From: mycal@netronix.com (Mycal Johnson)
Newsgroups: sci.electronics
Subject: Updated FM-10 Info File
Distribution: world
Date: Thu, 13 Aug 92 16:51:51 GMT
Organization: Netronix, Inc.



                        Ramsey FM-10 Info
                                by
                        mycal@netronix.com

2nd Edition
-----------
Here is a rough compilation of information about the Ramsey FM-10, and
BA1404 Stereo FM broadcasters.

It is in no way complete, nor do I take any responsibilty for its accuracy.
I know you haven't seen this statement but a 1000 times but here it is :
For informational purposes only.

I have been swamped with requests for information about amps, antennas and
other mods for the FM-10, so I decided to dig through my mailbox and notes
and compile this file.  I hope It helps, and if anyone has more information
about the FM-10 or FM transmitters, please send it to mycal@netronix.com
-or- gallaghe@sonoma.vax.edu.  I will try to update this file as new
information arrives or is found out.  A Postscript version with schematics
and board layouts is also not out of the question.

I would like to acknowledge the following people for the contibutions
and support:
                John Brewer -- brewer@anarky.enet.dec.com
                Alan Bryant -- uunet!csn.org!adb
                Greg Thornwall <uunet!wam.umd.edu!thorn>

If I missed anyone, sorry, please drop me a note and remind me.


FM-10 Mailing List
------------------
First Things First.  There is now a mailing list that deals with the topic
of the Ramsey FM-10 and other BA1404 based FM Stereo Transmitters.  Feel
free to join up and contribute.

To send a message to the mailing list, send your question, reply, comment,
or contribution to :

        fm-10@dg-rtp.dg.com

To add or delete yourself from the list, send a short message with
the function (add/delete/change address) along with the revelent e-mail
address to:

        fm-10-request@dg-rtp.dg.com


If you have any questions I can be reached at myca@netronix.com.

Once again I want to thank Ed Savage and the guys at Data General, NC for
making this list possible.


Recommended Test Equipment
--------------------------
An SWR/Power meter is a giant help, a CB to 2 meter one will suffice.
Power readings will not be accurate, but can be usefull for peaking.

The most important part is the SWR meter, this is very important when
making an antenna.



Ramsey FM-10 70mw output amplifier
----------------------------------
Provides 9db gain to bring the output power of the Ramsey FM-10 Stereo
transmitter from 8mw to 70mw.  All parts can be found at Radio Shack.


                          +12v
                          |
                          /
                          \ R1 *220 ohms(1/2 watt)
                          /
                          \
                 R2 9k    |       C2
               -/\/\/\/-----------||-----> output
              |         /
              |        /
              |   |  /
          C1  |   |/         <----------mps2222a (276-2009)
    in  --||------|\              -or-  2n4401
          ^       |  -> --
          |              |
          |              gnd
  currently on board

* you can also use 2 440 ohm 1/4 watt resistors run in parallel

I built this thing right on the underside of the FM-10 kit, C1 is the
cap that currently goes to the RCA ant jack, the 9k and the 220 ohm
resistor have to be bought, note that if you cannot find 220 ohms you
can make one by using 2 440 ohm resistors in parallel, and that a 10k
will work in place of the 9k but yealds poorer preformance (-5%).

Note that you can lower the resistance of the 220 ohm resistor to
about 200 ohms for more power, but do not do this unless you can
check to see if the transistor has gone into ocillation.

The mps2222a is from Radio Shack part number 276-2009, use this part! if
you substitute it for a 2n2222a you will get only half the gain.  Be
very carefull to get the leads in the correct orentation!

I have found that a 2n4401 can be used in place of the mps2222a with a
little better preformance, about 5mw more.  I think the 2n4401 can be
found at Radio Shack too.

C2 is of the same value of C1, I took the one that goes to the on board
antenna pad.

Important! the value for R2 that seems to be optimal is 205 ohms, but it
is very close to the sat point, If the amp seems noisy (interfears with the
TV etc) back this value off to 220 ohms.  If you lower this value below 200
ohms the power meter may read higher power but this will not be true, the
transistor will be spewing all kinds of junk and the power meter will
mistake this for higher output (in reality the signal we want will drop
considerably.)

Well thats it, effective range with a good antenna should be a little
over double.

-------
On Wed, 1 Jul 1992 13:16:47 -0600, "Alan D. Bryant" <adb@csn.org> wrote:
> The second stage idea didn't appear to do anything here, but I don't have any
> measuring equipment, so it may have been a small enough improvement that I 
> couldn't detect it.
>
Hmm, very interesting, I havn't tested it in the real world, just with
a HP power meter and spectrum analizer.  Also note that using a 2n2222a
I could only get 30mw, but when using the mps2222a I got 75mw.  This
was all into a 50 ohm load,  with a mismatched antenna it could actually
degrade preformance.  I was kind of amazed when I calculated the optimal
Rl and found it to be 52 ohms for that circut.
 
