MICROPOWER AM BROADCASTING – A SCRATCH-BUILT SSTRAN AMT3000

[ChrisSmolinski]

https://aa7ee.wordpress.com/2024/12/23/micropower-am-broadcasting-a-scratch-built-sstran-amt3000/

[Dave Richards]

I was going to post a link to this here, but you beat me to it Chris. Thanks! There's not a whole lot of information out there for people who are interested in building their own Part 15 gear, as it's such a niche pursuit. For radio hams who are into homebrew, we are spoiled. There are tons of articles on building ham radio equipment, dating back to the birth of radio, as well as many kits available. Not so much with Part 15 broadcasting.

Building this transmitter was a useful exercise. When I owned an original one, years ago, I had nothing to compare it with. Now, I'm able to evaluate the AMT3000 in the light of a little more experience. I'm mostly happy with it, but like almost everything I build, it gives me ideas for future experiments. I'm not thrilled with the simple single-channel audio processing, so I want to try bypassing it and feeding the transmitter with processed audio from my SW200. I'd also like to try a more efficient inductor in the output network, a circuit so that it can accept a balanced audio feed, and put the whole thing in a rugged weatherproof enclosure for outdoor mounting - if I ever get around to it! 

[ThaDood]

I've got to say, that puts my work to shame. All, very well done and nicely documented.

[tybee]

It's absolutely awe inspiring. Very attractive. Years ago I know you had been looking for an encloser similar to the Rangemaster box.. Now I wonder why to didn't build it to be an outdoor unit?

[Dave Richards]

Thanks ThaDood. I've benefitted a great deal from all the things I've read online over the years, so when I do something, I like to share.

You have a good memory Rich. I did find out that the enclosure used for the Rangemaster is this one -

https://www.mouser.com/ProductDetail/Hammond-Manufacturing/1590ZGRP123?qs=sGAEpiMZZMv151B%252BVDR3zBr88%252Ba5a7FeYoXfKyeAB0U%3D

I thought I'd start my build off as an indoor unit and go from there. If I did want to mount it outside, I'd also want to upgrade the inductors in the output network for a more efficient one wound on a large iron powder toroidal core, as used in the Rangemaster and AMT5000. I'd also want to include extra circuitry to allow the transmitter to be fed with balanced audio. Whether I'll ever get around to it is another matter though! 

[tybee]

...If I did want to mount it outside, I'd also want to upgrade the inductors in the output network for a more efficient one wound on a large iron powder toroidal core, ... include extra circuitry to allow the transmitter to be fed with balanced audio....

Now, I"ve never built anything, so don't know what I talking about, but I wonder why you didn't set out to apply those upgrades to the transmitter when you decided to build this mock-up to begin with?

Was it because of additional expense? Was it because it would have made it much more complicated to build? Why not set out to construct an outdoor unit to begin with? Why an indoor unit?

And Please dont misunderstand me, I am overly impressed with what you did and it inspires me to attempt to build something, even if it's just a crystal receiver.. but I dont understand why you wouldnt have applied those available upgrades when you did it the first time.

[Dave Richards]

It's a fair question Rich. There were a few reasons. Firstly, I wanted to completely replicate the circuit of the original AMT3000 to see how my build compared with the "real" one that I used to own. It's a tried and tested circuit, so I figured it was a good starting point for any changes or mods I might want to make. My only transmitter that was in operation at the time was a Rangemaster, which is mounted outside and operating 24/7. I thought it would be cool to also have an indoor unit to play around with. I don't have a burning need for an extra outdoor unit, which also played into my decision to build this one as an indoor unit.

[tybee]

Well its beautiful, I envy your talent and eye.