FM Transmitter Design
Dave Brillhart
transmits two 20-20K analog signals in stereo so that any commercial
FM receiver will pick up and understand the broadcast (~100M Hz carrier).
Ideally I'd like schematics and a parts list. Failing that, just some
pointers as to where to look for design tips would be great.
And yes, I plan to comply with any FCC regulations concerning total
output strength. Although at this point I don't know what they are.
I believe such a device is legal since there is a product on the
market to do something similar (Mr. Microphone :-).
My application is to build a mini transmitter to attach to the back
of my home stereo so that I can place a portable remote set of
speakers anywhere around the house without having to wire it up.
Thanks in advance for any information.
-- Dave
Steve McKinty - SunConnect ICNC
> I want to build a low-cost, low-power (1W or so) FM transmitter that
> transmits two 20-20K analog signals in stereo so that any commercial
> FM receiver will pick up and understand the broadcast (~100M Hz carrier).
> I believe such a device is legal since there is a product on the
> market to do something similar (Mr. Microphone :-).
Just because you can buy them doesn't make them legal :-)
In the UK (I don't know the US position) buying, sellling, and owning
radio transmitters is quite legal. Its using one without an appropriate
license that gets you in trouble. Theatres often have licenses for radio
microphones.
Having said that, if you only want to broadcast the stereo around the house
1W is far too much. 20-30mW will be quite enough to cover the whole street.
1W with a reasonable antenna can get you many tens of miles.
A less controversial method would be to use the wireless intercom approach,
where the signal is coupled into the household power wiring. You can then
plug the receiver into any AC outlet and get power + audio. I'm sure I've
seen such things advertised, although I don't know where. You can buy
the appropriate chips yourself, although you obviously need to be careful with
the safety aspects.
Steve
stu...@kuhub.cc.ukans.edu
> transmits two 20-20K analog signals in stereo so that any commercial
> FM receiver will pick up and understand the broadcast (~100M Hz carrier).
> And yes, I plan to comply with any FCC regulations concerning total
> output strength. Although at this point I don't know what they are.
> I believe such a device is legal since there is a product on the
> market to do something similar (Mr. Microphone :-).
>
> My application is to build a mini transmitter to attach to the back
> of my home stereo so that I can place a portable remote set of
> speakers anywhere around the house without having to wire it up.
I want to do this exact same thing, and have made some progress.
I purchased an FM stereo transmitter kit from DC electronics (arizona,
I think), which is a simple little kit that uses a BA1404 (?) stereo
FM modulator IC. NO luck with it yet, and I heard that might be because
most newer receivers with digital VCO tuning are very particular about
the freq, and the kit doesnt really have very good freq stability.
There were several articles in Radio-Electronics about a year ago
with this type of project, the author was exploring the use of
FM Modulators made for CD to car stereo adapters, by SONY and Pioneer,
but he hasn't mentioned it for some time now, and I can't find the
devices for sale locally. I have been thinking about asking the
author, but I can't find his email address. I think he lives in
arizona, too.
I usually have all the radios around the house tuned in, and I can
listen as I move from room to room, but it would be nice to listen
to CD's this way. There are commercial alternatives, but not very
attractive.
John F. Woods
>In article <1993Jun3.2...@mlb.semi.harris.com>, dbri...@dave.mis.semi.harris.com (Dave Brillhart) writes:
>> I want to build a low-cost, low-power (1W or so) FM transmitter that
>> transmits two 20-20K analog signals in stereo so that any commercial
>> FM receiver will pick up and understand the broadcast (~100M Hz carrier).
>> I believe such a device is legal since there is a product on the
>> market to do something similar (Mr. Microphone :-).
>Just because you can buy them doesn't make them legal :-)
>In the UK (I don't know the US position) buying, sellling, and owning
>radio transmitters is quite legal. Its using one without an appropriate
>license that gets you in trouble. Theatres often have licenses for radio
>microphones.
Since he said he wanted to comply with FCC regulations, I assume he's in the
US (complying with FCC regulations doesn't help very much in the UK :-).
Part 15 of the FCC regulations authorizes low-power transmitters that do not
interfere with licensed radio spectrum licensees; the "Mr. Microphone" he
refers to is one of these. The allowed power output in the FM band is probably
on the order of microwatts (nanowatts, even?) rather than 1W or even 20-30mW,
but that probably is sufficient to cover his house. (Actually, the
regulations are written in terms of radiated field strength rather than power
output.)
