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)
Wanna have your own page here, write
about your own experiences, own review, refute existing review,
add comments to existing review, publish your circuits ?
Contact
me
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