I am considering purchasing an EDM FM 10mw tx. It sounds like a pretty darn good deal. I just want to know what is the opinion about it on the part15 website so I can get a pretty good idea of how this little thing is.
-Travis
I am considering purchasing an EDM FM 10mw tx. It sounds like a pretty darn good deal. I just want to know what is the opinion about it on the part15 website so I can get a pretty good idea of how this little thing is.
-Travis
FM Transmitters "MUST" be FCC Certified for part 15 use. especially in this climate. none of the EDM stuff carries a FCC ID and is not certified.
buy and run at your own risk.
Best Try these if you want the absolute best and still be certified...
Landmark FM (FCC Accepted) (choice of inputs from balanced to unbalanced to USB)
http://www.landmarkfm.com/others.htm
Decade MS-100 (more expensive than landmark and no balanced input option)
http://www.decade.ca/MS-100.html
Thank You,
Rev. Robert P. Chrysafis
Universal Life Ministries
http://www.ulc.org
Moderator Hunterdonfree
http://groups.yahoo.com/group/hunterdonfree
There's also the ACC-100 from Panaxis: http://www.panaxis.com/pc-ACC100.html.
Frank
www.easthillradio.com
Best Try these if you want the absolute best and still be certified...Landmark FM (FCC Accepted)
But not all Landmark txs are certified -- see http://part15.us/node/835 for details.
//
There's also the ACC-100 from Panaxis: http://www.panaxis.com/pc-ACC100.html.
Yes, i forgot about the ACC-100. They are good as well 🙂
Frank
www.easthillradio.com
I certainly would not want to recommend that you do anything out of compliance with any regulation (although I don't even know (or want to know...) what country you are in). However, if you are in the USA, given that this is a Part 15 forum, do pay attention to what the others are saying, since they appear to have a lot of experience with compliance.
However, purely from an experimenter's technical (and not legal)perspective, the 10/100 has a great airsound and is very inexpensive for what it is. (Probably Part 15 certification is very costly and would add to the price of any transmitter.) Construction of the unit with the included enclosure and power supply is really simple with minimal soldering. It appears to involve much less work than other popular kits like Ramsey, etc.
Lacking sophisticated field strength measuring equipment (none of us around here have the big bucks for these units), you may be able to bring the EDM into compliance with appropriate attenuators, etc.
Good luck.
Hello all,
Many previous posts have addressed the issue of FCC compliance, but I notice that there are several new members of this board who may not have seen the discussions. So, I would add that in the US the FCC part 15 rules governing unlicensed operation in the FM band do not specify power. It can be misleading that some purveyors of transmitters rate their units in terms of milliwatts which might lead to the conclusion that this is a meaningful parameter with reference to the rules. It is not.
The rules specify a maximum field strength at at given distance. As mentioned in this thread, most, if not all of us, lack the equipment to assure compliance by direct measurement. The easiest way to control the field strength from a low power FM transmitter is to trim the antenna to achieve a certain range. The FCC states in a fact sheet, and not in the rules, that the expected range of a compliant transmitter with regard to field strength is 200 feet. If you are concerned about compliance then it appears that if you trim the antenna to get this range then you will be close to the limits of the rules.
As a point of reference, I have a 200 foot range (using a car radio) from my Ramsey FM-25A with the antenna extended 4 inches.
Neil
Hello all,
The rules specify a maximum field strength at at given distance. As mentioned in this thread, most, if not all of us, lack the equipment to assure compliance by direct measurement. The easiest way to control the field strength from a low power FM transmitter is to trim the antenna to achieve a certain range. The FCC states in a fact sheet, and not in the rules, that the expected range of a compliant transmitter with regard to field strength is 200 feet. If you are concerned about compliance then it appears that if you trim the antenna to get this range then you will be close to the limits of the rules.
As a point of reference, I have a 200 foot range (using a car radio) from my Ramsey FM-25A with the antenna extended 4 inches.
Neil
250 uV/M as measured from a distance of 3 meters.