I would think that either Popular Electronics or Radio Electronics (now
"Electronics Now", ulch) should have had a project like this at some time in
the past; perhaps an evening spent in a library looking through back issues
is in order.
A simple voice-grade monophonic transmitter would be a matter of one IC (the
MC 2822, if I remember the right number) and some parts (plus a crystal, which
would set you back about $10). A music-quality stereo transmitter would
probably be quite a bit more difficult, at least if you really cared about
the sound.
richard.b.dell
CHeck out alt.pirate, assuming you get it. One of the most common
devices used is (from memory) a BA-1404 chip .. all in one stereo
transmitter. Ramsey Electronics makes a kit for around $30 .. the
FM-10. I should be ordering one this weekend for my own stereo.
Richard Dell
Jim Campbell
For around the house use, you could use the FM-10 kit by Ramsey
Electronics, available at some hobby electronics stores or see the ads in the
back of electronics hobbyist magazines. Retail it's about $30. (don't bother
looking at Radio Shack). Range is maybe a city block or two. Stereo.
hope this helps...
-jim
--
Jim Campbell "The Tye-Dye Guy" | "Remember to tweet!"
ji...@megatek.com | You have just read the
WB6ZPB NSS#36691 ASA TNS NAC | mother of all sig files.
Mark Zenier
: I want to build a low-cost, low-power (1W or so) FM transmitter that
: transmits two 20-20K analog signals in stereo so that any commercial
: FM receiver will pick up and understand the broadcast (~100M Hz carrier).
: My application is to build a mini transmitter to attach to the back
: of my home stereo so that I can place a portable remote set of
: speakers anywhere around the house without having to wire it up.
See the July 1992 issue of Radio-Electronics / Electronics Now.
The cover story is an FM stereo transmitter using the ROHM BA1404
ic. Equivalent kits are available from Ramsey (the FM-10, beloved
of the folks who hang out in alt.pirate.radio) and a kit from
DC Electronics.
Mark Zenier ma...@ssc.wa.com ma...@ssc.com
ubs...@msuvx1.memst.edu
> For around the house use, you could use the FM-10 kit by Ramsey
> Electronics, available at some hobby electronics stores or see the ads in the
> back of electronics hobbyist magazines. Retail it's about $30. (don't bother
> looking at Radio Shack). Range is maybe a city block or two. Stereo.
>
Range is a city block or two! Is this legal? I am not familiar with
Ramsey Electronics, is there a phone #/address I can write for a catalog?
I am interested in getting a low power FM transmitter so I can use my CD
player on all stereos in the house, this one sounds like it has more than
enough power.
MCM Electronics has a "FM Stereo Transmitter Kit" for $29.95 but gives
no info as to the output power/range. Has anyone built this kit? Another
idea I had was to get a cheaper mono transmitter to transmit a IR remote
control signal back to the CD player. Is this possible?
Thanks,
Brian (UBS...@MSUVX1.MEMST.EDU)
as...@acad2.alaska.edu
is EXTREMELY temperature sensitive, and if one isn't careful will drift all
over the place. The drift can pretty well be eliminated by (in order of
importance):
Using the most temperature stable capacitor you can get for the
rough tuning capacitor (will be like 27 pf to 33 pf). I
_think_ this is C16 in the Ramsey kit, but I'm going by memory,
and so am probably wrong (grin). This is the single most
important thing I did.
Using a precision supply for the BA1404's Vcc.
Use a regulator (780x) for the rest of the circuit.
Other than that, these are great kits. I have two of them.
Luck,
Lee
========
Michael Covington
>> I want to build a low-cost, low-power (1W or so) FM transmitter that
>> transmits two 20-20K analog signals in stereo so that any commercial
>> FM receiver will pick up and understand the broadcast (~100M Hz carrier).
>> I believe such a device is legal since there is a product on the
>> market to do something similar (Mr. Microphone :-).
>
>Just because you can buy them doesn't make them legal :-)
>
>In the UK (I don't know the US position) buying, sellling, and owning
>radio transmitters is quite legal. Its using one without an appropriate
>license that gets you in trouble. Theatres often have licenses for radio
>microphones.
Wireless microphones and other such transmitters are legal here if the
field strength is below some rather low limit. 1 watt is, as you observe,
quite a bit too much.
