Need help picking a FM transmitter

Those units you have listed are a good start. If you want a plug and play unit, go with the C-Crane. They have really good audio quality and are FCC Part 15 certified.

The Ramsey FM 10C would be my first choice...for a couple of reasons. One..the unit is a kit and gives a perfect opportunity to become familiar with the innards of your transmitter as you assemble it. I own a Ramsey FM-100, which was in kit form when purchased back in 1997, and that unit is still operating perfectly today. I am convinced that the reliability factor in Ramsey products is top notch.

They may not have an FCC certification sticker, but when built properly they will operate within the parameters and spirit of Part 15...that is if they are not beefed up and modified with sloped wings and after-burner! I say that because there is a site out there showing a Ramsey AM-25 who's owner decided to "beef" it up by replacing certain parts with way overblown and over-rated parts...so overblown to the point that unit has to have a hefty fan on it because it now runs even hotter than the stock unit!

The Whole House FM unit...not sure on that one as I never owned one or tested one. But as it is a pre-built unit and FCC Part 15 certified, that is a good reason to consider it if you do not want to assemble a kit.

If your into electronics and kit building or building from scratch or from other designs, take a look at the forum's resource library for a variety of FM transmitter designs. Any one of them can be built for far less than the cost of any of the units you have listed.

Happy hunting and good luck!

RFB

Sorry to start this with a negative note but you should know that the Ramsey FM10C uses an LC oscillator to set the operating frequency. It will drift and will probably not work well with digitally tuned receivers. It is OK for experimenting but not for "set and forget" transmission. Their FM25 and FM35 series are crystal controlled and won't drift noticeably.

If you do a site search on the C Crane here you will find several threads about this unit.

Neil

The Ramsey FM25B was my first FM transmitter, and I liked it so much I got another one. Both of them were so liked by friends who borrowed them that they never returned.

The C.Crane is very well made and I use it to listen to programs I'm editing.

I was first in line to grab a Wholehouse 2.0 when it was new, and find its performance a close match to the C.Crane, with one added benefit: the stereo can be turned off.

That's interesting. My Ramsey FM-10 did stay on
channel after an initial drift. I don't remember the
particulars on when it stabilized but it did. I think
it took about 15 minutes and it would settle down.

I modified it to be mono so that if it was off a little,
it didn't matter. I had an FM DX set-up at the time.
The particular tuner had a center tuning meter. So
I tuned in a station 100 miles away, and then centered
the FM-10 right there.

If you put it in the sunlight it did drift, though. And this
was the FM-10. That's a couple of generations back
from the FM-10C. So I can't offer any opinion on the C
model.

I heard a story third hand about a guy that put some kind
of little heater in an FM-10 with some kind of feedback
loop(???) Sort of like a crystal oven except there was no crystal.
I don't recommend trying it though. And I have no idea how
he did it. The idea of little heaters inside a transmitter
scares me. I think there are too many things that could go
wrong. Still, it makes for an interesting story. And this was
back in the day when the FM-10 was the only game in town.
Probably about 20 years ago.

Best Wishes,
Bruce, Dog Radio Studio 2

Bruce, Dog Studio 2, I think the heater setup you are describing is a modified "crystal oven," minus the crystal. The idea behind it is to maintain a constant temperature to avoid frequency drift.

Carl is correct. The adding of a temperature compensating element near the tuning coil, or physically attached to the shield casing of the tuning coil can vastly improve the stability. I did just that with my FM 10 unit using a temperature compensator case that fit snug over a HC-6 crystal
from a very old and scrapped RCA FM tube exciter. All it needed was some voltage and a way to sense the temperature to control the voltage feeding the heating element.

Shaped and fitted the temperature "oven" right over the shield case of the tuning coil itself and wala.

The sensor was made with a simple diode, op amp and a differential amp. Kept the FM 10's frequency quite stable.

I did an experiment with a BA1404 based transmitter with an LC controlled oscillator. There was no temperature control of the circuit but it was in a stable 72 degree F environment. From "cold startup" the initial drift was +23 kHz. After thermal equilibrium with the enviornment was achieved after several hours of power on the drift was observed to be +/- 7 kHz, the cause of which I never determined. I will mention that the 1404 output was buffered from the antenna since lack of buffering can cause frequency pull.

