Thanks for sharing, very informative up to the point. I built the oscillator part last night. I wasn't happy with the waveform, may be I'll add a filter to remove harmonics. @0:45 It reads: tsu:zats
Hi Manuel and thanks for an interesting video. You may get rid of the clipping by biasing the second 2N2222 higher, ie. increasing the value of R8 to 15-20 kOhm. The harmonics probably are not harmful, since they will hardly produce any audible interfence.
7:50 - those transformers are nominally 455kHz but most can be adjusted up or down usually +-10kHz or even 20kHz just fine. If you need to change that more drastically, look on the base of the transformer, you may see a small tubular capacitor soldered into the base on the pins. Just snip it out and add a suitable capacitor for your desired freq. I've used the 455kHz transformers from 100kHz to nearly 1Mhz that way. Your replacement should of course be a stable capacitor - NP0/COG for ceramic, or air or polystyrene. Response will be tighter at the lower end of that range due to the high-C/L ratio. It will be rather wide at the high end of that range. You can of course pull the transformer lower just by adding capacitance (across R12 in the above diagram) and this can also be an air-variable for wide tuning. The low Q of the coil in the transformer somewhat limits using at as a front-end this way but it may be useful on the bench for something like a universal final IF strip. The value of the original intermal capacitor varies depending on how tight they wanted the original response and varies with the exact transformer spec. This is one difference between the various 455kHz IF transformers, the other difference being the coil tappings/impedances to suit for the various 455kHz IF amp stages in a typical rx.
I have had no problems tuning this transformer around the desired range, meaning somewhere from 455kHz to 460kHz. In fact, they can be tuned even further, but as most of the radios I've worked on are in this ballpark, that should not be a problem. My problem is achieving a cleaner signal.
@@electronicsoldandnew Oscillators can be finicky :) 1. You may find it works just fine even with that waveform as it is - I've even used a TTL square wave as a BFO before and it sounded half-OK. though there would have been extra mixing products all were outside the audio spectrum. Some high quality mixers (H-mode for example) use very sharp square-wave drives to increase 3rd-order IPs, though they need to be well balanced. 2. You could try making R6 somewhat variable; try something fixed 680R in series with a 1k preset, so you can twiddle it a bit from 680 to 1k680 ohms. Don't go too low though - hence the 680R. 3. You could try to change the feedback ratio of C4 to C5 - the total capacitance needs to be the same (1800+2200=4000pF) so you could simply try swapping them around to see if the distortion gets a little worse or better, then act accordingly. In theory, increasing C4 and reducing C5 increases the feedback, maintaining a sum total of 4000pF overall, so should (haha, should!) make it more linear. NP0/COG ceramics will be fine to test the theory. - I *think* I've got that right - though I've been awake over 30 hours now - it's either one way or the other, hence my suggestion to just swap the C4/C5 caps around to see if one is a little better than the other! Once you reach a certain point in the ratio of those caps though, it may fail to start reliably at some temperatures/stray capacitances/wind conditions/sea states/etc. In a perfect world you'd have the luxury of two big 2000pF air variables for C4 and C5 and you could just fiddle the ratios back and forth until the waveform looks best. Or even better, an unobtainable split-stator 4000pF air-variable cap. which is basically what those two capacitors are. 4. C6 might need reduced if the buffer amp is flat-topping/bottoming too much - this will reduce the drive to it but shouldn't affect the oscillator much at all (in fact it will load it less, a good thing) 5. Also bear in mind that oscilators are very high impedance devices and easy to upset so I'd prefer to do all my measuring after the buffer stage - the scope probe will always load the osc to some extent and can cause head-scratching (make sure you are on 10x on the probe too for best results). Probing the oscillator output at C6 can upset both the waveform as well as the frequency. Probing the buffer amp output avoids this entirely. All this assumes you have no problems elsewhere of course. Coming from a solderless breadboard I'd expect all your smaller capacitances to be well off but as it's a published circuit with known capacitances it should be OK on the PCB as long as you don't have bad ground loops.
That is a similar circuit to the one I made, many years ago, which I did use on the Grundig 2100 radio. Later I found someone selling the original SSB unit on eBay, this was so much better, because of the auto / manual signal gain level and noise filter. I did add a white LED to illuminate its dial.
I can imagine. I know that the socket at the back breaks it the AGC function so that you can incorporate manual gain control. If I could find a suitable plug for that socket, I’d be tempted to try some more experiments, but unfortunately I have no idea if such a socket is even available today.
@@electronicsoldandnew I had been looking for this plug myself, but with no luck. I did try to make a plug using nails and gluing them in a plastic base, it did fit okay, but then found the original SSB unit, so it wasn't required.
Interesting project, I did think about making one myself as i might get 2 of these radios soon. How about replacing L1 with a fixed inductor once you know the value it should have? And replace R1 with 2 pots for course and fine adjustment. or maybe a multiturn pot... I agree with those who suggest that Q2 is not biased enough, that causes the clipping. It's impedance might also load the oscillator to much. It also might need to be in an shielded box so that it doesn't interfere with the internal IF of the radio.
Perhaps the buffer transistor is being driven either off or into saturation? Can play with the bias. Also perhaps adjust the Colpitts feedback capacitor voltage divider ratio. This may reduce the oscillator amplitude. Thus not over driving the buffer. Also try degeneration in the transistor emitter.
The reason the wave form is ugly might be that the varactor diode rectifies some of the rf. The way to get around that is to use two varactor diodes back to back and to apply the control voltage to the junction between them. The capacity will of course be halved, but that can be worked around. Apply the control voltage through a hefty resistor or else some of the rf will be shunted to ground.
I think the bad sinewave is the result of to much gain. Barkhausen said that the gain has to be >=1 but if it becomes to high you get the bad harmonics. A Rc as a Pot of 1,5KOhm should help to adjust the gain
perhaps the dc bias of the first transistor can be of influence on the symmetry of the waveform.. Otherwise you could try to add a low-pass filter to get rid of some of the harmonics.
Just external vfo near by, can be better. So that you could tune every frequency, even with 5khz step am radios. I.m. signal 3703khz radio tuned to 3705, tune vfo to 3703 too and that's it.
I doubt that the varicap has a linear characteristic. I wouldn't get too excited about that. As for the sawtooth wave shape I agree with the other comment about playing with the feedback loop.
Hello, can you tell me what type you use the frequency meter. I need this type, can you write its name, or the location of the purchase, I live in France
It’s something like this one. I bought it some time ago and can’t remember now where I bought it, but they ship everywhere. www.ebay.com/itm/124545150203
Sounds like DeMaw put a 10k pot at the Output to control the level seen by the Radio's AGC. I don't see that on your schematic. What value POT did you use & does it just shunt the 460kHz to ground? Thanx & 73.
Thank you! I've a TenTec version of an external BFO & I find it swamps some radios. I'll try adding the pot. elektrotanya.com/ten-tec_1050_bfo_schematic_and_op_manual.pdf/download.html
Hi Great video, i will watch your others, i have a Marconi 2955, it does not have a sensitive receiver but it does demodulate AM/FM, I was thinking about doing this on the IF input, it uses 110khz IF on board AB5, Do you think this using a sig gen at around 110khz, Should this work. Thanks Dave 2E0DMB
@@electronicsoldandnew Hi , it's a radio test set I did try and inject with a cheap Sig gen , when I transmitted SSB , with into the test set, in am mode and used the sig gen to give the bfo I could change the pitch of my voice but it was to noisy I don't think the test set liked it, maybe there was a ALC acting against it, Thanks Dave
I was surprised to see you put that short across the inductor of the IF transformer. Makes me wonder what results you would have if you simply omitted the resistor AND didn't put a short in its place. The clipping is on the negative swing only....wonder if you could correct that with bias on the transistor(s). You could also experiment with replacing the 2222's with 2N3904's and see if there is any difference. (Probably wouldn't be, but might be worth a try anyway....you could confirm whether it was transistor related.) Have you checked the Data Sheet on the 2N2222's? I look forward to the next iteration of the circuit board. Speaking of the board...might I make a suggestion? I would suggest that you add components based on "height" when you are soldering them to the board. You know, SMD first, then the next tallest part, etc. Less likely to have a part (eg. IF Transformer can) in the way while you are soldering. I am sure you will get the clipping resolved! Keep up the excellent work!
the short wasn’t across the transformer. It was the resistor in series with the pot that biases (and tunes) the varicap diode. The short just allows the full 9V to be available for the tuning. I placed the components as I did to test out each part as I went along. Normally, this order is a no-no. I’m going to try some other transistors, biasing, etc. Can’t let a little oscillator beat me 😊
@@electronicsoldandnew , OK, I see my mistake now. I thought you were replacing R12 with the short, but you were replacing R3 instead. You will resolve the problem, I am sure of that! The more I think about it, the more I feel it is a bias issue. AH!!! The 2N2222 is a SWITCHING transistor! www.electroschematics.com/wp-content/uploads/2009/04/2n2222-datasheet.pdf The 2N3904 would probably be a better choice: www.electroschematics.com/wp-content/uploads/2012/11/MMBT3904.pdf
What a great project Manuel. I did have look at building one myself in the past but couldn’t get the exact coil I needed. The plan was here www.industrial-electronics.com/radio-elec_9.html. Yours looks more complex. It may not be the best waveform but it does work. Look forward to the next instalment. Regards Graham
I decided on this one because some other attempts produced unsatisfactory results. The key is frequency stability, and this one has that. I’m chipping at it with the help of some very good comments here because I want the wave to be cleaner, which, qui frankly, makes no difference to the operation but satisfies my OCD character 😊 At the end of this saga, I’ll send you a couple of boards if you like. They cost me nothing anyway as they are sponsored.
@@electronicsoldandnew I'm sure you will get it sorted. I've read through all the comments and theres a lot of suggestions. Probably a combination of some of them will do the trick. Thanks very much for the offer of a board to try. Funnily enough I had repaired a Satellit 2100 a year or so ago when I went down the same route as yourself trying to find the Grundig BFO and I did look at the circuit for it but decided against trying to replicate it
Study schematics a simple bfo example the relistic dx120 red can ok using a external cap the black one ok take out internal cap and add a external of choice around 120pf range + or - add a prodector transistor example relistic dx150 no need of gain control your using the radios agc a dpdt switch one half for am ssb the othe half for b+ switching just a example you will get good results with a simple circuit and taping in before the detector diode or pri side of last if and get quality audio like the top end radios
Too much feedback in the oscillator. Your waveform is clipped at the bottom. Need to be right next to the receiver without shielded connections or use a shielded wire connection to tame this little beast. Then try adding a pot as a squelch to the amp base. You need a clean sine wave that stretches and shrinks like a slinky on the oscilloscope when you turn the pot.
Neat little frequency counter!
Took me a week to get the BFO working on my Hallicrafters S20.
Your projects look very professional on those pcb’s.
thanks
Thanks for sharing, very informative up to the point. I built the oscillator part last night. I wasn't happy with the waveform, may be I'll add a filter to remove harmonics. @0:45 It reads: tsu:zats
Hi Manuel and thanks for an interesting video. You may get rid of the clipping by biasing the second 2N2222 higher, ie. increasing the value of R8 to 15-20 kOhm. The harmonics probably are not harmful, since they will hardly produce any audible interfence.
7:50 - those transformers are nominally 455kHz but most can be adjusted up or down usually +-10kHz or even 20kHz just fine. If you need to change that more drastically, look on the base of the transformer, you may see a small tubular capacitor soldered into the base on the pins. Just snip it out and add a suitable capacitor for your desired freq. I've used the 455kHz transformers from 100kHz to nearly 1Mhz that way. Your replacement should of course be a stable capacitor - NP0/COG for ceramic, or air or polystyrene. Response will be tighter at the lower end of that range due to the high-C/L ratio. It will be rather wide at the high end of that range.
