Hello group

Forgive me for not lurking a bit longer here, but there's plenty of
interesting topic here so I'm going to be reading for a while yet....


I have recently built a small FM-Broadcast-band transmitter. I did this a
year ago when I was spending a lot of time in the hangar working on my
car. I got tired of all the crap my local radio stations are playing, and
I simply don't have any locals that play anything decent.

So, I have my own collection of music that I wanted to pipe out to the
hangar.

The first option was MP3's and playing them into the hangar's radio's line
input via my laptop. Well, this got real old, real quick. I decided the
better option was to take my desktop and add a line output to a small
transmitter.

I built the transmitter (I'll get the URLs for the schematics if anyone
wants them - they're very basic, and I very slightly modified them) on a
Radio Smack breadboard I have, and it worked great. I even had it feeding
a 10-foot length of 75-ohm TV coax into a pair of 30-guage antenna leads
at the other end - I forget the actual length, but I think that each lead
(dipole) is about 4.75 feet. I don't have my scratch papers with me, so I
forget the numbers I used, but I think I was going for a half or 5/8
wavelength at center band (88.1 - 107.9 : 95.5???)

ON THE BREADBOARD, the thing worked beautifully. I live on an airpark
with a 2600-foot runway, and we live in the middle. I drove in my car
with a handheld FM receiver and I picked up the signal - barely - at the
end of the runway, so I have about a 1300-foot radius of signal. That was
then.

I decided I liked it enough to solder it together. Using a different
style of PCboard (e.g., it didn't match the breadboard) it no longer
worked. Same components, electronically the same positions. Triple
checked. Twice. Then rebuilt twice, and checked again. Didn't work.

I decided this year to try again, starting from scratch, on the
breadboard. Got it working again, if not as well, so I soldered again -
this time to a matching PC board pattern. This time it works, but very
very limited range.

I have tried various coils. Most homemade, one out of an old 49 MHz
Walkie Talkie, and some commercial from a Radio Splat variety pack. I'm
also using a ~ 20 to 40 pF variable capacitor from an old AM/FM handheld
receiver.

When I use a very short (e.g., 4 inches) antenna, it transmits, but only
to the bathroom (about 10 feet away). If I use longer wire, it has to be
coiled up, and is still very short range. I was using an external dipole
before and got great range (considering) from it, and I want to continue
using that.

I normally would think that one lead of the dipole goes to ANT OUT, and
the other to chassis ground (which for a 9-v battery-operated device, I
would expect to be the - leg). That kills it. If I have only the one
lead of the antenna hooked up, I can get some signal, but not very good
range (only slightly better than with 4" antenna). I discovered by
accident (using a bare wire coil and having a loose shield of a piece of
coax accidentally touching it) that by grounding the shield of the coax to
POSITIVE 9v that I can tune it. But, that was still not a very good
tuning. Range was okay, but still limited to about 20 feet.

I'm not too worried about it, except that I *KNOW* I am capable of a
1300-foot range with this thing, so I'd like to get at least a healthy
proportion of that back (I might use this as a community radio that would
have a total of about 60 homes in its range).

I find that the best result I've had over the past two days is with a bare
wire coil, about two turns, on about a 3/16 " diameter wind. Aircore.
Spacing about 1/16th to 1/8th of an inch. Unfortunately, I was unable to
test my range when the "accident" happened, and also, I have not been able
- with like components - to duplicate the "accident" exactly.

The transmitter itself works beautifully as far as tuning and stability
and clarity and volume, if there is no antenna. Any antenna at all, and
it won't tune.

I have looked on the web for information, but I've found nothing that
helps me... only websites selling commercial radios, kits, etc. that I
can't afford, being a poor college student. I've looked in the Radio
Amatuer's Handbook for 1993, the latest edition we have, but it didn't
help me - a bit too technical, and I'm a hands-on learner (also didn't
help that the handbook uses parts I don't have and can't buy from a local
Radio Slack store shelf). I also checked out the Antenna book from same
year, it was about as useful as the R.A.H.

