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Title: Solid State Class C Collector Modulation Post by: W1RKW on November 11, 2009, 04:20:47 PM Is there such a thing as collector modulation for solid state? Assuming the high level topologies are similar with the difference being the devices (hollow vs. solid state), how come I never see collector modulation, class C operation for instance when searching for a solid state version of a class C solid state AM transmitter even for low power apps? I would think that since the topologies are similar there would be many circuits.
Title: Re: Solid State Class C Collector Modulation Post by: N2DTS on November 11, 2009, 04:59:31 PM Like a cb set?
that is what they all do... Brett Title: Re: Solid State Class C Collector Modulation Post by: KF1Z on November 11, 2009, 05:12:59 PM I've been spending LOTS of time lately serching for just that!
CB's... Well, aren't they mostly low-level modulated? I guess the old one's weren't (AM only)... because they had a choke and mod-tranny. these days they are mostly SSB, with AM, FM added on. I have been trying to find a circuit that doesn't use a modulation transformer... Just straight series modulated. So far only basic outlines, nothing that is "tried-and-true". Title: Re: Solid State Class C Collector Modulation Post by: W1RKW on November 11, 2009, 05:13:44 PM Like a cb set? that is what they all do... Brett Yeah, I guess like a CB set but on a larger scale like 50watts or more. Is there a design restriction that these are not as prevalent as other topologies? Title: Re: Solid State Class C Collector Modulation Post by: N2DTS on November 11, 2009, 05:22:29 PM Its just like cb sets, and they make high power ones now disguised as 10 meter rigs, I had one, did 30 watts and had a collector modulator in it, along with the ssb and fm stuff.
I cant say if they are all made that way these days, but i think most are. Its just a matter of scale, bigger and/or more RF output devices, bigger heat sinks, bigger modulators... Its real easy to do 4 watts outand modulate it with 3 watts, you can get 20 watts of audio out of a small 5 pin to220 package these days.. Two in push pull would do 40 watts and modulate an 80 watt input final. They take almost microphone level input... Brett Title: Re: Solid State Class C Collector Modulation Post by: KF1Z on November 11, 2009, 05:31:49 PM Yeah, but that still means using a modulation transformer...
I haven't used one in a rig yet, and don't want to start now! ;) But, want to try Class C at 10 meters, and just use a series modulator/power supply, but of course would use mosfets. That's what I'm looking for anyhow... Sometimes just to lazy (or pressed for play time) to do some trial and error. Title: Re: Solid State Class C Collector Modulation Post by: N2DTS on November 11, 2009, 05:38:59 PM Well, if you dont mind the hit in efficiency, you could just do a solid state version of a cathode modulated rig with a pass tube / pass fet...
Title: Re: Solid State Class C Collector Modulation Post by: Steve - WB3HUZ on November 11, 2009, 06:18:09 PM Get the schematic for almost any CB from the mid/late 70's one. Every one I've looked at was series mod with no mod tranny.
Yeah, but that still means using a modulation transformer... I haven't used one in a rig yet, and don't want to start now! ;) But, want to try Class C at 10 meters, and just use a series modulator/power supply, but of course would use mosfets. That's what I'm looking for anyhow... Sometimes just to lazy (or pressed for play time) to do some trial and error. Title: Re: Solid State Class C Collector Modulation Post by: KF1Z on November 11, 2009, 06:22:50 PM Yes, the "Pass FET"... is what I'm getting at, was thinking "series modulated" was the same thing, though possibly wrong terminology.
But, not being an engineer... I need schematics, at LEAST as a good starting point... I just hate to waste hard to come by time by trying to figure out what has already been figured! Title: Re: Solid State Class C Collector Modulation Post by: KF1Z on November 11, 2009, 06:26:39 PM Get the schematic for almost any CB from the mid/late 70's one. Every one I've looked at was series mod with no mod tranny. Huh, I'll have to look harder! The ones I found all do have the mod transf... But those were all basically the same, infamous, board, that used the PLL IC (PLL-02A ?) configuration, that made them a breeze to put on 10m. Hmm... back to Google! Title: Re: Solid State Class C Collector Modulation Post by: WA1GFZ on November 11, 2009, 06:49:20 PM H mode modulator will be more efficient but any FET or transistor biased at a bit unter 1/2 power supply voltage will work fine as long as the heat sink is big enough to dissipate the heat.