You can of course pull the transformer lower just by adding capacitance (across R12 in the above diagram) and this can also be an air-variable for wide tuning. The low Q of the coil in the transformer somewhat limits using at as a front-end this way but it may be useful on the bench for something like a universal final IF strip.
The value of the original intermal capacitor varies depending on how tight they wanted the original response and varies with the exact transformer spec. This is one difference between the various 455kHz IF transformers, the other difference being the coil tappings/impedances to suit for the various 455kHz IF amp stages in a typical rx.
I have had no problems tuning this transformer around the desired range, meaning somewhere from 455kHz to 460kHz. In fact, they can be tuned even further, but as most of the radios I've worked on are in this ballpark, that should not be a problem.
My problem is achieving a cleaner signal.
@@electronicsoldandnew
Oscillators can be finicky :)
1. You may find it works just fine even with that waveform as it is - I've even used a TTL square wave as a BFO before and it sounded half-OK. though there would have been extra mixing products all were outside the audio spectrum.
Some high quality mixers (H-mode for example) use very sharp square-wave drives to increase 3rd-order IPs, though they need to be well balanced.
2. You could try making R6 somewhat variable; try something fixed 680R in series with a 1k preset, so you can twiddle it a bit from 680 to 1k680 ohms. Don't go too low though - hence the 680R.
3. You could try to change the feedback ratio of C4 to C5 - the total capacitance needs to be the same (1800+2200=4000pF) so you could simply try swapping them around to see if the distortion gets a little worse or better, then act accordingly.
In theory, increasing C4 and reducing C5 increases the feedback, maintaining a sum total of 4000pF overall, so should (haha, should!) make it more linear. NP0/COG ceramics will be fine to test the theory.
- I *think* I've got that right - though I've been awake over 30 hours now - it's either one way or the other, hence my suggestion to just swap the C4/C5 caps around to see if one is a little better than the other!
Once you reach a certain point in the ratio of those caps though, it may fail to start reliably at some temperatures/stray capacitances/wind conditions/sea states/etc.
In a perfect world you'd have the luxury of two big 2000pF air variables for C4 and C5 and you could just fiddle the ratios back and forth until the waveform looks best. Or even better, an unobtainable split-stator 4000pF air-variable cap. which is basically what those two capacitors are.
4. C6 might need reduced if the buffer amp is flat-topping/bottoming too much - this will reduce the drive to it but shouldn't affect the oscillator much at all (in fact it will load it less, a good thing)
5. Also bear in mind that oscilators are very high impedance devices and easy to upset so I'd prefer to do all my measuring after the buffer stage - the scope probe will always load the osc to some extent and can cause head-scratching (make sure you are on 10x on the probe too for best results). Probing the oscillator output at C6 can upset both the waveform as well as the frequency. Probing the buffer amp output avoids this entirely.
All this assumes you have no problems elsewhere of course. Coming from a solderless breadboard I'd expect all your smaller capacitances to be well off but as it's a published circuit with known capacitances it should be OK on the PCB as long as you don't have bad ground loops.
Lots to go on, thanks. I’ll keep tinkering and look at the points you gave.
It might help to push the transistors a bit farther down. Extra spurious noise with them up in the air.
That is a similar circuit to the one I made, many years ago, which I did use on the Grundig 2100 radio. Later I found someone selling the original SSB unit on eBay, this was so much better, because of the auto / manual signal gain level and noise filter. I did add a white LED to illuminate its dial.
I can imagine. I know that the socket at the back breaks it the AGC function so that you can incorporate manual gain control. If I could find a suitable plug for that socket, I’d be tempted to try some more experiments, but unfortunately I have no idea if such a socket is even available today.
@@electronicsoldandnew I had been looking for this plug myself, but with no luck. I did try to make a plug using nails and gluing them in a plastic base, it did fit okay, but then found the original SSB unit, so it wasn't required.
👍
Interesting project, I did think about making one myself as i might get 2 of these radios soon.
How about replacing L1 with a fixed inductor once you know the value it should have?
And replace R1 with 2 pots for course and fine adjustment. or maybe a multiturn pot...
