87.5 use for Part15?

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87.5 use for Part15?


 I am setting up a small broadcast with the intention of being Part 15 complient on the FM band this summer. I have already putchased the equipment to measure FS and have some know how on how to measure it.  I have read that Part 15 applies to anything in the 88-108mhz band, but what about the lower freq like 87.5? I have some devices that go down that low but these devices may be designed for use outside of the United States. So, can I transmit down there legally? I am using a Failsafe CZE-05B, in a basement using it's supplied antenna. It will be transmitting talk radio.

Measuring FS

CometGSR says:  "I have already putchased the equipment to measure FS and have some know how on how to measure it."

What "measurement equipment" have you purchased?

Was it expensive?

What FS readings do you observe on your measurement equipment?

Carl Blare

I don't have the station up

I don't have the station up yet. I did one test to make sure the transmitter worked. This summer I am going to try to get the FS right. I don't know if my FS equipment will be sufficient. I was going to try VHF 144mhz FS meter first, not sure if that is going to enough or not. Half the fun is getting the station legal. 

Quick Answer is No.

Part 15.239 of the FCC rules covers operation in the FM broadcast band and specifies the field strength limits for frequencies from 88 to 108 MHz.

It then mentions that operation outside of this band is governed by Part 15.209.  This part has a notation that operation in the band 76-88 MHz is not permitted except for perimeter protection systems.

You should read parts 15.239 and 15.209 for more information about this.



Stay out of the 144 MHZ Area

That is reserved for licensed Amateur Radio operators. (Hams) That's a sure way to land you in trouble with the FCC.

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

Highly aware of the 144mhz

Highly aware of the 144mhz band, but Ham equipment for measuring field strength is plentiful and (from the looks of it) can work throughout the VHF freqs. 

Thank you!

Thanks for the reply. I will stay above 88.1mhz. 

FS Meter

I read post #3 to say that he/she was going to try a FS  meter designed for the 2 meter band to measure FS in the FM broadcast band.  The results of this could be very interesting to us and I hope CometGSR will post what is found.

Many of us who use FM under Part 15 do not have any means of measuring the FS for compliance and instead rely on the FCC advice that the expected range of a FM transmitter should be about 200 feet.  Though the FCC doesn't specify the receiver/antenna used it is thought by many that this range using a car radio is "close enough" to be legal.



Another Way of Estimating

Several models of TECSUN portable radios have field-strength read-outs in dBu and S/N (signal-to-noise).

My TECSUN PL-310 also has an extremely sensitive FM radio, which is a very reliable indicator of where the signal fades into the noise, which happens when the reading shows 07dBu 07 S/N.

I set the power output of my FM transmitter so the fade-out is achieved at the street 100' from the building. The auto radio agrees with this setting, and loses the signal at the end of the driveway.

I don't go for the 200' because there's nothing in that part of the range except empty space.

Carl Blare


The transmitter you have is, just to let you know, even with it's own antenna nowhere near legal, unless you have an attenuator on the output to drastically lower the power.


In Canada, 87.5 is not legal for unlicenced use.

There *may* be a legal way to

There *may* be a legal way to transmit below 88.1 and that is with the new Whitespace rules that are being discussed/soon to be coming.  You would need to use a certified device, as per the FCC rules.  It is still unclear as to whether broadcasting would be allowed (the rules are mainly to allow the use of wireless microphones).

RE: Legality of the CZE-05B

I know of the controversial nature of the CZE-05B. It isn't the most ideal device but with it being in a basement and an attenuator attached, I am hoping to get this as close as possible to legal signals. This just gives me a chance to see if I like the hobby enough to move forward with it.

If all you're looking for is

If all you're looking for is a way to introduce yourself to the hobby, you'd probably be better off getting a Part 15 certified transmitter.  They don't have to cost a fortune.  I recently picked up a new Maxell P-13 off e-bay for $1 (plus shipping, which was just a few dollars).  It's Part 15 certified, and judging by the range I receive (200-300 feet with a car radio), it's pretty close.  It sounds almost as good as other FM transmitters I've used that cost hundreds of dollars (I can't drive the audio as hard as the Decade's, for example, but I can still get it pretty loud).

There are lots of other, similar, Part 15 transmitters available (such as the Maxell FMT-100) that are cheap AND certified.  Being certified isn't just about power.  Certification also sets limits on interference and spurious output, which these Chinese transmitters are famous for.  Just using one of those overpowered transmitters - even if you do intend to adjust it to legal level power settings) - may send out the wrong image.

Welcome to the hobby

Having your own little station is fun, and setting it up to sound just like a commercial station with you the program director and listening to "your" station that plays everything you like with jingles and you as DJ.

By the way what field strength meter did you get as we all wish there was something that is simple to use and doesn't cost $15,000?



Even after "modding" your CZE transmitter (power and antenna-wise) to comply with FCC part 15 requirements......there's the issue of pre-emphasis.

FM broadcast receivers used in North America are set for 75 uS (microsecond) de=emphasis; the transmitter MUST use 75 uS PRE-emphasis......nearly ALL those Chinese units use 50 uS pre-emphasis --- the audible result on a conventional receiver is less than stellar (ask me how I know....!!!!:()

There ARE a couple of Chinese transmitters that DO have switch-selectable pre-emph (0-50-75) might do well to check out ooe of these before proceeding.....

Good Luck!

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