A space heater was used to raise the environment to 76 degrees F and the drift was +20 kHz. I did not pursue this any further after concluding this was not acceptable for my intended use.

Your results with the FM-10C may differ and you may be able to stabilize it to your satisfaction and that is fine. I decided it was easier to purchase the FM-25 and be done with it. My FM-25 is in an environment where the ambient varies from 70 to 78 degrees F and the maximum drift in output frequency (checked about every three months) is 400 Hz at 90.9 MHz. Since this is very small I never bothered to try to correlate this with temperature.

Neil

Can transmitter drift be any way associated with power-line drift? As we've discussed, the 60hZ power regulation is possibly going to be relaxed even more than it has been, so how will that effect transmitters.

That reminds me of my early ham radio days.

My first transmitter was a 50C5 tube and a
bunch of other parts. The original circuit was
from 1968. It was called the "Bare Essentials
Transmitter." If you google that name you
will probably find the original article. On the
front cover of the magazine they stated -
"A ham transmitter you can build for only
7 dollars." My version lit a 15 watt light bulb up, but
it didn't work on my antenna. It was full of
weird RF products and VHF spurs. Later on
another guy gave me one that he made, and
it worked fine. Oh, the magazine was
Electronics Illustrated.

But that isn't the transmitter I'm on here to talk
about. It was my second transmitter - a 1956
Viking Challenger. Mine had problems. There
was some intermittent arching going on inside,
and it ran so hot you couldn't touch it. It also
ran 120 watts input, which was a lot of power
for a guy like me. So one day after almost
burning myself by touching the cabinet, I put
a gigantic blower on the top. It just bolted it
on. I transmitted a dead carrier on 3727 kHz,
and my ham friend across town said that he
could hear the blower! NO microphone! I
was transmitting in the CW mode! The blower
was vibrating the whole transmitter and
modulating it!

That transmitter and my Heathkit HR10B receiver
together were probably the worst ham radio
station in the world. I do have another HR10B
in my collection, and I love the radio despite
the fact that it really is not a great receiver.
But making contacts was very difficult. In a way
that was good, because I became a pretty good
norse code operator, and I could pull weak
signals out of interference with just my brain.

Could I do that today? Probably not.

Best Wishes,
Bruce, Dog Radio Studio 2 (Formerly MICRO1690/1700)

I haven't gotten into Part 15 FM, too busy working with AM and local programming, but if and when I do, my plan is to get a Decade MS-100. Quite pricey, but it's a professional grade Part 15 certified unit.

I do not know how it stacks up against, say, a Ramsey FM100B kit, but former users here say the Decade is very good unit.

HTH ...

The FM100B is not certified, and is waaay too powerful, even by Canadian standards (where we're allowed 4 times the field strength of the U.S.). It does sound almost as nice as the Decade, but the latter is clearly in a class by itself (certification, sound quality, build quality).

"The FM100B is not certified, and is waaay too powerful"

Well, it's up to the user to comply ... so says Ramsey. You can vary the output power of the pre-built unit from 0-1 watt ... dunno about the kit version. We should prolly check the Enforcement feed lists to see how many with FM100B units have been NOUO'd.

I had the one without the amplifier and it still blew the Decade (which is Canadian certified) away in terms of power. And that was with the short, telescoping antenna, which was nowhere near 1/4 wave (so was probably introducing quite a mismatch). Just for an experiment I briefly attached an external antenna and it reached across the island from one side to the other (at least a couple of miles).

Certification number or not...it is always the end user's responsibility to use these devices properly and within their designed parameters.

If the FCC felt units that are kits and put out a bit more juice than other units carrying fancy numbers..then those kits would have been taken off the market LONG ago.

So do not let some fancy FCC number give you the "ahh now I can play around and see what this thing can really do" go-ahead green light. Even if it does not have that fancy number....operate them both with a dose of common sense and above all else....RESPONSIBILITY.

RFB