I agree with those who suggest that Q2 is not biased enough, that causes the clipping.
It's impedance might also load the oscillator to much.
It also might need to be in an shielded box so that it doesn't interfere with the internal IF of the radio.
I’ve been experimenting with all the suggestions so far, and the result is improving. It’s great with all this help.
Perhaps the buffer transistor is being driven either off or into saturation? Can play with the bias. Also perhaps adjust the Colpitts feedback capacitor voltage divider ratio. This may reduce the oscillator amplitude. Thus not over driving the buffer. Also try degeneration in the transistor emitter.
The reason the wave form is ugly might be that the varactor diode rectifies some of the rf. The way to get around that is to use two varactor diodes back to back and to apply the control voltage to the junction between them. The capacity will of course be halved, but that can be worked around. Apply the control voltage through a hefty resistor or else some of the rf will be shunted to ground.
that might be it. going to experiment using your suggestion. Thanks
nope. still ugly 😊
@@electronicsoldandnew Ok. You cannot win every time.
no, but you learn how not to do it. you win either way 😊
I think it is a good idea to put the filter to the underside from the pcb it is shielded from the pcb , only a idea .
thanks
I think the bad sinewave is the result of to much gain. Barkhausen said that the gain has to be >=1 but if it becomes to high you get the bad harmonics. A Rc as a Pot of 1,5KOhm should help to adjust the gain
👍
perhaps the dc bias of the first transistor can be of influence on the symmetry of the waveform.. Otherwise you could try to add a low-pass filter to get rid of some of the harmonics.
I did all the bias tests and got no better results, unfortunately
Just external vfo near by, can be better. So that you could tune every frequency, even with 5khz step am radios. I.m. signal 3703khz radio tuned to 3705, tune vfo to 3703 too and that's it.
Also try terminating the output in a 390 ohm resistors. This would have the effect of lowering the buffer stage gain.
Try changing the bias on the transistors R5 and R9
Yo lo hice con la bobina amarilla, un zenner a 9V y la sintonía con un capacitor de 22 pF npo en serie con un pot multivueltas
cool
I doubt that the varicap has a linear characteristic. I wouldn't get too excited about that. As for the sawtooth wave shape I agree with the other comment about playing with the feedback loop.
I’ve been experimenting a lot and seem to have it under control. Am finalising the changed to the boards to order version 2.
Hello, can you tell me what type you use the frequency meter. I need this type, can you write its name, or the location of the purchase, I live in France
It’s something like this one. I bought it some time ago and can’t remember now where I bought it, but they ship everywhere.
www.ebay.com/itm/124545150203
Awesome project are you selling the kit to make this? I need one for my Grundig radio for ssb thanks
No, I don’t sell kits. It’s all DIY 😊
Might be worth trying a log pot to make the none linear tracking more linear, if that makes any sense at all?
makes perfect sense. will try it.
Can you put a low value 10 turn trimmer pot on the amp base bias to accurately tweak it ? That may reduce the clipping issue.
could do. will give everything a try.
Sounds like DeMaw put a 10k pot at the Output to control the level seen by the Radio's AGC. I don't see that on your schematic. What value POT did you use & does it just shunt the 460kHz to ground? Thanx & 73.
I used a 10k pot to adjust the output level. The newer version perhaps shows this more clearly.
Thank you! I've a TenTec version of an external BFO & I find it swamps some radios. I'll try adding the pot.
elektrotanya.com/ten-tec_1050_bfo_schematic_and_op_manual.pdf/download.html
I live your frequency reader.Is it available on line.
Yes. here's one:
www.ebay.com/itm/313593088394?hash=item49039ac98a:g:eycAAOSwm6Jg479o
. Is it possible to convert modern radios like radiwow or tecsun pl-310 with a DSL chip processor to get SSB ?
You’d need to use an external bfo.
@@electronicsoldandnew ok thanks I'll look for one , hopefully the chip processor in radiwow won't interfere with the cross connection.
