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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Mon 01, 2022 5:26 pm 
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Location: Omak,WA,usa
Hello Mike,
good thinking and I do think an Arduino would add to the news and far as the tiny coax yes I have some too plus used stuff from old vcrs and other stuff too .

Sincerely Richard


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 02, 2022 5:22 am 
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Location: Dallas, Texas, USA
Location: Dallas, Texas
Ok - I caused... and solved... my own problem.

I'd said "seems like the cap feeding the RF stage into the transistor was 'too wide'..." - well, I had stuffed a 0.1uF there, when I was stuffing all the other 0.1uF ByPass capacitors.

The one from the RF 'pin' (and the CD40103) to the base of MPSA18 (or the Gate of the 2N7000) is actually a 0.01uF cap (schematic reads 10 nF).
That makes sense because I had other (small) issues.
* Certain audio 'swamped' the receiver, became muddled (2N7000 or MPSA18)
* The ~600 Hz Tone when using the 2N7000, under battery or power supply, and worst of all:
* The 2000 kHz reading from a frequency counter... when held NEAR the antenna. TX was tuned to 1000 kHz. (Second Harmonic, but also ONLY with the 2N7000).
I replaced the 0.1uF with a 0.01uF and it seems a bit nicer audio AND range is a bit better - which makes sense. IF there's a 2nd Harmonic, the transistor (or FET) is wasting precious power amplifying it instead of our desired 1000 kHz.

I saw no 2nd Harmonic with the MPSA18 - it's been better behaved all 'round, but I can tell a difference.
I'd like to swap back to the 2N7000. In any case - audio is tip-tip, range is better. All 'round VERY nice and stable.

Helps to follow the schematic - duh.

Mike Yancey, KM5Z
Dallas, Texas


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 02, 2022 5:56 am 
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Hello Mike,
Maybe I should install a socket to try some different!
Sincerely Richard


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 02, 2022 2:55 pm 
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Location: Dallas, Texas, USA
Location: Dallas, Texas
Heh! Yes!
I socketed the transistor (after removing the 2N7000).

NOW, I'm thinking I need two more 'single' machine pins for the 100k / 2k resistor (gate / base).
That would set it up for convertibility between the two variants.

Mike Y


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 02, 2022 4:45 pm 
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Hello Mike,
That is using that old brain of yours :D
I have in my stuff some transistor sockets !

Sincerely Richard


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 02, 2022 10:18 pm 
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Location: Monroe GA 30656 (from Coventry, UK)
It lives! Here's the initial build, powered by a wall wart. I have the parts to build a linear PSU, but that will come later. I am impressed with the performance, although I have some hum. I have to spend some time looking into that, but just wanted to show it off. I haven't decided how to house it.
Also, while digging around in boxes, I found the original synthesizer that I built, and the LM386 TX. They were put together when I lived in Michigan, then packed away. I've lived in Utah, Nevada and now Georgia since then. I hope nobody minds that I posted photos of them. In fact, I wondered if it would be worth posting them in the classifieds.
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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 02, 2022 10:26 pm 
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Colin Ames wrote:
It lives! Here's the initial build, powered by a wall wart. I have the parts to build a linear PSU, but that will come later. I am impressed with the performance, although I have some hum. I have to spend some time looking into that, but just wanted to show it off. I haven't decided how to house it.
Also, while digging around in boxes, I found the original synthesizer that I built, and the LM386 TX. They were put together when I lived in Michigan, then packed away. I've lived in Utah, Nevada and now Georgia since then. I hope nobody minds that I posted photos of them. In fact, I wondered if it would be worth posting them in the classifieds.
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New AM TX_ARF.jpg

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Old Synth_ARF.jpg

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Old TX_ARF.jpg


How are you grounding your transmitter Colin? I found the only way to eliminate hum from the beta unit I constructed was to connect the transmitter ground to the copper cold water line in my home which is bonded to the electrical panel ground. Any other installation would have hum on the transmitted audio.

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


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 02, 2022 10:46 pm 
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Paul,
Thanks for the suggestion. I didn’t have access to a decent ground where I was testing it, so that will be my first area of investigation. I’m guessing that this will improve things.

Colin


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 02, 2022 11:52 pm 
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Colin Ames wrote:
Paul,
Thanks for the suggestion. I didn’t have access to a decent ground where I was testing it, so that will be my first area of investigation. I’m guessing that this will improve things.

Colin

Easy to test outside away from hum modulation inducing equipment. If no hum outside it's probably hum modulation.

Does hum disappear when audio cable is not attached?

Love those long lever switches.


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Wed 03, 2022 4:20 am 
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Hello Colin,
Nice Job and even with my old SStran3000 I found that when I installed a grounding rod it took care of my noise, and I am sure that will do the same !
Sincerely Richard


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Wed 03, 2022 2:18 pm 
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Tom,
I will test outside when I get the chance. The hum is not dependent on the audio cable, which is only 12" long and connected to an iPod Touch.

The piano style switches came from Tayda Electronics. I bought them in 2015 when I built the original synthesizer. I checked their website and they still have them, except they are now blue. Tayda isn't a bad place to buy stuff if you don't need Digi-Key delivery speed. I've used them a few times in the past, and bought a few of the parts for this project from them, plus some other stuff. Here's an example of their pricing.
Attachment:
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I almost mentioned them as an alternate supplier, but wasn't sure if that would add even more confusion, what with Digi-Key, Mouser, Jameco and Futurelec already in the mix.

Colin


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Wed 03, 2022 2:21 pm 
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radiorich wrote:
Hello Colin,
Nice Job and even with my old SStran3000 I found that when I installed a grounding rod it took care of my noise, and I am sure that will do the same !
Sincerely Richard

Thanks Richard. A grounding rod probably isn't on the cards, but I will experiment with various locations and other solutions. The hum isn't terribly bad, but I am sure with some effort I can reduce it.

Colin


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Wed 03, 2022 2:44 pm 
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As mentioned over the years hum can be a problem with short antennas. The local environment can have a huge impact on how noisy or quiet the carrier is.

In my case there are scant places inside the house where I can operate any of my transmitters without hum. But once I just go a few feet out onto the back deck the hum is not a problem. Which is why the videos are all outside. Adding the earth ground then only increases the transmission distance, and by a lot.

ACORNVALVE solves hum problems in pantry transmitters using loop antennas.

I think it was on ARF somewhere in the last month or so that somebody posted an old article where a fellow couldn't run an effective ground and he ended up wrapping his ground lead around the PC board of his SS Tran or Talking House. He was amazed at the difference it made. If anyone can remember where that was and can post it here it might make interesting reading.


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Wed 03, 2022 6:40 pm 
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Location: Dallas, Texas, USA
Location: Dallas, Texas
> The piano style switches came from Tayda Electronics.

I like Tayda. Some of their 3.5mm stereo jacks have been crap (the 'flexible' tail crumbled or fell off). But nearly all the rest is quite reliable. They had some Nichicon capacitors for a while - those got hoovered up. And they have Wima film caps (100VDC) which are very good.

I swapped my MPSA18 back to a 2N7000 (after changing the RF cap from 0.1uF to 0.01uF. Low Tone on carrier STILL!
So, I looked over the PCB and found a few OTHER areas where I had put a 0.1F bypass cap. Low & Behold - there were 3 others that should've been 0.01uF. When I was stuffing the board, I must've mentally defaulted to 0.1F Wima caps.

After replacing 3 of those (basically feedback from pins 8 & 16) it now has a silent carrier on a 2N7000 and the Frequency Counter doesn't show 2000 kHz when the probe wire is wrapped around the antenna wire.

Bypass Caps are Important! (play the "The More You Know!" public service video). And must be the RIGHT value, 0.01uf (10nF) in this case.
Next time I'll pay the extra $ for the printed overlay layer! That would've reminded me which spots got 0.1 and 0.01.

Mike Y


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Sat 06, 2022 12:45 am 
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Put it in a Radio Shack project box that I bought many years ago but never used. I thought it best to house it before I keep moving it to different locations to find the best performance. Before I put it in the box I did try it outside the house, running the same wall wart on an extension cord, the hum was still the same. I moved it to the other side of the house and connected ground to the ground rod. The hum subsided substantially. Unfortunately there's no way I can leave the transmitter in this location. The next step in the project is to build the linear power supply, when I get the opportunity.
One thing I did find was that the nylon nut and bolt for the inductor had a really sloppy fit, so I wrapped some Teflon plumbing tape around the bolt, which tightened it up sufficiently.
Attachment:
Cased_ARF.jpg
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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Sat 06, 2022 8:56 pm 
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Location: Dallas, Texas, USA
Location: Dallas, Texas
Nice implementation, Colin.
I've chosen a metal case, but then again, I'm not certain.

