Great video Mike! I built a "series tuned" 4-foot loop (24 T #14) and fed it to my common base 2N3906 (PNP) single ended transistor. The loop is the "L" and the C is connected from the loop to GND. Since at resonance a series circuit has max current, it is fed to the emitter via a blocking cap. This is a current driving approach to the emitter/base junction. The collector has a 4:1 to my 50-ohm load (receiver) .I was able to receive SAQ (17.2 KHz.) in Sweden. I like your P-P approach. Thanks Mike! Bob N3SWL
Mike, really great and interesting video. I would like to comment that I (and I'm sure others) like the deep dives. Your videos do both basics and advanced, all-in-one without leaving anyone out. I have been learning Fusion-360 and 3D-Printing; the learning curve has been a bit steep but I'm now past the tutorials and looking for the intermediate and advanced topics. As Amateurs, a portion of us should strive to learn more technical details and actually build things using those concepts--technical curation, is as important as equipment curation!. Many of us (even back-in-the-day) did not have good access to mentors and parts; so these videos serve to allow us to 'fill-in' and either expand or solidify our knowledge. So, (to-me) I really appreciate your videos, just the very way you are doing them. Also, you have a great channel-community, and I like going through their comments as well. 73 & Thanks to All...
A very enjoyable video, as usual. Feeding the power input through the centre-tap of the transformer is a very familiar technique to me from my early days with the UK Telephones. If a similar transformer were used at the input you could produce a "phantom" circuit. These could be used to provide power or DC alarm feeds to other equipment further down the line. You could repeat the process with another circuit and obtain a two-wire phantom circuit which could be used as an additional speech path.
Hi, great video as always! In the unbalanced amplifier, it is unfortunate that you loose one half of the signal in the 6dB attenuator. Since you are already using a transformer, could there be a (improved) solution using (easily) modified transformer?
I must admit I was exited when I saw that the latest installment in this series was available. Thanks Mike, very interesting and excellent explanation of circuit operation. Of course, curious to know if you did get around to removing the 3dB pad and if it made any difference? Also, did you perceive any other differences over the previous circuit, like any possible change in S/N ratio?
Very well-thought-out design. I like seeing good theory employed. You don't see that much anymore. Nowadays, most just employ devices that embody someone else's work.
I like models, but the problem is that setting up the model takes longer than a rule of thumb formula that gets you in the ballpark. Thanks for watching!
Very interesting, Mike, thanks! I like this design over the first one mostly because it uses common 2n2222A transistors, a few of which I may even have in my motely collection of parts. About the only thing I don't have is the type 43 or 75 toroid but that should not be hard to find. I realize that both amps use 'balanced' inputs but I'm not clear on how a loop antenna, which generally has two wires for signal and ground (unbalanced?), are attached to the amp which has four inputs. It's probably very simple, like paralleling the input wires, I'm just not familiar with the way it is shown on the schematic Can you explain this? Also, can the gain of the 2n2222A transistors be increased if it becomes necessary? Just curious. Thanks again. 73 KD2ORG
The loop is a very low impedance antenna and it is balanced which does help with noise. Two unbalanced amplifiers back to back form a balanced input. So ground is in the middle. More gain can be had by strapping two more transistors onto the outputs of the first two.
GD dear OM, TKS FER NICE VIDEO, JUST A QUESTION: WHY IN YOUR VIDEO, CIRCUIT BOARD OUTPUT CONNECTIONS ARE DIFFERENT FROM SHEMATIC DIAGRAM? TKS FER ANSWER AND BEST 73's.
I use an illustration tool called Canvas. I learned it and it still works on an old version. The nice thing is that it is pure art and I can make the schematics look like they are period correct.
Hi Mike. Great video again. Although not the balanced circuit I thought you were going to build (which is shown in a previous video in the series, and the one I've been using for a couple of years). Wonder if you've investigated the frequency response of this common base amp. I appreciate that the loop, that you connect to, will have a big influence. But my current balanced amp rolls off around 10MHz (even with a small 1m CSA single turn loop).
can you not do what ham Chavdar Levkov LZ1AQ did and use a LAN cable between the Loop antenna amplifier and the interface box that connects to the radio via a coaxial cable.
