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Hello I am a novice and I am looking for a solution to my problem. I do mobile drive in movies for college campuses and golf clubs. I have gotten requests to utilize a system where viewers can tune in on their
radios in cars or golf carts. The question is utilizing Part 15 equipment, would something like the SS Tran 3000 AM work, or AM band or should I be looking at FM? Most situation would be in parking lots or soccer fields and transmission distance
of about 100 yards or football field, tops. Advice appreciated.Thanks in Advance
Randy in Orlando
Total posts : 45366I would go with AM since Part 15 AM can give you a coverage area of well over 100 yards, all from a single transmitter and antenna.
Where as in FM, the field strength is incredibly limited to 250uV at 3 meters from the transmitting antenna. That equates to about 300 feet with a simple dipole or telescoping whip antenna and under optimum conditions. To cover an area the span of 100 yards, you would need several FM transmitters scattered in the coverage area and all would have to be either synchronized for the same frequency (very difficult to do) or each transmitter on a different frequency and cause confusion to the audience as to which particular frequency to tune for best reception.
AM would be the solution here. And since most new vehicles now are equipped with AM radios which pick up HD and C-QUAM Stereo, you can run an AM C-QUAM Part 15 transmitter and transmit full hi fi stereo audio on the AM band.
RFB
Total posts : 45366RFB
Thanks for your response. I have been watching an SS Tran AMT3000, would this do the trick in stereo? What kind of a transmitting antennae set up would I need for a soccer field?
Thank you!
Randy in Orlando
Total posts : 45366Can I assume you present your mobile drive-in theater on college campuses? If so the FCC rule 15.221 (b) allows higher power for campus radio stations. Of course you’d then need a more powerful transmitter, and I do not know what to suggest.
In the case of plain 15.219 step up to the AMT5000 or the Hamilton Rangemaster 1000.
What do you use for a screen?
Where do you locate your projector?
Is it a nighttime operation? At night there is a lot of AM radio background noise coming from sky wave signals.
BACK AGAIN
Some more thoughts
FM might be worth testing…….
Get your antenna high in the air with this
http://www.ltaprojects.com/Use an industrial grade transmitter like this
http://www.comtek.com/bst25.htmlThat will put you on the lower edge of the dial, around 87.7.
Talk to Comtek about the legality.
Total posts : 45366That 15.221 applies to the college only. I do not believe it would cover someone’s operation that is not full time related to the college to allow a higher power.
The operation is not focused around educational radio per say, but merely a wireless link for movie sound. If the operation is directly linked to and administered and funded and controlled by the educational institution, and set up by the educational institution, then I believe the slightly higher power levels allowed could apply.
But don’t be fooled by that provision. It ONLY allows higher field strengths and power levels ON the campus only. Beyond the campus parameter, that signal must meet the strict 15uv @ 30 meters from that campus parameter.
Not easy to do with a free radiating antenna element sticking in the air. For CC systems its not difficult at all, but if you take a look at the history record of college radio stations operating under the Part 15 rules, there were very very few of them that set up their stations to operate from an antenna, they went carrier current, or applied for non-commercial licensed radio service.
Also that Comtek unit, is not authorized to operate under Part 15.239. It is authorized to operate under Part 15.231 (76-88Mhz) and Part 15.209 (100uV@3m). Regardless that the unit can transmit on the lowest channel in the FM band, the unit is not authorized under Part 15 to “broadcast” on that frequency or operate under the conditions to which the Op is intending.
RFB
Total posts : 45366All events are at nigh time. We use inflatable front projection screens. If the FCC rules allow college campus higher power radio stations, your saying an SStran AMT3000 would be overpowered on any frequency? This is a big test, are you aware of any places that rent transmitters?
I really liked the price on the SStran AMT3000, will look into MT5000 or the Hamilton Rangemaster 1000, used if possible..
As for antennae placement would I need to get an antennae up high foe AM as well as FM?
Comtek looks pricey.Thanks again you are a big help Carl, as I am lost!
Randy in Orlando
Total posts : 45366“I have been watching an SS Tran AMT3000, would this do the trick in stereo?”
No, not without some modifications to the AMT3000 or any of the other well known transmitters such as its big brother AMT5000 or a Rangemaster or Procaster. None of them transmit in C-QUAM.
There used to be an individual who made kits of AM C-QUAM transmitters, but no longer does and it is very difficult to find one even on ebay.
However there is one company out of Greece that does make a Part 15 compliant AM C-QUAM transmitter.
ASPISYS AMAX-1 AM C-QUAM Transmitter
I have two of these units both running my LPB carrier current transmitters and their performance is right up there with licensed Part 73 C-QUAM exciters. They are a trustworthy company and I have had no problems dealing with them. Fast shipping and insured and great tech support after the sale.
As to an antenna, the first question that should be asked is will your antenna system be permanent, or would it need to be mobile from one location to another? If so, are these different locations willing to allow you to install a permanent 3 meter antenna so all you have to do is simply be on site and hook up?
If the antenna cannot be permanent, then you can create a mobile 3 meter antenna and use ground radial wires extending from it. Simply lay them down onto the ground below and at the center of your antenna mounting stand, use 10 to 20 foot long solid copper grounding wire and arrange them like spokes in a bicycle wheel with the antenna at the center. Roll up the ground wires when done and pack er all up and head on to the next location.
