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 Post subject: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Thu 15, 2018 11:03 pm 
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This is not my design and certainly not new. I have found several variants of this on the Internet. The advantage of this approach is that the oscillator runs continually at +5v without modulation and feeds into the base of the 2n3904 transistor. The 386 circuit then feeds the audio into the collector of the transistor through a 1mh choke. The 386 is tolerant of a wide range of voltages. I ran it up to +12 volts without a problem but it did get pretty warm. 9 volts seems to suit it. You can run this entirely off of a 7805 regulator or use the 7809 for the 386 and transistor. In this configuration mine draws about 250ma. This setup is less sensitive to voltage, modulation and distortion. I ran the oscillator straight into the base of the transistor. Takes only a few minutes to make the change and cost is about $.02 One thing I did notice was that you can reduce power output by just reducing voltage to 386 and transistor then simply reset the modulation. This also opens up the use of oscillators that are not able to be modulated.

I would be interested to hear someone else's results.

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Last edited by black85vette on Feb Mon 19, 2018 5:25 am, edited 2 times in total.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Mon 19, 2018 5:02 am 
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I simplified the schematic to just include the modification since there is plenty of documentation on the construction of this circuit. The schematic from the first post was removed since it was not how this should be built anyway. This is my first attempt at using schematic software rather than using Visio.


Attachments:
Capture.JPG
Capture.JPG [ 22.65 KiB | Viewed 1767 times ]

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Mon 19, 2018 11:44 pm 
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Hi Rick,

I experimented a bit this afternoon and will post a slight mod to your circuit that works better here. One difference here is likely my inductors, handwound single layer stuff. Used a single 9v supply to LM386, 9v through 7805 regulator for the 1.000mHz ESC oscillator. Had some weird looking output at first. Making changes I'll post later this evening gave a much more normal output and decent modulation. The total 9v current draw was 132ma, most of which seems to go through the transistor, so....

More output than the "stock" version with FAR more current draw. Can be scaled back.

Drawing to come in a couple of hours!

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Tue 20, 2018 12:27 am 
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Thanks Rich. I also ran 9v and then 7805 to the ECS. I noticed the current and measured it at the 9v supply and then the emitter to ground. Another change I tried was to drop the 1mh choke to .5mh. Output went up but of course it increased current as well. Looking forward to your changes.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Tue 20, 2018 3:01 am 
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Resistor to Q1's base reduces current draw by the oscillator. There is a small increase in radiated output with the resistor around 75 ohms, dropping off slightly above and below that value, I am not sure why. The circuit will work with much higher resistor values (and corresponding lower oscillator current) but modulation quality suffers. I noticed a sort of double peak, two peaks very near each other, while adjusting C2 for max output and could see the output waveform was distorted when adjusted to one peak but not the other. The 1mHz waveform at the collector of Q1 is very dirty with ringing and with two distinct voltage pulses per cycle, both pulses are many volts greater than the 9v supply. Kickback from square waves into the inductors I suppose. My 'scope is an ancient 20mHz model so I cannot be sure I was seeing an accurate representation, one of the pulses looked much narrower than the other. I have no experience with antenna matching networks so while poking around trying to understand what I was seeing, I noticed a dramatic reduction of the narrow pulse peak when a small value capacitor was placed from collector to ground. The capacitor simultaneously increased the broadcast output a small amount. 33pf was enough to eliminate the double tuning peak I had noted. Values up to 100pf seemed to also give slightly more antenna output. There was no further output increase with higher pf values and I suspect any capacitance places unwanted load on Q1. I've arbitrarily suggested 75pf but to be honest, I am uncomfortable putting any capacitor from collector to ground because it is just sucking away energy that might better be given to the antenna, so I hope to understand the problem better. Perhaps one of our forum experts can help?

Presumably L1 is still needed. I tried a higher value for it and didn't notice any difference. If reduced power output is desired, you have suggested that reducing voltage to the LM386 is effective, which will lower collector voltage and current. I initially had a resistor in series with L1 and that did the trick also. Perhaps a resistor can be placed in series with the emitter instead of L1, I'm thinking that may allow the base resistor to be increased (thus lower current consumption by the oscillator)?
Attachment:
ECS b85v rev1.JPG
ECS b85v rev1.JPG [ 35.78 KiB | Viewed 1715 times ]


Following traces are unmodulated, upper waveform at Q1 collector, 10v per division, without capacitor on left, with 200pf capacitor on right. Lower trace on each is simultaneous pickup by clip lead near antenna, voltage unknown. Notice antenna output with capacitor slightly higher. Notice slight distortion in antenna waveform without capacitor.

edit: I forgot to mention, the narrow peaks can be MUCH higher voltage when antenna is not well matched. This is normal?
Attachment:
waves nocap and cap.jpg
waves nocap and cap.jpg [ 100.6 KiB | Viewed 1713 times ]

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Last edited by richfair on Feb Tue 20, 2018 3:42 pm, edited 1 time in total.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Tue 20, 2018 3:10 pm 
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I ran some short tests last night. On L1 I am using 1mh and saw a big increase of output and current with a .5mh so I have stayed with the larger. I will go back and measure the current with different values and see what I get. C3 does not have much effect on mine. Putting it in and out while monitoring the output showed a very slight decrease when in the circuit for me. Pretty minor so I am leaving it in for now. The resistor was interesting. I varied the value and output has a significant drop initially and then goes through several peaks and dips. Didn't spend much time with it but I will be leaving a small resistor in there as well.

I have a variable ferrite core antenna from a radio that I use for the antenna match. I set the capacitor to minimum, peak with the inductor and then fine tune with the cap. I suspect we see different results due to antenna and matching set up. I don't see two distinct peaks. My scope does show the ringing but with a single peak. BTW; are you using an earth ground with the transmitter? I have mine connected to a copper rod just outside my shop.

Also planning on putting a pot inline with the emitter and see what it does with the current and output.

Edit:

Did not like the pot in the emitter. Had some odd effects on the waveform. So did putting a resistor inline with L1.

Changed values of L1. At 220uh current was 232ma. At 1mh it was 170ma. At 2mh it was 150 ma. Staying at 2mh and dropping the input to the 386 to 5v off the 7805 current was 131ma. Change of inductance had some effect on ringing but mostly changed amplitude of the signal. So voltage and inductance seem to be a good way to reduce output and current.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Wed 21, 2018 3:35 am 
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Rick,

We retired last summer and I didn’t set up my shop until the winter. For now my radio ground is the AC wiring with a ground rod by the meter. I also have metal siding and roof which complicates matters. Probably will install a proper rf ground after the ground thaws this year. None of that matters for this.

Lots to report today, I’ll try to keep this short. No ferrite in my inductors, just homebrew air coils. I don’t have a way to quantify what is actually being radiated by my antenna, just power draw and relative radiations to a nearby clip lead. In all cases when I calculated an input power, I could see a corresponding change in radiated power to the clip lead. That correlation gave some encouragement.

I tried running the LM386 on 5v which was effective at knocking down power draw. I also saw poorer modulation (more distortion) when compared to running the LM386 on 9v and using resistor R2 to reduce power input. R2=47 ohms gives me 85mw input to Q1, near as I can tell by measuring voltage drop across R2 (during zero modulation) and hope that my meter is not too freaked out by whatever rf seeps through L1. One could trim R2 down to get a full 100mw, doubtful it would make a practical difference though. When I run the whole circuit on 5V, with a wire in place of R2, I estimate something like 125mw into Q1, with total 5v draw around 55-60ma (I recall, I didn’t write it down). R2 could be added to make power legal but considering lower modulation quality with LM386 on 5v supply, I opted for the resistor with 9 volt supply. Total current draw of the circuit (as shown below 9v to LM386, R2=47) is around 80ma into my 10 foot extension cord antenna. So, a bit less efficient than with 5v only but I’m okay with that for this build.

(A related question, how does one measure 35Z5’s input power according to part 15? My guess is the oscillator IC uses about 15ma when loaded to my antenna, which means 67mw input (4.5v x .015a). 35Z5’s circuit is more efficient than this circuit, so the extra output power has a steep price considering the difference between 100mw and 67mw is less than 3 db, which is trivial.)

My L1 is 150uH (give or take a couple of uH), DC resistance 3.3 ohms. It is effective at blocking 1mHz to LM386 output pin 5. A 360uH (8.6 ohms) gives no better isolation. A 390uH with lower resistance (0.8 ohms) is no better or worse. Unless your antenna is being loaded far more efficiently than mine, I don’t see why there is such a difference of current between you and I.

I temporarily swapped in a 2n4401 for Q1. It is a lower-gain, higher current device with somewhat higher capacitance, identical breakdown voltages. The crazy ringing and harmonics waveform at Q1’s collector disappeared, replaced by a single clean voltage spike. C3 needed to be removed with 2n4401. I reinstalled 2n3904 because it gives me slightly stronger radiated output (for the same input power) with no visible downside as long as C3 is present (which I have increased to 200pf because it works!). I also tried a 2n4123, similar gain to 2n3904 but with lower capacitance. I would have kept it except it's breakdown voltage is too low for the voltages developed.
Attachment:
ECS b85v rev2.jpg
ECS b85v rev2.jpg [ 37.56 KiB | Viewed 1674 times ]



edit: These traces compare square wave drive on Q1 base vs. collector output for 2n3904 and 2n4401, in above circuit (C3 as noted) using 9v supply to LM386. Surprisingly, the radiated output from 2n4401 was only slightly less than 2n3904. I cannot measure harmonic content of radiated output. Good board layout and short leads should clean up the square wave.
Attachment:
2n3904 driver.jpg
2n3904 driver.jpg [ 105.77 KiB | Viewed 1668 times ]

Attachment:
2n4401 driver.jpg
2n4401 driver.jpg [ 60.52 KiB | Viewed 1668 times ]

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Last edited by richfair on Feb Wed 21, 2018 5:04 am, edited 1 time in total.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Wed 21, 2018 4:55 am 
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As long as you are trying different transistors, do you have FET you can use? This is similar to circuits I worked with in the Class E transmitter thread where I used an IRF 510. By far it's the simplest and most promising xmitter I've tried, and I'm thinking of returning to it.

I fed mine with the $12 MW frequency synthesizer. The transmitter performed ok with the power source was the LM386, but it was better when fed with 12V in series with a modulation transformer (perhaps because the 386 was more isolated?). Unmodulated output was easy to calculate and measure because of the fixed DC voltage to the drain.

Anyway, I'd love to compare your readings with mine if you happen to have an IRF510 laying around.


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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Thu 22, 2018 12:01 am 
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Rich;

Still trying to figure out inductor L1. With the 1 mh I used the modulation looks about the same with 5v or 9v. Some of this is a subjective evaluation of music being played but I also ran an audio oscillator and observed the waveform being output. I was looking for any distortion to the peaks of the signal and also at what percent of modulation that occurred. It runs pretty clean to about 90%. I have a pretty good supply of these 1mh inductors. If you want I can send you a couple of them.

Just to confirm; when I am giving the current I am measuring the 9v supply that feeds the 386 and 7805 to the oscillator. I swapped out my 2n3904 and LM386 just in case I managed to damage one of them. Still seeing the overall current around 180ma. I even put one of my incandescent dial lamps in line with the power. I can tune the antenna with it. LOL

Rick

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Thu 22, 2018 11:53 pm 
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Mac, I don’t have any mosfets here only n-jfets. That project will have to wait for another day.

Rick, your L1 may have lower DC resistance than mine which would explain why your currents can be higher particularly if R2 is a straight wire. To test this theory I measured current with 5v supply using different L1 coils. Is your 1uH choke about ½ ohm? My 150uH air coil is 2.3 ohms. Using 5v supply and no R2, supply current is 96ma. Sub’d in a 1.1 ohm 390uH coil, current jumped to 113ma. It stands to reason a lower DC resistance would allow higher current (and higher rf emission). If absolute max output is your goal then a choke with low resistance is better, although I noticed distortion could also rise. When R2’s value is greater than a few ohms L1’s DC resistance becomes less important. When I ran the circuit at about 200mw, 9 volt supply and R2=22 ohms, I saw no significant difference between my 150uH/2.3 coil vs. 390uH/1.1 coil. Either value was just as effective at blocking rf to the output of LM386 and no difference of rf output or modulation depth. I also experimented with R1, between oscillator and Q1 base, and am choosing to leave it at 75 ohms with 2n3904.

Left pix below with 5v supply, 103mw output (R2=8.0 ohms), max undistorted modulation 90%.
Right pix with 9v supply, 104mw (R2=47 ohms), max undistorted modulation 94%.
The pinch-off rounding is sort of visible. I should have superimposed the generator’s output to make it more obvious.

Attachment:
compare 5v to 9v 100mw.jpg
compare 5v to 9v 100mw.jpg [ 83.69 KiB | Viewed 1623 times ]

For both setups above the unmodulated carrier, as picked up through a clip lead, is the same strength, in other words practically the same rf radiation. Roughly the same total current draw from the 9v supply (I am measuring the same way as you). Modulation figures were calculated at the point of curve “flattening”. 9 volt supply can modulate a bit deeper AND I believe with less distortion. The trough area, negative modulation, tends to round more with 5 volts as it pinches off. I assume this is because the transistor is operating at a different part of its curves and I attempted to overcome that by inserting a diode between Q1 emitter and ground (diode bypassed with a cap). While that improved modulation, allowing complete pinch-off and beyond, it came with some power waste and lower rf output. I removed the diode but might explore this more later.

The next image attempts to show modulation rounding (distortion) near pinch-off. This was taken with audio tone just under the point where the modulation curve begins to flatten. The generator’s output is superimposed using the scope's 2nd channel. Compare the deviation from sinetone at the modulated “trough”, negative modulation, compared to the positive modulation peak. The negative deviation is greater.

Attachment:
5v modulation pinchoff.jpg
5v modulation pinchoff.jpg [ 48.13 KiB | Viewed 1623 times ]


I noticed some audio high frequency roll-off in my radiated signal. About 2db reduction at 10kHz, about 6db at 20kHz. There is no roll-off on LM386’s output or at the collector of Q1, so I believe it is caused by the Q of the matching network and/or antenna “system” (or lack thereof). How much does the antenna and ground figure into this problem?

I am liking this transmitter variation. Easy to adjust power for full legal limit and beyond. Although not as efficient as 35Z5’s original, and therefore perhaps not as appropriate for battery supply, it works very well with just a few extra components. Thanks for this, Rick!

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Fri 23, 2018 12:57 am 
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Rich;

I measured the two inductors I have been using. The 1mh has a resistance of 11 ohms and the 220 uh measures 2 ohms. I will go back and verify all of my current measurements.

Modulation is about the same as your results with 5v and 9v.

My intent for this configuration was not more power. I wanted to separate the modulation from the oscillator. Now it is just a matter of fine tuning to have it run as clean as possible at legal power. The extra power consumption is not an issue since Tom has a good efficient design already. Controlling power is part of the objective since I have radios all over the house. At full legal power my radios on the far end of the house are happy but in my office some of the radios distort with too much signal at max AVC. I am thinking that switching an extra inductor into the circuit along with changing voltage to the 386 gives me options.

Interesting idea about inserting the diode. I may have to check it out. I think I have about 10 different diodes in my stash.

Thanks for all your help with this.

Rick

Edit; just to be sure my meter was not whacky measuring current I put a 1 ohm 1 watt resistor in the circuit and measured the drop across it. Using the 1mh / 11 ohm inductor and no other resistors. Unmodulated carrier.

With 9 volts to 386 total was 250ma and through the transistor only was 207ma
With 5 volts to 386 total was 196ma and through the transistor only was 158ma

Now I am starting to wonder about the transistor. Can't recall where I got them but likely eBay for a whole bag of them. This circuit is not complicated and I can't account for the difference in current. I think I will send you a couple of the transistors and one of the inductors to be sure we are measuring the same components. I also don't think it is in the matching circuit. All I do is peak it for the 5 and 9 volts. I do use a large tuning capacitor for my breadboard testing so I can match a wide range of inductors and antenna lengths. It is similar to an AA5 radio tuning cap but this one is single gang. I put it close to the minimum, peak the inductor and from then on just peak with the cap. Trying to keep the capacitance as low as possible.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Fri 23, 2018 6:02 pm 
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Rick, it may be a difference in transistors. I have a batch of 2n3904 and 2n4401, plastic case, both bought through Mouser 4 or 5 years ago in bulk. I don't recall the manufacturer, but here's why I think it is down to the transistor. When I swap in 2n4401 the current draw with low values of R2 can go very high indeed, heating quickly.

After some thought, I have inserted a diode 1n4841 in series with the emitter, just as before, bypassed by .047uf. This makes Q1 behave much more rationally and in fact I can swap 4401 or 3904 with no practical difference of current or rf output. rf output will drop, make it up with smaller R2. If my instincts are right, the rf output will be the same with the same milliwatts input to Q1. A big plus with the diode is more linear modulation. Easy to see improved pinch-off.

I want to explore this more, run a new set of measurements with the diode+cap (cap is required!). Won't be able to do that until this afternoon. If this doesn't work for you, then by all means send me some parts so we can get to the bottom of it.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Fri 23, 2018 6:21 pm 
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richfair wrote:
I want to explore this more, run a new set of measurements with the diode+cap (cap is required!). Won't be able to do that until this afternoon. If this doesn't work for you, then by all means send me some parts so we can get to the bottom of it.


I will do both. The diode is interesting and if we can end up with a design that tolerates differences in transistors then it will be better for others to build. I have some parts headed your way today.

Rick

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Fri 23, 2018 9:47 pm 
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Rick, I will send you a couple of these 2n3904 and 2n4401. Please PM your address. I am sure I have it somewhere but...

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Tue 27, 2018 7:53 pm 
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Hi Rick,

Thank you so much for the parts, they were very helpful! This circuit now performs well with the range of gen purpose small signal npn devices I have here, including two versions of 2n3904, 2n4401, 2n4123. I’ve tried to describe my understanding of its operation at the bottom of this post. One important note, 2n3904 and 2n4401 both have max collector voltage of 60v. I am seeing up to 55 volt spikes under certain conditions (badly mis-tuned tank), which is a little close for comfort. Okay for homebrew if one is prepared to replace a blown part. I have had no problems yet. Normal operating conditions are much lower, around 10-15 volts peaks.

You sent me two inductors, a 220uH/1.9 ohm and a 1mH/11 ohm. I’ve been using a 150uH/3.2 ohm. They all are equally effective with one caveat. Different parts have different DC resistances, which is in series with R2 and will alter current draw (and output power). You observed less current consumption while using the 1uH part. This may be due only to its higher DC resistance, nothing to do with inductance. The 1mH’s higher inductance may be just high enough to begin to restrict high audio bandwidth. I saw some roll-off at 20k, a couple db’s compared to lower inductances. I leave it to you and others who can hear the difference!

I find the LM386 power rails should be “stiff”, it helps to place a 100uf cap very near it across its power leads. A cap on the chip’s pin 7 is inadequate and in fact I am leaving pin 7 unconnected, getting full benefit from the 100uf cap. Another difference from our earlier attempts is that I am feeding audio to the LM386 audio using its + input pin, which is contrary to 35Z5’s design. I do this in order to ground the – input pin, which shifts the DC bias of the chip’s output (pin 5) higher by several 10ths of a volt. I have not found a downside to using this arrangement and I intend to use the - input for pre-emphasis in my own transmitter.

With schematic values shown using a 9v supply, including an LED wired full-time as on/off/peaking indicator, I calculate almost exactly 100mw into my antenna. It puts out a strong and clear signal. While not a super-efficient design (800mw from the supply for 100mw output, that’s 12.5%), nowhere near as efficient as the 35Z5 design, it sounds good and can easily put out the legal power limit. I put a scope probe on the junction of the tank coil and variable cap. After re-peaking to make up for the probe I was astonished to see over 125 volts p-p at 0% modulation and nearly 275 volts p-p at full modulation! I am sure that with no probe to load it down the actual p-p voltage is higher. I have no prior experience with transmitters and at first I did not believe it possible, so I dug out an NE2 neon lamp. It glows when I hold a lead in my fingers and touch the bulb’s envelope to the antenna or around the top of the tank coil. My tank coil is nothing special, just a 400uH magnet wire coil on a plastic bottle, and I am awestruck as I am sure the early radio experimenters were.

I mentioned in an earlier post that I have some high audio frequency roll-off visible on the radiated signal. It must be the Q of the tank circuit. I can detune the tank a bit which greatly improves response, but this of course reduces radiated output. Is there a better way to reduce Q than to detune the variable cap? Maybe the output circuit (Q1) is not low enough impedance?

