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Stereo FM Stereo Transmitter circuit kit how do i ham free project FM bug BH1416 BH 1416 BA1404 BA 1404 ROHM,BH 1415 BH 1415 Multiplex rohm,Wireless Audio Link IC
ROHM's BH 141x Stereo FM Transmitter Chips


30th March 2000 (date of initial posting on the mailing list)


Ok Ladies and Gentlemen,

I visited the ROHM site at www.rohm.com.

Wonder what all you can stick into a 2$ chip these days !!!!!!

The new BH series slated for Mid 2000 release do pack a punch ---

Stereo Generation ( MPX and Pilot)
Preemphasis
Limiter
PLL Control
RF Oscillator
RF Buffer stage

No Pilot peaking capability
No Pilot ratio adjust

Here is a synopsis of the specification PDFs

BH 1414 : Top of the range, only Surface mount so maybe you do not see it in Kit form soon

BH 1415 : SMT and DIP format. Less features but same basic specs as BH 1414

BH 1416 : SMT and DIP. Unlike other two, this one does not need a PIC to feed the frequency data and other information. It uses 4 switches instead. As this cannot allow you 200 different settings to cover all stations between 88 - 108 MHZ, you are allowed only 14 different frequencies: Seven in the 76.8-78 MHZ range and the Seven in the 88-89.2 MHz range, even
frequencies with 200 KHz jumps.

Quickly, remind me, which country does odd frequencies and which does evens ???

The PDFs show 50 uS equalisation only. Its a no-brainer to convert to 75 uS.

My guess is that after that rash of BA1404 based kits, we should slowly be seing a rash of BH kits. They will intrinsically be better because the BH has PLL, Pre-emphasis, Limiter builtin while the simplistic BA1404 did not. ( NOTE : The BHs are not direct replacements of the BA 1404)

The PDFs do not show an MPX filter. My guess is that the kit builders will also ignore this important part. Please Please Please guys, do it right !!! Just because a PDF does not show it does not mean that these filters are not necessary.

See my NJM2035 page for basic ideas on MPX notch filters.

An external Brickwall Audio filter is not necessary as that is built into the chip.

Unfortunately, the BH series again just chop the L & R signals at 38 KHz without using weighted oversampling techniques. This would have been so easy in the chip and would have greatly increased signal purity. ( Please see my "Stereo for Dummies" page for explanations on how weighted oversampling helps clean up MPX signals)

The BH1416S should be seen first in the kits as it is in DIP format and does not need a PIC. Downside is that it will allow only 7 frequencies in the regular FM Band.

Yet at the low cost and low end range, heck it is an excellent offering for the church, dorm, campus thing.

It would also be the basis of the first PLL based bugs around. Now you can have a bug kit that you can wear on the body and it will not waver in frequency. All the beginner kits I built / reviewed shifted frequecy by 100-200 KHz when somebody approached the kit. You could use 88-89.2 if you wish to receive on a regular radio and use 76.8-78 if you wished to be a bit
covert.

No need for the high end guys to loose sleep though. Harmonic distortion remains the same at 1-3% Channel separation remains at 20-40db ie still a low end chip which is great for the destined applications - Wireless speakers, CD to car radio convertors and a bunch of multimedia applications yet to come.

One funny I noticed with the BH1416 is that it has no built-in way to have a "PLL Lock" LED. Makes it among the first PLLs I have seen that cannot tell you the lock status.

Maybe the BH1414 and 1415 can tell the PIC about their status, but the initial PDFs are lacking in any kind of details here. Infact there are many components without a value on the PDFs.

So there is a race on. Lets see who comes up with the first BH141x kit !!!!!

( Dec 2002 : A little bird tells me KITS R US in Hong Kong is aiming for this spot. Look out everyone)


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