I was originally testing at 1000 kHz, and that's fine as that goes. But I think I hadn't understood this was kinda optimized for the higher frequencies.

At 1000 kHz, I was getting 10 to 15 foot ranges.
I thought maybe it was because my wire was at an angle or the transmitter was on a Steelcase desk (metal all 'round).

Anyway, with all my issues out of it, I assayed the area for 'unused AM frequencies' and tuned (switched?!) to 1540 kHz.
It was strong. Very strong. So I carried a little Arvin "Check Mark" transistor around with me. Strong in the utility room (metal washer/dryer). Strong in the kitchen.
In fact, it never weakened.
I finally made it out the door and half way to the mailbox before it juuuust started to fade a bit. It was probably a little over 70 feet.
This house has a metal roof, so - unknown if that would've played a role.

Edit: Oh, yes - I used radio-locater.com to get a list of frequencies in the area.
https://radio-locator.com/cgi-bin/locate

I think we most of the FM slots taken: https://radio-locator.com/cgi-bin/locat ... 1&x=12&y=5
Quite a number free under AM, though (barring skip from some clear-channel stations).

I chose 1540 because it's in range of my pre-80s radios (which is most of 'em).

Mike Y
Dallas, Texas


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Sat 06, 2022 9:47 pm 
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Thanks Mike. I used this case because I already had it, and was trying not to spend any more on the project. I did wonder if a metal case would help to screen the board from outside interference, but for right now I will stick with the plastic. As for the operating frequency, I set mine to 1600, where it works well, but like you I have some radios that don’t tune that high, so I will readjust it.

Did you ever give further thought to the Arduino driven LCD or OLED frequency readout? That would be an interesting mod. How would you implement it?


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Sat 06, 2022 10:50 pm 
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Location: Dallas, Texas, USA
Location: Dallas, Texas
Colin Ames wrote:
Did you ever give further thought to the Arduino driven LCD or OLED frequency readout? That would be an interesting mod. How would you implement it?


I wrote the code for it last night! I have enough stuff to put it together (probably tomorrow / Sunday), so I'll test it in proximity with the "MH Transmitter."
What I sketched out is a counter and two VoltMeters - in rotation with a push button.
I might test the Input Voltage (9V / 12V) and the voltage at the tuning LED, or just above the current limiting resistor.
And, I dunno. Maybe I'm just getting too fancy here.

If it's noisy, it goes in a box (metal or plastic) alone with the little regulator.
If it's not, well, I'll consider using an older 1-line, 8 char display.

I also have a little Bluetooth receiver, by which I can put streaming material on the air (like: https://www.retrococktail.org/ !)
A sample project is this one, entirely built from cheap modules:
https://www.instructables.com/Minty-Tun ... argeable-/


Mike Y, KM5Z
Dallas, Texas


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 09, 2022 3:13 pm 
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Location: Dallas, Texas, USA
Location: Dallas, Texas
Ok - I decided: No Arduino, no fancy Freq Display, no Metering.
Keepin' it Simple.

Enclosure is an LMB Heeger 'Interlocking Series' box. This box was used for something previously, but I've forgotten, but I've had it a long time.
Regulated Power, Audio, and Tuning Inductor all on one end (right). Tuning LED on top.
I probably will have room to put a regulator in the other end, for 'any' general wall wart.

I'm uncomfortable with the way the antenna is handled, but - I might have an RCA jack that can mount up there. Tidy it up.


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 Post subject: Re: Macrohenry Transmitter Construction
PostPosted: Aug Tue 09, 2022 4:50 pm 
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Mike,
Simple is probably best, although the frequency display would have been cool! It looks tidy.

I need to modify mine slightly, by bringing the tuning LED to the outside of the box, as well as the adjustable core. The fact that I didn’t do this from the start was just bad planning, I guess.


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