DESCRIPTION: 35Z5’s design uses the voltage and current available from the LM386’s high current output to modulate the power input to a crystal oscillator. It works very well just a handful of parts. This circuit adds a few parts for a different approach that provides deeper modulation and higher output. Q1 operates as a high speed switch controlled by the oscillator (1mHz). Current to be switched is provided by the LM386, and is switched into the tank matching circuit at the oscillator’s frequency. R1 lowers current draw from the oscillator into Q1’s base, which is otherwise wasted as heat. Q1 is not a perfect switch and some current is required into the base, so R1 can be tweaked for a particular Q1 device if necessary. A diode in series with the emitter changes Q1’s DC operating points and seems to allow more consistent performance from one device to another. A downside is that it reduces maximum available drive current (from LM386) through Q1. R2’s value can be lowered to compensate. A second downside is the base voltage can travel even lower below device cutoff(due to tank coil’s kickback). For some devices, this apparently slows down the device’s recovery time at turn on at every cycle of the oscillator. A diode from base to emitter will clamp the base’s negative voltage and decrease turn-on time, thus allowing slightly higher total output. I use a base-ground clamp instead. A bypass cap at the emitter diode ensures good ac ground and seems to improve modulation linearity, more or less depending on the Q1 device. C10, 200pf, is often not necessary and gives no benefit for most Q1 devices but for some devices I have here (including a batch of 2n3904) its presence increases radiated output. I don’t fully understand the mechanism involved so I won’t attempt to explain it. Try it for yourself and if you don’t see a benefit then leave it out.

edit: schematic updated here, same schematic as in post #55: http://antiqueradios.com/forums/viewtopic.php?p=2823766#p2823766


Attachments:
Modified 35Z5 transmitter rev3 sml.jpg
Modified 35Z5 transmitter rev3 sml.jpg [ 95.86 KiB | Viewed 1375 times ]

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Last edited by richfair on Mar Wed 07, 2018 9:32 pm, edited 2 times in total.
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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Tue 27, 2018 8:32 pm 
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Well gentlemen, I'm impressed... Glad my basic transmitter(designed without any real engineering experience) was at least good enough to merit refinement...

Thank You!!

This Tx was originally presented by Mike Toon, but I had issues with feed back into LM386 causing oscillations and high current draw... My intent was build a stable unit without those problems, bypass cap on audio input and coil between audio and osc cured those issues... Also RF tuning is of my design... I did try switching audio input but unable to determine that it made a difference so left that as original...

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Wed 28, 2018 3:10 am 
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Rich; Nice job!

I changed mine to match your schematic. I have a few 1n4148 on hand. I agree with your conclusion on L1 so I went to a 220 uh that I had. I did not use the LED so I ended up putting in a 75 ohm wire wound pot that I had in the junk box for R2 and just dialed in 90 ma total on the 9v supply with no modulation and antenna properly peaked. Sounded much cleaner there. As it approached 120 ma the audio was degraded. Not sure why. C10 did not give me any more signal but the carrier waveform was cleaner, so regardless it will stay. D2 does improve the modulation. No distortion of the peaks that I could see all the way to almost 100%. The main thing is the excess current I started with mostly just created heat with the 386 getting to about 140 degrees along with the inductor. I am interested to try some other transistors and see how they work.

This now adds about 9 components from the original but still is within the "easy" build category that will fit on a protoboard. Does not add much cost either. Now that it is more stable I think I would like to experiment with other oscillator sources including Macrohenry's synthesiser.

Rick

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Wed 28, 2018 4:01 am 
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Tom, the key is your tank matching circuit. It really builds up a head of steam.

Rick, thanks for letting me play with you! I fully intend to use this with my compressor/limiter version as soon as I am able to return to that project. Macrohenry suggests to use a mosfet instead of transistor. A mosfet should really rock 35Z5's tank!

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Wed 28, 2018 4:55 am 
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richfair wrote:
Rick, thanks for letting me play


It's a good team effort. I enjoy collabortive work. Particularly since I lack the solid state background to do this alone. I really appreciate this forum.

Edit: Tom; I appreciate your work to get this circuit stable originally. Makes it possible for almost anyone to build and get it to work properly. I now have 2 of the original ECS transmitters and also one of your two tube designs which is still my workhorse. Thanks for your contributions.

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Last edited by black85vette on Feb Wed 28, 2018 5:15 am, edited 1 time in total.

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 Post subject: Re: Variation on the 35Z5 ECS oscillator transmitter
PostPosted: Feb Wed 28, 2018 5:03 am 
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Excellent work, guys! This is a fine candidate to take the place of the SSTrans kit. As Rick pointed out, this version can employ a separate frequency synthesizer. In earlier versions, that wouldn't work because the frequency synth can't be directly amplitude modulated like a crystal oscillator can.

Next, if reliable audio processing is made available as an easy add on, then circuit boards can be ordered and all those folks looking for an AM transmitter can be directed to a transmitter that hits on all cylinders (except for tubeophiles!) :P

I think this work is an admirable tribute to 35Z5's design, building on its elegance.


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