Can anyone put toward such an animal?
Don't know what you are asking here? Are you wanting to know which FM transmitters have 75 US pre-emphisis?
While it's quite over my head I took a quick look around, mainly to figure out what your talking about.. I see a lot of others in the past were seeking a transmitter with a preemphisis of 75 (and higher wattage) for transmitting indoors while still maintaining part 15 compliance outside the enclosed structures...
It's a discussion I dont recall hearing before, but now that you mention it I see discussion all over the place.. Anyway, for what it's worth, the following discussion thread someone named Craig appears to answer your question:
https://darkliferadio.proboards.com/thread/974/modify-chinese-transmitters-75us-emphasis
Excerpt:
After doing extensive research, I was able to finally determine exactly how to modify basically most every Chinese manufactured FM transmitter for 75us pre-emphasis, the USA broadcast standard ! Without having the luxury of actually viewing the circuit boards of many available FM broadcast transmitters manufactured in China, I can assume with a high degree of confidence that in all likelihood they all utilize the commonly utilized BH1414K Audio Link integrated circuit in their designs. .....
.... I have successfully completed changing my ST-15B to 75uS from 50uS. Pins 2 and pin 21 of BH1415F ic have the pre-emphasis delay. The original Chinese 50uS uses 2 ( 2200 picofarad) surface mount capacitors. To change it to USA standard remove them and replace them with (3300) picofarad caps. What a difference it makes!!! The massive booming overkill of low frequency “bass” is gone and the transmitter sounds just like a professional radio station. I hope this helps someone. Craig
What about the Ramsey's? Weren't they manufactured in the US?
If not, maybe an easier solution would to listen to your station on a radio manufactured in another country (50usec), thus more compatible with the Chinese transmitters. Just a thought. - Not that I really know what I'm talking about, but it does seem to make sense.
Any transmitter designed in the USA or Canada is 75 uS....Decade, BVE(Broadcastvision), the new Procaster FM, Rolls, Ramsey.
So the Canadian standard is 75us too?Any transmitter designed in the USA or Canada is 75 uS....Decade, BVE(Broadcastvision), the new Procaster FM, Rolls, Ramsey.
I certainly don't know, this topic is new to me, but there are claims (or perhaps I should say opinions) such as this one found here who say the specs are false: https://www.tapeheads.net/threads/fm-transmitters.104818/
"Some of these transmitters claim to use 75 µs, but that's a lie. They're all 50 µs"
That of course may be heresy, but in the same thread is indicate that no modification is needed because 75us can alternately still be accomplished with proccessing ...
"You can build a passive or active circuit to provide the 75µs pre-emphasis, buy a standalone processor, or use a broadcast processor software such as Stereo Tool. You could also play around with using a graphic equalizer to boost the high end and attempt to match the 75µs curve."
Is that accurate? If so it seems to make the built-in capabilities of the transmitter a moot point.. but I'm guessing that's probably not true as I've not seen anyone else suggesting that. Maybe he meant khz.
Any transmitter designed in the USA or Canada is 75 uS....Decade, BVE(Broadcastvision), the new Procaster FM, Rolls, Ramsey.
And so you've answered to the original question.
I keep posting this thread because although I have no interest In Part 15 FM, I found this 75 uSec thing interesting since I never heard of it. I thought the only basic difference between countries FM transmissions was the kHz spacing. Its interesting to learn that a European or Chinese made receiver will have distorted bass here, and if they use an American radio there it will sound tinny. I hope all my blabbering in this thread wasn't too overboard... saying the most when I know the least. Fortunately Mark answered the question cut and dry.
@richpowers I am not sure if Canada is 75 uS but it would make sense that the two countries are harmonized with this. The transmitters are made for the USA in mind even the Canadian manufacturers like Decade and Procaster(ChezRadio)
@mark I agree, it most certainly makes sense both countries use the same standards.
