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 Post subject: Looking for two beta testers for AM Transmitter
PostPosted: Sep Thu 09, 2021 3:17 am 
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I'm getting close to finishing work a crystal controlled LM386 transmitter that mates my frequency synthesizer with a typical LM386 transmitter. Main design goals are:

100mW capability

12 volt DC power source

Audio input that works with phones, stereo amps, mp3 players, etc.

Keep it inexpensive

5 foot plug-in antenna so it can fit anywhere and be moved easily

Stock tuning at the high end of the MW band for best antenna efficiency. If the low end is desired, more wire can be added to the loopstick.

Onboard LED antenna tuning and modulation monitor (see it working in video)

Circuit board no bigger than 3.5" x 2.8" so I can get the best price at ExpressPCB ($51 per 3 boards). Here's a photo of a 12V linear regulated power supply board they made for me that is the same size, 3.5" x 2.8" .

Attachment:
2021-09-08 20.43.56.jpg
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Although it's advisable to directly solder the ICs, IC sockets would be included in the parts list for those who prefer them.

The board can support two versions: Bipolar output transistor (my favorite), or a FET. FETS can have different pinouts and the board natively accommodates that.

When my board order of three comes in, I'll keep one to work with, so I'll have two extras. Right now I'm looking for two volunteers who have the time to populate the other two and test them and report on results. I'll supply the boards and parts for these two at no charge. Once these are beta tested and fine tuned, then I can take orders for as many boards as demand requires, sell them at my cost, and provide a list of parts from Mouser or DigiKey. If a bunch of folks want one, it would be more cost effective for me to just order and supply the parts and divide the cost equally among the takers as long as providing a kit doesn't run afoul of the FCC.

I solved the problem of noise noted in a current thread by installing a bypass capacitor.

The loopstick is made of 16 feet of # 36 magnet wire scramble wound on a syringe body. I put double sided tape on the syringe where I want the wire, chuck the other end in a drill and run it at slow rpm while running my thumb and forefinger with the wire back and forth to create a basketweave style coil. It's very easy and fast. The ferrite core is made by Fair-rite, ordered from DigiKey. It's mated to the end of a 1/4" nylon bolt with heat shrink. The nylon nut is attached to the end of the syringe with hot melt glue or even tape. It's a dandy and performs far better than a fixed inductor with a variable cap.

I'm on my second iteration using the iron-on PCB method, so it's still somewhat cobbled together. In the following YouTube videos I took today, you can see the board with the functioning LED antenna tuner and modulation indicator If you use good speakers or headphones you can hear how good it can sound.

https://youtu.be/KPmtawKGQTE

https://youtu.be/-BVA3rKnknI

The power supply board shown above is already designed and tested. Because it's the same form factor as the transmitter, the transmitter can be mounted on top of it and to fit neatly in the same enclosure.

I receive boards about a week after I order them, which I plan to do in a couple of days. If you are interested in being one of the two beta testers, and have the time and are willing to post here to help with the development, just reply here so we all know (no need to PM me.)


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Thu 09, 2021 3:29 am 
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I would give one a try.

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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Thu 09, 2021 3:53 am 
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I just remembered that on the other thread, N2LXM and Colin expressed interest in a board when the bugs are worked out. It doesn't sound like that translates into willingness to beta test, but after Paul who definitely will beta test, it would only right to give each them first dibs as a beta tester (if either chooses) since they spoke first. You guys want to weigh in?


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Thu 09, 2021 4:10 am 
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Your call. I am willing to help if need be.

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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Thu 09, 2021 2:25 pm 
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Be glade to Beta test one for you. Count me in.


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Thu 09, 2021 3:38 pm 
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Good deal. I will get both of you guys your boards after I have received them. I have a little bit more configuring to do before I send the order. PM me your address is so I can get them in the mail.


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Thu 09, 2021 3:48 pm 
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Where's the 386 TX schematic? How does it work?
The output of synthesizer can directly drive a 2n7000 mosfet modulated by 386 chip. A handful of coils and capacitors match it to 6ft antenna. Last time I tried, the audio quality rivaled that of FM.


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Thu 09, 2021 4:43 pm 
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Dare4444 wrote:
Where's the 386 TX schematic? How does it work?
The output of synthesizer can directly drive a 2n7000 mosfet modulated by 386 chip. A handful of coils and capacitors match it to 6ft antenna. Last time I tried, the audio quality rivaled that of FM.

Correct. Mosfet gate is directly driven from the output of the synth, or bipolar through a 2K resistor. Drain is fed by the LM386 output through 10 ohm resistor and choke. IRF 520 works as well as 2N7000 and the bipolar MPSA18, but IRF540 works with less output. Focusing on the upper end of the MW band, all that's needed to match to antenna is the 10pF cap to ground and the loopstick to the antenna. Scope probe near the transmitter picks up a nice clean sine wave.

