 2020 12:31 am 
Member

Joined: Nov Sun 07, 2010 7:16 pm
Posts: 788
Location: Manchester, MI
This could be an artifact of the programming in the PIC. There's a lot going on in there between signal acquisition and display multiplexing and, let's face it, lots of coders don't know what they're doing so it's easy to miss a boundary condition. It's hard to say what changes were made on those versions.

Personally, I don't use PICs. Although they have lots of capability, I never liked bumping into their limitations.

For the price of those, you really can't complain.

If you want to go to the original source, check out this link:
https://www.qsl.net/dl4yhf/freq_counter ... unter.html

You will notice that he says to not complain to him when the cheap kits off of ebay screw up. :mrgreen:


Top
 Profile  
 
 Post subject: Re: Strange problem with ALL these Chinese frequency counter
PostPosted: Oct Tue 27, 2020 11:57 pm 
Member
User avatar

Joined: May Sun 10, 2020 2:55 pm
Posts: 528
Location: Bridgman, MI
had a thread like this..
viewtopic.php?f=8&t=378404

_________________
only the dead fish go with the flow


Top
 Profile  
 
Post New Topic Post Reply  [ 21 posts ]  Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: John Limbach and 13 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB