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Bitx40 and PLJ-6LED Frequency Counter


simplesource4@...
 

Hi,


I just got my license a month ago and have been sitting on my bitx40 until I got it. I also ordered a PLJ6-LED frequency counter off of ebay to mess around with, as seen here. Is there any way to keep the analog VFO on the bitx40 and use a frequency counter to display the VFO frequency? From what I understand I would have to find a way to measure the frequency of the crystals on the board then add or subtract the offset and put that into the frequency counter. Is that correct? Has anyone here done this with their bitx40 yet? I apologize in advance for such a noob question, I'm slowly but surely modifying my bitx40 and it has been a great introduction to electronics!


George King
 

The PLJ6 does not work when the VFO freq must be subtracted from the IF freq as in the Bitx40.  The PLJ6 works fine when the VFO is added to the IF as in a 20M radio.  I have used a PLJ6 in a 20M MFJ radio and it works very nicely.

It is supposed to work in subtraction mode but there must be a bug in the firmware.  I don't know anyone who has gotten it to work in subtraction mode.

73,  George


On 2/3/2017 8:55 PM, simplesource4@... wrote:

Hi,


I just got my license a month ago and have been sitting on my bitx40 until I got it. I also ordered a PLJ6-LED frequency counter off of ebay to mess around with, as seen here. Is there any way to keep the analog VFO on the bitx40 and use a frequency counter to display the VFO frequency? From what I understand I would have to find a way to measure the frequency of the crystals on the board then add or subtract the offset and put that into the frequency counter. Is that correct? Has anyone here done this with their bitx40 yet? I apologize in advance for such a noob question, I'm slowly but surely modifying my bitx40 and it has been a great introduction to electronics!



Jerry Gaffke
 

Some have gotten the analog VFO to work well enough by changing some parts, search for NPO in this mailing list.  Most people here are moving to the Raduino or similar, as the Si5351 is far more stable.  But playing with stuff like that counter is how you learn.

If it works as advertised, that's a very nice frequency counter for $10.  

Says "dual frequency design, intermediate frequency value and plus / minus mode can be preset"  which suggests to me you can enter an intermediate frequency of 12mhz and it will display the correct transmitting frequency by reading the VFO.  You may have to read the manual.   Otherwise, could measure the VFO frequency and subtract that from the 12mhz IF frequency of the Bitx40 using a hand calculator.  As you suggest, it may not be exactly 12mhz, you could measure the BFO frequency at the emitter of Q11 to get an exact figure.

Also need to to figure out  how to hook it up to the VFO without disturbing the VFO too much or injecting display noise into the radio.  Maybe you just clip the counter's probe into that VFO.  Or may require  a resistor network, a one transistor buffer, coax, shielding, bypass caps, ...      


John Backo
 

Hey, welcome to the fraternity. What's your call sign?

The PLJ frequency counters are nice devices. It should work well.

Do not connect it directly to the oscillator. Never do that with a counter or anything else for that matter. Install a capacitor in the counter input line of about .01 uF and try connecting it to the emitter of Q8, or maybe the collector of Q7. Even somewhere around pin 6 of the mixer transformer if that is easier. The capacitor is to isolate any DC getting into or out of your circuit to prevent pulling. Actually you should use the smallest value which allows the counter to operate but usually .01 or .001 uF is fine. Sometimes pulling occurs with the capacitor as the oscillator output is too light. Usually using a smaller capacitor fixes that. And since the diode ring mixer requires ~7 dBm to operate (and that is what you are driving), the oscillator output should be fine.

Note to AF: Perhaps a small change to the circuit board could be made to provide a place to attach a counter? There is probably space for it already.

Why do you want to see the value of the VFO? Don't you really want to see what the receive frequency is? The counter comes with instructions
about setting the proper IF offset to display the receive frequency which is also the transmit frequency in this case, or at least it should. Your IF will be about 11.998 MHz and the VFO will be about 4 MHz. But neither one of them is fixed. You will have to determine it. It is easy to measure the VFO as it occurs directly.
Don't worry about the exact IF frequency-- set your offset to get the receive frequency. That will turn out to be the IF frequency. You may get a rough idea by taking a quick measurement of the BFO.

The easiest way to verify the receive frequency (and hence your offset) is to find a group of stations engaging in a net.
They usually do it every day on the same frequency. Then compare your readout to the known net frequency. If you don't know
what it is, get a QSO and ask to confirm it. One thing's for sure: if you can talk to them, you're on their frequency. (It is relatively easy on 20m as the Maritime Net is on all over the US at 14.300 MHz every day; 40m may be a bit harder. Usually nets are in the early morning while everyone is getting ready to go to work -- but they are there every day).

Related to that is setting the IF frequency. As Asher says, you get to choose how bad the rig sounds! If you are happy with it, fine.
Leave things alone. But you can vary the BFO (and hence the IF frequency) with C107. That capacitor is not present on the board as received.
If you wish to change the way things sound, you have to install it. I usually try to match my homebrew rigs with my Kenwood rig for sound.
Works every time.

Again, welcome aboard...and remember the only stupid question is the one you don't ask.

john
AD5YE


 

John, I guess it is W5AGK !

73 Raj

At 04-02-2017, you wrote:
Hey, welcome to the fraternity. What's your call sign?


John Backo
 

Yes, Raj, I think it is though I haven't heard that from him.

Regarding the PLJ-6LD counter, there is an interesting video on YouTube examining and demo-ing the unit. Google it.

I have found a web page with the manual too, in English. You can download it but it is the Chinese version. Only the web page has
the English version (in PDF).

http://pan.baidu.com/share/link?uk=369802936&;shareid=584144

Hope this helps.

john
AD5YE


simplesource4@...
 

Hi everyone,

thank you very much for the help and advice so far. I followed John's advice and hooked the counter up to the emitter of Q8 and tried the collector of Q7. As George mentioned in the first reply it won't work with the bitx40 sadly. I went and measured the BFO and found my offset and when the offset is subtracted the counter displays nothing but 0's. Too bad it doesn't work, it's a neat little counter! If I ever get a 20m radio I'll try it out on that. So far I have decided to try this kit out and see how well it works. And my call sign is KM4ZCT. Lastly, I want to thank you guys again for the help. I was a bit discouraged messing with amateur radio at first but playing with the bitx40 has actually made me excited and wanting to use my license instead of letting it sit like I have!


John Backo
 

Sam:

It's going to be one of the combinations in the formula RF = IF + VFO. If you know the IF (by measuring the BFO frequency), then subtracting VFO from IF will give you a positive number, i,e, RF. You can measure both IF and VFO, therefore you should be able to display RF. Once you get that close, you can make a minor adjustment to get it exact (by QSO or listening to a net on a known frequency. Note that the frequency adjustment may appear to go in reverse since ~12-5.0 = 4.0 and ~12 -4.7 = 4.30. In other words, tuning your VFO down tunes the RF receive frequency up. It's the nature of the beast without special programming (which is one of the reasons why most of the earlier 40m rigs used ~4 MHz as the IF).

You and George are right about a negative number. Without special programming, the display will just show all zeros. Supposedly this device has that programming, but apparently no one has been able to find it. It may be that the original ones did (and do), but the copies do not. With Chinese merchandise, one can never be sure beforehand...

I notice in the YouTube video, that he showed how to get the negative offset, but he did not demo it, so i can't be sure it was verified. It's possible that the original merely uses reverse tuning with a negative offset. But it is possible to get a positive result from one of the combinations above and one of the entries on the lcd menu. That should suffice. Does your counter show you the BFO frequency? Does your counter show you the VFO range from low to high? If it does, and you can figure on paper which combination will give you a positive result, then you can make it work after tweaking it a bit.

Ordinarily, on higher bands the combination is IF + VFO = RF(display). Here, you will probably have to use IF - VFO = RF(display). This is not atypical of most frequency counters and a higher IF.

Hope this helps

john
AD5YE