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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Tue 09, 2021 3:18 am 
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Thsnks, Rich, for reminding me of those. IIRC they were dry transfer, right?

Good news, you can still buy dry transfer.

https://www.amazon.com/dry-transfer-let ... +lettering

Takes some practice.


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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Tue 09, 2021 5:05 am 
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Hi Richard and Richard, its me Richard. Who's on first?

Guys, thank you so much for these suggestions, they are very helpful!

Dry transfer, now that's a possibility too. I go 'way back to the days of wet transfer decals followed by spray lacquer. At least with the wet stuff you could move things around until the bits lined up well. It is harder with dry transfer and complicated without reference lines. I have a level that shoots a straight laser line, maybe I could rig that up somehow. I'd still need to space letters by eye. But yeah, it's a possibility and the price is right.

I'm still considering Avery transparency material, https://www.avery.com/blank/labels/94259/gc-film. It could be wrapped around the edges of the panel so the edges would be trapped behind when the panels are in place. Might have trouble wrapping around the curved corners but that would prevent label edge curl and also avoid visible label edges. It, like dry transfer, would need to be coated with a protective spray. I considered just fixing a second sheet onto the first after printing. Bubbles would be hard to avoid, but with practice and a pristine work surface is possible... probably some trial and error, at least I could adjust text size, spacing, and perhaps even have a graphic or something, before committing onto the metal panels.

A quick look around for engravers hasn't been satisfying. Several hours of driving involved. I can ask a local Facebook group for suggestions since there are some very unusual artists all around and maybe one of them could help out. As was said earlier, enclosures are one of the harder parts of this hobby for some of us!

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Tue 09, 2021 9:30 am 
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You can make water slide decals with a laser printer. Possibly with inkjet too. Iā€™ve used laser printer to make decals that get fired on ceramic items, and the iron bearing toner melts into the glaze. But you can just as easily not bring it up to 1800F+ and have ordinary decals that you can slide around to your heartā€™s content. I forget where I bought the decal material from, but I found online somewhere.

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Tue 09, 2021 12:21 pm 
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Location: Burke, VA 22015
Hi Richard,

It's very nice to see various pieces of an ambitious project coming into a professional looking package. The audio processor using the THAT chip and automatic antenna tuner are outstanding. I may try to do something similar.

I have a Talking House transmitter that I got cheaply from an ARFer and I was thinking of stealing its antenna tuner until I found a cheap screw-drive linear slide with 90mm (3.5") length. That's probably long enough to drive a small ferrite bar for a variable inductor.
Attachment:
90mm_linear_stage_1.jpg
90mm_linear_stage_1.jpg [ 111.26 KiB | Viewed 1331 times ]


For panels, I have used both engraved panels from Front Panel Express and panels made from PCB material. Engraved panels are expensive. I now use mostly PCB panels which are very cheap and look acceptable. Here are two examples.
Attachment:
Engraved_Panel_1s.jpg
Engraved_Panel_1s.jpg [ 167.54 KiB | Viewed 1331 times ]

Attachment:
PCB_Panel_1s.jpg
PCB_Panel_1s.jpg [ 147.16 KiB | Viewed 1331 times ]

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Tue 09, 2021 5:53 pm 
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anchorman, YES, waterslide decal printer paper. That is a good option, too, and one I hadn't even thought to look for. I'll make a choice soon.

Binh, your panels look very professional. Can you describe how they were made?

The linear screw mechanism looks great. The one you linked has faster travel speed than cheap ones I looked at. It claims about 25mm per second top speed, which is nearly the same as my home brew which is roughly 2 seconds for 2.5 inches end to end. Of course slower speeds are easy. My homebrew's minimum travel speed is quite slow, about 30 seconds from end to end. It could be slowed more but motor speed becomes increasingly erratic below that until it wants to stall. Speaking of travel distance, I had originally thought to have a 4 inch travel (4 inches in plus 4 more inches out) but scaled it back due to space vs. cost considerations. By shortening travel distance, with the ferrite and coil form materials I have, I also shortened the frequency range it could resonate. Some recalculation and rewinding with different wire size helped but did not give me back my original full range.

