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Hi There,
Hi There,
I am new to this forum and new to Low-power radio. We are looking to purchase a couple of self contained part 15 compliant transmitters to serve our ranch property in Alpine, TX. The Procaster and the Rangemaster look to be great units. Can any of you refer me to other units that may be better for our application?
thank you
Total posts : 45366If you would like to operate more than one unit, and you’d like to sync the units so they operate on exactly the same frequency, the Rangemaster would be your choice.
The Procaster has a number of cool features, but does not offer syncing.
From the Procaster web site:
“Multiple Transmitters – Synchronization
Many people ask if the Procaster can be synchronized such that larger areas can be covered using multiple transmitters. The answer is no – the Procaster was designed to be a “standalone” unit…”From the Rangemaster web site
http://www.am1000rangemaster.com
“Multiple Transmitters:
Need more range? It is possible to use more then one Rangemaster unit to cover more area. The easiest method is to spread them out over you area about 1/2 mile to 3/4 mile apart and synchronize the audio only. Because the units are crystal controlled and can be fine tuned to exact frequency this will work, they won’t heterodyne unlike PLL controlled AM transmitters. ”Experimental broadcasting for a better tomorrow!
Total posts : 45366Nice mini comparison by SCWIS but I will add that if my information is correct the Rangemaster allows for synchronizing the carriers in addition to the audio. The audio can be synchronized for either transmitter and not just the Rangemaster.
The quoted comment from the Rangemaster site “Because the units are crystal controlled and can be fine tuned to exact frequency this will work, they won’t heterodyne unlike PLL controlled AM transmitters.” is partially correct. Crystal controlled oscillators can be set to the exact operating frequency and if stable enough can maintain their frequencies so heterodyning is not audible, yet heterodyning will still happen due to drift and, if it is low enough in frequency, will appear as periodic fading and reinforcement of the signal similar to nightime distant stations’ signals. If the carriers are synchronized, as I think they can in the Rangemaster, then this doesn’t happen but there will be nulls in the patterns where the signals overlap which will appear according to the listener’s position.
It is conditionally true that phase locked loop (PLL) controlled units may have issues as alluded to in the comment “they won’t heterodyne unlike PLL controlled AM transmitters.” since simple PLL circuits, though crystal controlled, have their output frequency controlled by an error voltage. As is true of proportional control systems there can be and usually is a steady state error which allows the frequency to be different than that desired and this can change in response to circuit conditions even if the crystal is perfectly and always on frequency. However there are PLL circuits which are proportional plus integral which can hold the output frequency to the stability and accuracy of the crystal and for which the quote above would fail and there would be no performance difference between a crystal only oscillator and a PLL synthesizer. I do not know what the Procaster uses but I suppose I am just raising the question.
It would be good if the manufacturers of these units could comment here about this.
Neil
Total posts : 45366Neil wrote: If the carriers are synchronized, as I think they can in the Rangemaster, then … there will be nulls in the patterns where the signals overlap which will appear according to the listener’s position.
This is an important observation which (apparently) is unrecognized by Rangemaster.
The link below leads to a plot of the total radiation from two identical Part 15 AM systems located 2 km apart, whose antennas radiate equal power, at an identical r-f frequency and phase.
Directional AM broadcast stations use forms of this technique to generate the radiation patterns they are required to have by the FCC. Of course, all of those patterns have far fewer nulls and lobes than in this scenario, because the individual radiators at AM stations are much closer together.
If the r-f phases of these two Part 15 AM systems in the link are not accurately locked then the pattern shown would change constantly.
http://i62.photobucket.com/albums/h85/rfry-100/SyncedPart15Systems.gif
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Total posts : 45366So, there you have some additional points to consider.
As far as the balance of your question, “are there other units to consider” that’s tough to say.
LPB – http://www.lpbinc.com – discontinued their Part 15 unit a few years ago, as did Radio Systems, http://www.radiosystems.com/lowpower.html, and several others. The options are fairly limited at this point.
Experimental broadcasting for a better tomorrow!
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