From: Mycal.Johnson@mailbox.bison.mb.ca (Mycal Johnson)
Newsgroups: sci.electronics
Subject: 02/FM-10/BA1404 FM FAQ
Date: 24 Sep 92 16:55:49 CST

other filters.
it won't knock the harmonics down as much as the other two designes but
the good thing about this one is that it uses standard off the shelf
parts.  the inductor is one of those molded jobbies that looks like
a resistor so you can make this very small.

use the above cap values depending on which freq range you want to operate
at.  ie. if you run 87-90 use the 88mhz vals,  90-103 use 102mhz vals,
and above that use 107mhz vals.

use fixed value parts!

....

I built the 7 element Chebyshev, I substituted .12 uh inducters for
the .132 and .15 uh for the .152.  Also I put 10-50pf var caps in place
of the 33pf's and 10-90pf varcaps for the 68pf's.  After a bit of tweeking
I got -45db on the 2nd harmonic -55db on the 3rd -65 on the 4th, every thing
else was off the scale.  That is much better than -25db,-27db,-30db,-40db...
-40db off the fundamental is required by FCC.
[Actually the fcc says no more than .7mw out on any harmonic when dealing
with VHF equiptment, thats on top of the -40db requirement.  But if you
are running 1 watt out -40db is .1mw]

I have found that peeking (buy tuning the var-caps) for maximum power output
into a 50ohm load will give you close to maximum attenuation on the harmonics.

Also the Fc can be raised or lowered quite a bit,  I tried +-10Mhz (of 88Mhz)
and could tune the Fc there.

I am going to stick with the .12uh and .15uh inductors because I can get them
for $.25 apiece at HSC,  But I may try winding my own later on, especially if
I use it on a high power output device.  These molded inductors don't look
like they can handle much power, but I have run 2 watts through them without
problem..  On a side note, I don't think the Q of these inductors is that
high,  I think that if you wound the above mentioned #12 coils you would
have a higher Q, hence, greater preformance on the filter.

On a second try I built another filter useing variable inductor cans, and
used fixed caps, this one seemed to have better preformance than the
last one, it was also much more stable.  Var caps are not very stable,
so I would reccommend using fixed caps.

[Also of intrest is that the FM-10 puts out about 8-9mw and the 2nd harmonic
is -25db off.  The FM-4 Kit by ramsey puts out 130mw and the 2nd harmonic
is only -12db off, which means the 2nd harmonic of the FM-4 is about as
powerfull as the FM-10.]

FM-10 Myths
-----------
1) The fm-10 puts out 100mw of power.  This is not true, or at least not
true for the Ramsey FM-10's that I have tested.  They put out between
8 and 15mw when driven with a 12volt supply.

2) The fm-10's output can be cranked up by reducing the value of R9.  This
like the above is not true.  R9 and R10 are optimized for maximum output
and greatest harmonic suppression at 12volts.  There are much better ways
of getting more output power than to mess with this output stage.

FM-10 Improvements -
--------------------
(Some from ACE magazine.)

Stereo Pilot Mod
----------------
One of the first problems experienced with the FM-10 is difficulty
in getting the stereo pilot to operate correctly.  One solution is to
replace C7 and C8 with a 38khz crystal,  this works the best and is
recommended.  If you cannot find a 38khz crystal, you can make your life
a whole lot easyer with a couple part changes.  As indicated on the
Ramsey schematic, about 110pf is necessary to tune the oscillator.  The
components supplied to achieve this are a small fixed value capacitor (C7)
abd a slightly larger value trimmer (C8).  Since proper setting of the
trimmer occurs within a very small 'window' (about 5% of the trimmers
range), it can bet difficult or impossible to adjust the pilot to 19khz
and have it stay put.  This can be cured by increasing the value of c7 to
100pf and replacing c8 with a 6-50pf trimmer (Radio Shack #272-1340);
a 5-30pf trimmer will do the trick.  The RS trimer will not fit the holes
in the pc board; one needs to cut the leads off a spare resistor and
solder them to the legs of the trimmer (just use bits of wire) to mount
it on the component side of the board.

Crystal Mod
-----------
        old set up       new setup
          c8               c1 xtl        where c1=10pf  and xtl=38khz
        |-||-|           |-||-|\|-|
        | c7 |           |        |      v8=var cap
        |-||-|           |        |      c7=cap
        |    |           |        |

Remove C7 and C8, replace with 38khz crystal and 10pf cap.  Note that
the 10pf cap and the crystal ar running series and the old cap setup
is running in parallel.


Treble Boost Mod
----------------
Treble boost (pre-emphasis) improvement.  The FM-10 appears to have
been designed by someone outside the United States since it operates
at the European audio standard of 50 microseconds.  Receivers in the
US are set up for 75 microsecond de-emphasis.  R3 and R6 determine the
time constant for the pre-emphasis curve.  Replacing them with 75K ohm
resistors (standard value 68K ohm is close enough) will result in
improved audio response.

A much better pre-empasis/input circut is shown in the July 1992 issue
of "Radio Electonics".  Not only do they use 75K ohm resisters in there
pre-empasis, but they filter stray RF signals by inserting a .001 cap
between pin 1 (of the BA1404) and ground, and pin 18 and ground.

It has been noted that the above mod may actually cause distortion on
cheaper stereo receivers, since they were mass produced for the world market,
they were designed for the European audio standard, which Japan and other
Asian nations use too.  Try it out, let me know what works for you.


