Jump to content
Light-O-Rama Forums

FM Transmitter question


oj70chevy

Recommended Posts

Good advise. I am going with the EDM for the quality not the distance. The most distance I need is 2 houses down as everyone here has many bushes and trees. the longest distance you can see my house from is two houses down in ether direction. Thanks for the info. i plan on using the lowest setting. and on a side note what or how could I do a test to verify beside driving around to make sure i am not causing any issues for the men in black.

Link to comment
Share on other sites

  • Replies 136
  • Created
  • Last Reply

Top Posters In This Topic

  • Timon

    13

  • oj70chevy

    13

  • PMC

    12

  • George Simmons

    10

I for one put the blame stright on the FCC because of the way they require one to test. There is no good low cost field strength meter the average person could test with available at a reasonable price. It would have been much better to have had an alternate testing method.

Next, there is absolutely no, let me repeat, NO reason to be putting any antenna on other than a simple quarter wave or rubber ducky antenna. As soon as you start adding gain antennas you going to violate part 15.

Now how do we stay within Part 15 and still have enough signal? Well this is what I'm doing. I'm putting a Part 15 transmitter inside a CG-500 or CG-1000 case feed with a cat 5 cable. The cat 5 will supply stereo audio, RDS data (future) and power and yes you can get all that through a single cat 5. The whole point to this is to be able to put the transmitter outdoors close to the street so you don't have to violate Part 15.

Rant on
Now at the risk of offending someone, anyone who knowingly violates Part 15 needs their head examined and deserves any fine they might get. That may be harsh but rules are rules and if you break them then expect a knock on your door.
Rant off

Link to comment
Share on other sites

Timon wrote:

I for one put the blame stright on the FCC because of the way they require one to test. There is no good low cost field strength meter the average person could test with available at a reasonable price. It would have been much better to have had an alternate testing method.

This answer is simple, you have to purchase a FM Modulator or Transmitter that is Part 15 Compliant, it will have a certification sticker on the chassis and it will be printed on the box, all others that are sold without the FCC approval are Not Part 15 compliant so no testing is needed because it is already illegal. If you purchase a FCC legal/part 15 Compliant transmitter and you add an antenna, oops there goes your certification, now you can add external antennas to UN-certified transmitters and you can use them but you still have to be Part 15 which is 250 microvolts per meters 3 meters from the antenna
and yes you need to get that measured, which loops us back to your original post
But as I stated on here, if you stay within the 1-10 Milli-volt range you are still in violation but at least your not 1 to 20 watts

Next, there is absolutely no, let me repeat, NO reason to be putting any antenna on other than a simple quarter wave or rubber ducky antenna. As soon as you start adding gain antennas you going to violate part 15.

Very true

Now how do we stay within Part 15 and still have enough signal? Well this is what I'm doing. I'm putting a Part 15 transmitter inside a CG-500 or CG-1000 case feed with a cat 5 cable. The cat 5 will supply stereo audio, RDS data (future) and power and yes you can get all that through a single cat 5. The whole point to this is to be able to put the transmitter outdoors close to the street so you don't have to violate Part 15.

Something I never talked about on here but if you want to go the distance and still be Part 15 its called a "Leaky CoaxDescription of "Radiating Coax" or "Leaky Coax" transmissionLeaky coax is a special type of coaxial cable that is designed to radiate or leak the RF signal traveling within it. In essence the cable is the antenna or radiator. This cable is designed to radiate the signal by a controlled amount, allowing nearby radios to receive the signal radiating from it. Leaky coax systems are usually designed by engineers to insure compliance with Part 15 regulations.This is so you can go the distance, like laying the cable along your property for 1000's of feet and still be Part 15, tunnels use Leaky Coax

Rant on
Now at the risk of offending someone, anyone who knowingly violates Part 15 needs their head examined and deserves any fine they might get. That may be harsh but rules are rules and if you break them then expect a knock on your door.
Rant off"

Could not have worded it better myself
Link to comment
Share on other sites

PMC wrote:



Something I never talked about on here but if you want to go the distance and still be Part 15 its called a "Leaky CoaxDescription of "Radiating Coax" or "Leaky Coax" transmissionLeaky coax is a special type of coaxial cable that is designed to radiate or leak the RF signal traveling within it. In essence the cable is the antenna or radiator. This cable is designed to radiate the signal by a controlled amount, allowing nearby radios to receive the signal radiating from it. Leaky coax systems are usually designed by engineers to insure compliance with Part 15 regulations.This is so you can go the distance, like laying the cable along your property for 1000's of feet and still be Part 15, tunnels use Leaky Coax



Speaking from experience, leaky coax remains an expensive inefficient option, especially for the hobbyist.

