EQ for Pre-emphasis curve

[dave radio]

Hello,

Seems that many, if not most all, made in China FM transmitters are manufactured pre-set for 50µs curve.

Stuck with 50µs in my transmitter, is there a simple EQ curve that can be set in pre-broadcast processing to match the USA 75µs de-emphasis in FM tuners?

If you can post the appropriate curve I sure would appreciate it, as I don't feel comfortable having to identify and solder the necessary component(s)

Thanks!

Dave 

EDIT TO ADD:  Well, nearly 3 weeks past, a number of looks, and nobody responded.  Maybe general consensus being "not that hard of a thing to sort out - just use your ears" kind of thing.

I'd already sorted it out to best of my ears kind of thing, just thought someone might have something specific to add.

No Problem!

[Kage]

Seems a few of these questions have popped up recently. I replied to a post here with some ideas..
darkliferadio.proboards.com/thread/1110/150-watt-fm-transmitter-chinese?page=1&scrollTo=4947

The issue with finding the proper curve using LC filters is going to be directly related to input and output impedance of the filter which needs careful matching to the TX input and line level outputs to it. For this reason alone it's probably best to use active filtering either with a simple OP Amp circuit or an actual stereo equalizer.

As for finding the correct curve you'd need tightly controlled EQ settings where you can trust how many decibels you are adding or subtracting from each EQ band. Parametric EQing might be better for this because of its broadly defined curve for simplicity.

The curves are listed online showing the start and stop bands for pre-emphasis in broadcast FM for various countries.
To add 25uS to the 50uS curve will require even more fine tuning. At that point I'd break out the scope and take measurements with a frequency sweep from input to filtering right to the output where it goes into the transmit circuit to make sure it sweeps in accordance to the 75us standard.

Of course all of this is probably *waaaay* more complicated than need be. I'd call it quits after doing some "by ear" fine tuning too making sure to not over-modulate which is most important anyway, or try removing pre-emphasis at the TX (either through filtering it out or removing components that do it) and let the processing do it which is always the best way.

[dave radio]

Well I tried eqing diff frequencies and decided less is better.  Deleted this post content as in the end it didn't sound all that great.

Rock on!