How many Part 15 FM transmitters can I put in a constellation, each 200' from a base station?
How many Part 15 FM transmitters can I put in a constellation, each 200' from a base station?
Applied Wireless http://www.appliedwireless.com/index.cfm makes what appear to be decent little microwave units with good specs, very small, not too expensive. I was thinking I could use one base station transmitter mounted with a BCB transmitter and a half-dozen receivers with BCB transmitters. That should get good coverage in smallville here (Friday Harbor, WA), dontcha think?
As I recall the only limit in the rules to the number of transmitters applies to those which are user built which is five. This is a gray area since if the transmitters are built from kits they may not be considered user built in the intent of the rules yet they are not considered preassembled either.
There is no limit to the preassembled units such as the CCrane.
The link you posted timed out for me and I will try later.
Neil
I was interrupted during my last post so I am adding that there was some discussion here or on another board about what the FCC considers "co-ordinated" transmitters. You might want to do a search on this. My recollection is that the FCC doesn't want these used under part 15 though there is nothing in the rules of which I am aware which prohibits this.
Neil
I always like to put the Canadian perspective forward, as I've noted that there are a few of us here and posting.
In Canada, there is actually a rule that states that only ONE transmitter can be used to transmit a broadcast source. Presumably if you want to use more than one transmitter, you have to have a different source. This, I would imagine, is to stop people using co-ordinated transmitters to broadcast the same signal. The rule does not come from Industry Canada, but from the CRTC, in one of their conditions exempting micro-broadcasters from the need for a CRTC broadcast license (one of our quirks, you have to deal with two government agencies here and actually get 2 licenses - if you want to be licensed - one from Industry Canada and one from the CRTC). Of course, a micro broadcaster has to meet Industry Canada guidelines for signal strength, purity, etc. which is found in the BETS-1, BETS-4 and BETS-5 documents (they cover both the AM and FM band perspectives and can be found on the Industry Canada web site).
If anyone in the U.S. thinks the FCC Part 15 standards are unclear, all they have to do is to read the above cited references to see REALLY muddy waters.
I'm not entirely sure what the FM limit is for transmitters.
I'm assuming there is none.
"There is no limit to the preassembled units such as the CCrane."
OK, thanks much. I wasn't sure if that only applied only to AM. I'm thinking about going with Decade MS-100's. Start with one, then add the 900 mHz TX and RCVR and another Decade whenever it can be financially supported, and so on. I'd probably go with dish antennas, maybe even home-built ones.
Kits cannot be altered or they can lose their certification. E.g., you can tune, but not alter the approved circuitry in a SStran, and it is not a 'system'. There are no limitations on hand-built units made from scratch under experimental conditions, but they must still comply and follow good 'engineering practices', whatever the FCC determines that to mean (another example of purposed ambiguity). IIRC those are the ones which don't allow more than 5 units ... but I'm unsure about that, I'll have to explore more. And neither accounts for antenna systems, so that comes under other regs.
"The link you posted timed out for me and I will try later."
I just tried it, came up right away. Probably was being updated or busy. These appear to be very nice professional-type units.
Ken,
Kits don't have certification so there is no problem experimenting with or modifying them.
As far as "purposed ambiguity" with good engineering practice is concerned an engineer knows what this means and it is not ambiguous. It is not as subjective as it may appear to a layman. Many times good practice goes beyond the physical design and construction and includes competent testing and documentation. I would not expect a hobbyist to perform at the level of an engineer but from what I have read here many who post do write about checking their rigs for modulation, spurs, harmonics, and other function. In my opinion, this is most likely sufficient to satisfy the FCC good engineering practice statement.
The link did work for me later and they look like nice devices. They operate on the same band as the "Rabbit" I mentioned in another thread. It does seem from their description that their range is about the same as a part 15 AM unit though.
Neil
"They operate on the same band as the "Rabbit" I mentioned in another thread. It does seem from their description that their range is about the same as a part 15 AM unit though."
I haven't seen a "Rabbit" (other than rabbit ears ;)), but those devices are Part 15 units, and at 900 mHz they aren't vulnerable to much interference ... which means the signal is clear over the operating range, and won't affect the transmissions in the FM bcb. Further, if I replace the antennas with highly directional dishes, we can get much more range between satellites. That makes them useful as remote STLs, which is the goal.
Ken,
The mention of the Rabbit was here: http://www.part15.us/node/2179#comment-8394
I understand what you are proposing regarding the STL application and it is a good idea which I hope you pursue and report here about.
One of the FCC "gotchas" is that with certified devices the antenna provided with the unit must be used to maintain certification and authority to operate. There are also restrictions regarding multipoint reception which may apply.
I am not trying to talk you out of this but you should know what you are dealing with before investing money and time.
Neil