I have been using a Rangemaster AM1000 transmitter for almost five years now, and not a week goes by where someone doesn’t call or send an e-mail asking how I enjoy using it, or if the unit is worth the money that I paid for it. I hope to answer all these questions and more here in this document…
Read the rest of Todd’s Review here: www.toddjenkins.com/radio17
I have been using a Rangemaster AM1000 transmitter for almost five years now, and not a week goes by where someone doesn’t call or send an e-mail asking how I enjoy using it, or if the unit is worth the money that I paid for it. I hope to answer all these questions and more here in this document…
Read the rest of Todd’s Review here: www.toddjenkins.com/radio17
Be sure to note Todd’s photos at the bottom of the page – very nice antenna/transmitter mounting information.
Visit Rangemaster here: www.am1000rangemaster.com
WEAK-AM says
Ideal Setup?
I am curious to know whether anyone has ever had the opportunity to set up a Rangemaster over a full (90-plus) quarter wave radial system out in the country somewhere, and what kind of performance you were able to get with it? Field strength measurements, range tests, etc?
WEAK-AM
Classical Music and More!
Rich says
RE: Ideal Setup
This is fairly easy to calculate, actually. A 90-degree monopole with a “broadcast” type radial ground system generates an inverse distance field of about 306 mV/m at 1 km for 1 kW of applied power.
Reducing the applied power to that of an (otherwise) legal Part 15 AM tx at 75 mW output means that the 1 km field would be reduced by a factor of SQRT(0.075/1000), to a value of about 2.65 mV/m.
//
WEAK-AM says
Real World Test?
Thanks Rich, I know it’s fairly easy to calculate the theoretical field. BUT, I am curious to know how the Rangemaster actually performs, in its supplied configuration (not with a 90-degree monopole but with the 102″ whip) when installed over a highly efficient ground plane (which would be legal), and including its own particular efficiency factor (which so far as I am aware, nobody has actually measured).
WEAK-AM
Classical Music and More!
Rich says
Real World Guess
Sorry, I did too quick a read on your post. The real world, measured data you asked for will be interesting — if anybody can provide it.
For a rough idea until then, see this * calculation *.
My calculation assumes that the Rangemaster system is not elevated above the broadcast radial ground system while connecting to it with a long, radiating conductor, and that the original broadcast monopole no longer is present.
The answer is dependent on the operating frequency, and Rangemaster power output with matching system loss, for both of which I made some rather optimistic assumptions in my calculation.
Note how narrow the audio bandwidth can be for such a situation (down 3 dB at 700 Hz). This system would not sound very good even on a narrowband receiver.
//
12vman says
A Question..
I noticed in your calculation that you used the output power figured at .050 watts. The Rangemaster can be adjusted to the 100 mw. level. Will it make any difference if that level in the formula was to be changed?
Thanks in advance..
~Don
Rich says
Answer
Don, FCC Part 15 AM limits the input power to 100 mW. But the important parameter in the analysis I did is the output power of the transmitter, and that depends on the circuit design and the net load attached to the transmitter. I estimated 50 mW of output power, but it might be lower than that, from some posts I’ve seen.
In any case, for powers other than 50 mW you can multiply the field strengths in my calculation by the square root of the ratio of the new power to 50 mW to find the field for that new power.
For example if the power output was 25 mW, the 1 km inverse distance field would be SQRT(25mW/50mW) * 384 mVm = 271.5 mV/m.
//
WEAK-AM says
That’s why I would like to see actual test results
I agree that the power output would not be 100 mW (that would mean 100% efficiency, which is impossible), but I don’t think we’ve got any authoritative data on what it actually is. The transmitter I built used Class E amplification and was designed to deliver maximum power into 50 ohms, so it was easy to measure the power level. In my case, I was able to get 94 mW output, which is not inconsistent with the results obtained by others (e.g. Nathan Sokal of Design Automation).
Nobody seems to know for sure whether the output of the Rangemaster is operating Class C or Class E. The schematic suggests that it could be Class E, but proof is lacking and I haven’t been able to test it. But maybe I’ll pull mine down off the roof and do some measurements if nobody else has any data.
Rich’s data suggests a loaded Q that I suspect is unrealistically high due to losses in the output matching network of the transmitter. From my experience, there is no way to achieve that high a value, particularly when using a ferrite toroid. Therefore, the audio will not be restricted to 700 Hz, and the radiated field will be much less even if the ground losses are extremely low.
Even if we knew the conducted output power, that isn’t saying what the unit is capable of radiating, which is why I am interested in actual radiated measurements.
Where I am going with this is that I suspect (and I am starting to become convinced) that even with an ideal setup, the amount of co-channel interference on the AM band in most U.S. locations is starting to make useful Part 15 operation impractical, even with the best equipment available.
WEAK-AM
Classical Music and More!
Rich says
Adjusted Calculation
Rich’s data suggests a loaded Q that I suspect is unrealistically high due to losses in the output matching network of the transmitter. From my experience, there is no way to achieve that high a value, particularly when using a ferrite toroid. Therefore, the audio will not be restricted to 700 Hz, and the radiated field will be much less even if the ground losses are extremely low.
If you post your estimate of the r-f loss of that matching network, I’ll be glad to re-run the numbers showing the 1 km field, and expected bandwidth.
//
WEAK-AM says
Hard to guess..
Thanks Rich. Without knowing the particular type of Ferrite (or maybe it is a powdered iron core), it’s pretty hard to make an accurate assessment of the losses in the output matching network. But it seems that a Ql greater than 200 would be unlikely to be achieved. I looked on Amidon’s web site, but they don’t seem to have the curves online. I have more references at home and I’ll take a look.
WEAK-AM
Classical Music and More!