The information contained in the file is in no way complete, nor do I take any responsibility for its accuracy. With that in mind, along with the above paragraph I must say :
"This file for informational purposes only."
Also I am working on a some Postscript files that will contain instructions on how to build some equipment that is to complex for ASCII art. You might want to check the FTPable archives every month or so.
I would like to say thanx to all the people that contributed to the information in this file. The list has grown quite long, and some of the contributors would like to remain anonymous. So for now I am going to forgo all the names, if this is not up to your liking please let me know.
But for now you can use the dg site. This is a place to put/find schematics, reviews, stories, etc. related to the FM-10 and other BA1404 based FM transmitters. Currently a 350mw amp plan, 800mw amp plans, "Radio is my bomb" text, slim jim plans/info and the BA1404 spec sheet are located there.
People can FTP into dg-rtp.dg.com with user anonymous and password
Free Radio Berkeley now has an archive on CRL. It can be accessed at 'ftp://ftp.crl.com/usrs/ro/frbspd'.
Frank Haulgren (haulgren@henson.cc.wwu.edu)
RRB
PO Box 3038
Bellingham, WA 98227-3038
A note on power meters. I recommeded the above power meters because they are inexpensive and most people that are interested in hacking a FM-10 have very limited funds. These are by no means accurate, but they will give you some idea what is going on. If you can spend the money you can get an accurate power meter that is designed for this band, but the cost is 10-15 times more.
A rf probe could also be used as a replacement for a powermeter, construction details below.
A 50ohm non inductive load is also very helpful, for low power applications a 50ohm 1/4 or 1/2 watt carbon resistor works well. This can be used to tune up your kit and amp without interfearing with anyone. Also note that you can run as much power you want, legally, as long is it doesn't radiate.
A VOM is also very helpful. High I would put out the extra bucks and buy one with a freq counter (if you shop around, about $60-$70). Buy the one that covers audio to 20MHz(or more). If you are serious about electronics you need one of these!
Most CB loads use a 2-watt carbon 50-ohm resistor.
You can build your own, as wimpy or as studly as you want by running resistors in parallel to create 50-ohms. ie, 2 100 ohm 1/4 watt resistors will create a 1/2 watt 50 ohm load...
Do not use 50 ohm wire wound resistors, they are not 50 ohms at radio frequencies.
-----
---------\ Sample Dummy Load where -****- = 50 ohm
---|--****-- / mounted in UHF connector. carbon
--------- resistor
-----
--probe tip-----||-----/\/\/\-------to center of 50 ohm coax.
.01uf | 4.7M -------to braid
___ |
\_/ |
--- |
| |
cliplead for gnd--------------------
Anyway, the Diode ( arrow-points to ground) should ideally be a Schottky diode (low rf capacitance). Although a 1n914 will work. To use, just hook up to your digital Meter, set on DC voltage. You will get very close to RMS RF Voltage. (this probe was specified for a 10Meg Ohm meter).
To calculate power into a KNOWN purely resistive load (a.k.a. a dummy) use:
e^2/R
Where e is the RMS RF voltage, R is resistance :-)
This is also useful for checking inputs and outputs of low power RF units, since the inexpensive power meters don't seem to do real well below 1watt.
So I dusted off the old stacks of Radio-Electronics and found two articles that may be of intrest.
In the January 1993 issue they have a "build your own digital voice changer" using a simple Real time digital signal processor. I think that this design is very simalar to the voice changing telephones. It basically raises or lowers your voice pitch. A place called LNS Technologies @ 1-800 -886-7150 sells the kits for $59.
In there September 1992 issues they have a "build this dsp voice-effects board" using a little more complex, programmable, real time digital signal processor. The software they include contains a harmonizer, echo, reverb, and pitch. The kit is sold by American Disributors Inc for $105 @ 1-800-877-0510. You can also write your won software but the programmer is several hundred $$.
DC electronics has a Robot Voice Kit for $15. I don't know how well this works or what it sounds like, but it clames to be adjustable for many different effects.
Ramsey Electronics, Inc.
793 Canning Parkway
Victor, New York 14564
Phone (716) 924-4560
FAX (716) 924-4555
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 yields poorer performance (-5%).
The 2N4401 can be found at Radio Shack too. Using the MPS918 instead of the 2N4401 can produce up to 150mw. C2 is of the same value of C1, I took the one that goes to the on board antenna pad.
Important! the value for R1 that seems to be optimal is 220 ohms, but it is very close to the sat point, If the amp. seems noisy (interferes with the TV etc.) back this value off to 240 ohms. If you lower this value below 205 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 that's it, effective range with a good antenna should be almost triple.
L1 - should be replaced with a 1-turn 1/4" diamater coil, identical
to the stock L2 shown in the PA-1 manual.
L2 - no change required
C1 - no change required
C2 - should be replaced with a larger trimmer capacitor. Use a trimmer
that will go up to at least 125pF.
C3 - no change required (*)
C4 - should be replaced with a larger trimmer capacitor. Use a trimmer
that will go up to at least 125pF.