I've never seen a Talking House mechanism and know nothing about it other than that it exists.

One of my first decisions was whether to use a stepper or brushed motor. I have no previous servo experience (other than using printers) and I still view the decision as a nearly equal choice between different benefits. Although steppers are very precise, I did not know what to expect as far as acoustic noise or emi radiation. I believe steppers need a relatively hefty current spike to move from one step to the next, which would seem to be an invitation to noise troubles. As it turned out, I had simply traded one type of noise for another. Bypass caps on motor brushes and extra filtering around the motor controller have taken care of most of it. Obviously, noise is not a prime concern since you wouldn't be running the motor while broadcasting on one frequency.

There is no need for stepper holding current with either screw gears or any gears of high enough ratio. A benefit of steppers is their insensitivity to changing motion resistance. They will either jump to the next phase or not. Because I have a brush motor, I coded an anti-stall routine to make sure my motor, at very slow speed, does not stall due to future wear or stiffening lubrication. Such a routine is only possible when a tach output from the motor is available. Steppers don't need a tach output since you are already able to count the exact number of steps/rotations.

I chose a brushed motor based on how current is consumed in smoother quantities instead of spaced pulses. Not only is this a noise consideration, I hoped it would help me control power needs. That ended up being unimportant but I note my motor choice consumes under 100ma at full speed, less with reduced speeds. One final sway of my decision was that the vendor, Pololu.com, has many different gear ratios within their motor lines. If I had made a bad choice of gear ratio I could just swap in a new motor with a more appropriate ratio. In the end my first choice, 99:1 is, a good one.

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Tue 09, 2021 10:30 pm 
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This is a great discussion. I too would like to know a little bit more about how Binh's panels are made, whetherr he has them professionally made or makes them himself. I've had some luck in making a PCB panel etched with ferric chloride and then filling in the etched places with black paint. Then I nickel plate the surface. It doesn't look as good as I would like it to. Therefore Binh"s black painted surface with white lettering looks really good and is an approach I had not thought of.

Another approach would be to print the lettering on the transparency film and embed the whole thing in a clear epoxy or acrylic. This is how I made the numbered knob on the transistor radio in my avatar. This one shown in the photo had bubbles in it where I mixed epoxy furiously to create bubbles. To get one that's bubble free requires different technique. I do have one that is completely clear that I'm using as I decided I didn't like those bubbles after all. The epoxy I used is a product called Pour On, which is designed to be used for restaurant table tops that have a thick clear coating of epoxy that's very flat and not mottled. It also is somewhat flexible, not that you can feel it, but things like forks and knives make dents in it and they self-heal.

So the steps would be to print your transparency as desired. Build a box in which the panel fits perfectly. Poor in the epoxy to your desired depth let's say 1/16 or 1/8 of an inch., then lay in the transparency from starting from one end and going to the other so that there's no air bubbles underneath the transparency, and then make sure that the whole top side of the transparency is covered with the epoxy. You wouldn't need to have a big transparency the size of the panel because the edges of even small pieces of transparency miraculously disappear in the epoxy when they are embedded. It needs to be on a perfectly flat surface. It can end up as glossy as you want, as shown in the top edge of the radio below.

http://www.tompolk.com/radios/catalinca ... angle1.jpg

Attachment:
6002tranangle1.jpg
6002tranangle1.jpg [ 93.16 KiB | Viewed 1242 times ]


One other approach would be to use a single sheet of transparency film and reverse print it so that the unprinted side is protection for the printed side.


Last edited by Macrohenry on Mar Wed 10, 2021 7:09 pm, edited 3 times in total.

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Wed 10, 2021 4:21 am 
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Richard and Tom,

Both panels shown are professionally made.

The first one was made by Front Panel Express. Its drawing was created using their front panel designer software. The software gives an instant pricing for the panel and permits the design to be sent for fabrication. The example shown is an engraved black anodized aluminum panel. The engraved letters were not paint filled to save cost.