I know that without the schematics (sorry, I don't have time to get them
now, but I will later if needed), and without seeing the device, it would
be hard to tell me what's going wrong. I will take any advice into
consideration though.

Many TIA and 73 de KE4EDD
--
__ ____
/ _| | _ \ Unregistered Linux User #18,000,002
| |__ | _ \
\__/ |___/ Learning is the ONLY substitution for EDUCATION!

I said I'd get the schematics, here they a

http://www.reconnsworld.com/transmit/fm_trasm.gif

Actually, mine were printed out from that page, but it seems the guy has
added a whole bunch more since I was there. I printed this out a year ago
(12/13/2002) and he added some stuff in mid-2003... Got a 3W transmitter,
a 15-18W transmitter, an IC-based stereo transmitter, a 48 MHz beacon
transmitter... neat stuff indeed.

Anyway, I've gotten a couple of ideas from looking at the more complicated
designs, and I'm going to try a coupld of things and see what works and
what doesn't. I'm still very interested in any thoughts the groups has to
offer about why mine works as marginally as it does...

TIA and 73
--
__ ____
/ _| | _ \ Unregistered Linux User #18,000,002
| |__ | _ \
\__/ |___/ Learning is the ONLY substitution for EDUCATION!

I said I'd get the schematics, here they a

http://www.reconnsworld.com/transmit/fm_trasm.gif

Actually, mine were printed out from that page, but it seems the guy has
added a whole bunch more since I was there. I printed this out a year ago
(12/13/2002) and he added some stuff in mid-2003... Got a 3W transmitter,
a 15-18W transmitter, an IC-based stereo transmitter, a 48 MHz beacon
transmitter... neat stuff indeed.

Anyway, I've gotten a couple of ideas from looking at the more complicated
designs, and I'm going to try a coupld of things and see what works and
what doesn't. I'm still very interested in any thoughts the groups has to
offer about why mine works as marginally as it does...

TIA and 73
--
__ ____
/ _| | _ \ Unregistered Linux User #18,000,002
| |__ | _ \
\__/ |___/ Learning is the ONLY substitution for EDUCATION!

Hi,

Further to my e-mail, having seen the schematic now, it
is probably the antenna which is screwing things up.

Firstly, take the antenna off the collector of the
oscillator and either link-couple it (a couple of turns
with one end grounded) or tap it down the tank coil till
the oscillator starts reliably. You are not looking for an
exact match here but a way of coupling energy more
efficiently into the antenna without the oscillator
thinking that it's his mother.

Secondly, the base biassing you have on the oscillator
is too dependent on individual transistor parameters. I
suggest that you connect the base to ground through another
10K and then adjust the emitter resistor until you have 5
to 10 mA flowing through it. You can tell when you have it
about right by measuring the voltage across it. Touching
the circuit near the coil with your finger should also show
some variation in voltage if the circuit is oscillating.

Finally, you appear to be relying on the battery for an
RF return circuit which is not good. Try placing a
capacitor of about 0.01uF between the supply and ground,
close in to the oscillator.


Cheers - Joe

Hi,

Further to my e-mail, having seen the schematic now, it
is probably the antenna which is screwing things up.

Firstly, take the antenna off the collector of the
oscillator and either link-couple it (a couple of turns
with one end grounded) or tap it down the tank coil till
the oscillator starts reliably. You are not looking for an
exact match here but a way of coupling energy more
efficiently into the antenna without the oscillator
thinking that it's his mother.

Secondly, the base biassing you have on the oscillator
is too dependent on individual transistor parameters. I
suggest that you connect the base to ground through another
10K and then adjust the emitter resistor until you have 5
to 10 mA flowing through it. You can tell when you have it
about right by measuring the voltage across it. Touching
the circuit near the coil with your finger should also show
some variation in voltage if the circuit is oscillating.

