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Best low power, Part 15 compliant AM transmitter?

Many of our visitors are interested in experimenting with low power radio while staying within the limits of the law.  It's fun to broadcast to your neighborhood without having to look over your shoulder for that tinted-windowed FCC SUV heading down your block.
     As we have shared in previous posts, it's generally agreed that low power AM broadcasting under Part 15 has the best opportunity for useful legal range, due in part to the opportunities for experimentation under the "100 mW power input and 3 meter antenna" subpart in the regulations.
     Happily, there is a nice selection of certified Part 15 AM transmitters and Part 15 compliant (meaning the transmitter complies with the letter and spirit of Part 15 without being certified by the FCC), AM transmitter kits on the market today.
     Of course, quality and compliance can be expensive and kits require a significant investment in time and a certain skill level to complete, so, which AM transmitter is best?
     I think we can all agree that "best" means range - so, of the popular AM transmitters on the market today, which has the best range?  Sure, you can research online but all I've ever been able to find is a wide range of opinions and hyperbole and very few facts.
     Wouldn't it be great if an unbiased report were created, where sensitive measuring equipment was used by skilled operators to test a collection of transmitters in a straight up, head to head, identical conditions comparison where we could learn once and for all which transmitter would deliver the best bang for the bucks (or effort)?
     Enter the Hobbybroadcaster.net AM Transmitter Challenge, a Herculean effort undertaken by the talented and dedicated Bill DeFelice and a cadre of capable assistants who put in the time and, from the sounds of the report, no small amount of work in designing, coordinating and delivering the final word on legal low power Part 15 compliant AM transmitter range.
     So, which one won?  You'll need to visit Bill Defelice's most excellent web site dedicated to legal, low power radio experimentation, www.hobbybroadcaster.net, and find out for yourself.
     Check out The AM Transmitter Challenge on Hobbybroadcaster.net and start planning your Part 15 compliant operation today!
     A huge lowpowerradio bog "Thank You!" to Bill and his team for their selfless efforts in fianlly settling this contentious topic with a repeatable, fact based approach to range measurement.


David Chamberlain said...

There were problems with the AM transmitter challenge that Hobbybroadcaster refuses to admit, particularly with the testing of the AMT5000.

The tests were supposed to show which transmitter was the best, as delivered to a novice broadcaster. However, the AMT5000 is delivered as a kit, while all the others are assembled. The AMT5000 tested basically came from an unknown source, and had unknown build quality, while all the other transmitters came from either the manufacturer or distributor.

The operational documentation supplied with the AMT5000 is oriented towards the more technical user (after all, you supposedly had to build the kit to get to the point where you are installing it). The testers had difficulty with this documentation and they claimed that they could not get hold of the manufacturer for clarification. But instead of halting the testing until they DID get the answers, they forged ahead into the darkness, and the results are suspect, to say the least.

The AMT5000 really should not have been included in the shootout. While it did quite poorly in the final results (most likely because of the described testing issues), there is plenty of ancedotal evidence from others who have used it to suggest that it ranks right up there with the Rangemaster or ProCaster, if not better.

Hobbybroadcaster is supposedly doing a followup complete review of the transmitter (although it has been coming for quite a while now). It will be interesting to see what they say about it in that review.

Low Power Radio Guy said...

Hi David,

Thank you very much for stopping by and sharing your observations! If you have any performance data or other information you'd like to share, please let us know at low power radio at gmail dot com. We'd be happy to pass it along to our readers.

David Chamberlain said...

I have been involved with low power broadcasting for coming up to 10 years now - I launched my BETS-1 (the Canadian equivalent of Part 15) FM station in 2006 on Bowen Island, BC.

During that time, I have experimented with and used numerous AM and FM transmitters.

The folks at Hobbybroadcaster have to be commended for generally doing a good job in the AM Transmitter challenge, except for the problematic AMT5000 results. I have never used an AMT5000 myself, so I have no particular axe to grind, one way or another; but as I stated, others have reported exceptional results with proper installation.

Generally, my experiences with the other transmitters have matched up with the results of the Challenge. Unfortunately, the equipment required to actually measure field strength is very expensive, so I have had to rely on physical measurements for range, and qualitative measurements (i.e., my somewhat subjective ear) for sound quality.

I achieved the best range (and the best sound) from a Rangemaster, followed closely by the ProCaster, with the Talking House lagging considerably behind, both in terms of range and sound.

One transmitter that I have had great results with, and that was not considered in the Challenge, was the Talking Sign (likely because it is not currently in production) - this was the precursor to the ProCaster and made by the same folks. With an installation similar to the ProCaster, I was actually able to achieve better range (over a mile), although the sound quality was not as good.

I eventually ended up using FM, as Canadian unlicensed regulations are somewhat more liberal than those in the U.S. (AM regulations are almost identical). In Canada, the maximum field strength for a BETS-1 transmitter can be 100uv per meter at 30 meters. If you can get your FM antenna up high enough to negate the influence of ground reflection interfering with your signal, you can get significant range to a sensitive receiver; in my case on Bowen Island, the target audience was a ferry lineup (car radios can have sensitivity of under 1uv and they have great selectivity as well). My transmitter was located in a building at the top of a hill overlooking said ferry lineup, and I was able to achieve a range of up to 1km (just over half a mile).

That was a very specific application, however, and in general use, with much less sensitive receivers, AM gives you much more usable range.

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