> I've been playing around with antennas a little myself.  Made up a weird
> concoction I'll have to describe to you at some point.  No real test results
> from it yet.
I would like to hear about the details of  what you have come up with when
you get it all up and running.  The $19 RS CB power meter would probibly
come in handy for doing antenna and power tests, It would be alot better
than nothing.


ANTENNAS
--------
Also Do you have a good antenna?  I think that is the most important
thing that  you can do for extended range.  I built a 1/4 wave ground plane using
a uhf connector and 4 lengths of copper plated brazing rod (found at
the local welding shop).  Works great and only cost $3 dollars to make.

use the formulas out of your FM-10 manual  234/freq=length of rod.

insert the 4 ground plane rods in the 4 holes of the UHF connector, stick
them through about 1/4 inch and solder.  Solder the radiator in the top
of the UHF connector (you may have to grind it a bit to fit.)  Then bend
the ground plane rods to a 45 degree angle to the radiator.  There you
have it a very effective antenna, just connect with a 50 ohm cb cable
to your amplified ramsey, stick the antenna in a tree or in another high
place and you should have 1.5 miles of solid coverage (when using the
above amp).

Also If you have an SWR meter you can cut the rods a little longer and start
clipping the ends off a little until you get the best SWR reading.

                                               |
        |              |                       |    = brazing rod
        |              |                       |
        |              |
      -----          -----                    -----  = uhf connector
      | - |         /  -  \                     -
      |   |        /        \
      |   |       /           \

be carful when you bend the brazing rod, don't break the connector.  Grab
the rod right below the connector with a pair of vice-grips (or the likes)
and bend the brazing rod at that point.

I have been told that you can shorten the radiator and make the ground
radials longer to lower your radiaton angle, but I havn't tried this, nor
do I know what this would do to the antenna impedence.


On The Road
-----------
Old magnet mount CB antennas can make great moble antennas,  just take all
of the base load out of them and cut the radiator to 1/4 wave length.
If you need a longer radiator than the one that comes with the antenna
use the above mentioned brazing rod.

I've tried this antenna and it works great!  It rivals my di-pole at home and
you can drive to a high, optimal location for your broadcasts.

You could also try a 5/8 wave length antenna, this would give you 2+db gain,
or almost 2x power gain on transmit.


Filter design for FM Radio Transmitters.
----------------------------------------
It is very important to have a clean signal,  the way 99% of all people
who get busted for illegal transmitting is that the people that live
around them complain about interfearance.  Do not do this, keep everyone
happy, including yourself, be clean.

When you amplify a signal, you get unwanted byproducts these are called
harmonics.  The show up at multiples of your starting frequency.  For
example if you amplify a 50mhz signal you may get echos on 100mhz, 150mhz
200mhz, 250mhz...  If you walk on your neighbors tv, the local fire depart-
ment, or anyone else, you are going to get nailed.  If you are only on
the FM Band, you will hardly be noticed.

...
I have looked into the filter design more, I have come up with these two:
(basically scailed from the charts in the ARRL handbook).

Filter Design: 7 element Chebyshev
I run @ 88.1 so my 1st harmonic is 176.2
This filter seems ideal.

Fc               3db     20db    40db
85.8mhz         95.9mhz 116mhz  148mhz

              .132uh    .152uh     .132uh
        -----()()()-----()()()-----()()()-----
          |          |          |          |
<-50ohm   - 33pf     - 68pf     - 68pf     - 33pf  50ohm->
          -          -          -          -
          |          |          |          |
        --------------------------------------

Filter Design: 5 element Chebyshev
Not as good as above, but thrown in anyway.

Fc               3db     20db    40db
81.8mhz         105mhz  147mhz  222mhz

             .128uh     .128uh
        -----()()()-----()()()-----
          |          |          |
<-50ohm   - 30pf     - 62pf     - 30pf  50ohm->
          -          -          -
          |          |          |
        ---------------------------


The tuff part in the above is winding the coils. 3t of #12 wire 1/2" diam
should be about .12 uh. 4t is .17 uh. (but ugh, #12 wire is big stuff).
I may just make all the coils 3t, and bend them around a little while
watching the analizer.  Maybe use var-caps too.  Well I will build this
weekend and try tuesday.  I will let you know how it goes.

mycal

....

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 -
--------------------
(Most from ACE magazine.)

1) 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.


2) 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 filtering of 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.


3) 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.

From: Greg Thornwall <uunet!wam.umd.edu!thorn>
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.

...
From: Greg Thornwall <uunet!wam.umd.edu!thorn>
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!).
...

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


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






Mycal Johnson                          _
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