Currently building a new receive loop for HF, part your design and part of one by LZ1AQ I found. Learning curve is steep enough I keep hitting my head on it. If you know what you are doing, you're not learning anything, right? Trying to condense this a lot, my SDR is weak on the low side. Actually it's deaf as a post below 8mhz, that was fixed with a few component changes I found online, but still needs a lot of gain below 8mhz. LZ1AQ uses a common emitter amplifier after the common base to drive the transformer. He is using 220 ohm resistors across is like you did with the 180 ohm resistors. After watching this video and embarrassing amount of times, you mentioned a 9:1 transformer would be an option instead. I understand why your amp needs the resistor, but not the one by LZ1AQ. The collector of a common emitter transistor is a current source, right? So my question is: I took a T50-2 core. I twisted 7 conductors and 19 turns fit. I put 6 windings in series with a center tap, and the 7 winding was the output. It kinda works on a breadboard. On a scale of 1 -10, how bad of a plan is this? 10 being the worst btw.
If you need more gain - yes add the extra amplifiers strapped on. But the T50-2 is a powdered Iron core that is low perm, made for resonant circuits in the MF/SW range, rather than for transformers and it will be lossy compared to a good old Type 43 Ferrite with a few extra turns.
@@MIKROWAVE1 thanks. any chance of an explanation of how to figure what the impedance ratio should be? The website I got cores from showed .5 -10 mhz for the type 2
@@clytle374 Yes that range for high Q tuned circuits but not for broadband transformers. You should do better with 9:1 from a matching standpoint, but with the extra gain of the added stages, it may not be worth the bother. He didn't think so and just added the swamping resistors.
@@MIKROWAVE1 Thanks again, FT50-43 shows Wideband Transformers 5 - 400 MHz and Power Transformers 0.5 - 30 MHz. So I'd ruled it out before. I don't understand the terminology yet. Trying a wind on the -43 core now. Need to get it off the breadboard, just trying to get a feel for this still.
2n2222 can be had in a SOT223 for the power you need. You are also wrong about collector impedance. Take a look at the curves for a 2N2222 and you will see that at 15mA, a change in collector voltage make almost no current change.
Which explains why it worked at low voltage out of regulation! And I had two issues with the original 5109 / 3866 amp. 1. the thing was oscillating trying to drive the coax, thus the pad solution broke that up. And a transistor with less GBW would be fine down here anyway. 2. The regulator was oscillating at a low chop frequency due to insufficient input capacitance. Both issues were faily hidden at 630M until you got a larger signal causing intermod.
@@MIKROWAVE1 I have found that often a resistor is needed in the path bringing the power to the regulator. Long wires look like tuned circuits near the 50MHz(ish) where an LM78xx loves to oscillate. The capacitor on its pins is often not enough to hide the tuned circuit from the very willing oscillator. BTW: for a non-radio purpose I used the SOT223 version of a 2222 to oscillate at about 90MHz. It didn't take much current to get them to reliably make enough gain for the circuit. It has been in production for over 20 years now.
Great video Mike! I built a "series tuned" 4-foot loop (24 T #14) and fed it to my common base 2N3906 (PNP) single ended transistor. The loop is the "L" and the C is connected from the loop to GND. Since at resonance a series circuit has max current, it is fed to the emitter via a blocking cap. This is a current driving approach to the emitter/base junction. The collector has a 4:1 to my 50-ohm load (receiver) .I was able to receive SAQ (17.2 KHz.) in Sweden. I like your P-P approach. Thanks Mike! Bob N3SWL
Mike, really great and interesting video. I would like to comment that I (and I'm sure others) like the deep dives. Your videos do both basics and advanced, all-in-one without leaving anyone out. I have been learning Fusion-360 and 3D-Printing; the learning curve has been a bit steep but I'm now past the tutorials and looking for the intermediate and advanced topics. As Amateurs, a portion of us should strive to learn more technical details and actually build things using those concepts--technical curation, is as important as equipment curation!. Many of us (even back-in-the-day) did not have good access to mentors and parts; so these videos serve to allow us to 'fill-in' and either expand or solidify our knowledge. So, (to-me) I really appreciate your videos, just the very way you are doing them. Also, you have a great channel-community, and I like going through their comments as well.
