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

Organization: Netronix, Inc.


You've seen it before, and now you get to see it again.  New updated version!

mycal

--------------------- cut ------------------------------------------------

                        Ramsey FM-10 Info
                                by
                        mycal@netronix.com

3rd 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.


Other Places to Look
--------------------
alt.radio.pirate is another good forum to find or post information on these
kits.  Although you may not have pirate asperations, many of the things
talked about can benifit everyone.

other places to scan, sci.electronics and the amature radio groups.


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's Address
----------------
Ramsey Electronics, Inc.
793 Canning Parkway
Victor, New York 14564
Phone (716) 924-4560
Fax   (716) 924-4555


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 5 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
      | - |         /  -  \                     -
      |   |        /        \
      |   |       /           \


The final antenna should look like this:

                                |
                                |
                              // \\

        That is 1 radiator pointing strait up and 4 ground plane
        radials.

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


Very simple filter.
-------------------

                      .15uH
from fm10      >------()()()------> to antenna
                  |          |
                  - c1       - c2
                  -          -
                  |          |
                 ---        ---
                  -          -

      88mhz   102mhz     107mhz
c1     62pf     54pf      50pf
c2     62pf     54pf      50pf

its basically a scaled down verson of the 

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

Newsgroups: sci.electronics