The second panel is a double-sided PCB with black solder mask and white silk screen. The copper foils serve as a shield. Its drawing was created with a PCB layout software and exported as Gerber files. Since my layout software only has one font, the lettering was created with TurboCAD with a more preferable font and exported as a dxf file. These two types of files were merged and edited with GraphiCode, a graphical CAM software. The final Gerber files were sent to PCBWay for fabrication, just like any other normal PCBs. PCBWay is a Chinese fab house I've used for many years. Typical turn around is less than one week. This particular panel only costs $2.40 each in a small quantity. Shipping by DHL is not cheap but can be amortized over the quantity.

An advantage of using PCB as panels is that supporting circuitry can be put on the back side. This approach is used by Four State QRP Group for their Ozark Patrol regen receiver. Some pictures are shown here.

Tom, the knob produced using your method looks awesome. For EMI shielding, a metal foil could be sandwiched with the transparency.

Richard, thank you for your useful reasoning behind the motor selection for the linear stage. I probably lean towards the stepper motor since the control algorithm is somewhat simpler.

I found another slightly more expensive linear stage with 100mm length and a larger moving table from the same vendor. With two switchable coils in binocular format like those used in Talking House transmitter, that travel length is long enough to cover the tuning inductance for the entire broadcast band. I will need to watch out for the current consumption and noise. I don't think noise is a difficult problem to tackle since steppers are used in many sensitive electronics such as the old floppy drive.

Below are pictures of the TH antenna tuning mechanism captured from a YT video (too lazy to open mine for taking picture) and the 100mm linear stage.
Attachment:
TH5_Antenna_Tuner.jpg
TH5_Antenna_Tuner.jpg [ 162.19 KiB | Viewed 1288 times ]

Attachment:
100mm_linear_stage_1.jpg
100mm_linear_stage_1.jpg [ 415.04 KiB | Viewed 1288 times ]

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Wed 10, 2021 3:44 pm 
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Tom your tuning knob looks great just the way it is! The texturing from bubbles is beautiful with the radio's cabinet. BTW, for some reason the radio image does not show up inline in the thread (using MS Edge) but opens okay in a separate window. That's weird.

Binh thanks for helpful details about your panels and Front Panel Express. There are so many great ideas presented here! Maybe I should re-title this thread to mention homebrew panels. Probably would avoid confusion that caused the other thread to be needlessly locked. Oh wait, I don't think I am allowed to re-title.

I have been thinking for weeks that I could fix my narrow'd frequency range by adding a fixed series inductor switched in or out as needed. I cannot "unsee" the TH image so I searched a YT video. It appears TH has been doing a switch-in-or-out approach with two variable inductors. I think I can make a quick YT video of this transmitter's operation which may be of interest.

Binh, my concerns about noise were focused on nearby audio paths. Digital operations were oblivious. Until quenched, emi was able to modulate the carrier enough to disrupt accurate measurement of antenna peaking. A simple audio mute while auto-peaking would have been an effective fix, too.

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Wed 10, 2021 5:33 pm 
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richfair wrote:
BTW, for some reason the radio image does not show up inline in the thread (using MS Edge) but opens okay in a separate window. That's weird.


I know exactly what you mean. I use different browsers on my phone. My Dolphin Browser simply has the word image there, whereas Firefox shows it in line.

I tried removing the image tag and it just shows up as a link that's clickable which forces the reader to click on it like you had to do. It's both more cumbersome and more intuitive just to click on the untagged link I tried. So in my edit I left that link in there along with the inline link for those whose browsers display the inline link with the image tag.

For what it's worth I made that posting from my phone where it's much easier just to provide a link than it is to upload an image, which of course works better. I've since edited it by using ARF's posting photo procedure.


