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Post by part15engineer on May 9, 2018 21:19:51 GMT
I was given an inovonics 702 RDS encoder so now I have RDS on the fm side.
just for a reminder the setup is part 15 compliant running into a dummy load using well shielded cable and goes about 75-100ft max to a sensitive portable.
RDS is static and does not show the dynamic music info so it reads,,,
"Variety 1560 AM 90.7 FM The Greatest Hits of the 40's Thru The 80's"
it still displays even on the fringes. has pretty good weak signal decoding at least on my portable..
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Deleted
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Post by Deleted on May 9, 2018 22:44:53 GMT
May Be the First
Part15Engineer, to me your Variety 90.7 is the first Part 15 FM station I've heard of to have RDS.
I think "RDS" means "Radio Data Stream", which displays text on certain FM radios if so equipped.
We are aware that the EDM low power FM transmitter can be ordered with RDS included, but I saved some dollars by not ordering that version.
We also know that Stereo Tools is capable of generating 75 uS Pre-Emphasis and RDS, but so far as I know none of the part 15 FM transmitters accepts the type of raw input that would utilize the features, but I also think I'm wrong about that, but I might be right.
Anyway, Variety 1560am 90.7 FM is perhaps the most progressive part 15 radio station in the known universe, and I do not mean anything political by that unless you are politically progressive, which I think you might be.
I've been in the sun. Can anyone tell?
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Post by Boomer on May 10, 2018 1:29:50 GMT
Adding external RDS would need a more professional transmitter with a wide-band input, with no pre-emphasis or other audio processing. On a commercial transmitter it's usually a BNC connector input with coax running to it from the stereo exciter.
Coax is used because the input is accepting signals above the audio range for the stereo, RDS and other subcarriers, in the low RF frequency range. The input should have a response that's flat from less than 1 hz to 100 khz with flat phase response.
As Carl sez, Stereotool should be able to do RDS, and Burnill's Radio Optimizer software claims to do it too.
I've never heard of a real Part-15 radio station using RDS, but a friend's phone had a short range FM transmitter in it that sent title and author information, using RDS, to a participating radio. The phone was on the car seat transmitting with the radio tuned to it and scrolling the titles to the songs.
Boomer
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Post by part15engineer on May 10, 2018 1:59:01 GMT
i'm using a Bext transmitter going through a dual bandpass cavity into a dummy load the whole works goes about 100ft tops to a sensitive portable radio.
i'm feeding it with RDS from the inovonics 702 and stereo from an optimod 2200
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Post by thelegacy on May 11, 2018 16:51:25 GMT
I can't remember if it is possible to dend RDS on AM or not?
With FM pretty much being a No No in the USA I'd rather not do any experiments (Even At Low Power) in my area for I'm sure we have the Radio Sheriff's out watching for one screw up on my part. I've been lucky not to be banned from ever getting a LPFM or LPAM license if ever there was such an animal in the future.
If AM can do it I'd like to try that in the future alongside C-Quam AM Stereo. Could be fun.
I do wish the cable TV companies would consider allowing Hobby FM Broadcasting on Cable. People could set up their own FM station that way and it would be legal. Years ago around 1979 Harry Hill High School in Lansing, Michigan done just that and had tons of listeners. The School For The Blind considered the sane thing but Continental Cable-vision pulled the plug on Cable FM. Too bad really because that was one way we would listen to WRIF and WIOT without waiting for the ducting effect.
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Post by part15engineer on May 13, 2018 22:34:50 GMT
here is my new arrangement for FM, i start with 2-3W (not sure if it is 2 or 3) i go into a 3db loss dual band pass cavity, then into a splitter which splits the power between dummy load and antenna (another 3db loss) then into an actual 3 db attenuation and then into another 20db attenuation then into a half wave dipole and figure another 3 or so db on top of all these system losses for cable and connector loss.
my range? between 100-200ft (depending on direction and weather conditions) bingo!!!
so i have a very clean part 15 compliant (as close as i can be without a FIM) fm stereo transmission system with RDS and i lined up the 19khz pilot and rds injection with a pira p275 analyzer so i have all the correct injection levels.
thing sounds beautiful and is very spectrally clean!!!
No Chinese splatter junk here!!!
at 3 watts of injection results in a whopping 0.0016W of input to dipole.
RDS is not possible on AM unless you do IBOC / HD AM
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Deleted
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Post by Deleted on May 13, 2018 23:56:08 GMT
Home in the Range
Part15Engineer Reports: "My range? between 100-200ft."
How are you judging your range?
The way I judge mine is with a TECSUN PL310 Radio which has about the best FM sensitivity a radio can have, and I decided to clip my FM range at 100' because there is nothing beyond that point but open space.