Most wireless carriers have shied away from using leaky coax in applications like tunnels, in-building, etc, due to the cost per foot, and cost of install. There are cheaper more efficient ways to distribute signal, indoors or out.

It was what seemed like a good idea when first developed, but never gained any traction.
Link to comment
Share on other sites

"Radiating Coax" or "Leaky Coax" transmissionLeaky coax is a special type of coaxial cable that is designed to radiate or leak the RF signal traveling within it. In essence the cable is the antenna or radiator.". I almost added that to my post but at $3 to $5 or more per foot plus the technical requirements to put it in I felt is was more than most DIYers could handle. If however you have a large area to cover it might be worth it.

In my case I only have a 50' frontage and the forward gable is 25' or so from the curb. If I put the transmitter in the middle of the house on that gable, see www.facebook.com/warrenlights , I should have good coverage for at least 2 to 3 houses in either direction.

Link to comment
Share on other sites

Timon wrote:

"Radiating Coax" or "Leaky Coax" transmissionLeaky coax is a special type of coaxial cable that is designed to radiate or leak the RF signal traveling within it. In essence the cable is the antenna or radiator.". I almost added that to my post but at $3 to $5 or more per foot plus the technical requirements to put it in I felt is was more than most DIYers could handle. If however you have a large area to cover it might be worth it.

In my case I only have a 50' frontage and the forward gable is 25' or so from the curb. If I put the transmitter in the middle of the house on that gable, see http://www.facebook.com/warrenlights , I should have good coverage for at least 2 to 3 houses in either direction.

There are definitely a lot of options to over-engineer what we want to do. I'd love to see the home/hobbyist application where leaky coax becomes the best solution.

A decent transmitter, efficient antenna, designed for the FM band, and with good coax/connectors, 99% of all FM challenges are resolved.
Link to comment
Share on other sites

I have designed a few Leaky Coax and yes, it is technically challenging but you can research a way to do it cheaply on the net, I used quad shield RG6. 3000 ft of RG6

Also another option, and this is for those who have multiple transmitters

daisy chain them, I buy my FM transmitters for $30.00 each. take 2 or 3 or 4 of them and place them about 300 to 500ft feet apart run your audio through Cat5 cable because of the wavelength is so far apart and create a "network" there is nothing in the FCC rules about linking transmitters together. and if you space them at about 500ft you can create a "cellular" network for your FM broadcasting.

I was going to do this for a local casino near me that wanted me to sequence a 1/2 mile of trees along a road and this is what I was going to do to make it heard and still keeping everything Part 15

I had a 70v Pa system and I used a single 2 wire 22gauge cable and the audio was mono, but it sounded good

"The Picture"

I attached a way I did my broadcasting for the last 3 years I never had a problem receiving my audio and the antenna is the white wire wrapped around the telescopic antenna which was my back-up Ramsey which I have since retired to the workbench, I now use a Shed and I put this transmitter in the rafters and I took this LOR case and built another controller.


Attached files 313965=17134-100_5448.JPG

Link to comment
Share on other sites

Paul, I'm betting that some are thinking right now, how do you keep them from stepping on each other. You and I know why but for those that don't here is the reason.

There is an effect when broadcasting FM call capture. If there are two or more signals on the same frequency and your in between them your FM radio will capture the strongest one even if the difference is very small.

There is an area between them where the signals are almost equal and some radios will want to hunt but move yourself a few feet toward either one the signal will clear right up.

This doesn't work with AM as you'll hear both plus a lot of whistles.

Oh OMT, Paul where do you get good $30 FM transmitters?

Like the picture, that's just what I was planing other than using a CG case rather than LOR's. In addition keeping it outdoors keeps the FCC from coming into your house.

