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 Post subject: Barebone 74HC4053 AMTX
PostPosted: Aug Fri 14, 2020 8:17 pm 
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Posts: 398
For 6-9MHz but with it will work from 1 to 30MHz.
100% modulation and output will drive 50ohm. If input to IC is < 100mW then it would make a wonderful low power MW transmitter with 1MHz crystal. As simple as it gets..


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Sat 15, 2020 12:42 am 
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Joined: Aug Thu 06, 2015 2:20 am
Posts: 283
I was hoping you could make some changes to your schematic that would make it clearer for any interested in the technique of using the mutiplexer.

Anyone with a Windows computer can use Microsoft Paint to create schematics faster than drawing them and taking a photograph of them.

Chromebook users can use a Java online extension called PAINT.

.https://jspaint.app/#local:51b1b171acab7

Linux users can use a very similar program called Kolourpaint4.

Simply cut and paste symbols from other schematics on the internet. After creating a few schematics you will have your own library of components.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Sat 15, 2020 5:38 am 
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Joined: Mar Thu 01, 2018 1:30 am
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My laptop is dead. I've ordered a new one. I drew another image in a haste but it is understandable. Chip is 74HC4053. The oscillator collector resistor and feedback capacitor may need some tweaking. The crystal can be 1 to 30MHz.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Sat 15, 2020 5:11 pm 
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Joined: Aug Thu 06, 2015 2:20 am
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Thank you, but why in both of your schematics are there two Pin 2's and no Pin 12?


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Sun 16, 2020 7:50 am 
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Sorry one pin is 12, not 2. My absent mindedness.
Could you draw a proper schematic?

I guess proper matching to a wire antenna is also important.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Sun 16, 2020 5:21 pm 
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Joined: Aug Thu 06, 2015 2:20 am
Posts: 283
Dare4444 wrote:
Could you draw a proper schematic?

I don't know whether my schematic is proper or not, but I thought that the technique was interesting.

RF from the oscillator is DC coupled into Pins 9,10 and 11. This toggles 3 switches at the RF rate.

The antenna is connected to Pins 4, 14 and 15. These pins are switched between Ground and the DC output of the LM386 which is connected to Pins 1,3 and 13 which amplitude modulates the output at the antenna.

Grounding Pin 6 enables the switches.

Three switches are used in parallel to increase the output capability.


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Last edited by LM386 on Aug Sun 16, 2020 9:16 pm, edited 2 times in total.
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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Sun 16, 2020 5:47 pm 
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Yes. Schematic is correct. The DC coupled oscillator should trigger the switches just fine. They are connected in parallel to lower the on resistance by a factor of three from 80ohm to 27ohm. RF output should be around 2mW with 2Vpp swing of LM386;at 5V as the chip is looking into a 27 + 50 ohm load. Power is thus wasted in the switches and rest of it is coupled to the antenna. A 50ohm to 1.5K L match should get us maximum range from this simple TX. A single 2n7000 in class AB mode will also amplify the signal provided its DC power input remains <100mW when no audio is present.

But the chip and a wire antenna is enough to cover your living room with high fidelity AM. It sounds fantastic as distortion is very low. 100% modulation is not a problem. It will work from 500KHz to over 30MHz.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Mon 17, 2020 12:09 am 
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Joined: Aug Thu 06, 2015 2:20 am
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I thought that a block drawing would better explain the simplicity of the technique.


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Last edited by LM386 on Aug Mon 17, 2020 3:15 pm, edited 1 time in total.
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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Mon 17, 2020 1:35 pm 
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Location: Burke, VA 22015
I built an AM modulator based on the same technique more than two years ago.

https://antiqueradios.com/forums/viewtopic.php?f=12&t=340999

It is basically based on the buck switching power converter. The audio output from the LM386, offset to about half the power supply voltage, is chopped by a square wave at a desired carrier frequency. This results in a unipolar AM signal that can be transformed to bipolar by a high-pass filter. For a perfect 50% duty-cycle square wave, there are only odd harmonics in the AM output. For square waves with unequal on and off cycles, there will be even harmonics. These harmonics can be filtered out by a low-pass or band-pass filter such as the antenna matching network.

I used BJT transistors for the switches instead of an multiplexer IC to minimize switch loss and not to be restricted by low supply voltage. The main drawback with my version is that it cannot handle very high modulation index due to non-zero saturation voltage of the transistors. In retrospect, there exist switch/multiplexer ICs with low on-resistance and high operating voltage such as the DG1413EEQ quad SPST switch with 1.5ohm on resistance and 24V operating voltage. Probably it's time for me to reconsider using this IC instead of discrete transistors.

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Binh


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Mon 24, 2020 6:08 pm 
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Hi,
Whats happens if switch between audio and -audio (inverse phase), instead audio and ground?

My AM modulator with 4053 switch between audio and adjustable bc bias, but, never tried to feed a inverse phase audio to this point.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Mon 24, 2020 7:27 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 398
Then carrier is suppressed and it puts out DSB.
Try it with two lm386 and a 2n3904 phase splitter for driving the audio chips. The output can then be fed into a IRF510 mosfet for a few watts of power on 40/20m ham bands.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Tue 25, 2020 6:35 pm 
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Location: Warner Robins, GA
Some time this afternoon when I get home I'll draw up a schematic in Microsoft Paint.

Now can the XTAL and transistor be replaced with a TCXO? Maybe then a switch arrangement could be used to select between several TCXO for different frequencies.

I wonder if it is possible for instance to use two TCXO and maybe two more of those switches to select between the two TCXO so one could put out a signal on two frequencies. Would only be practical if using no antenna tuner though.

I'm very tempted to build this and once I get the money I might just breadboard it.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Tue 25, 2020 8:26 pm 
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Joined: Mar Thu 01, 2018 1:30 am
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Great. I'll draw updated schematic with modulation adjustment pot. 74hc4053 is good for SW but for MW CD4053 is okay. Cheap on eBay from China


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Wed 26, 2020 12:18 pm 
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Posts: 398
This is better.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Wed 26, 2020 3:24 pm 
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Cool. I've been a bit under the weather, but if I feel better when I get home from work I'll draw it up in Microsoft Paint.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Wed 26, 2020 4:58 pm 
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Posts: 398
Also add 1k resistor and 10u cap between pin 1 and 8 of LM386.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Wed 26, 2020 5:26 pm 
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Ok.

I may just build one of these.

In my current two tube AM transmitter I use a LM-386 to drive a VU meter so if I do build this circuit I'll add the meter to it.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Sun 30, 2020 5:12 pm 
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Great! I believe the range would he less than 10 feet without a proper 6ft matched antenna.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Sun 30, 2020 10:55 pm 
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Oh ok.

So the antenna would need to be 50 ohms right?

Could I feed it to another stage to boost the output and make it higher impedance or would that require a tuned collector circuit for maximum power transfer?

Keeping in mind I would want it to be the legal output and no higher if possible.


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 Post subject: Re: Barebone 74HC4053 AMTX
PostPosted: Aug Mon 31, 2020 10:08 am 
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Yes. Place a low pass filter and then connect a dummy load of 50ohm and then measure the voltage peak with a diode probe. This should give power output in mW. Also measure the input power to the 74hc4053 chip. It should not exceed 100mW with no modulation present. If power output is decent (15mW for example) and DC input is less than 100mW then only a matching network would be required to match the chip's output to a high impedance short wire antenna to cover your entire house. Modulation is high quality and approaches 95% to 100%


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