Schematic for synth is at this link http://www.tompolk.com/radios/frequencysynthesizer/freq_synth.png, although the board now has some modifications. Schematic for LM386 is still in my head, but you can easily derive it from the board layout below.

I'm still experimenting with the input to the LM386. Seems some audio sources want to see a lower impedance than that provided by the 10K pot, so I need to see what happens with a 1K pot. And I want to find a way to add a couple of 10K resistors to sum the L & R channels so a 3.5mm stereo jack can be used.


Attachments:
Image22.jpg
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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Sat 11, 2021 3:06 pm 
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Wow, the PCB looks fantastic. Nice work man. What would be the price of the complete kit?


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Sat 11, 2021 10:52 pm 
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Dare4444 wrote:
Wow, the PCB looks fantastic. Nice work man. What would be the price of the complete kit?

Most of the parts, including the PCB ($21) are about $56.00. The PCB might be noticeably less in a bulk order. This is without the 12V supply. A complete linear regulated 12V supply with the matching size PCB (another $21) would be about $34.00 so the unit would be AC powered without a wall wart.

The following parts list is presented as two clickable images so it's easy to read. If anyone wants to start building now, it's pasted in text below the images. (I don't know how to keep the formatting when pasting text. ) It iincludes parts highlighted in yellow that are higher grade than probably needed. The whole list includes some parts that beta testers may find are not needed. There will be three of us installing the minimum number of parts. If the extras are not needed, the PCB can be simplified to omit them.
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AM TRANSMITTER WITH SYNTHESIZED FREQUENCY
Resistors Value Quantity Digikey Price Parts Price Digikey # Mfg #
1/4 Watt 10 1 $0.10 $0.10 S10CATR-ND NMF14FTC10R0
1/4 Watt 1K 3 $0.10 $0.30 RNF14FTD1K00TR-ND RNF14FTD1K00
1/4 Watt 2.2K 2 $0.10 $0.20 RNMF14FAD2K20CT-ND RNMF14FAD2K20
1/4 Watt 4.7K 2 $0.10 $0.20 S4.7KCATR-ND RNMF14FTC4K70
1/4 Watt 10K 4 $0.10 $0.40 RNF14FTD10K0TR-ND RNF14FTD10K0
1/4 Watt 47K 8 $0.10 $0.80 RNF14FTD47K0TR-ND RNF14FTD47K0
1/4 Watt 100K 3 $0.10 $0.30 RNF14FTC100K-ND RNF14FTC100K
Pots 1K 1 $0.58 $0.58 2368-500E-0346-ND 500E-0346
Ceramic Caps 10 pF 1 $0.10 $0.10 2747-CCD-107S100JK02-ND CCD-107S100JK02
22 pF 1 $0.10 $0.10 2747-CCD-208B220KK72-ND CCD-208B220KK72
33 pF 1 $0.33 $0.33 1928-1287-ND FKP2O100331D00KSSD
100 pF 1 $0.10 $0.10 2747-CCD-109B101KK02-ND CCD-109B101KK02
Poly Alternative 100 pF 1 $0.41 $0.41 FKP2G001001D00JSSD 1928-1265-ND
1 nF 1 $0.29 $0.29 445-175035-1-ND FG28X7R2A102KNT06
10 nF 2 $0.38 $0.76 445-173172-3-ND FG18C0G1H103JNT06
47 nF 1 $0.54 $0.54 1928-1505-ND MKP2D024701C00JSSD
Ceramic Caps 100 nF 5 $0.23 $1.15 399-4151-ND C315C104M5U5TA
Poly Alternative 100 nF 5 $0.66 $3.30 1928-1386-ND MKP1D031003G00JSSD
10 uF 1 $0.17 $0.17 493-15134-ND UFW1H100MDD
100 uF 1 $0.24 $0.24 493-15119-ND UFW1C101MDD
Trimmer cap 60 pF 1 $0.77 $0.77 2447-GKG60015-ND GKG60015
Diodes 1N4148 1 $2.75 $2.75 2721-1N4148-ND 1N4148
LED LED 1 $0.00
Transistor 2N3904 1 $2.70 $2.70 2368-2N3904-ND 2N3904
Transistor MPSA18 1 $0.00 Not available from DigiKey * either transistor or FET, not both
Transistor Alt. 2N5232A 1 $0.69 $0.69 1514-2N5232APBFREE-ND 2N5232A PBFREE
FET 2N7000 1 $2.00 $2.00 2368-2N7000-ND 2N7000 * either transistor or FET, not both
IC CD4060 1 $0.68 $0.68 296-2060-ND CD4060BE
IC CD4046 1 $0.65 $0.65 296-36086-5-ND CD4046BEE4
IC CD40103 1 $1.68 $1.68 296-14080-5-ND CD40103BE
IC LM386 1 $1.36 $1.36 296-44414-5-ND LM386N-1/NOPB
Crystal 10.24 mHz 1 $0.54 $0.54 300-6022-ND HC-49/U-S10240000ABJB
$0.00
IC Socket 8 pin 1 $0.47 $0.47 ED90048-ND 110-44-308-41-001000
IC Socket 16 pin DIP 3 $0.74 $2.22 ED90050-ND 110-44-316-41-001000
Audio Jack 3.5 mm stereo 1 $1.43 $1.43 889-1822-ND ACJS-MV35-3S
Switch Power 1 $0.00
Switch 16 pin DIP 1 $0.91 $0.91 206-8 CT2068-ND
Syringe 1 $0.00
Ferrite core 1 $0.73 $0.73 4061287011 1934-1044-ND
1/4" Nylon bolt 1 $0.00
1/4" Nylon nut 1 $0.00
#36 magnet wire 16 feet 1 $0.00
Choke 2 mH 1 $0.68 $0.68 RLB1314-222KL-ND RLB1314-222KL
Circuit board 3.8" x 2.5" 1 $21.00 $21.00
Antenna wire 5 feet 1 $0.00
Antenna post 1 $0.00
Antenna connector 1 $0.00