According to Wikimedia the only countries to use 75 μs are the US and South Korea, it doesn't mention Canada in this regard: https://en.m.wikipedia.org/wiki/FM_broadcasting
"The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit. In most of the world a 50 μs time constant is used. In the Americas and South Korea, 75 μs is used. This applies to both mono and stereo transmissions.
.. According to a BBC report from 1946, 100 μs was originally considered in the US, but 75 μs subsequently adopted."
However the Canada's spectrum standards clearly show 75 is the standard:
https://ised-isde.canada.ca/site/spectrum-management-telecommunications/en/devices-and-equipment/broadcasting-equipment-standards/broadcasting-equipment-technical-standards-betsdevices-and-equipment/broadcasting-equipment-standards/broadcasting-certificate-exempt-radio-apparatus-6
A.1.3.2 Method of Measurement
The standard test set-up shall be used. The normal 75 microsecond pre-emphasis shall be employed. The audio input to maintain a constant modulation level of 25%, 50% and 100% shall be determined at a sufficient number of points over the frequency range 50 to 15,000 Hz to enable curves to be plotted.
All the subsections to follow also specify "The normal 75 microsecond pre-emphasis"
Any transmitter designed in the USA or Canada is 75 uS....Decade, BVE(Broadcastvision), the new Procaster FM, Rolls, Ramsey.
AND THIS ALSO DEMONSTRATES A VERY STRONG ADVANTAGE GAINED BY BUYING A US OR CANADIAN PART 15 MANUFACTURED TRANSMITTER. It's just going to sound a lot better than a Chinese 50us is capable of producing here.
On a side note, there was someting in the same Wiki link above that jumped out at me..
"Stereo FM
.. .. In the late 1950s, several systems to add stereo to FM radio were considered by the FCC. Included were systems from 14 proponents including Crosby, Halstead, Electrical and Musical Industries, Ltd (EMI), Zenith, and General Electric. .. .. Many revenue-starved FM stations used SCAs for "storecasting" and other non-broadcast purposes. The Halstead system was rejected due to lack of high frequency stereo separation and reduction in the main channel signal-to-noise ratio. .. .."
I've grown to have become fascinated with William Halstead who's reffered to above. He had really led an incredible and productive life and most all of it involved substantial advancements and utilization of radio.
He also was the man who, (within months of the FCC creating Part 15) established use of part 15 AM for travels information.
Preemphasis is just a method to reduce noise in the signal, by boosting the treble on the transmitter side, and then performing deemphasis (reducing the treble) on the receiver side.
Both the transmitter and receiver need to boost and reduce the treble by the same amount, or you'll get distortion.
75us is the standard for both the U.S. and Canada. It really doesn't matter where the transmitters and receivers are manufactured, as long as they have the same level of preemphasis and deemphasis.
Many Chinese transmitters, including some Part 15 certified ones (such as the Whole House 3) support both 50 and 75 us. If you're broadcasting in either the U.S. or Canada, it is likely your receiver performs 75us deemphasis, so you would want to choose 75us preemphasis on the transmitter side. I haven't seen an option to change deemphasis on any receivers.
The effects of choosing the wrong values are obvious, as things just don't sound right. I made the mistake of adding 75us preemphasis in the sofware I use to generate RDS, so was effectively doing the preemphasis twice (once in the software, once at the transmitter). It was pointed out by Carl Blare (who is dearly missed) that the trebles on the broadcast signal received by my SDR sounded distorted, and he was right. Removing the software generated preemphasis solved the problem.
Preemphasis is just a method to reduce noise in the signal, by boosting the treble on the transmitter side, and then performing deemphasis (reducing the treble) on the receiver side.
Yeah, that's something I found interesting, the way the emphasis followed by de-emphasis -which decreases the entire signal, both noise interference and treble - but the treble is still able to come thru since it had been raised above the noise for transmission. Essentially the treble overpowers the ratio of noise that's always inherent in transmission...
I probably didn't say that right but I do grasp the technique and purpose for it. It seems I came across something about some alternate FM techniques that have been used but I've probably already gone as far down that rabbit hole as I expect to go! But it is interesting and it somehow reminds me of... something.. else..