Finally, you appear to be relying on the battery for an
RF return circuit which is not good. Try placing a
capacitor of about 0.01uF between the supply and ground,
close in to the oscillator.


Cheers - Joe

Joe McElvenney wrote:

Hi,

Further to my e-mail, having seen the schematic now, it
is probably the antenna which is screwing things up.

Firstly, take the antenna off the collector of the
oscillator and either link-couple it (a couple of turns
with one end grounded) or tap it down the tank coil till
the oscillator starts reliably.

Okay, I've not had the experience with this, but my father has. I
normally would ask him for help, but lately, he has been irritated when I
have asked, I suppose because he thinks I already know a lot of these
ideas. Anyway, having used your reply, I was able to get him to explain
what you meant.

In my discussion with him, he mentioned that because of the simplicity of
the radio, I would have what amounts to line loss by link-coupling the
antenna. He suggested the tapping bit. After explaining that to me, I
recall now having seen schematics that used that technique. I think
that's what I'll try.

You are not looking for an exact match here but a way of coupling
energy more efficiently into the antenna without the oscillator thinking
that it's his mother.

If I get the image you're trying to send, I must say that's one effective
way of getting your point across ;-)

Secondly, the base biassing you have on the oscillator
is too dependent on individual transistor parameters. I
suggest that you connect the base to ground through another
10K and then adjust the emitter resistor until you have 5
to 10 mA flowing through it. You can tell when you have it
about right by measuring the voltage across it. Touching
the circuit near the coil with your finger should also show
some variation in voltage if the circuit is oscillating.

Sounds easy enough. I assume you mean the base of Q2?

Finally, you appear to be relying on the battery for an
RF return circuit which is not good. Try placing a
capacitor of about 0.01uF between the supply and ground,
close in to the oscillator.

And this seems to be standard practice, the capacitor. I've seen
reference to that on just about every circuit dealing with oscillators (I
have a small collection of "Engineer's Mini Notebooks" from Radio Snap,
along with a book from an old electronics lab kit I got about 14 years
ago. Shouldn't be a problem to implement.

Cheers - Joe

Thanks for the help, Joe - I'll let you know how it goes when I get the
chance. Right now my father's needing my help loading a trailer with some
carpet and then we're off to our old house to see if the carpet can fit in
anywhere. After that I should have a few hours to tinker, I'll try this
then.

Cheers to you, and 73 de KE4EDD
--
__ ____
/ _| | _ \ Unregistered Linux User #18,000,002
| |__ | _ \
\__/ |___/ Learning is the ONLY substitution for EDUCATION!

Joe McElvenney wrote:

Hi,

Further to my e-mail, having seen the schematic now, it
is probably the antenna which is screwing things up.

Firstly, take the antenna off the collector of the
oscillator and either link-couple it (a couple of turns
with one end grounded) or tap it down the tank coil till
the oscillator starts reliably.

Okay, I've not had the experience with this, but my father has. I
normally would ask him for help, but lately, he has been irritated when I
have asked, I suppose because he thinks I already know a lot of these
ideas. Anyway, having used your reply, I was able to get him to explain
what you meant.

In my discussion with him, he mentioned that because of the simplicity of
the radio, I would have what amounts to line loss by link-coupling the
antenna. He suggested the tapping bit. After explaining that to me, I
recall now having seen schematics that used that technique. I think
that's what I'll try.

You are not looking for an exact match here but a way of coupling
energy more efficiently into the antenna without the oscillator thinking
that it's his mother.

If I get the image you're trying to send, I must say that's one effective
way of getting your point across ;-)

Secondly, the base biassing you have on the oscillator
is too dependent on individual transistor parameters. I
suggest that you connect the base to ground through another
10K and then adjust the emitter resistor until you have 5
to 10 mA flowing through it. You can tell when you have it
about right by measuring the voltage across it. Touching
the circuit near the coil with your finger should also show
some variation in voltage if the circuit is oscillating.