--
:- Michael A. Covington, Associate Research Scientist : *****
:- Artificial Intelligence Programs mcov...@ai.uga.edu : *********
:- The University of Georgia phone 706 542-0358 : * * *
:- Athens, Georgia 30602-7415 U.S.A. amateur radio N4TMI : ** *** ** <><
Dave Brillhart
a FM-10. It should be in this week!!
Next question, assuming I have the FM-10 up and running:
********************
I would like to build a battery powered FM receiver and audio amp in a
"black box" to power a couple of remote speakers I could carry out
in the garage or out in the backyard.
Can anyone recommend where I could find a "low-cost" but moderate sound
quality receiver kit that would work good with the FM-10 transmitter.
It would have to be able to track the FM-10 carrier (since I haven't
built it yet I don't know how big a deal that is).
Thanks in advance for any info!!
*********************
-- Dav
richard.b.dell
I also ordered my FM-10 this weekend. Depending on your budget,
I would suggest a cheap stereo FM portable designed to drive
headphones. I have several, bought for boys, all were variously
between 5 and 15 dollars. One of those, driving a stereo speaker
amplifier, either homebrew or one of those commercial amplified
speakers I see around (but have never priced .. I prefer the headphones).
CHeck the FAQ on FM-10 (I havne't looked at it in detail yet.)
It may have ideas on increasing stability, etc. I have read
about a regulated supply, and there are some other mods. If
you want to keep in touch (email), I will let you know of any mods
I might preform, and any results.
--
Richard Dell
David Grieve
: smck...@sunicnc.France.Sun.COM (Steve McKinty - SunConnect ICNC) writes:
: >In article <1993Jun3.2...@mlb.semi.harris.com>, dbri...@dave.mis.semi.harris.com (Dave Brillhart) writes:
: Since he said he wanted to comply with FCC regulations, I assume he's in the
: US (complying with FCC regulations doesn't help very much in the UK :-).
: Part 15 of the FCC regulations authorizes low-power transmitters that do not
: interfere with licensed radio spectrum licensees; the "Mr. Microphone" he
: refers to is one of these. The allowed power output in the FM band is probably
: on the order of microwatts (nanowatts, even?) rather than 1W or even 20-30mW,
: but that probably is sufficient to cover his house. (Actually, the
: regulations are written in terms of radiated field strength rather than power
: output.)
Just for the record, the equivalent document in the UK is MPT 1336 available
from the Radio Communications Agency (1 copy is free I believe). This
covers "licence exempt" things like low-power walkie-talkies, baby monitors
etc. I believe the limit is 1mW.
David.
Rick Harrison
> One thing to be aware of with the BA1404 kits is that the xmting frequency
> is EXTREMELY temperature sensitive, and if one isn't careful will drift all
> over the place. The drift can pretty well be eliminated by (in order of
You forgot the best alternative of all, replace the inductor-
capacitor tank tuning circuit with a crystal.
John F. Woods
For those who want to look into that:
Not having the schematic in front of me, that might or might not be trivial,
but it's unlikely to be difficult. A crystal would probably run about $15
and take 3-4 weeks. These will be custom-ground crystals (unless there's
been a BIG run on BA1404 transmitting crystals :-), so you'll need precise
frequency and loading information. JAN Crystals (1-800-JAN-XTAL) and Crystek
(1-800-237-3061) are generally the cheapest sources.
Chris Elmquist
Has anyone successfully done this ? What sort of oscillator design is
used in the BA1404 (so that proper crystal parameters can be chosen) ?
I have one BA1404 design which uses a crystal for the pilot tone oscillator
but I have yet to see one that has a crystal controlled RF oscillator.
--
Chris Elmquist, N0JCF
chr...@n0jcf.vware.mn.org
elmq...@SSESCO.com
Marshall Levin
>In article <1993Jun3.2...@mlb.semi.harris.com>, dbri...@dave.mis.semi.harris.com (Dave Brillhart) writes:
>> I want to build a low-cost, low-power (1W or so) FM transmitter that
>> transmits two 20-20K analog signals in stereo so that any commercial
>> FM receiver will pick up and understand the broadcast (~100M Hz carrier).
>A less controversial method would be to use the wireless intercom approach,
>where the signal is coupled into the household power wiring. You can then
>plug the receiver into any AC outlet and get power + audio. I'm sure I've
>seen such things advertised, although I don't know where. You can buy
>the appropriate chips yourself, although you obviously need to be careful with
>the safety aspects.
>Steve
Ever seen a stereo intercom?