John,
You are correct in pointing out that the rules limit the field strength for p15 FM to 250 uV/m. but how does the hobbiest/experimenter translate this to the enjoyment of the hobby? I hope my suggestion is useful.
My take on this is that there are two reasons that folks engage in hobby broadcasting.
One is that people enjoy programming and sharing their love of music and commentary with others.
The second is that some get engaged in the technology and think about transmitters, milliwatts, antennas, and so on. You might guess correctly that I am in this group.
There are many good posts on this board from both part 1 and part 2 folks. This board is "where it is happening" for part 15. Keep posting. I would like to see more experience based stories from both groups
Neil
Hello guys
I have the LCD model. Audio is great. Range on 10mw will get you 100m. And 100mw will get you about 1 mile if set up the right way. I reccomend using the antenna that they supply. For two reasons it saves you time having to make your own. And second you don't have to worry when there is a storm. You must order the power supply with it or you could load it with the wrong power and blow the thing. Metal case is also neccessary to avoid a high pitch squeal
Using the FCC's comments about range is probably not the best way to measure Part 15 compliance; that may be what they expect the range to be, but they are quick to say in their circular that these are not the rules (and in fact, they also state that they expect AM range to be 200 feet, and there are many FCC approved installations that get far, far greater range than that). They also don't specify the type of radio used to achieve that range.
The actual rules in the U.S. state that an FM transmitter has to have a field strength of 250 uV/m at 3 meters (in Canada it's 1000 uv/m). Physics dictates what the distance covered will be.
If you have an unobstructed view to your FM antenna, then you can easily calculate what the field strength will be at a given distance; it's basically the simple inverse of that distance. So the strength will be 125uv/m at 6 meters, 62.5uv/m at 12 meters, etc.
If you have a radio for which you know it's sensitivity, you can then easily determine whether you are in compliance with the regulations or not. As an example, most car radios (which have antennas about a meter in length) have sensitivities for FM mono in the 3uv range with quieting - for a sensitivity of 3.8uv, that translates to about 192 meters or 630 feet. Of course, any obstructions will dramatically reduce the field strength. The sensitivity of portables is much less (along with the selectivity, which I have found to be the limiting factor; most portables were not designed to stop the bleeding over of strong signals onto weak ones). And if you broadcast in stereo, expect to cut your usable distance by a factor of up to 10 (that same car radio that will quiet with a 3.8uv mono signal probably requires 30uv for stereo with quieting).
You can also expect greater distances if you can tolerate noise (the absolute sensitivity of the radio is generally called the RF sensitivity, which determines the weakest signal you can expect to hear, with a lot of noise - some Marantz home stereos from the 1970s were in the 1uv range).
So the easiest, seat of the pants way to determine if you're Part 15 compliant - get a clear path to your transmitter, determine the sensitivity of your radio with quieting, find the the maximum distance before your signal gets noisy, and if you use the above example, if it's greater than 630 feet, you probably are not legal. Not a field strength measurement, but a lot more accurate than the 200 feet rule.
Thanks for the very good and clear writeup of the part 15 FM situation.
I do not intend to detract from what you posted, though physical reality might.
The weakness for measuring field strength is in the receiver and receiving antenna since the actual sensitivity of the receiver and the gain of the antenna are not known (to at least this) consumer. I have no idea of these specs. for my radios.
Even if known from factory specs., a slight deviation due to manufacturing tolerances may vastly affect the range and therefore the assumed field strength. Consider that a receiver specified at 3 uV sensitivity may actually have a sensitivity of 1.5 uV for a certain degree of quieting. This would translate to half the allowed field strength allowed by the rules. Perhaps the antenna or coax diminishes the signal delivered to the receiver by 1/2. This, unless known and accounted for, would lead one to believe that the 3m FS is OK when in fact it is double the limit.
It is a difficult problem for folks with average equipment and information to assess compliance. True, the 200 foot suggestion is not much in the way of guidance, but it is probably in error on the conservative side.
Your ideas are valid, but I fear the unknowns at the receiver end make reasonable estimates of the field strength difficult.
Neil