73 & Thanks to All...
I love the way you explain the circuit theory. I never heard it explained quite that way but it makes sense.
A very enjoyable video, as usual. Feeding the power input through the centre-tap of the transformer is a very familiar technique to me from my early days with the UK Telephones. If a similar transformer were used at the input you could produce a "phantom" circuit. These could be used to provide power or DC alarm feeds to other equipment further down the line. You could repeat the process with another circuit and obtain a two-wire phantom circuit which could be used as an additional speech path.
Those hybrid and phantom circuits were magic known only to Telephone Engineers Gods...
I learn so much watching your videos and this is no exception. Thank-you.
Thanks for the comments and for watching - especially the long boring ones!
Hi,
great video as always!
In the unbalanced amplifier, it is unfortunate that you loose one half of the signal in the 6dB attenuator. Since you are already using a transformer, could there be a (improved) solution using (easily) modified transformer?
I must admit I was exited when I saw that the latest installment in this series was available. Thanks Mike, very interesting and excellent explanation of circuit operation. Of course, curious to know if you did get around to removing the 3dB pad and if it made any difference? Also, did you perceive any other differences over the previous circuit, like any possible change in S/N ratio?
Yes it did and the common base amp was very stable with the coax load. No issues.
Very well-thought-out design. I like seeing good theory employed. You don't see that much anymore. Nowadays, most just employ devices that embody someone else's work.
I like models, but the problem is that setting up the model takes longer than a rule of thumb formula that gets you in the ballpark. Thanks for watching!
Thanks, good learning experience.
Very interesting, Mike, thanks! I like this design over the first one mostly because it uses common 2n2222A transistors, a few of which I may even have in my motely collection of parts. About the only thing I don't have is the type 43 or 75 toroid but that should not be hard to find. I realize that both amps use 'balanced' inputs but I'm not clear on how a loop antenna, which generally has two wires for signal and ground (unbalanced?), are attached to the amp which has four inputs. It's probably very simple, like paralleling the input wires, I'm just not familiar with the way it is shown on the schematic Can you explain this? Also, can the gain of the 2n2222A transistors be increased if it becomes necessary? Just curious. Thanks again. 73 KD2ORG
The loop is a very low impedance antenna and it is balanced which does help with noise. Two unbalanced amplifiers back to back form a balanced input. So ground is in the middle. More gain can be had by strapping two more transistors onto the outputs of the first two.
GD dear OM, TKS FER NICE VIDEO, JUST A QUESTION: WHY IN YOUR VIDEO, CIRCUIT BOARD OUTPUT CONNECTIONS ARE DIFFERENT FROM SHEMATIC DIAGRAM? TKS FER ANSWER AND BEST 73's.
Hi Mike - always enjoy your videos. What program do you use to create your schematics? They look great. Regards.
I use an illustration tool called Canvas. I learned it and it still works on an old version. The nice thing is that it is pure art and I can make the schematics look like they are period correct.
Hi Mike. Great video again. Although not the balanced circuit I thought you were going to build (which is shown in a previous video in the series, and the one I've been using for a couple of years). Wonder if you've investigated the frequency response of this common base amp. I appreciate that the loop, that you connect to, will have a big influence. But my current balanced amp rolls off around 10MHz (even with a small 1m CSA single turn loop).
I have not looked at it at higher frequencies, but I suspect that it should work with the right ferrite and if not add more gain and feedback.