Mycal
Doing this may get you a stable signal but I fear much too stable to
modulate a WFM signal. You could add a dual tank circut tuned
above and below the crystal and try to modulate the osc that way, but
I havn't tried that yet.
PLL is in my opinion the only way to go.
mycal
---------------------------------------------------------------------------
PGP key on request. my...@netacsys.com
\ //
"..unfortunately we can't control the actions // \
of everyone." President Clinton 04/20/93 No Risk, No Rush
Rick Harrison
I saw a circuit design for a device that you plug a CD player
into and it transmits the audio to your car radio; it used a
BA1404 chip and had two frequency control crystals (so you
could chose the one that gives best results in your area).
I'm not sure exactly where I saw this -- a lot of data goes into
and out of the office here -- but it clearly is possible. Due
to excessive work, I have not had a chance to experiment with
this idea. Hopefully one of you who has time on his hands will
work out the details and tell us how it is done.
Steve McKinty - SunConnect ICNC
> smck...@sunicnc.France.Sun.COM (Steve McKinty - SunConnect ICNC) writes:
> >A less controversial method would be to use the wireless intercom approach,
> >where the signal is coupled into the household power wiring.
>
> Ever seen a stereo intercom?
No, but I've seen plenty of 2, 3 and 4 channel ones, its just a matter
of two chips, tuned one per channel.
Steve
--
Steve McKinty
Sun Microsystems ICNC
38240 Meylan, France
email: smck...@france.sun.com BIX: smckinty
Rick Harrison
> Doing this may get you a stable signal but I fear much too stable to
> modulate a WFM signal. You could add a dual tank circut tuned
> above and below the crystal and try to modulate the osc that way, but
> I havn't tried that yet.
>
> PLL is in my opinion the only way to go.
Many "real" FM broadcast transmitters use a crystal to control the
center carrier frequency. Correct me if I'm wrong, but wasn't FM
broadcasting invented before PLL circuits came into existence?
------------
Rick Harrison
bbs-...@jwt.oau.org
ro...@mother.mentorg.com
Please let me know.
You can also Fax the scheme to: Rob Hendrikse
Fax: 02990-47931 (holland)
Thanks in advance.
Rob Hendrikse
Software engineer
Mentor Graphics
Email: rob_he...@mentororg.com
Dave Medin
Not having my schematic in front of me either, I think that a crystal would
not substitute in the BA1404 at all. The problem has to do with
oscillator tank "Q." An LC tank can be pulled off-frequency (which is what
you're trying to do for cheap FM) much easier and to a wider bandwidth
than a crystal, as the crystal has a much higher "Q." If you were to
use a varactor (a diode that changes capacitance with applied reverse
voltage), which is a common scheme, the crystal would also produce
rather unlinear modulation over the several KHz of deviation
you could get out of it...
If memory serves, the BA1404 uses the tank frequency-pull approach.
With a PLL-based FM circuit, this would be different as all the crystal
would be doing would be providing a fixed center frequency reference.
--
--------------------------------------------------------------------
Dave Medin--SSD Networking Phone: (205) 730-3169 (w)
Intergraph Corp. (205) 837-1174 (h)
M/S GD3004 Internet: dtm...@ingr.com
Huntsville, AL 35894 UUCP: ...uunet!ingr!b30!catbyte!dtmedin
* The opinions expressed here are mine (or those of my machine)
Larrie Simon Carr
>
>In article <XXJR5B...@jwt.oau.org> bbs-...@jwt.oau.org writes:
>
> >
> > as...@acad2.alaska.edu writes:
> >
> > > One thing to be aware of with the BA1404 kits is that the xmting frequency
> > > is EXTREMELY temperature sensitive, and if one isn't careful will drift all
> > > over the place. The drift can pretty well be eliminated by (in order of
> >
> > You forgot the best alternative of all, replace the inductor-
> > capacitor tank tuning circuit with a crystal.
>
>Doing this may get you a stable signal but I fear much too stable to
>modulate a WFM signal. You could add a dual tank circut tuned
>above and below the crystal and try to modulate the osc that way, but
>I havn't tried that yet.
>
>PLL is in my opinion the only way to go.
>
>mycal
>
The Hardware Hacker in Elec Now talked about using crystals. I believe
that you could.
--
Larrie Carr lar...@sfu.ca
MicroElectronics and Sensors Group
School of Engineering Science
Simon Fraser University, Burnaby, B.C, Canada V5A 1S6