* - at higher power levels (>15 watts), this capacitor should be
replaced with a trimmer at goes up to at least 200pF.
FM xmitter --- SWR Meter --- PA-1 --- Power Meter --- 50 ohm dummy load
Starting with C1 and C3 about 1/2 turn from closed, tune C2 and then C4 for maximum power output. If the SWR is much over 2:1, you will need to adjust C1, C2, and C4 to reduce it to an acceptable level. Watch the output power while you do this. Sometimes, tuning the trimmers for minimum SWR will peak the power output, whereas other times the power output will drop markedly. Avoid trimming the capacitors that have a large negative effect on the power output. After several iterations of adjustment, you should have decent power gain and low input SWR.
Note: Watch for sudden jumps in power output that you can't linearly tune through. If you encounter this happening, chances are your SWR between the transmitter and amplifier will go way up, too. This is a sign that your amplifier is oscillating and you will need to tune it out of this region for proper operation.
Use the formulas out of your FM-10 manual 234/freq=length of rod.
Example : 234/88Mhz = 2.66 feet * 12 in/feet = 31.9" -or-
234/108Mhz= 2.17 feet * 12 in/feet = 26"
 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 miles of solid coverage (when using the
above amp.).
<p>
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.
<br clear>
<pre>
The final antenna should look like this:
| ^
| |
// \\ sky ground --horizon--
|
v
That is 1 radiator pointing strait up and 4 ground plane
radials. (sorry for this extreme description, but there
has been some confusion.)
</pre>
<p>
Be careful 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.
<p>
Try not to have anything metal near the radiator, this will effect
the radiation pattern. The radiation pattern should look a lot like
a doughnut surrounding the radiator, though deformed a bit.
<p>
I have been told that you can shorten the radiator and make the ground
radials longer to lower your radiation angle, but I haven't tried this,
nor do I know what this would do to the antenna impedance.
<p>
<h3>On The Road</h3>
Old magnet mount CB antennas can make great mobile 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.
<p>
I've tried this antenna and it works great! It is better than my di-pole
at home and you can drive to a high, optimal location for your broadcasts.
Also with this setup you need very little coax cable. Line loss using
RU-58u can be killer @ 100MHz.
<p>
You could also try a 5/8 wave length antenna, this would give you 2+db
gain, or almost 2x power gain on transmit.
<p>
<hr>
<h2>Filter design for FM Radio Transmitters.</h2>
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 interference. Most of this interference
is caused by harmonics. Filters cut down these nasties. So don't
draw attention to yourself, keep everyone happy, including yourself,
be clean, use a filter.
<p>
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 echo's on 100MHz, 150MHz
200MHz, 250MHz... If you interfear with your neighbors TV, the local fire
department, or anyone else, you are just asking for trouble. If you are
only on the FM Band, you will hardly be noticed.
<p>
Many FM transmitters are designed without adequate filtering on the
output. Add to this the fact that most pirate radio operators lack
spectrum analyzers with which to tune up their equipment, and it is
easy to see that many stations are likely to be full of spurious
outputs. You're a lot more likely to attract the attention of the
FCC if you wind up interfering with all your neighbors television
sets because of spurious emissions than you are if you emit a clean
signal. While more elaborate 5- and 7-element filters offer greater
attenuation of harmonics, I have found the following design to be
simple and very useful. Furthermore, several of these filters may
be chained together in series to produce even better filtering**.
<p>
If you make L1 with the 18 gauge wire as indicated and use capacitors
rated at 50 volts, the power handling capability of this filter will
be around 20 watts. If you use 100 volt capacitors, it should be
able to handle 50 watts or more. The insertion loss of the filter
is generally less than 1dB if you stay below the F(0db) point.
<p>
Here is a schematic for a 3-elemement
lowpass filter :
<img src=){kind=spacer}
The following table summarizes 5 different variations of the 3-element lowpass filter. I have constructed and tested some of these myself and find that they work as advertised. The attenuation figures shown below were produced by spice.
C1 C2 L1 F(0db) F(3db) F(6db) F(10db) F(20db)
33pF 33pF *(1) 113MHZ 138MHZ 163MHZ 200MHZ 320MHZ 39pF 39pF *(2) 98MHZ 119MHZ 140MHZ 173MHZ 293MHZ 47pF 47pF *(2) 95MHZ 112MHZ 130MHZ 160MHZ 270MHZ 52pF 52pF *(2) 92MHZ 107MHZ 125MHZ 152MHZ 255MHZ 56pF 56pF *(2) 90MHZ 105MHZ 121MHZ 147MHZ 246MHZ 62pF 62pF *(2) 87MHZ 101MHZ 116MHZ 140MHZ 235MHZ
*(1) - 2 turns #18 wire with a 5/16 inch inner diameter. Wind snugly
at first. If SWR is objectionable, increase spacing between
coils a little bit at a time.
*(2) - 2 turns #18 wire with a 3/8 inch inner diameter. Wind snugly
at first. If SWR is objectionable, increase spacing between
coils a little bit at a time.