Very interesting, thanks for sharing. 👍
This circuit is simple and it worked even better when I removed the output pad. It is very stable driving coax, compared to the first amplifier.
Is there a reason that the 2N2222s are metal packages? (TO-18 maybe?)
They were originally all in metal. Plastic came later and the plastic ones may not do well with a lot of heat.
@@MIKROWAVE1 ah-ha! thank you!!
can you not do what ham Chavdar Levkov LZ1AQ did and use a LAN cable between the Loop antenna amplifier and the interface box that connects to the radio via a coaxial cable.
Currently building a new receive loop for HF, part your design and part of one by LZ1AQ I found. Learning curve is steep enough I keep hitting my head on it. If you know what you are doing, you're not learning anything, right? Trying to condense this a lot, my SDR is weak on the low side. Actually it's deaf as a post below 8mhz, that was fixed with a few component changes I found online, but still needs a lot of gain below 8mhz. LZ1AQ uses a common emitter amplifier after the common base to drive the transformer. He is using 220 ohm resistors across is like you did with the 180 ohm resistors. After watching this video and embarrassing amount of times, you mentioned a 9:1 transformer would be an option instead. I understand why your amp needs the resistor, but not the one by LZ1AQ. The collector of a common emitter transistor is a current source, right? So my question is: I took a T50-2 core. I twisted 7 conductors and 19 turns fit. I put 6 windings in series with a center tap, and the 7 winding was the output. It kinda works on a breadboard. On a scale of 1 -10, how bad of a plan is this? 10 being the worst btw.
If you need more gain - yes add the extra amplifiers strapped on. But the T50-2 is a powdered Iron core that is low perm, made for resonant circuits in the MF/SW range, rather than for transformers and it will be lossy compared to a good old Type 43 Ferrite with a few extra turns.
@@MIKROWAVE1 thanks. any chance of an explanation of how to figure what the impedance ratio should be? The website I got cores from showed .5 -10 mhz for the type 2
@@clytle374 Yes that range for high Q tuned circuits but not for broadband transformers. You should do better with 9:1 from a matching standpoint, but with the extra gain of the added stages, it may not be worth the bother. He didn't think so and just added the swamping resistors.
@@MIKROWAVE1 Thanks again, FT50-43 shows Wideband Transformers 5 - 400 MHz and Power Transformers 0.5 - 30 MHz. So I'd ruled it out before. I don't understand the terminology yet. Trying a wind on the -43 core now. Need to get it off the breadboard, just trying to get a feel for this still.
This is normally used as a UHF amplifier topology but maybe using BFR96S might be better.
For SW probably. For LF, the old 2N2222 is OK.
2n2222 can be had in a SOT223 for the power you need.
You are also wrong about collector impedance. Take a look at the curves for a 2N2222 and you will see that at 15mA, a change in collector voltage make almost no current change.
Which explains why it worked at low voltage out of regulation! And I had two issues with the original 5109 / 3866 amp. 1. the thing was oscillating trying to drive the coax, thus the pad solution broke that up. And a transistor with less GBW would be fine down here anyway. 2. The regulator was oscillating at a low chop frequency due to insufficient input capacitance. Both issues were faily hidden at 630M until you got a larger signal causing intermod.
@@MIKROWAVE1 I have found that often a resistor is needed in the path bringing the power to the regulator. Long wires look like tuned circuits near the 50MHz(ish) where an LM78xx loves to oscillate. The capacitor on its pins is often not enough to hide the tuned circuit from the very willing oscillator.
BTW: for a non-radio purpose I used the SOT223 version of a 2222 to oscillate at about 90MHz. It didn't take much current to get them to reliably make enough gain for the circuit. It has been in production for over 20 years now.
What's the wire size for T1 ?
It looks to be 26 gauge or so.
Yup 28 or 26.
Yup 28 or 26.
@@MIKROWAVE1 - Thanks, Mike. This is something that is left out most of the time; don't know why.
resistance? Heir Boltzmann.....It looks to me like these are classical designs!
I'm just old.