I set the variable power in the Ramsey 35B FM Transmitter so that the TECSUN drops from signal to noise at 100', with the added reading provided by the dBu meter on the radio, which shows 07 dBu at the drop-off point.
The FM signals inside the building are ideal by doing this.
If I ramped the RF power up for 200' the reception throughout the yard would improve, but I use AM for the yard.
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Rich
Full Member
RF Systems Engr (retired)
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Post by Rich on May 14, 2018 10:18:07 GMT
... 3 watts ... results in a whopping 0.0016W of input to dipole. ... Just to note that a 1/2-wave, center-fed dipole generates the maximum legal, free-space field permitted by FCC ยง15.239 when only 0.000 000 011 43... watts (about 11.43 nanowatts) flows across its feedpoint terminals. A feedpoint power of 0.0016W is over 145,000 times greater than 11.43 nW. |
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Post by part15engineer on May 14, 2018 12:46:52 GMT
I have a Radio Shack DX398 and the system completely dies out at about 200ft. my Broadcast Vision part 15 certified modulator pushes more range to that dx398 then my commercial system does.
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Post by part15engineer on May 15, 2018 14:09:44 GMT
it's 2W (found out from someone more knowledgeable on this exciter than me) injection so this results in 0.00097W of power with all my system losses.
still not part 15 according to rich's calculations but the systems range to a good sensitive portable is only 200ft so I kind of wonder if anyone will care.
the fm is not meant to reach an audience anyways it is for my own experimenting and learning purposes.
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Deleted
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Post by Deleted on May 15, 2018 15:21:51 GMT
The Whole PictureThe 200' measure for determining FCC compliance under part 15 is not just a rumor floating around, therefore should not be ignored nor neglected when considering the subject. Quoting the FCC:
Unlicensed operation on the AM and FM radio broadcast bands is permitted for some extremely low powered devices covered under Part 15 of the FCC's rules. On FM frequencies, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR (Code of Federal Regulations) Section 15.239, and the July 24, 1991 Public Notice (still in effect). The quotation is taken from this FCC document: FCC Low Power Radio General InfoThis earlier document is also referenced: FCC Document from 1991 Still in EffectDiscussing 15.239 in isolation without also referencing these FCC guidelines is incomplete.
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Post by Druid Hills Radio on May 15, 2018 15:27:03 GMT
FCC = Ambiguity. "Effective Service Range"
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Deleted
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Post by Deleted on May 15, 2018 15:44:26 GMT
Never Ending Ambiguity
Druid Hills makes note of the FCC language: "Effective Service Range"
An important statement within the documents stating the 200' guideline for part 15 FM.
What it says to me is this: It says that within the 200' allowable range the signal can register with full quieting on an average FM radio.
But whether an FCC inspector would come to the defense of a station employing such a definition is the ambiguity... shot in the dark; best guess; risky assumption; could go either way.
No matter how a hobbyist approaches the problem there is no certainty.
Within this FM predicament is a fundamental unfairness... the responsibility is put on the FM operator, but the ambiguity is that of the FCC itself in its slip-shod failure to present accessible procedures that address the persons seeking to operate within the rules.
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Post by part15engineer on May 15, 2018 16:14:57 GMT
i'd be happy if the fcc specified a mW power level to the terminals of a 1/2 wave dipole as an alternative to the f/s rules like they do with 15.219.
say 1, 10, or 25, 50, or 100 mW power which many popular kit and prebuilt transmitters employ. there could be language such as what is present in current part 15 regs requiring certain spectral purity requirements and limit operations to odd channels and bandwidth to 200khz within the band limits of the licensed fm band. also could allow the use of part 73 type accepted exciters provided enough attenuation on the output to bring the power to terminals of a dipole within the specified power limits. i'd like to se it be 1 Watt to the terminals of a dipole and 30m antenna height limit above ground level if using a tower or 3m above the building it is mounted on but I know that will never happen. we could limit operations to individuals who don't own any interest in other licensed stations and limit this class of stations to 5 to an individual nationwide and that at least one of the stations reside where the individual running it resides. all stations must be within 25km of the operators residence and operators are limited to using only 1 frequency for and operation providing simulcasted programming. this will prevent big religion and big broadcasters from usurping all the available frequencies. I see lots of possibilities for rural and suburban area where there is still room to squeeze in stations.
the rules that a part 15 transmitter must not cause interference but must accept interference should be enough to mitigate any concerns of interference to licensed stations but we all know that is not the issue. interference concerns are only a small part of the equation, 99% of the concerns are based on taking away listeners and thus revenue from licensed stations.
and to that I say if you are afraid of a extremely limited range flycaster taking away a small part of your listeners then you have way bigger problems then the flycaster station.
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Post by thelegacy on May 15, 2018 20:50:26 GMT
I could not have said so better myself especially dealing with AM.
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