U


SSTran
AMT 3000
AM Transmitter

One of the things that has done more to enhance the enjoyment of my vintage radios is the ability to program my own radio station to feed my favorite music and Old Time Radio Shows to them. Actually I've been fooling around with low power transmitters since I was a kid. It all started with a Tiny Tim AM transmitter. This looked like a toy walkie-talkie but was actually designed for one-way broadcasting to any AM radio. After the initial fun wore off I removed its built-in crystal microphone and replaced it with a connecting wire for a direct input to be fed from our Webcor phonograph using a dropping resistor I selected through trial and error. I knew nothing of pads, proper loading or impedance but it didn't matter…with this arrangement I could listen to my records anywhere in the house and even out in the yard. Of course the range was very limited and the audio quality was miserable - notably inferior to real broadcast stations. Still this was one of the most exciting toys I had and it was a thrill to be "on the air" with my own station.

As it happened my Uncle had an electronics background and when he saw my setup he said, "We can do a lot better than that!" In actuality, he had previously bread-boarded an AM transmitter for his own sons, but they were never bitten by the bug, so they gladly turned it over to me. It was about a one foot square peg board with three tubes, a big variable capacitor, a transformer and spring clips for audio input, antenna and ground. All the wiring and connections were completely exposed so he gave me a quick safety tutorial. "Don't ever touch the live wires," and he also explained that I should never be grounded when I was using it…that is, don't use it outdoors or in the cellar. It boggles the mind that never once did I get shocked by that rig…but can you imagine that today? Lawsuits would be flying everywhere.

Well my uncle's home brew transmitter was a revelation. Almost certainly illegal, I had no idea what its power output was (it could have been a watt or so), but with the array of wires and aluminum poles I strung up on the roof I was able to hear it for several blocks with ease. For my 13th birthday I received a Lafayette RK-142 mono reel-to-reel tape recorder. Now I was able to produce programs for my station then listen to them while I rode my bike around the neighborhood, transistor radio precariously taped to the handlebars. My friends would bring their records to the house and we would play all the top hits. We were having a great time!

That transmitter was not, however, without its problems. For one thing, it had a nasty hum. For another it was evidently rich with harmonics, as I later learned that my transmissions were interfering with my neighbor's police monitoring hobby. At age 15 I received a telegram from the FCC office in Boston, requiring me to cease and desist immediately! I never understood why the neighbor didn't let me know I was causing him grief but that was neither here nor there…it was the end of my mini broadcast station for a long time. The transmitter did have a second lease on life though when I attended college. Broadcasting from the 18th floor of my high rise dormitory, with a wire antenna hanging down to about the 3rd story level, the station covered most of the campus. I eventually handed that transmitter over to someone else to operate, as my activities were in conflict with my involvement with the campus student radio station. Unfortunately I never reclaimed the transmitter at the end of the school year and that's the last I heard of it.

It wasn't until years later that I again became interested in mini broadcasting. Having started collecting radios and also having an interest in Old Time Radio shows I started experimenting with every mini AM or FM transmitter I came across; from a Radio Shack wireless lapel mic to toy broadcasters. All were fun but none were satisfactory for real listening, suffering from miscellaneous noises such as whine and hum, miserable audio quality and limited range. They were, after all, toys, and that's just how they performed.

I heard through some internet discussion groups of a new company called SSTran. Their website proclaimed that their new AMT3000 series AM transmitter were high fidelity with wide, flat frequency response, low distortion, and flexible grounding options to eliminate hum. I bought one and spent the weekend assembling it and I've got to say that this is without a doubt the finest home AM transmitter I've ever seen. Part 15 compliant it is completely legal as long as it is used with the supplied wire antenna. In that mode it will cover your home with a strong signal that will extend well out into the yard as well. You can also buy or build a base loaded vertical antenna which will increase the legal range up to 2 miles should you wish to do so. However for my uses feeding radio programs to my household radios the much simpler wire antenna is more than adequate. I have mine hooked up to the output of my computer's sound card and using the free Winamp player from http://winamp.com , I can create playlists that play for days on end without repetition.

SO HOW WELL DOES THE SStran WORK?
Unbelievably well - and for several reasons.

First, the manufacturer's claims that this is a high fidelity unit are not exaggerations…with the proper input signal my station sounds just like the "big boys" with full modulation and strong, clear audio. There is little background noise…the configurable grounding system is partly to thank for that. In reality, the short wire antenna does impose some high frequency limitations with any AM transmitter compared with a full sized antenna but this is inherent in short wire antennas for AM and in any case, can be compensated for with a bit of judicious equalization. The AMT3000 also offers a jumper selectable high frequency boost for added clarity if desired…most present day AM stations use similar equalization and I found that my station sounds most like commercial stations with this boost activated. Transmit frequency is settable via dip switches and is crystal controlled for rock solid performance. Versions are available for 9 KHz or 10 KHz spacing. And although the unit is monophonic, for ease of hookup to a stereo sound source it has dual RCA input jacks which are internally combined to mono.

Another unique and welcome feature of the AMT3000 is it's built in audio limiter. This is a very deluxe design which, if you understand the theory, will let you not only coax maximum undistorted audio from your station (as commercial stations do), but also let you set the "sound" of your station by controlling how the program material's dynamic range is handled. With very low levels of compression you will hear most of the volume variations in the source material which might be preferable for classical music. At the other extreme you can set it for tighter compression like most AM music and talk stations do, so every song or program will be maintained at a nearly constant volume. This kind of control is a real boon to people like me who have collected music and programs from many sources, all at different volume levels. Even my Old Time Radio shows are much easier to listen to through the SSTran than they are directly. I was always bothered by the fact that the quiet sections were hard to hear while loud portions would blast me out of the room. Now they can all be comfortably heard as they were originally broadcast and that is a major improvement not available on any other comparably priced mini AM or FM transmitter. I have collected many Old Time Radio Shows (OTR) on my computer and it is a real treat to listen to them on my vintage AM radios without being at the mercy of my local broadcasters.

USING THE SSTRAN AMT 3000
In many ways, owning this little marvel has transformed the way I collect and listen to music and OTR. I have created playlists in my computer for every style of music I like, such as 40's Hit Parade, Oldies by decade etc. And of course, all my OTR shows are also in the computer. I plug in the SSTran and turn on radios around the house. This is a real attention getter when friends visit. As I mentioned it puts out a strong signal throughout the house and about half a block down the street…the optional base loaded vertical can legally extend coverage out to 1 - 2 miles. I have been using my AMT3000 for over two years and it is as stable and solid as a rock. I have no doubt it would operate 24/7 indefinitely.

Comments or questions? Email me at jay@radiointel.com

Jay Allen

 


   

| Disclaimer | Feedback | About | This page was last updated: February 1, 2006 |
Copyright ©2002-2006 Radio Intelligencer. All rights reserved