There is no need to negative bias the final just bias to zero which is below cut off. Just a class e without a shunt cap. A low pass filter on the output is all you need. Jay W1VD has added a parallel tuned circuit between both sides of the drains of a push pull to clean up the waveform. He is getting very good efficiency without any tuning required Title: Re: Solid State Class C Collector Modulation Post by: KF1Z on November 11, 2009, 06:56:47 PM Frank,
I had played with Jay's Class-D designs a bit, at low power (5 watt carrier, pair of IRL510's). Question is... can that Class-D design be made to play friendly at 29mhz? Title: Re: Solid State Class C Collector Modulation Post by: WA1GFZ on November 11, 2009, 07:11:54 PM Why not. IRF510s will work on 6 meters.
Title: Re: Solid State Class C Collector Modulation Post by: KF1Z on November 11, 2009, 07:24:48 PM Why not. IRF510s will work on 6 meters. In Class-D ? Title: Re: Solid State Class C Collector Modulation Post by: DMOD on November 11, 2009, 10:02:31 PM You can AM modulate the voltage on the drain of an RF Power Mosfet.
See page 5 of 6 which is the app. note for a Class C circuit. http://www.ixysrf.com/pdf/switch_mode/de275_102n06a.pdf Phil - AC0OB Title: Re: Solid State Class C Collector Modulation Post by: KD6VXI on November 11, 2009, 11:54:09 PM Yeah, but that still means using a modulation transformer... I haven't used one in a rig yet, and don't want to start now! ;) But, want to try Class C at 10 meters, and just use a series modulator/power supply, but of course would use mosfets. That's what I'm looking for anyhow... Sometimes just to lazy (or pressed for play time) to do some trial and error. Search Series Class A modulator. I've designed a series modulator that I did well marketing to the HiFi CB crowd. Remove the final and driver Vcc, and insert my modulator Vcc at that point. Line level into the board, and you have modulation control, carrier control and supermodulation / ultramodulation controls as well. I also did one that had negative peak clipping on it, but didn't like the overall effect. There is a BIG market to the channel 6 guys with this now, I finally threw in the towel after my wreck and gave it pretty much to my competitor, MotorMouth. But take a look at any CB rig for ideas. The SSB radios used collector series modulators, the 138/139, 142/146/148/2000/grant/washington bases did as well. ALL the Galaxy offshore crap is now series modulated, and you can also take a look at their schematics and learn the different voltages needed to get it to work high level modulated Class C, as well as when they rebias it for SSB. The reason people don't use series modulators is they are inefficient. BUT, as simple as a TIP31 to modulate to 25 watts PEP driven from a simple audio amp, nothing to sneeze at. My series modulator, outboard, has a total parts count of 12 devices. All ordered through Mouser. 20 bucks a board to build, > 100 out the door + shipping :) I've even played with doing it at the amplifier level, and breadboarded one up to the 600 watt (PEP) level, using a quad of 2879s. SUPPOSEDLY, after showing this off at a couple breaks, another Channel 6 guy came up and said I stole my design from Dentron, as they had something in the wings. Truth be known, I copied and improved upon the textbook one from Lou Franklin's Understanding and Repairing CB Radios. I BELIEVE you can find that online with google books or something else. VERY simple schematic. Next year the person I gave up the competition to should be marketing a modulator that has line level inputs, and can hook up to a 16 device amplifier, equating to nearly 2.5 kw PEP output, AM... High Level. --Shane Title: Re: Solid State Class C Collector Modulation Post by: KD6VXI on November 11, 2009, 11:57:10 PM Get the schematic for almost any CB from the mid/late 70's one. Every one I've looked at was series mod with no mod tranny. Huh, I'll have