Sounds easy enough. I assume you mean the base of Q2?

Finally, you appear to be relying on the battery for an
RF return circuit which is not good. Try placing a
capacitor of about 0.01uF between the supply and ground,
close in to the oscillator.

And this seems to be standard practice, the capacitor. I've seen
reference to that on just about every circuit dealing with oscillators (I
have a small collection of "Engineer's Mini Notebooks" from Radio Snap,
along with a book from an old electronics lab kit I got about 14 years
ago. Shouldn't be a problem to implement.

Cheers - Joe

Thanks for the help, Joe - I'll let you know how it goes when I get the
chance. Right now my father's needing my help loading a trailer with some
carpet and then we're off to our old house to see if the carpet can fit in
anywhere. After that I should have a few hours to tinker, I'll try this
then.

Cheers to you, and 73 de KE4EDD
--
__ ____
/ _| | _ \ Unregistered Linux User #18,000,002
| |__ | _ \
\__/ |___/ Learning is the ONLY substitution for EDUCATION!

Circuit Breaker wrote:

Thanks for the help, Joe - I'll let you know how it goes when I get the
chance. Right now my father's needing my help loading a trailer with

Well, I got the chance.

Worked marvellously. I now have that same 1300 foot range I had before.

Yeah, big deal, I know, but this is big for me - first "properly working",
tunable, hard-soldered FM transmitter for me that can go farther than my
bathroom.

Only problem now is getting rid of the 60-cycle hum from my homebrew power
supply. Should be simple enough, and today I added the missing .1 uF
electrolytic capacitor to the power terminals (was missing, don't know why
I never put it in before). Still have the hum though. That's okay, this
problem should be very well documented in the ARRL handbook. I'll go
consult it.

I plan to revamp my cheesy little freewebs website - I'll be posting the
schematics of things I built and found to be useful. This transmitter
will definitely be among them.

73, de KE4EDD
--
__ ____
/ _| | _ \ Unregistered Linux User #18,000,002
| |__ | _ \
\__/ |___/ Learning is the ONLY substitution for EDUCATION!

Circuit Breaker wrote:

Thanks for the help, Joe - I'll let you know how it goes when I get the
chance. Right now my father's needing my help loading a trailer with

Well, I got the chance.

Worked marvellously. I now have that same 1300 foot range I had before.

Yeah, big deal, I know, but this is big for me - first "properly working",
tunable, hard-soldered FM transmitter for me that can go farther than my
bathroom.

Only problem now is getting rid of the 60-cycle hum from my homebrew power
supply. Should be simple enough, and today I added the missing .1 uF
electrolytic capacitor to the power terminals (was missing, don't know why
I never put it in before). Still have the hum though. That's okay, this
problem should be very well documented in the ARRL handbook. I'll go
consult it.

I plan to revamp my cheesy little freewebs website - I'll be posting the
schematics of things I built and found to be useful. This transmitter
will definitely be among them.

73, de KE4EDD
--
__ ____
/ _| | _ \ Unregistered Linux User #18,000,002
| |__ | _ \
\__/ |___/ Learning is the ONLY substitution for EDUCATION!

On Sat, 03 Jan 2004 01:16:14 -0500, Circuit Breaker
wrote:

Circuit Breaker wrote:

Thanks for the help, Joe - I'll let you know how it goes when I get the
chance. Right now my father's needing my help loading a trailer with

Well, I got the chance.

Worked marvellously. I now have that same 1300 foot range I had before.

Yeah, big deal, I know, but this is big for me - first "properly working",
tunable, hard-soldered FM transmitter for me that can go farther than my
bathroom.

Only problem now is getting rid of the 60-cycle hum from my homebrew power
supply. Should be simple enough, and today I added the missing .1 uF
electrolytic capacitor to the power terminals (was missing, don't know why
I never put it in before). Still have the hum though.

Not surprising. You want something *much* higher in value (a couple of
thousand uF).
--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill