BFO as first detector

Hi

I've been reading a few books on electronics lately so I haven't had the time to work on the circuit. The programs I'm using are: LiveWire and PCB Wizard. They are from "New Wave Concepts" I've been using the simulator mostly to debug and test little circuits for learning purposes. I found that most of the stuff thats been published on the net is bogus at best (I don't think the simulator is at fault here)

The simulator is only capable of reading "lvw" files, which is a proprietary format. I have ExpressPCB and ExpressSCH as well (both are freeware) but I didn't like them as much.

The cool thing is that I can snap-in various measuring equipment that I obviously don't have in real life such as an oscilloscope, watt meter, logic analyzer, etc. It also comes with input equipment such as a signal and word generator. This are very useful virtual instruments!

The biggest lacking point regards with crystal oscillators and actual sound output (well, in my case it never outputs sound when I put a speaker in the circuit, but it does output if I use a buzzer)

I don't know if theres a software that allows to design diagrams and export to various known formats, if there is I'd love to have it!.

Attached is the actual diagram, with the changes made (I couldn't find any audio connectors in the simulator so I used a 2 pin terminal block as a stand-in) and the other coil is placed in the circuit, so I don't have to run wires through the screen just to run the simulation.

Higher voltage is depicted in red. I ran the simulation by 8 seconds. The output is very low (peaks at 20mV) is this correct?. It behaves as an AC pulse and there is no current being shown (0A) Perhaps the simulator can't cope with induction but shouldn't the circuit still show a bigger output? - I tried changing the variable inductor and the pot is set to minimum resistance so it should give me an output... right? 


Thanks again for your support, it's quite rare in most forums to find this kind of help!




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Update: without the 220 cap at the output I get a 1.8 volt in the AF Out, however changing the potentiometer doesn't change the volume. I also managed to "explode" (the simulator is capable of depicting failures, etc) the R15 and R12 as I changed the pot to the absolute minimum. Changed them to 1 watt and solved the problem. When I change the pot, the 1.8v is constant and at maximum resistance there is no noise in the output, just a clean 1.8V.

ksightler: Sorry, I don't really know how to fix this, it's the first time I've seen it. If it helps, I'm using Google Chrome and the language of my OS is US English, so is the keyboard. I could stop using them if that helps, as I did in the first post.

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You are fine... it just might help to delete the Apostrophe's... so your cut and pastes are legible... It must be something with HTML??

BTW welcome to the forum...
Keith

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Adnimo;

Great, now we are getting somewhere! You are still 2nd guessing me:- the circle with a dot is a standard diagram for a Motorola jack, Audio OR RF, although the terminal block will work, its just that I am picky, maybe. It seems to me your software may be blind. 

The old saying, about computers, "junk in, junk out," is still true, we just have to avoid putting in junk! 

Since you can measure voltage, measure the RF ac voltage at the collectors of Q1 and Q2, it should be 5 to 8 volts ac, on each; then TEMPORARILY disable the oscillators Q1 and Q2, IF they are working. If they are not, we will have to find out why, but I can tell you why there was no audio at the output..... the frequencies were too far apart. (IF they were working.)

Boyoboy, would I like to have that software, I have to do my simulations on a "bread board" by plugging parts into it.... they can self-destruct, if there is an error.

Check the collector voltage of Q's 3,4, and 5.... it should be 6 volts, each, for class A amplifiers. You can set, each, by changing the bias resistors R7 for Q3, R8 for Q4, R11 for Q5. A lower value decreases the collector voltage because of a higher collector current, a higher value increases collector voltage, because of less collector current. It has to suck that current through the collector load resistors.

Also, volts at the emitter end of R15, are close enough, you can adjust this with R13.... or EASIER, change R15 to 330 ohm. (1.8 volts across 100 ohms says it is 18 milliamps) So 330 ohms should bring it up to about 5.9 vdc, THEN adjust R13, not before, to reduce the voltage. When you have 1volt dc at R15, with 330 ohms for R15, it should be ABOUT 11.6 vdc at Q5's collector.

For 0.45 vac AF output, 1 volt dc would be lots!  Even 1.5 v is OK. To get 1 volt dc, with 330 ohms emitter resistor, you have to increase R13 until it measures 1 or 1.5 vdc, at the emitter.

If the oscillators are working, read the frequency of the Q! oscillator, and adjust the ... I just discovered a small error, not a fatal one but important.... coil A, HAS to be 5 mHY,  NOT 10mHY..... 10 is too big, it will give about 21.2 kHz.... 9 or 10 kHx away! ANY way, change it and check Q1 osc frequency, then set Q2 frequency, to match, plus 850 hz. Tell me what you get for frequency of each oscillator.

 Now disable both oscillators by breaking the + volts to each.... Q1 and Q2....you can TEMPORARILY remove R3 and R4.... it will do the trick. Then play with the bias resistors and collector voltages, in the AF part, until they are right. The bias resistors may have to be around 220k ohms, to give 6 v (+V/2).

When you get the AF working.... um..... biased, try feeding a 1 kHz tone at the junction of C17, and D1 and D2.... but VERY low level, like, start with 0.001 vac at 1 kHz and increase, until you get a response at AF out. do not exceed 0.7 volts of AF at the AF out..... 0.7 vac can deafen you! If you are using 16 ohm earphones at the output, and you should, that is a bit over 30 milliwatts..... loud.

Now, if the AF works, restore the two resistors R4 and R5 and, hopefully you will find 850 Hz AF at the output. Of course, adjust VR1 until you get 0.35 to 0.45 vac, 850 Hz or so, at the AF output. The resistors R2 and R10 may have to be 220  kohms, for the oscillators to work well. This means they will be running at around 43 mw and should run cool.

Oh yes, change the terminal block for a phone jack of whatever type your software recognizes.
Its easier to cope with, than a terminal block. 

This is called trouble shooting.

So, good so far, let me know after "trouble shooting."   (Gotta find my breadboard....)

goldigger

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		Quote:			Posted by adnimo
	goldigger: Im not second guessing you!, Its just that the software doesnt have any audio jacks to play with, only terminal blocks (yuk!) Its also missing many ICs and other components. If only I knew how to add them...  - Also I didnt know that was the standard diagram for them, but it still doesnt have any jacks at all to put on the circuits so Im stuck in that sense. *Yes, I thought it was probably that....  It should not be too difficult to make components, and install them. Take stab at it.... it might be easier than it appears. "Boyoboy, would I like to have that software" There are a bunch of freeware alternatives on electronics simulators, for instance this company offers a bunch of good programs: You are not allowed to view links. Please Register or Login http://www.linear.com/designtools/software/ This should be worth a try: You are not allowed to view links. Please Register or Login http://www.gpleda.org/index.html And of course the PCB Wizard freebie alternative can be found at: You are not allowed to view links. Please Register or Login http://www.expresspcb.com/ Finally, this Java applet: You are not allowed to view links. Please Register or Login http://www.falstad.com/circuit/ -- is a full blown (or close to) simulator, I really enjoy the fact that it comes with tons of circuits to play with (I really mean TONS!) Being Java its a little slow, but usable nonetheless. Im not sure about precision in this case, LiveWire for instance has a precision toggle that enables a finer simulation at the expense of CPU cycles, I reckon the Java simulator uses doubles (64bit floating point values) which would be the theoretical practical size on real-time applications with consumer hardware. * WOW! Hey the cub taught the old fox how to snoop around the chicken house! I never thought of searching for freebies.... good idea, I shall try some of those links. I am not so sure about the Java, this machine is picky about Javascript. In all cases, being able to actually see the flow of current is very helpful for novices like me. *I agree, when I started in electronics, I had my uncle's army training manual, a piece of paper and a pencil.... and grade 6 math! I should drink a coffee or two before I start the trouble-shooting or else... I might not get very far at all! *Coffee! YAAAARRRRGGGGHHHH! All I have is tea! Being a type 2 diabetic, I HAVE to have my coffee, they say it protects the liver, and mine is constantly assaulted by my diabetic medicine (metformin), which has other bad effects, too (if I take it at less than 3 hours apart. 4 hours is just right,) but some times I forget....I get too wound up in the forum, and lo... my blood sugar is LOW normal, just as tho' I DID take the meds.  Will post an update soon. Thanks again for your help, Id be cursing the PCB right now if it werent for this forum. * Yes, well, GoldDigger1950 is watching over our shoulders.... just letting me take the heat.    *I had another thought, if you can measure ac and frequency, take a measure at the collector of Q4, to see if there is any RF or hi frequency AF (ac volts and frequency). Also, I think I know why the parts "blew up," if there was RF at Q4 collector, it is not getting filtered out and over drove the final transistor. Eugene52: Thanks for the pdf, Im still reading it but its certainly useful. Funny how I wasnt even born by the time it was published (6 years shy from my birth!) and yet it contains valuable, timeless information. It goes to show... New doesnt necessarily mean better. *The PDF which Eugene posted is interesting and has loads of information..... I am going to look at it again. GoldDigger1950: Well its certainly a bug, links should only be escaped by the boundaries set by the RFC standard on HTML, etc. SMF is based on PHP, I just find it strange that they would still have such a bug... Perhaps a plugin is messing things up?. In all cases even a software developer can only guess so much :p - For now, no apostrophes for me. I dont really mind though, I could even send in Morse code just to get help from you guys. Not that Im particularly good at that... I dont even have a Ham license for that sake ( Is it still a test requirement? - I guess I should ask at the local office, but I remember it was at least a requirement of ~20 WPM in most countries ) *Audio Morse or dots and dashes.... I am a bit rusty  but could read 18 wpm, once. (VE7EQP, me.) No Morse requirement, anymore, in Canada, I got my certificate in 1986, then they overhauled the system and I got "grandfathered," as they call it... basically it means I am an ADVANCED Ham.

goldigger

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