Forget about the Comtek unit, its not authorized to operate in the manner in which your proposing. It is not a Part 15.239 FM broadcast band transmitter. It is an IFB/monitor extension unit authorized under 15.231 for intermittent and periodic transmissions, not a constant broadcast. Besides all that, the unit cannot exceed 100 microvolts per meter at 3 meters from its antenna…even weaker than a Part 15.239 transmitter which can operate at 250 microvolts per meter at 3 meters!
RFB
Total posts : 45366The portable ground radials seem like they could be an underfoot safety hazard… you don’t want people walking around in the dark stumbling over the wires.
The AMT5000 is more efficient than the AMT3000, it will put more juice into a good antenna, and the power input to the final can be set higher than the 100mW standard……
I think also the Hamilton Rangemaster has the adjustable power control, and it comes ready built, whereas the AMT5000 is a kit.
The Comtek is expensive…..and I figured that a movie would qualify as “an intermittent” event. The Comtek must exist for some reason. If it’s illegal to use, why does it exist?
Total posts : 45366“The Comtek is expensive…..and I figured that a movie would qualify as “an intermittent” event. The Comtek must exist for some reason. If it’s illegal to use, why does it exist?”
Those are often used on live remote television newscasts for the anchor’s IFB earpiece. The receivers are placed on a shelf in the set’s table and can feature multiple IFB outputs or feed a common IFB distribution amp to each news anchor. The TX would be feeding audio from the remote live truck where it has all the other gear doing the transmission back to the main studio ENG pickup dish or dome, probably has a director operating a video switch console, and audio operator operating an audio mixer console, and an engineer close by who put it all together and thanks Comtek for developing a close range wireless solution to a remote operation so there is less wires to run, break, choke, trip over, disconnect during “ON AIR”…all sorts of things like that.
And Carl..it is NOT illegal to use under Part 15.231. It IS however illegal to be using it under Part 15.239 because the Comtek unit is certified under Part 15.231 and not under Part 15.239.
RFB
Total posts : 45366it cuts off at 87.8 mhz and operates under part 74 according to the manual on the comtek wensite.
Total posts : 45366HERE IS A LINK to some Comtek Info on my website.
Scroll down the page to the picture of the Comtek and click on the picture.
Total posts : 45366“it cuts off at 87.8 mhz and operates under part 74 according to the manual on the comtek wensite.”
Looks to me like another typo on the wensite…like Radio System’s wensite. 😉
Regardless, the device is not intended or authorized to operate for Part 15.239 uses.
And since the Op will be running an unlicensed transmitter in locations where there will be licensed stations and no doubt an engineer or two or administrator of the college, I would be adhering to Part 15 like stink on #@^!…know what I mean?
The Op will be running an unlicensed transmitter in an area where recently there has been a lot of FCC actions going after violations. To me it would make sense to be doing this thing by the book 200 percent and then some..given the factors and environments and things.
Now if the Op had enough receivers meant to operate with this transmitter and gave it to every viewer that shows up, and have enough of them, he could use the Comtek unit and feel confident and prove to an FCC inspector that he is using the transmitter as designed with its intended receiver/s for short duration transmission of audio content for close range reception to these specific receivers which obviously are not “general public” radios like that in your car, then perhaps.
But lets not overlook something really more important. The Comtek operates right at the bucking heads of the old ch 6 TV band and the FM broadcast band. Remember how finicky the FCC was..and still is about transmissions in that range of frequencies!!
And the permissible field strength is WEAKER than that allowed for Part 15.239!!!!
So what would be the point in using a weaker transmitter, and more expensive one to boot, when maximum coverage is the goal in the Op’s intent and be legal?!
RFB
Total posts : 45366This thread is confusing, over my head, I’m just an AV guy. I don’t think it would matter if I transmitted a soundtrack in stereo or not. I just want to do the job so they can hear the soundtrack.
Tell me what could I expect with an AMT3000 and a 10′ antennae at night on a college campus soccer field?Randy in Orlando
Total posts : 45366This is a better debate than the ones done by those peculiar candidates…
The Comtek has been ruled out……. an FM transmitter with Canadian power levels is not ruled in….. we are zeroing in on AM as the best means for this job.
But what about the nighttime sky wave noise problem?
Total posts : 45366The potential for night sky wave could pose a problem depending upon the conditions AND operating frequency.
First, lets slow down the in-rush of info onto the Op.
Ok your asking about the AMT3K unit. From what I have read here and elsewhere from owners of the AMT3K, it does the job very well with a proper antenna and ground system. It also does a fair job with a simple 10 foot long piece of wire connected to the antenna jack, but that won’t cover an area the size of a soccer field or football field or parking lot of the same size.
Not clearly or free from any sky wave stuff.
The mobile antenna proposal I gave earlier is your best choice. Consider this.. your projection system is somewhere safe..right?
Well why not put the AM system there as well? Surely a 40 foot square area can be secured so you can lay down 10 10 foot long wires for a ground and the antenna/coil on a short stand at the center?
Within the library are some good reference material to making your antenna system and ground system, all of which can be mobile and no more of a hassle to put up than all the projection systems and air screens and current method of delivering the sound.
RFB
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