HFU HF Underground
Technical Topics => Part 15 AM and FM Station Operation => Topic started by: tybee on September 29, 2020, 2223 UTC
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In a previous thread about the FCC refusal to grant higher part 15 FM limits for churches during the covid epodemic... I mentioned that perhaps the churches should look into how the new Walmart Drive-in movie parking lots are doing it - and the answer is..evidently, they are using the FCC Certified part 15 AXS-FMTD fm transmitter manufactured by BMV (Broadcast Vision Entertainment)
It cost $299 and boast a range of 'up to 300 feet in all directions.
https://broadcastvision.com/drive-in-wireless-audio/
It seems that 300 foot would be sufficient for most church parking lots, but I suspect those churches are really desiring to reach the surrounding area of homes... But anyway Pia had suggested that if churchs wanted to extend their fm range then simply use more transmitters... With that in mind, a single transmitter could not likely cover one of the Walmart Supercenter parking lots to supply audio of the film's, so, presumably multiple transmitters are being employed for each location..
But wouldn't multiple FM transmitters on the same frequency interfere with each other the same as it does on AM??? Maybe different sections of the parking lot provide different frequencies.. I don't know, but here's what little I do know about the Walmart Drive-in operation:
In 2003 Robert De Niro, Jane Rosenthal and Craig Hatkoff, founded the Tribeca Film Festival, Tribeca Film Festival International, Tribeca Cinemas and Tribeca Film distribution, all of which partake with numerous partnerships with other companies and organizations.. in this case Walmart to provide free outdoor movies in their parking lots -- and what Tribecca uses for its film festivals is the formentioned certified Part 15 ASX-FMTD.
Personally, I still think using AM would be the better option for both Wa!mart and the churches. I wonder why they continue to focus on the FM option.
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..Personally, I still think using AM would be the better option for both Wa!mart and the churches. I wonder why they continue to focus on the FM option.
Because the AM in a modern car sounds like sh*t, and some don't even have it. That coupled with the finicky nature of most LPAM antennas verses the 'set it and forget it' nature of a small FM setup. I suspect the folks running these things are not engineering caliber people.
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Hi Tybee, if 300 feet is the maximum range that the Decade can reach, I could see a lower range for stereophonic sound, since car radios will blend the channels when the signal is weaker. For a movie, the audience would want the soundtrack to be in stereo.
For that reason I think AM might not be so good for movies, radio-restricted mono sound wouldn't be what the viewers expect. On the other side, I could see AM for a pastor's voice at a church, and preaching is commonly heard on AM stations. An AM transmitter like the Talking House can be used, and it's almost as easy as AM, the automatic tuner, just provide a mono feed.
Multiple transmitter FM shouldn't have the interference potential of AM with transmitters on the same frequency, due to FM's capture effect, but FM can still interfere when transmitters are equal strength, or signals are weak at the receive location, then they could intermodulate with each other and cause distortion.
Good questions, now I want to see a WalMart movie.
Bear
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That looks like a $17 lighter plug transmitter in a bigger case with a telescopic antenna.
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"That looks like a $17 lighter plug transmitter in a bigger case with a telescopic antenna."
I sent an email to them and got some PDF's back.
It's a little better than that. But you can get 5/15 watts from China for half the $$.
I also sent an email to Parkinglotradio, that's going nowhere.
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