Parts Total Price $51.64
$0.00
Power Options $0.00
Power Jack Coaxial 1 $0.62 $0.62 2057-ADC-H-010-1-ND ADC-H-010-1
12 Volt Power Supply Below
Transformer 12V 1 $8.81 $8.81 237-1602-ND TCT3-03E07AE
Diodes 1N4007 4 $0.09 $0.36 2439-1N4007-ND 1N4007
Regulator LM7812 1 $1.97 $1.97 LM340T-12/NOPB-ND LM340T-12/NOPB
Capacitor 100 nF 2 $0.23 $0.46
Capacitor 470 uF 1 $0.53 $0.53 493-5931-3-ND UVR1V471MPD1TD
Capacitor 1000 uF 1 $0.89 $0.89 493-12594-3-ND UVK1V102MHD1TO
LED LED 1 $0.00
Resistor 2.2K 2 $0.10 $0.20 RNMF14FAD2K20CT-ND RNMF14FAD2K20
Circuit Board 1 $21.00 $21.00 Custom
$34.22


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Sat 11, 2021 11:12 pm 
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Check www.futurlec.com cheap components!


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Sun 12, 2021 12:42 am 
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Dare4444 wrote:
Check http://www.futurlec.com cheap components!


Well, I know what I'm doing tomorrow: Repopulating the spreadsheet with Futurlec pricing. $47 vs $61 for three boards AND they use ExpressPCB files.


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Sun 12, 2021 8:14 pm 
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OMG, using futurlec reduces the parts price to about $22.00, including the circuit board IF there's a minimum order of 10. That's $8.90/board, whereas 3 boards is about $16/board.

Futurelec doesn't have all the parts, so six would need to be ordered from Digikey or Mouser. Digikey has the ferrite bar, Mouser doesn't so it makes sense to order the rest of the parts from Digikey.

I'm ready to order the beta test parts from futurlec and I'll try later today to order the PCBs from them to see how they compare with ExpressPCB that I know are good.


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Tue 14, 2021 4:11 am 
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This is a PCB artwork that follows the guidelines and recommendations discussed in the other threads. The top ground plane is not shown to reveal the bottom traces. Hopefully it does not exhibit the same problems you have been experiencing.

I can have 30 of these boards produced by my favorite fab house in less than a week for $1.33 each. With express international shipping, the total cost amounts to $3 more than what you paid for three boards. I will be glad to send you one for testing and compare notes.
Attachment:
AM_TX_2.png
AM_TX_2.png [ 53.09 KiB | Viewed 780 times ]

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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Tue 14, 2021 5:55 pm 
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bb.odin wrote:
This is a PCB artwork that follows the guidelines and recommendations discussed in the other threads. The top ground plane is not shown to reveal the bottom traces. Hopefully it does not exhibit the same problems you have been experiencing.

I can have 30 of these boards produced by my favorite fab house in less than a week for $1.33 each. With express international shipping, the total cost amounts to $3 more than what you paid for three boards. I will be glad to send you one for testing and compare notes.
Attachment:
The attachment AM_TX_2.png is no longer available

Thanks, Binh, those are amazing prices. I should probably take you up on your offer.