Link to comment
Share on other sites

Timon wrote:

Paul, I'm betting that some are thinking right now, how do you keep them from stepping on each other. You and I know why but for those that don't here is the reason.
At the very low power generated by these units, the "multipath" is minimal and separating the FM transmitters about 300 to 500ft is the sweet spot, I have tested this and I have had no problems, when driving down the road there is a wisp of changing "sites" but no overlap if you get overlap separate the units some more you have to remember.....very low power of Part 15 is lower than 1mW
There is an effect when broadcasting FM call capture. If there are two or more signals on the same frequency and your in between them your FM radio will capture the strongest one even if the difference is very small.

There is an area between them where the signals are almost equal and some radios will want to hunt but move yourself a few feet toward either one the signal will clear right up.

This doesn't work with AM as you'll hear both plus a lot of whistles.
Yes, this is for FM only, AM Part 15 has a better coverage area

Oh OMT, Paul where do you get good $30 FM Transmitters?
This model is only a 8 channel, I got a 40 channel and I bought 4 of them when they were discontinued, I still have 2 of them in the box. this is an 8 channel and check its frequencies, but there are others that perform the same way, and yes it is FCC certified

Like the picture, that's just what I was planing other than using a CG case rather than LOR's. In addition keeping it outdoors keeps the FCC from coming into your house.

Here is a picture of the back of my FM transmitter you can see its FCC certified


Attached files 313969=17135-FCCID.JPG
Link to comment
Share on other sites

DonFL wrote:

Neat idea re the network of transmitters.

We'll have to agree to disagree on the benefit to humanity that leaky coax offers...:P

agreed, I was just tossing options around, keeping everybody informed of all ways to push a signal and keeping legal
Link to comment
Share on other sites

Timon wrote:

Paul, I'm betting that some are thinking right now, how do you keep them from stepping on each other. You and I know why but for those that don't here is the reason.




Maybe I'm reading this wrong, but it appears you are saying "Paul and I are smarter than the rest of you". I hope that I AM reading it wrong and that is not what you are meaning. I would have just left that comment out and posted the rest.
Link to comment
Share on other sites

shfr26 wrote:

Timon wrote:
Paul, I'm betting that some are thinking right now, how do you keep them from stepping on each other. You and I know why but for those that don't here is the reason.




Maybe I'm reading this wrong, but it appears you are saying "Paul and I are smarter than the rest of you". I hope that I AM reading it wrong and that is not what you are meaning. I would have just left that comment out and posted the rest.

Naw, I don't think that's what was intended, I don't even like saying I'm a Professional Radio Engineer, I just do what I do like everybody
I mean really, like everybody here I play with Christmas Lights all year long, and spend hours at a time trying to make something blink & fade a certain way for just 3 seconds for a part of a song that nobody even notices :P
Link to comment
Share on other sites

No, I was just saying the most people would think that the two signals would step on each other. Paul and I being Hams understand about FM capture where the average Lay person would likely not. It was just to inform those that didn't know.

Link to comment
Share on other sites

Timon wrote:

No, I was just saying the most people would think that the two signals would step on each other. Paul and I being Hams understand about FM capture where the average Lay person would likely not. It was just to inform those that didn't know.

Not to nitpick, but I believe Paul said he wasn't a ham...but yet he DOES, I'm sure, understand capture effect.;)

And I've met several hams who probably couldn't explain capture effect, and, obviously, non-hams who could.

For the record, I've been licensed as a ham for 35 years, 28 of those as an extra (AE4DW).

I think Pete's point is, your comment came across a bit condescending, whether you meant it that way or not.
Link to comment
Share on other sites

And that brings us to today's point to ponder - the old "PTP", to speak in lay person terms.

Have any of you licensed Hams ever come across any licensed Cheese? Seems like some interesting possibilities...

Link to comment
Share on other sites

And no, I'm not a Ham Operator, I'm a AM/FM Radio Broadcast Engineer
(Chief Engineer for 22 years)
I did 50kW 3-Phase AM directionals and to many FM's to mention, okay I'll mention
I worked for 17 radio stations in my career

I can get my ham ticket, but as I stated radio is a job for me, not a hobby
this here is my hobby that I have to broadcast for people to hear and my system sounds great,

But I'm obligated as a licensed FCC Operator to pass knowledge along to those who aren't broadcast educated to know what the rules are and what they are doing, and all the Amateur Radio Operators on here have to same obligation to educate, its our jobs and its what we do

here is a video from 2011 and I recorded the audio right off one of my handheld portable FM radios connected right to my camcorder

Link to comment
Share on other sites

Guest
This topic is now closed to further replies.

×
×
  • Create New...