Jump to content
Light-O-Rama Forums
Sign in to follow this  
Elizabeth Perrone

FM Transmitter

Recommended Posts

Paul C wrote:

I used this antenna to video my house from up on the adjacent hill. Three houses distance is fine. As far as the FCC is concerned, the total watt out put is still the same so there should not be a concern, so I have been told by some of my HAM operator friends. Actually the output is reduced by the longer wire adding to some DB loss. To my knowledge the signal does not walk on other stations.

Share this post


Link to post
Share on other sites

Here is a review of the lower-priced EDM LED vs. the Ramsey FB25B.

This is from the EDM yahoo group ... from a member.

http://lightorama.mywowbb.com/view_topic.php?id=17299&forum_id=80

I agree that I don't know how much distance people really need for a light show.

I can see if you live in the country or on significant acreage that further distances might be warranted, but in town, it seems like a block should suffice for most.

Share this post


Link to post
Share on other sites

Paul C wrote:

As far as the FCC is concerned, the total watt out put is still the same so there should not be a concern, so I have been told by some of my HAM operator friends.

That's not correct. FCC part 15, section 15.239 limits the field strength of an unlicensed FM transmitter to be less than 250 microvolts/meter at a distance of 3 meters. The part 15 regulations don't specify a limit to the total power output.

On the other hand, FCC part 97 (which governs ham (amateur) radio), section 97.313 (;) limits transmitter power to 1.5 kW. There is no restriction to the field strength of the transmission.

This is why a ham radio operator will invest heavily in efficient antennas, in order to get the most transmitted field strength, also knows as Effective Radiated Power, from the transmitter power allowed. This thinking is deeply ingrained in most ham radio operators, so it is not surprising that they will assume the same thing applies to low power FM radio transmitter limits. But this is not the case.

In a Christmas light display, there are only two reasons to locate the antenna away from the transmitter:
  1. To get the signal closer to your audience (cars); and
  2. To keep the signal away from your computer and LOR network.

To use the antenna to get additional distance is the same, in the FCC's eyes, as turning up the power, of which both the Ramsey and EDM transmitters have easily enough to exceed the FCC regulations.

Share this post


Link to post
Share on other sites

Thanks for the info Steven, will definitely lower its output to a hundred feet or so. that is all I really need. I actually put the antenna on the unit as a way to make it to the street , but found it went much further.

Share this post


Link to post
Share on other sites

Excellent post Steven!!! Very well written and easy (for even me) to understand !!

** folks, please read his post above **

That's related to why many folks incorrectly assume that if they buy an FCC certified transmitter (which EDM and Ramsey units are not) ... that this will automatically makes them FCC Part15 compliant (in operation), which is an incorrect assumption.

Perhaps using it unmodified and in average conditions, then maybe. Those units can only be 10mW (or less) and have built in antennas which are generally poor, or just short wire antennas like what the EDM ships with. An example of a certified unit would be Panaxis ACC100 (lousy, trust me) or a CCRANE.

But if I person then takes an FCC certified transmitter and attaches a really efficient antenna ... they are much more likely to now be in violation again because of how far the power goes using that better antenna vs. the included (crappy) wire antenna.

Similarly, if you place the unit up high in a really efficient location, you could also violate part15 power technically, or accidently, even with an FCC certified transmitter. So as Steven said ... getting the better range certainly increases the odds your in violation of Part15 power transmission limits.

So thats why I think the goal should be 'just as much range as you really need and not much more'. So if your show has viewers for 3-4 houses away ... then maybe thats your max (non breaking up sound) range. Thats why having adjustable power seems to easiest way to limit your range, IMHO. Both Ramsey and EDM units can do this ... and turning a dial is pretty easy.

If you buy a fixed power unit, you are stuck with what it does. Then your only tweaking options are to pimp or de-pimp out the antenna and to tweak the antenna location. Some folks, way more in the hacking side would also use non-standard voltages ... which is certainly not for everyone and probably not advisable.

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.
Sign in to follow this  

×
×
  • Create New...