Hi Great video, i will watch your others, i have a Marconi 2955, it does not have a sensitive receiver but it does demodulate AM/FM, I was thinking about doing this on the IF input, it uses 110khz IF on board AB5,
Do you think this using a sig gen at around 110khz, Should this work. Thanks Dave 2E0DMB
I don’t have experience with that receiver, so I can’t say. Just try it.
@@electronicsoldandnew Hi , it's a radio test set
I did try and inject with a cheap Sig gen , when I transmitted SSB , with into the test set, in am mode and used the sig gen to give the bfo I could change the pitch of my voice but it was to noisy
I don't think the test set liked it, maybe there was a ALC acting against it,
Thanks Dave
I was surprised to see you put that short across the inductor of the IF transformer. Makes me wonder what results you would have if you simply omitted the resistor AND didn't put a short in its place.
The clipping is on the negative swing only....wonder if you could correct that with bias on the transistor(s). You could also experiment with replacing the 2222's with 2N3904's and see if there is any difference. (Probably wouldn't be, but might be worth a try anyway....you could confirm whether it was transistor related.) Have you checked the Data Sheet on the 2N2222's?
I look forward to the next iteration of the circuit board. Speaking of the board...might I make a suggestion? I would suggest that you add components based on "height" when you are soldering them to the board. You know, SMD first, then the next tallest part, etc. Less likely to have a part (eg. IF Transformer can) in the way while you are soldering.
I am sure you will get the clipping resolved!
Keep up the excellent work!
the short wasn’t across the transformer. It was the resistor in series with the pot that biases (and tunes) the varicap diode. The short just allows the full 9V to be available for the tuning.
I placed the components as I did to test out each part as I went along. Normally, this order is a no-no.
I’m going to try some other transistors, biasing, etc. Can’t let a little oscillator beat me 😊
@@electronicsoldandnew , OK, I see my mistake now. I thought you were replacing R12 with the short, but you were replacing R3 instead.
You will resolve the problem, I am sure of that! The more I think about it, the more I feel it is a bias issue.
AH!!! The 2N2222 is a SWITCHING transistor! www.electroschematics.com/wp-content/uploads/2009/04/2n2222-datasheet.pdf
The 2N3904 would probably be a better choice:
www.electroschematics.com/wp-content/uploads/2012/11/MMBT3904.pdf
thanks Wayne. I’m going to try swap out the transistors and see what happens.
Does it work with cw?
absolutely
What a great project Manuel. I did have look at building one myself in the past but couldn’t get the exact coil I needed. The plan was here www.industrial-electronics.com/radio-elec_9.html. Yours looks more complex. It may not be the best waveform but it does work. Look forward to the next instalment. Regards Graham
I decided on this one because some other attempts produced unsatisfactory results. The key is frequency stability, and this one has that. I’m chipping at it with the help of some very good comments here because I want the wave to be cleaner, which, qui frankly, makes no difference to the operation but satisfies my OCD character 😊
At the end of this saga, I’ll send you a couple of boards if you like. They cost me nothing anyway as they are sponsored.
@@electronicsoldandnew I'm sure you will get it sorted. I've read through all the comments and theres a lot of suggestions. Probably a combination of some of them will do the trick. Thanks very much for the offer of a board to try. Funnily enough I had repaired a Satellit 2100 a year or so ago when I went down the same route as yourself trying to find the Grundig BFO and I did look at the circuit for it but decided against trying to replicate it
Study schematics a simple bfo example the relistic dx120 red can ok using a external cap the black one ok take out internal cap and add a
external of choice around 120pf range + or - add a prodector transistor example relistic dx150 no need of gain control your using the
radios agc a dpdt switch one half for am ssb the othe half for b+ switching just a example you will get good results with a simple
circuit and taping in before the detector diode or pri side of last if and get quality audio like the top end radios
Too much feedback in the oscillator. Your waveform is clipped at the bottom. Need to be right next to the receiver without shielded connections or use a shielded
wire connection to tame this little beast. Then try adding a pot as a squelch to the amp base. You need a clean sine wave that stretches and shrinks like a slinky
on the oscilloscope when you turn the pot.
👍
Great learning experience.
👍