https://www.reddit.com/r/pirateradio/comments/1i49bxc/question_about_bh1415f_preemphasis/
created by KubaPro321 on 18/01/2025 at 15:01 UTC*
4 upvotes, 2 top-level comments (showing 2)
Hello, so I've got a CZE-01A transmitter with togglable 50µs and 75µs, i've found caps which i suspect to be the preemphasis, but a friend's been saying that when they're removed that there would be no audio anymore, so what i wanna do is remove the 75µs caps (because i live in europe) so the 75µs setting would be no preemp, would this work?
EDIT: Case closed, i removed the capacitors for 75µs and now 75 actually means 0, so this does work, so in combination with mono, this is mpx input
EDIT 2: after multiple hours using the BH1415F as a modulator (with Stereo Tool) i can say that it's great, on some frequencies there's weird interference (like on 95 the transmitter interferes with itself but not as much on 89.1) but it's fine
EDIT 3: also what you could do is apparantly disconnect pin 5 of the bh1415f chip and connect your own signal there, apparantly you'll have a pure fm modulator then, because from pin 5 it goes to a vco and then to the chip's rf counter pin, this is according to that friend but without stereo and premphasis it should be fine, if you don't have a lpf or a harsh limiter
Comment by AddressNulled at 19/01/2025 at 04:03 UTC
1 upvotes, 1 direct replies
I wouldn't bother myself, you could change the caps on pin 2 and 21 but this chip still doesn't really have the performance to make the work with it in my opinion. I do think removing them entirely isn't a solution, no where in the data sheet does it show them just floating.
If you actually want good audio quality get a transmitter you can feed an external MPX into, not ones using this chip.
Comment by Dismal_Concept6546 at 21/01/2025 at 12:56 UTC*
1 upvotes, 1 direct replies
Mine has through hole components not smd and i would like someone who knows to tell us the values of components for 50us and 75us preemphasis. I dont know if now is running on 50 or 75 an so i want to check because i am in Europe. I am running it on 50mw power! Just for home use!
I just found on the manual of Ramsey FM25b which also uses bh1415f that the capacitors are 2200pf for 50us and 3300pf for 75us!
I had a transmitter in the past that not worked at all when i removed the 1nf caps and kept only the 50k resistors. I tried that so i could have external pre emphasis and audio processing. The transmitter was a Ramsey Fm110b with analog stereo coder and vco/pll on the same board! Great unit but i shorted it some way and i cannot find the same any more. It was engineered by John Ramsey. Great little unit delivering 15 watts on high power using a mosfet on the output.