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
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