Here's where things stand on this project. Right now I want to order just three boards for beta testing.

1. Parts for beta test have been ordered from Futurlec.
2. 3 boards ready to be ordered from ExpressPCB, ~ $20 each.
3. 3 boards almost ready to be ordered from Futurlec, ~$15 each.

Now I need some help in understanding professional PCB ordering. I'm afraid I'm confusing top side and bottom side. First here's a photo of the DIY board I made using ExpressPCB software but with the DIY iron-on transfer method. I would think the "TOP side" is the side where you can see the components. So the following picture is the top side, correct?

Attachment:
2021-09-13 13.23.58.jpg
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In this case, the traces are on the bottom side. However, in the following ExpressPCB screenshot, they show the orange traces to be TOP layer, green traces and ground plane, BOTTOM layer. IThe boards I order from ExpressPCB have the majority of traces (orange) on the opposite side of where the components are placed. Yet their software labels that as the UPPER layer, which to me means TOP side.

In the following ExpressPCB screenshot, the board is fabricated such that the green traces and ground plane are what you see when you populate the board. The orange traces are on the other side of the board, so you are seeing them here with X-Ray vision. So you turn over the board to see the orange traces (which would then appear in reverse) to solder the components.

Attachment:
Image28.jpg
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This works with ExpressPCB, but I want to give Futurlec a try. Here's what they sent me. Is it the same thing, or is it in reverse?


Attachments:
Image33.jpg
Image33.jpg [ 212.28 KiB | Viewed 753 times ]
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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Tue 14, 2021 6:03 pm 
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I not the board fab expert you are looking for, but referring to the PCB as "component side" and "solder side", would remove any ambiguity.

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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Tue 14, 2021 7:13 pm 
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Macrohenry wrote:
This works with ExpressPCB, but I want to give Futurlec a try. Here's what they sent me. Is it the same thing, or is it in reverse?

It's not the same thing. The traces are put on the top side which is the same side as the components and silk screen. The ground plane is put on the bottom side. This is ok but that's not what you want. To avoid confusion, you need a layer stack-up instruction such as this:

Layer 1 Copper (Top/Component Side) - Ground Plane
Layer 1 Silkscreen
Layer 1 Solder Mask
Middle Layers (if any)
Layer 2 Copper (Bottom/Solder Side) - Traces
Layer 2 Silkscreen (if any)
Layer 2 Solder Mask (if any)

Since there is a ground plane, there is no need to route the ground traces. You can simplify routing by getting rid of them. See my board which doesn't have any ground traces where there is a ground plane on the other side.
Attachment:
AM_TX_3.png
AM_TX_3.png [ 62.24 KiB | Viewed 718 times ]

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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Tue 14, 2021 9:23 pm 
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bb.odin wrote:
Since there is a ground plane, there is no need to route the ground traces. You can simplify routing by getting rid of them. See my board which doesn't have any ground traces where there is a ground plane on the other side.
[/attachment]


Ah, yes, makes perfect sense. I'll look into how to connect to ground plane with the software I'm using.


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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Fri 17, 2021 4:36 am 
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I rearranged the small audio amplifier's input section to include the resistive summing node for the left and right channels. I also managed to squeeze in your visual tuning aid circuit while keeping it away from the high-voltage antenna output. I added a bypass capacitor in the emitter circuit to quiet down the RF and a base-protection diode. The base is coupled to the antenna by a gimmick capacitor of about 0.7pF. The only place available for this RF-rich circuit is unfortunately close to the sensitive crystal network. Hopefully it doesn't cause any interference. At this point, my version of the board is functionally equivalent to yours. I had 30 boards on order (for $62 total) and should get them in 5 days. Here is how its component side and bottom sides should look like (when viewed from top):


Attachments:
top_view.png
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xray_view.png
xray_view.png [ 89.84 KiB | Viewed 605 times ]

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 Post subject: Re: Looking for two beta testers for AM Transmitter
PostPosted: Sep Sat 18, 2021 1:13 am 
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Macrohenry wrote:
OMG, using futurlec reduces the parts price to about $22.00, including the circuit board IF there's a minimum order of 10. That's $8.90/board, whereas 3 boards is about $16/board.

Futurelec doesn't have all the parts, so six would need to be ordered from Digikey or Mouser. Digikey has the ferrite bar, Mouser doesn't so it makes sense to order the rest of the parts from Digikey.

I'm ready to order the beta test parts from futurlec and I'll try later today to order the PCBs from them to see how they compare with ExpressPCB that I know are good.


Futurlec all genuine, Thailand based. I used to order from them.
Another indian site is https://www.electronicscomp.com/

They are even cheaper!


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