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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Sat 20, 2021 7:50 pm 
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I'm finishing my panels with inkjet-compatible water slide decals. I bought a pack by Hayes Paper company. They print just like glossy photo paper and are as easy to work with as any decals I remember, with a benefit that after messing up, new ones can be printed. I have lots of memories of buying pre-printed decals for my home hi-fi gear, back in the day, but having to assemble words out of leftover letters, and having them wrinkle and be crooked. Ah, good times. It wasn't long after that that I stopped worrying about labels. Most of my gear just has snips of printed paper captured under Scotch clear tape. The stuff lasts for years and years.

I strongly considered a product like Pour On to go over these decals. Although it would be practically indestructible when done it would also most likely not be clear. There are numerous mentions of the product, and competitive products, coming out of the can yellow-tinted even before mixing. I'm using simple and easy spray-on clear coat, guaranteed to not yellow, which I'm sure will get scratched eventually. So be it. A scratch won't really matter on my test bench.

Here's the work in progress. I included a curled up decal failure. It was on the front panel and looked good but I decided to start over. Decals don't stick well to brushed aluminum and it was obvious that the first scratch would partially dislodge surrounding material, because the decal's strength is greater than adhesion strength to the brushed aluminum. For the next attempt I first sprayed a light clear coat over the aluminum which was then rubbed with denim (to remove any bumps). THEN decals over that. MUCH better adhesion now. Currently spraying more clear on top. It won't be like a bar table finish but I think good enough for me. I'll post when finished. BTW, there will not be decal material over the LCD. A bezel (from the LCD's manufacturer) that includes a clear window goes there.


Attachments:
panels in progress.jpg
panels in progress.jpg [ 544.67 KiB | Viewed 1112 times ]

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Sun 21, 2021 12:06 am 
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Oh my, that looks fabulous.

Thanks for the tip on the clear coat before decal.


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 Post subject: Re: Richfair's am transmitter build
PostPosted: Mar Sun 21, 2021 6:26 pm 
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Panel work looks very nice. I am still using a label maker. :-(

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Apr Mon 05, 2021 4:42 pm 
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Finished! Thank you all for your interest and encouragements. Anchorman, your suggestion about water slide decals was just what I needed!

I wouldn't normally make a video but I want to demonstrate details that are difficult to convey through pictures and text. I figured, after going this far, what harm might come from burning a few more days botching a video? Notwithstanding "shaky cam"!
https://youtu.be/T_u3K0KbsHQ


Attachments:
AMT finished front angle2 crop sml.jpg
AMT finished front angle2 crop sml.jpg [ 209 KiB | Viewed 952 times ]
AMT finished rear2 crop sml.jpg
AMT finished rear2 crop sml.jpg [ 243.67 KiB | Viewed 952 times ]

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Apr Mon 05, 2021 5:33 pm 
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Wow Richard, you've out-done yourself. Very nice build!
I will now be embarrassed to show my creations.


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 Post subject: Re: Richfair's am transmitter build
PostPosted: Apr Mon 05, 2021 6:47 pm 
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A masterpiece.


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 Post subject: Re: Richfair's am transmitter build
PostPosted: Apr Tue 06, 2021 1:43 am 
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Richard,

Thanks for the video. Your project requires expertise in several areas: rf, audio processing, control system, software and pcb layout. To borrow your words, this is far beyond informal hobby level work. Well done with the exception of the last minute audio circuit shield.

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Apr Tue 06, 2021 3:03 am 
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Excellent video. It was nice to see the antenna auto-tuning in action.


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 Post subject: Re: Richfair's am transmitter build
PostPosted: Apr Tue 06, 2021 5:03 am 
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This is so well done! Including the video. THANKS for inspiring us.


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 Post subject: Re: Richfair's am transmitter build
PostPosted: Apr Wed 07, 2021 2:12 pm 
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bb.odin wrote:
Well done with the exception of the last minute audio circuit shield.

^^^ :lol: Har!

Thank you all for your kind remarks. They are very much appreciated.

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 Post subject: Re: Richfair's am transmitter build
PostPosted: Apr Wed 07, 2021 8:19 pm 
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Amazing stuff.


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