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 Post subject: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Thu 12, 2022 7:28 pm 
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Macrohenry's Frequency Synthesized Transmitter

Presented here for ARF members' use is an inexpensive and simple-to-build Part 15 AM transmitter whose frequency is set and stabilized by a standard PLL frequency synthesizer. It consists of the mating of Macrohenry's $12 frequency synthesizer and an LM386 based transmitter.

Pictured below are two builds. The first is inside a $10 aluminum box from Amazon. The second build pictured mates the transmitter board with a second board containing an AC mains power supply and onboard audio compressor/limiter/constant volume circuit. That enhancement is used when you have a wide variety of source material recorded at different volumes.

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This transmitter features:

Excellent fidelity and range: No noticeable noise or volume change over 50 feet
Rock solid frequency stability, PLL based, set by 8 position DIP switch
Covers full 530-1710 kHz MW band in precise 10KHz steps so transmitter can operate in the far upper end of the band where operation is more efficient
Ease of construction: Ground plane PCB commercially produced in the USA
Constructed with standard parts, widely available and ubiquitous, less likely to become obsolete
Single supply power, easily and noiselessly powered by 12V battery or linear/analog wall wart (switchers can be noisy)
Compact 5 foot antenna
Simple antenna tuning with built-in LED resonance indicator
LED doubles as modulation indicator

LM386 transmitter topography has been developed in great part by members here on ARF. You can search posts by 35Z5 and Mike Toon for examples of these elegantly simple and effective fixed frequency transmitters.

The $12 frequency synthesizer was first presented by Macrohenry and successfully used by others prior to wider adoption by ARF members. In 2015 ARF member Colin Ames took orders for PCBs and distributed them among ARF members. viewtopic.php?f=12&t=285198&hilit=synthesizer That was for a single sided board and prices are up now, this uses plated through holes, so best not to expect an $8 board.

One of the biggest benefits of this transmitter is that it's been developed by active ARF members. The design and operation are widely understood by those here and free help is available. Simple circuits like this are prone to be customized and modded. For example, as pictured above, an audio compressor board can easily be mated to this transmitter. Such circuits have appeared in recent threads.

If you want to know more about the circuit and its development here on ARF, here's that thread: viewtopic.php?f=12&t=401983 A BIG THANKS for suggestions from richfair and bb.odin, and processhead, who beta tested.

Here's a YouTube video of the transmitter playing. Audio source is local FM station. Video and audio are recorded with my smartphone. Note the absence of noise and fading as I walk through the yard.

https://youtu.be/_M1BUnnKl0Y
https://youtu.be/KPmtawKGQTE Testing during development showing tuning LED acting as modulation indicator.
https://youtu.be/llyl60evRCs Test with Phil Collins music

HOW CAN YOU GET ONE? HOW MUCH?

1. PCB: I order from Express PCB and will supply boards to ARF members at my cost plus mailing. ExpressPCB is not the least expensive but their boards are as good as it gets. Price is dependent on quantity.

2. PARTS: I'll supply a parts list. Last year I got most parts from Digikey for under $55.00. I also ordered most from Futurlec for under $25.00, but it took weeks to get those. Included in the parts list at separate cost are parts for a linear power supply, as switching power supplies are not recommended. Last year's price spreadsheet is attached here as an Excel spreadsheet. It will need to be updated.

To order PCBs, I need to know the quantity to order. I'll be taking orders for boards until May 31. After that, I'll contact all recipients to have them send me the board cost plus my cost to mail to them. Currently there are no plans to provide a complete kit. This offering is best seen as a DIY project where there will be plenty of support.

Current price estimates from ExpressPCB:

Double sided ground plane, plated through holes, no silkscreen or solder mask. This means that you'll need to refer to a parts placement sheet as the parts will not be labeled on the board itself. See first photo in this posting for an example.

5 boards, $21.41 each
10 boards, $14.30 each
15 boards, $11.93 each
20 boards, $10.75 each

Add silk screen component side, solder mask both sides
10 boards, $18.06 each, max quantity 10 (Would need to be separate orders if more than 10 members want one)

If you want one, you can post your request and questions on this thread. If you want to use the ExpressPCB file to order on your own, PM me with your email address and I'll email you the ExpressPCB file. I prefer not to use PM for ongoing conversations, so please post questions here so all can benefit, thanks.


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Last edited by Macrohenry on May Fri 20, 2022 4:43 pm, edited 3 times in total.
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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Thu 12, 2022 8:07 pm 
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Joined: Apr Wed 13, 2022 4:55 am
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Location: Solana Beach, CA 92075
I would like to buy one PCB/kit. Thanks! Michael


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 3:34 am 
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Location: Equinunk PA 18417
This is a wonderful offer! Macrohenry's transmitter is inexpensive yet a very, very good performer with excellent audio quality, very low audio distortion, deep modulation, and a legally-strong rf output. It compares well to any and all other part-15 legal transmitters. As Macrohenry said, various iterations of the circuit have been built by many folks on ARF and elsewhere, it is a proven approach, and most are stunned that so few parts can work so well. I was. The PLL frequency control is a great advantage that allows (re)tuning to any standard US broadcast frequency (with 10kHz spacing) with stability and accuracy. If I didn't already have my own versions of this thing I would order without hesitation.

I believe this PLL circuit can be easily modified for 9kHz channel spacing if desired, using a different master crystal, but that's for another discussion.

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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 5:01 am 
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richfair wrote:
This is a wonderful offer! Macrohenry's transmitter is inexpensive yet a very, very good performer with excellent audio quality, very low audio distortion, deep modulation, and a legally-strong rf output. It compares well to any and all other part-15 legal transmitters. As Macrohenry said, various iterations of the circuit have been built by many folks on ARF and elsewhere, it is a proven approach, and most are stunned that so few parts can work so well. I was. The PLL frequency control is a great advantage that allows (re)tuning to any standard US broadcast frequency (with 10kHz spacing) with stability and accuracy. If I didn't already have my own versions of this thing I would order without hesitation.

I believe this PLL circuit can be easily modified for 9kHz channel spacing if desired, using a different master crystal, but that's for another discussion.


Thanks for the kind words, Richard.

I forgot to add that for those of you who missed Colin's order of the $12 frequency synthesizer, this board can be populated with just the frequency synthesizer parts so it can be used as a rock solid signal generator or in another transmitter. It tunes below 450 kHz. I used it to align my 1941 AA5 using the prescribed 1720, 1400, and 600 KHz signals. As currently configured it will not do 455 or 456 kHz, as it tunes in 10 kHz increments. I'm working on a simple add on to get those IF frequencies.

Yes, it could be could be configured with 9kHz with modifications.

Just a reminder, if you want a board, please post the quantity you want here, not in PMs. I'm not keeping track of it in PMs.


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 7:57 am 
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Can we get a schematics diagram, so that we can learn what this is? (I clicked through the links but the pictures -supposedly the schematics- don't show up)


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 10:11 am 
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I'd like to add that if anyone experiences hum with the transmitter try a 1:1 audio transformer on the audio input to isolate the transmitter ground from the audio cable ground if all else fails to eliminate the hum.

The reason the transformer can reduce hum is because without it the audio cable ground and the grounds of whatever the audio cable is connected to acts as part of the transmitter's ground for the antenna.

The transformer prevents that from happening as it does not pass RF.

In my only transmitter build I used the Edcor WSM-15K/15K transformer and I saw an immediate reduction in hum whereas before then the hum would change somewhat as I moved the audio cable around.

Far as the LED tuning indicator is it possible to replace it with a meter and series resistor? Also can a VU meter be added in the circuit somewhere?

Those two things may be beneficial for some.

In my transmitter build I use both and its so easy to tune and easy to set the audio level so I do not overmodulate.

Of course if the compressor is used and set for max modulation without distortion a VU meter becomes unnecessary.


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 3:59 pm 
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Tube Radio wrote:
I'd like to add that if anyone experiences hum with the transmitter try a 1:1 audio transformer on the audio input to isolate the transmitter ground from the audio cable ground if all else fails to eliminate the hum.

In all the testing I've not experienced or heard of hum being a problem. The frequency synthesizer is not susceptible to hum and the modulation section is no more susceptible to hum than any of the various LM386 transmitters already in use for years by ARF members. Due to noisy AC power lines in my house, I power my units with a 12 volt battery and I place it away from noisy AC lines. In one of the videos you can hear how noisy my power lines are when I temporarily unclip the power so the noise is the only signal on the radio, then the noise completely disappears when the transmitter is fired up.

Noisy houses: Even though my units and the others I've heard of are hum free, it's appropriate to note that for any Part 15 transmitter used, hum might be heard on receivers if such transmitter is located in the wrong parts of a noisy house. This is why Acornvalve advocates loop antennas for pantry transmitters. I don't know that an audio input transformer would help that unfortunate situation. However, if one chooses to build the matching AC power supply board, there is room on that board for an audio transformer.

Tube Radio wrote:
Far as the LED tuning indicator is it possible to replace it with a meter and series resistor? Also can a VU meter be added in the circuit somewhere?

Yes.


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 4:18 pm 
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Suppose it may just be my transmitter but without the audio transformer the level of hun changed eith the position of the audio cable, however it was connected to a mixer which used a grounded power cord.

With the audio transformer I noticed lower hum and moving the audio cable had no effect on the hum.

However my transmitter was built in a metal case so it is grounded via the power cord.

That might make a difference in whether an audio transformer does anything for the hum.

My reasoning for isolating the transmitter circuit ground from the audio cable ground is that I figured anything connected to the ground circuit of the transmitter would act as part of the antenna ground.


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 9:06 pm 
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szoftveres wrote:
Can we get a schematics diagram, so that we can learn what this is? (I clicked through the links but the pictures -supposedly the schematics- don't show up)


Schematic added to OP


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 9:13 pm 
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I would like two boards please.


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 9:24 pm 
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As one of the beta testers for Macrohenry, I can attest that these transmitters offer a lot of bang for the buck.
My point of reference for part 15 transmitters is a SSTRAN 3000 that I have had for some time now.

Macrohenry's transmitter is right up their with the SSTRAN in basic performance.

Like many of you have noted, to get the best performance out of ANY part 15 transmitter, you need to be willing to put in the effort to find the right spot in your housed to set it up. I believe ANY part 15 transmitter can be subject to hum if care is not taken to place it where the transmitter signal is not radiated into power, audio, and grounding conductors.

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...... how hard can it be?


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Fri 13, 2022 9:58 pm 
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duplicate post deleted.

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...... how hard can it be?


Last edited by processhead on May Sat 14, 2022 2:54 am, edited 1 time in total.

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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Sat 14, 2022 2:13 am 
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Joined: Nov Wed 04, 2020 5:40 pm
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Location: Scranton PA. 18505
If you have the gerbers, have you tried PCBway for prices? I get many small simple boards done for less than $1 each.


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Sat 14, 2022 2:42 am 
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HALLI wrote:
If you have the gerbers, have you tried PCBway for prices? I get many small simple boards done for less than $1 each.


Only format I have is ExpressPCB. From a recent thread they were the one that got the most votes. I'm open to other companies that multiple ARFers like. That would be the first requirement not to order from ExpressPCB. The second requirement would be to find a way to use ExpressPCB file with another company. NOTE: Any chosen company needs to be able to do plated through holes. ( e.g. farcircuits.net doesn't do plated holes.)

It probably goes without saying that if enough members order boards to get them down near that $10 - $11 range, it may not be the cheapest but it's gonna be highest quality.


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Sat 14, 2022 2:17 pm 
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Macrohenry wrote:
but it's gonna be highest quality.


Exactly. a quality board makes for a good kit that people will love building.

I've built kits with anything from quality to cheap boards and I prefer quality boards as they are much easier to solder without worrying about pulling a pad or trace.

If not for my two tube part 15 transmitter that I so dearly love and recently buying four 6GY6 tubes for it, I'd be buying one of your kits.


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Sat 14, 2022 3:29 pm 
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I would like three boards with silkscreen but I am not too picky. If most orders are for the regular boards, I’ll take three of those anyway.
Thanks for your efforts


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Sat 14, 2022 11:36 pm 
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Current status and projected price:

mjgillen -1
Dale Saukerson 2
eduardoa 3

Total 6 boards at $21.61 each.

If silkscreen is desired by those who've already spoken up, let me know. We would need ten orders, all ten wanting silkscreen and it would be $18.06 each.


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Sun 15, 2022 12:31 am 
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Location: Ventura, CA
What's the dimensions of the board so I can report what a full service place would charge? (with longer lead time though)
Also if you have it, the number of holes, smallest line and spacing.

Dave


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Sun 15, 2022 2:46 am 
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Location: Dallas, Texas, USA
I’ll take two (2) pcb’s, please!

Thanks,
Mike Yancey
Dallas, Texas


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 Post subject: Re: Ordering PCBs: Part 15 PLL Synthesized Transmitter Board
PostPosted: May Sun 15, 2022 3:38 am 
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ai6vx wrote:
What's the dimensions of the board so I can report what a full service place would charge? (with longer lead time though)
Also if you have it, the number of holes, smallest line and spacing.

Dave

2.5" x 3.8" 202 holes, though I may have over counted. Some holes are plated through. Also, ExpressPCB drills holes sized appropriately for the component, not just generic holes. It makes populating and soldering a more satisfactory experience. I have no experience with other PCB makers and don't know if they do the same.

Current status and projected price:

mjgillen -1
Dale Saukerson 2
eduardoa 3
Mike Yancy 2

Current total is eight, inching toward the first price break heading down to $14.30 from $21.61.


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