to look harder! The ones I found all do have the mod transf... But those were all basically the same, infamous, board, that used the PLL IC (PLL-02A ?) configuration, that made them a breeze to put on 10m. Hmm... back to Google! Do NOT confuse a modulation transformer with a hash filter. I've had that argument with more than one person.... Like, the Cobra 148 has a BETTER modulation transformer from the phillipines, or the one with the yellow sticker on top. TRUTH BE KNOWN, NOT A SINGLE SSB RADIO UNIDEN / COBRA MANUFACTURED SINCE 1982 HAS HAD A MODULATION TRANSFORMER IN IT!!!!!!!!!!!!! So, head over to CB Tricks, and check out the Galaxy radios section. Pull up one of the dual final radios, and copy the mud-u-lator out of it. They are good for 40 watts PEP out of the box, and if you change the pass transistor, I've used that circuit to 100 PEP. --Shane Title: Re: Solid State Class C Collector Modulation Post by: KF1Z on November 12, 2009, 12:47:08 AM Ok Shane,
No no mistaken the transformers I am refering to are audio transformers... The primaries driven by either an audio amp IC, or a push-pull pair of npn's...., one secondary to the speaker/PA speaker, and the other secondary has V+ on one side, and the other side to the collector of the RF PA collector... Title: Re: Solid State Class C Collector Modulation Post by: KF1Z on November 12, 2009, 01:07:02 AM You can AM modulate the voltage on the drain of an RF Power Mosfet. See page 5 of 6 which is the app. note for a Class C circuit. http://www.ixysrf.com/pdf/switch_mode/de275_102n06a.pdf Phil - AC0OB Well sure .... that's how my Class-E, and Class-D rigs operate... I've just never built a Class-C amp before! ;D Title: Re: Solid State Class C Collector Modulation Post by: Ian VK3KRI on November 12, 2009, 05:58:15 AM I have an aircraft band (110Mhz) AM transmitter here that uses a 28V VHF power transistor run at 12 volts with a push pull audio stage and conventional modulation transformer . Just replace your Class B modulator tubes and class C tube with NPN transistors and you've got the circuit .
Ian VK3KRI Title: Re: Solid State Class C Collector Modulation Post by: N4LTA on November 12, 2009, 09:00:50 AM To get 100% modulation, you generally have to modulate the driver stages also.
A 10 watt output 25 volt IRF510 transmitter has a collector current of approx .6 amps which gives a drain impedance of about 42 ohms. If you have a small solid state amp of 15 watts or so you need a modulation transformer with a turns ratio of 3.25:1 a 120 volt to 36 volt filament transformer might work if it is fairly large so it won't saturate. The old ARRL Handbooks had SS modulators that used filament transformers to modulate tube stages. Anything close should work as most SS amps can match most load impedances from 2-16 or so as they are current source type amps. The power output generally drops as the load impedance rises. You could also use a small PWM modulator. Pat N4LTA Title: Re: Solid State Class C Collector Modulation Post by: WA1GFZ on November 12, 2009, 11:41:14 AM Class E like class D does not need to modulate the driver. If you have enough voltage swing on the gate. There is no advantage of driving the gate past saturation and the reverse transfer C is low providing isolation at negative peak. Reducing gate drive with modulation will hurt efficiency
Title: Re: Solid State Class C Collector Modulation Post by: Opcom on November 12, 2009, 10:08:37 PM modulate the 12V leenyar. Most can be made to work OK on the ham bands. If you do that be sure it is properly biased for AB. Most today are not biased at all. The new ARRL handbook has a very nice SS linear design.
Title: Re: Solid State Class C Collector Modulation Post by: W1RKW on November 13, 2009, 02:42:30 PM so if one were to build a class C AM transmitter using a solid state BJT or FET or more plus a transformer for modulating the B+ at a 50w or so level could it be done ?
Title: Re: Solid State Class C Collector Modulation Post by: KF1Z on November 13, 2009, 03:01:08 PM Yup, that's what it looks like.....
Me, I don't want any steenkin' transformers :-) Title: Re: Solid State Class C Collector Modulation Post by: WA1GFZ on November 13, 2009, 03:02:33 PM Yes, But be aware a BJT input impedance changes when set up as Calss B,C,D.
A FET is constant since it is controlled by a resistor. Title: Re: Solid State Class C Collector Modulation Post by: Steve - WB3HUZ on November 14, 2009, 10:34:21 AM You could do it w/o a transformer. It would be easier and much more versatile than the Class E designs.
so if one were to build a class C AM transmitter using a solid state BJT or FET or more plus a transformer for modulating the B+ at a 50w or so level could it be done ? Title: Re: Solid State Class C Collector Modulation Post by: Opcom on November 14, 2009, 12:19:30 PM You could do it w/o a transformer. It would be easier and much more versatile than the Class E designs. so if one were to build a class C AM transmitter using a solid state BJT or FET or more plus a transformer for modulating the B+ at a 50w or so level could it be done ? I'm not going to agree with the anti-iron naysayers. It could be done. The only real obstacle is finding a usable transformer and deciding on the audio output stage type to be used. Either push pull requiring a center tap on one of the windings or totem pole and capacitor coupling the stage to the transformer. It's fairly easy to see that if 12V is being used, a 24V CT transformer would be a decent place to start for a push pull stage's winding. For the 'secondary', a slightly higher voltage would be in order just like the tube stuff. I've seen alot of xfmrs floating around with 18-30VCT and 30-45VCT widnings, each rated 4-8A. What to do with the 120V winding? feedback maybe. or ignore it. Feedback or some kind of frequency EQ should be considered when using power iron for audio but that is not hard to do. This does noit have to be hi-fi, just clean over the audio range. The low end is not an issue since the iron is 60Hz. The high end of 3-5KC might need some attention and some loss in a power transformer can be expected up there. If you find one rated 50-400Hz, that would be better. Another source might be the output transformer from a 50-100W transistor PA power amp. There are some of those floating around in broken condition for a few bucks. In fact, repairing one and transplanting the guts to your project might be worthwhile. Those are often tapped autransformers which would be perfect for selecting your choice of modulation voltages. The other challenge is the question of DC magnetization of the winding used as the modulating secondary because power transformers are not designed to carry DC in a winding. A good thing to help here would be to use a xfmr rated 2-3X the necessary power level. big core won't saturate as easily and a 150VA transformer is still not very large. The same technique as used in tube stuff could be done, finding a suitable choke for the DC current of the final and cap-coupling the mod winding to it. 5000uF is about 0.3 Ohms at 100Hz so the cap is easy to find, even a 20,000uF for some overkill. Chokes can be had from old low voltage high current power supplies such as motorola base station units. It might take a coule in series. It's not unusual for those nasty old ferroresonant DC supplies to be choke-input. The choke is often hidden under the chassis. So, what voltage for the B+? 12V? 50W input - would be about 3 ohms. 10mH is 7 Ohms at 100Hz, and I bet there are some 20-100mH 4A chokes or better out there in junque if looked for. I just stripped out some 24V supplies from RCA film chain projectors to get the rackmount chassis&panels and the chokes were 8A. I have not measured the L yet. OK well there is a budget for space requirement for the iron so that's what it comes to if that is a concern. Hopefully, you will succeed in building a "heavy metal" solid state rig. Title: Re: Solid State Class C Collector Modulation Post by: Opcom on November 14, 2009, 12:23:36 PM You could do it w/o a transformer. It would be easier and much more versatile than the Class E designs. so if one were to build a class C AM transmitter using a solid state BJT or FET or more plus a transformer for modulating the B+ at a 50w or so level could it be done ? I'm not going to agree with the anti-iron naysayers. It could be done. The only real obstacle is finding a usable transformer and deciding on the audio output stage type to be used. Either push pull requiring a center tap on one of the windings or totem pole and capacitor coupling the stage to the transformer. It's fairly easy to see that if 12V is being used, a 24V CT transformer would be a decent place to start for a push pull stage's winding. For the 'secondary', a slightly higher voltage would be in order just like the tube stuff. I've seen alot of xfmrs floating around with 18-30VCT and 30-45VCT widnings, each rated 4-8A. What to do with the 120V winding? feedback maybe. or ignore it. Feedback or some kind of frequency EQ should be considered when using power iron for audio but that is not hard to do. This does noit have to be hi-fi, just clean over the audio range. The low end is not an issue since the iron is 60Hz. The high end of 3-5KC might need some attention and some loss in a power transformer can be expected up there. If you find one rated 50-400Hz, that would be better. Another source might be the output transformer from a 50-100W transistor PA power amp. There are some of those floating around in broken condition for a few bucks. In fact, repairing one and transplanting the guts to your project might be worthwhile. Those are often tapped autransformers which would be perfect for selecting your choice of modulation voltages. The other challenge is the question of DC magnetization of the winding used as the modulating secondary because power transformers are not designed to carry DC in a winding. A good thing to help here would be to use a xfmr rated 2-3X the necessary power level. big core won't saturate as easily and a 150VA transformer is still not very large. The same technique as used in tube stuff could be done, finding a suitable choke for the DC current of the final and cap-coupling the mod winding to it. 5000uF is about 0.3 Ohms at 100Hz so the cap is easy to find, even a 20,000uF for some overkill. Chokes can be had from old low voltage high current power supplies such as motorola base station units. It might take a coule in series. It's not unusual for those nasty old ferroresonant DC supplies to be choke-input. The choke is often hidden under the chassis. So, what voltage for the B+? 12V? 50W input - would be about 3 ohms. 10mH is 7 Ohms at 100Hz, and I bet there are some 20-100mH 4A chokes or better out there in junque if looked for. I just stripped out some 24V supplies from RCA film chain projectors to get the rackmount chassis&panels and the chokes were 8A. I have not measured the L yet. It is also not hard to bias a transistor power stage. It's done just like with linear amps, using a diode and resistor. The resistor is usually variable in audio amps so the bias can be set to some value and the diode or diodes are to be mounted on the heatsink to control the bias. OK well there is a budget for space requirement for the iron so that's what it comes to if that is a concern. Hopefully, you will succeed in building a "heavy metal" solid state rig. Title: Re: Solid State Class C Collector Modulation Post by: n4wc on November 14, 2009, 01:40:37 PM In the aviation world the VHF com band is still AM. I believe the King KTR 900, KX 170, the Collins 618M3 and the 618M5 all use hi-level collector modulation by controlling the collector through a series regulator transistor. In the King versions the driver stage is modulated, not sure about the Collins. All of these units are final test set to 85% modulation max and negative peak limited to about the same. No mod xfmrs as far as I can remember. All of these units operate on 28Vdc except the KX 170(13.75Vdc).
73 Bill N4WC Title: Re: Solid State Class C Collector Modulation Post by: WU2D on November 15, 2009, 10:26:14 PM Most of the classic late 70's solid state CB's used high level Heising or Transformer, at first push pull audio and later audio chips and bricks with complementary symmetry. See attached - The Midland uses push pull, the old Hygain Board uses center tapped Heising off a TA7205 amp.
Mike WU2D Title: Re: Solid State Class C Collector Modulation Post by: Jim KF2SY on November 16, 2009, 09:27:19 AM so if one were to build a class C AM transmitter using a solid state BJT or FET or more plus a transformer for modulating the B+ at a 50w or so level could it be done ? Not sure if everyone talking about the same thing here? Why not series modulate using PWM FETS's and LPF? (Use higher B+ on the PWM for swing) |