One of the guys on the other group I belong to brought up how some of the drive-in theaters he worked with operated their system. They had a transmitter that they hooked up a long run of "leaky" coax to with a 50 ohm resistor at the far end. The coax was buried under the field where the cars parked and radiated along it's entire length. No one place exceeded Part 15 limits but the whole area had enough signal to be picked up on all but the worst car stereos. Matthew Chambers, CBT, NR0Q Owner/Engineer *M Chambers Communications Engineering LLC* PO BOX 855, Moberly, MO 65270 Mobile (660)415-5620 www.mchambersradio.com
On Thu, Apr 2, 2020 at 3:54 PM Jim Walls via AMSAT-BB amsat-bb@amsat.org wrote:
On 04/02/2020 11:27, Scott via AMSAT-BB wrote:
Can anyone recommend a low-power transmitter for broadcast on the
commercial FM radio band? An LPFM license can be acquired asap, but the first order of business is finding some hardware.
As you can imagine, church gatherings are out of the question so I've
been asked to see if I can locate a "drive-in theater" type transmitter for short-range broadcasting to car radios.
Getting a LPFM license is not as easy and fast as you think. As for Part 15 transmitters, there are lots of them out there. There are also many available that are claiming to be license free, but not really meeting the Part 15 limits (especially if you put a "real" antenna on them). One of my other addictions is running a music synchronized Christmas light show. Almost every person running a music synchronized light show is running their music over an FM transmitter - sometimes in addition to outdoor speakers. There are several very commonly used transmitters. Search Amazon for CZE-05b and you will find lots of hits
- that's what I'm using. In my case, I have a homebuilt "real" antenna,
but I put a in line attenuator between the radio and the antenna to keep at least close to Part 15 limits.
As for the drive-in theaters, my assumption is that they are supposedly operating under Part 15, but I would be willing to bet that a lot are exceeding the field strength limits of Part 15 by at least a bit - directional antennas come to mind. I do know that the last time I did a FCC license search for the FM band, the nearest drive in theater (with their four screens) did not show up in a licensed listing.
-- 73
Jim Walls - K6CCC jim@k6ccc.org Ofc: 818-548-4804 http://members.dslextreme.com/users/k6ccc/ AMSAT Member 32537 - WSWSS Member 395
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