Anti-Drift Mod
--------------
The FM-10 can drift a bit, but there is a simple solution that can help
minimize transmitter instability.   The FM-10 was designed to be
inexpensive and cost-saving measures with components are inevitable. Disc
ceramic capacitors are less expensive than silver-mica caps, and also much
less stable.  Simply replace c16 with a silver-mica, tantalum or negative
temerature compensated disc (say anywhere from N150 to N750) cap of the
same value.


==============                  ==============
==============  Other Raw Info  ==============
==============                  ==============


the 2sc2570 is supposedly replaceable with an ecg10.  Also I have used
an MRF901 for a replacement, but it yealds 2.5mw less output.

The MRF239 can be used a a direct replacement for the Ramsey 2 meter PA
kit.  Cost is around $14 bucks.

Mycal,
I called the company that produces the BA-1404 chip. The company is the Rohm
Corp. in TN. They sent me some interesting data on the chip: some electrical
characteristic curves, list of distributors & representatives, application
diagram and some similar block diagrams that comes with the FM-10. If you
want any more info just write or call them up and they will send it free! 

Their address & number is:

Rohm Corporation
Rohm Electronics Division
3034 Owen DR
Jackson Business Park
Antioch, TN 37013

PH:  (615)-641-2020 (ask for someone who deals with the BA-1404)
FAX: (615)-641-2022

Also they have:

PO Box 1399
Antioch, TN 37011-1399
                                                --Greg  (KD3SU)

38Khz Crystals....

> > Does anybody have any idea where to find 38KHz crystal (H-18).
> 
>   Don't know what a H-18 is, but you can use a C-2 type quartz crystal
> for 38.000KHz by Epson America, Epson part number C-2 38.000KA-P, which can
> be ordered, for example from Digi-Key Corporation (1-800-DIGI-KEY), Digi-Key
> part No. is SE3314
 

Thanks Andrew, I've got the DK catalog H-18 is a solder welded case and C-2
is a cylinder type.  I don't know if there is any difference in specs between
them.

Aaron B.

...
I have some more stuff on another company that sells "pirate"
electrical kits. Panaxis productions, PO Box 130, Paradise, CA
95967-0130 (916)-534-0417 ($1.00 for a catalog). They have a bunch
of FM & AM transmitters from 20mW to 10W! They only sell PLANS for
the high power transmitters here to the US and will sell kits for
export elsewhere. They have a PLL FM oscillator (500mW) for sale in
kit form for $129.00 (better stability!).

Sorry for the delay - been super busy at work.  The address I have for
Panaxis Productions is PO Box 130, Paradise, CA  95967-0130.  The phone
number is (916)534-0417.  My catalog has a $1.00 price printed on it,
but I think they're $2 these days (still a bargain).  I'm going to send
my 2 bucks and get a new copy and see what fun stuff has been added.

My little station consists of the "MMC1" Macromod Compander set for 2:1
compression, connected to the "SG" high performance stereo generator
connected to the "FME" PLL FM exciter.  Besides the Panaxis stuff, I
have a homebuilt mixer console and of course, the 1 transistor PA.

Prices from my catalog (which is likely to be out of date) are:

Code    Plans   PCB     P+P     full kit
----    -----   ---     ---     --------
MMC1    12.00   18.00   26.50   87.00
SG      15.00   13.50   26.50   105.00
FME     17.50   15.00   24.50   129.50

While looking for my Panaxis catalog, I ran across a catalog from
Communication Concepts, Inc. that has kits based on some of the AP
Notes in the back of the Motorola RF devices data book (another
must-have).  They have a couple of 300 watt (!) kits that cover the
10-150MHz range (AR305 and AR313).  There's another article (AN1037)
that's a 300W amp specifically for 88-108MHZ FM broadcast use (but CCI
didn't have it in their catalog back when I got my copy).  CCI is
at (513)426-8600 or (513)220-9677.
...
 Many responded that they want to know more about the Oregon Comm Sys
line of stereo PLL Fm transmitters.

Here is their address and phone number:
OREGON COM SYSTEMS
1257 Siskiyou Blvd
Suite 132
Ashland,Oregon 97520

TELE: 503-271-3294

Models are stereo, 100mw output,PLL frequency syntehsis.
Some come with audio mixers also.
All are wired and tested.
This would appear an ideal unit for driving a linear amp.
Harmonic output is not specified,however low pass filter designs are
not difficult.
They also stock antennas.
The FM units are rated with an audio response of 10 to 15 kilohertz +/- 2 db.

Frequency coverage: 88-108 mhz
RF output 100 milliwatts
Frequency Stability +/- 100 hertz
Response (audio) 10 hertz to 15 kilohertz +/- 2db
Input level: 500mv
cost: $109.00  Delux stereo models 149.95

------------------
------------------


Well I have more info, but it is not organized enough even for this rough
sheet.  Given time I will polish it an post it.

Once more If you have any info, I stress "ANY", about this subject please
drop me a byte or two.

have fun,

mycal@netronix.com




-----------------------------------------------------------------------------
                                     ?
Pirate Radio?  Whats that?        @ o o @                mycal@netronix.com
                                     O

                            Just Say Know to Drugs.

 * Origin: The Electronic Mailbox (1:348/7.0)

Newsgroups: sci.electronics