The AM Transmitter Challenge has arrived

Good Morning Geets,

This is how I chose my transmitter(s). Based on conversations with Phil B. I initially purchased an AMT3000. In fact I bought 2 over a short period of time. I was pleased with the audio quality and the quick responses from Phil when I had questions including how to modify the transmitter to remove/add components to accommodate a different antenna. However, no matter how hard I tried, I could never get good results with an external monopole and the range was poor, though Phil was patient with my questions. He suggested that rather than get frustrated I should put it aside for a while. Good advice actually. The second AMT3000 I tried to incorporate in a college setting with the transmitter mounted on the roof of a three story building using a 3 meter wire antenna with the transmitter grounded to the lightning protection scheme on the roof. Sounded great but range was still poor.

So I convinced the powers that be to purchase a Rangemaster 1000. Mounted on the same roof using the same ground, I was able to achieve a car radio range of about a mile in any direction. Now with arrangement the audio was not as good as the AMT3000 so I lent an Ultradyne processor and dramatically improved the audio. Later we added a 222 processor as well. Results were so good that I added a Rangemaster to my home station. Like Phil B., dealing with Keith was a pleasure.

Lastly I could not resist purchasing for 4 bucks a Rev 1, Talking House. Range was poor using the supplied wire antenna. Audio as describe in other posts not so good. Also the transmitter FM'ed. In fact if you tapped on the chassis it FM'ed. So... a few months ago I purchased a second V5 without the audio enhancements. I like buying things in twos. Installed that same as version 1, the audio was a bit better but still FM'ed. I used a laptop with the latest version of StereoTool with US AM selected and it sounds much better. However, with the supplied wire antenna near a window facing the front of the house, the noise free signal on a car radio was about 200 feet with it fading into the noise at about 1/10 of a mile.

So my next experiment is to ground mount the second Rangemaster, drive it with StereoTool and see what happens. I already know that roof mounted at 15 feet (yes long ground wire) it gets out about a mile.

That's my story and I'm sticking to it.

I'm in Canada, and our rules are more complicated (if that's possible) here. We have 2 sets - RSS210, which expressly forbids broadcasting, and BETS, which are the rules for broadcasting. For FM, they are essentially identical, and allow for 4 times the field strength of the U.S. It's AM that's the kicker - RSS210 is pretty much identical to Part 15 (with a 100mw to the final stage rule), but BETS is based on field strength only and it's pretty limited (250uv/m at 30 meters). As a rule (pun intended), FM (mono) is generally the way to go - with our enhanced field strength, and a sensitive car receiver at the other end, you can achieve up to 1km line of sight range (with quieting), although typical range is 1/4 to 1/2 km with obstructions. Much less of course with your typical, less sensitive, consumer radio.

That being said, at least under the RSS210 rules, theoretically you should be able to achieve greater range with AM, and I've experimented with a number of transmitters to see if it would be worthwhile to switch to AM. The problem with AM is that you have a relatively small noise free range - static gets introduced relatively quickly and increases gradually until you lose the signal. Range depends to some extent on how much of that static you can stand before you don't want to listen. FM signals, on the other hand, tend to be either there, or not, and once they're not, they degrade rapidly. I don't have a FIM, so I had to establish some consistent standards for listenability during my tests.

Another point - all the Industry Canada AM and FM transmitters are certified under RSS210. BETS does not require certification, but if Industry Canada comes calling, you have to show that you're compliant. For FM, that's no problem, but AM is another matter. All of the manufacturers deliberately ignore these considerations, and to be honest, I've never heard of anyone getting into trouble for using an AM RSS210 certified transmitter for broadcasting.

For me, the Rangemaster (although it's not certified in Canada) worked the best, getting a listenable (to my standards) 1 mile range and even more in some directions - but the static free range was less than any FM transmitter I've used. The ProCaster (certified) also did well, getting a range of between 1/2 - 3/4 mile in a similar installation. I've owned numerous Talking Houses (again, not certified here) and had wildly differing results, from virtually no range to range similar to the ProCaster (with an ATU/whip) - but never beating it. The Talking Sign (certified) was an interesting transmitter (manufactured by ChezRadio prior to the ProCaster). Similar to the Talking House with a wire antenna, I managed to achieve a listenable range of almost that of the Rangemaster, and without the quality control problems of the Talking House (I own 3).

But the bottom line is that none of the AM transmitters were so much better than my FM ones that I was willing to risk entering into the RSS210 versus BETS debate for broadcasting. In fact, in terms of sound quality versus range, my FM transmitter outdoes every one.

I use a Decade MS-100 running in mono mode. Mounted in a weatherproof box installed on a rooftop of a building on a hillside overlooking my desired coverage area (and thus minimizing obstructions), I was able to achieve that 1km range to a sensitive (less than 2uv with 40db quieting) car receiver. I also found out that car receiver sensitivities (and antennas) vary widely - some at best were only able to receive the signal at a distance of 1/2 km, no obstructions. Range to consumer radios was significantly less, around 200-300 meters at most (and generally less). The Decade is certified under RSS210, which means that it is compliant with BETS.

Unfortunately, I've never tested the AMT5000 but do own a built one and will eventually test it alongside the Rangemaster. And that's why I was so concerned about the results from the Challenge. I don't think the 5000 was given a completely fair test in terms of what it is capable of doing and that's borne out, at least in ancedotes, by the numerous positive results from others who have used it. It would have been definitive if its output could have been measured by a FIM in a known, ideally tuned state. Right now it is unclear whether or not the transmitter was tuned correctly, and those involved in the Challenge are more interested in assigning blame (and trading insults) rather than getting it right. Who knows, perhaps the AMT5000 would have blown the Rangemaster right out of the water, and made the decision of FM vs AM even more difficult for those of us living in Canada.

Having never owned the 5000 my comments would be nothing more that unqualified opinions. So therefore I can't comment. I have heard/read somewhere that the Rangemaster is also Class E.

That's the problem. The Challenge doesn't give us the definitive answer re the AMT5000. All we still have is ancedotal evidence and opinions until a better test for that device is performed.

pascoradio said:

Having never owned the 5000 my comments would be nothing more that unqualified opinions. So therefore I can't comment. I have heard/read somewhere that the Rangemaster is also Class E.

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As I posted in other places, why didn't the person that loaned the AMT5000 complain? That to me is more important than all the comments in the world from others.

Who knows? Perhaps they didn't know how to tune the transmitter either. Or perhaps they didn't use it all that much and it was just an experiment (the fact that they were just using the wire antenna on it kind of supports that idea). We don't know who he or she was, what their level of experience was, in short - we know nothing about them. But ultimately, I don't particularly care why they didn't complain, as I go by what was actually done, and then the explanations afterwards by the testers. But if you or others care, perhaps the guy can be asked and the answers posted here.

Well I am getting bored with the round-table discussion that's obviously going nowhere since both side have their minds made up, it is pointless to interject my uninformed opinion since I am a technical slouch.