I constructed my filter in a tiny aluminum enclosure with female
chassis mount BNC connectors mounted for the input/output. I soldered
C1 and C2 between the center connector and ground on each BNC connector
and soldered L1 between the two center pins on the BNC connectors.
** You can make a 5 element filter using the above parameters by using the following configuration :
input o---+---uuu---+---uuu---+---o output
| L1 | L2 |
C1- -C2 - C3
- - -
| | |
gnd o---+---------+---------+---o gnd
Were C1=C3, C2 = (C1 * 2), L1 = L2, and the C1, L1 values are taken from
the above chart.
[Also of interest is that the FM-10 puts out about 8-9mw and the 2nd harmonic is -25db off the fundamental (frequency we are broadcasting on). The FM-4 Kit by Ramsey puts out 130mw and the 2nd harmonic is only -12db off the fundamental, which means the 2nd harmonic of the FM-4 is about as powerful as the FM-10. db is log10, ie 3db is 2 times 6db is 4 times...]
On a 2nd note: I replaced c7 with a 68pF cap and found it much easyer to tune a rock solid 19KHz at the test point.
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 are running series and the old cap setup is running in parallel.
*** Note : If you have an FM-10 you can call Ramsey and get this mod for free!
A much better pre-emphasis/input circuit is shown in the July 1992 issue of "Radio Electronics". Not only do they use 75K ohm resisters in there pre-emphasis, 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.
*** Note : the FM-10a kit comes with both sets of parts so you can select European or American audio standard.
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 temperature compensated disc cap of the same value. Even better is to cut the leads of the capacitor as short as possible and mount it directly on the bottom of the circut board.
BA1404s and other FM Broadcaster kits can be found at :
D.C. Electronics
phone: 1-800-467-7736 & 1-800-423-0070
fax:1-602-994-1707
They sell BA1404s for $2 a piece, seems to be the best deal going. Also they Sell 38KHz crystals for $5.99, which is also a fair deal, the crystals are tiny ones like the digi-key ones, but a different brand and work without problems or the Digi-Key ones.
38KHz Crystals can be obtained by calling :
Digi-Key at 1-800-DIGI-KEY.
38.000 KHz by Epson America, Digi-Key part No. is SE3314
(see notes on crystal mod on using this crystal, also note that
this is a cylinder type crystal and kinda delicate. you are probably
better off getting the 38KHz crystals from D.C. Electronics.)
FM KITS FROM FREE RADIO BERKELEY
Kits to let a thousand transmitters bloom. Lots of FM transmitter and amp kits, mail, email or call for more info. Reasonable prices. Can be slow to deliver (2 weeks to 3 months but promised to get better.)
Free Radio Berkeley
1442 A Walnut St., #406
Berkeley, CA 94709
Voice mail: (510) 464-3041
E-mail: frbspd@crl.com
Mouser Electronics
(800)346-6873
(817)483-9384 fax
Giant Catalog! 239pages of parts!
Just about everything.
No min order for north america.
$100 min for overseas.
RF Parts (transistors)
1320-16 Grand Ave
San Marcos, CA 92061
Just about any RF transistor!
Dalbani
2733 Carrier Ave.
Los Angeles, CA 90040
(800)325-2264 USA
(213)727-0054 WORLD
(213)727-6032 FAX
RF transistors and other
semiconductors + more catalog=
178pgs $20 min order
Panaxis Productions makes some very high quality FM transmitters. The
last word in Transmitting, tons of kits.
Panaxis Productions
PO Box 130
Paradise, CA 95967-0130.
(916)534-0417
Catalogs are $2, well worth it, a must have item.
A little taste of there catalog :
MMC1 Macromod Compander for 2:1 compression
Plans $12, PCB $18, P+P 26.50, Full kit $87
SG High performance stereo generator
Plans $15, PCB $13.5, P+P 26.50, Full kit $105
FME PLL FM exciter
Plans $17.5, PCB $15, P+P 24.50, Full kit $129
More expensive than a FM-10 but much higher performance.
A company called Progressive Concepts sells plans for a 88MHz to 108MHz
amp. The power curves show that 12mw in will yield 2.5 watts, but can
be driven harder for up to 12 watts. (I have not seen these plans)
Plans only in U.S., $16 (a bit spendy, ouch!)
Progressive Concepts
1313 N. Grand Ave. #291
Walnut, CA. 91789
If your looking to purchase a FM-10 kit (or a PA-1 kit) and can't find one
locally try :
Ramsey Electronics, Inc.
793 Canning Parkway
Victor, New York 14564
Phone (716) 924-4560
FAX (716) 924-4555
Should be ~$30
The makers of the infamous BA1404 :
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 BA1404)
FAX: (615)-641-2022
Also they have:
PO Box 1399
Antioch, TN 37011-1399
The MRF239 can be used as direct replacement for the Ramsey 2 meter PA-1 kit. Cost is around $14 bucks.
Newark also has the 38KHz crystals for $2.90 ( I don't know Newark's address, this was sent to me in the mail, will try to find it though.)