299 lines
15 KiB
Plaintext
299 lines
15 KiB
Plaintext
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WB8EOH Gizmo Report
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(Very Long)
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The Ramsey FM-10 is a low power FM stereo transmitter kit that is easy
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to build and has many practical applications around the home and
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ham/swl shack. After living with one for several weeks, I could never
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go back to life before I acquired this little "freedom machine". The
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audio quality and stability of the signal give the unit many HI FI
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type applications, and indeed I am already planning to buy another
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unit to patch into the Audio/Video system.
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Egad, you mean you have to BUILD this thing?
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When my XYL saw that this package I had spent fifty bucks on consisted
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of a couple of polyethylene bags full of plastic bugs and little
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metalic button like pieces, she shook her head in dismay. Though I
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tinker with computer and radio gizmos all day long, I will admit that
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the past 20 years have seen me become an "appliance operator" more
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content to sit back and PLAY than get in there and tear into the
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circuitry, much less build something from scratch. Well, the folks at
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Ramsey have honed the art of kitbuilding, and even a klutz like me CAN
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have the satisfaction (like in the old Heath ads) to say "I built it
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myself".
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Constructing the FM-10 was in part a happy trip down memory lane. In
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my distant youth, one of my happiest memories was the construction and
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operation of an Allied Radio Knight Kit #83Y706 three tube AM Phono
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Oscillator. This wonderful little gadget paved the way not only for
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my interest in Ham radio, but also got me interested in broadcasting,
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a field which put bread on the table for many years. Well in the more
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than 30 years between the two kits, things sure have changed.
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First right off, don't even think about dragging out the old Weller
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soldering gun and the old roll of Kester solder. First thing I had to
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do was borrow a low wattage iron, and get some super thin solder. The
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Lifetime Supply of solder I bought in 1968 (five pounds) was fine for
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antenna work, and gobbing up audio connectors, but the old stuff is
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actually WIDER than many of the separate connections on the FM-10 PC
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board. EGAD these components are TINY.
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Kudos to Ramsey for the way their whole concept. The manual is very
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well written. My only problem was I did not get the companion booklet
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on how to build a kit (the generic HOW TO SOLDER book). Well I hoped
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that the instructions that came with my 1957 Knight Kit still applied,
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because I remember them. Heat the component, don't glob it all over
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the place, and try not to melt the PC board. I was on my own to
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develop a technique. Ramsey even takes this into account by having
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you mount some of the larger "landmark" components first, namely three
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RCA jacks (left and right audio and the antenna jack).
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Now I wanted this thing to work. I would not be able to face Elaine
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if it became necessary to send the completed unworking mess back to
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Ramsey for their $18 an hour bail-you-out plan. So I took absolutely
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extrordinary steps. With a (borrowed) digital meter, I measured every
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resistor, even though Ramsey gives the color code for each one in the
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manual as you install it.
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One of the nicest touches is the GIANT print of the PC board, upon
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which you place all the components in the same place they will go in
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the final kit. I did this with most of the components, except for the
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multitude of .01 capacitors, which I left neatly together (Ramsey
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uses a masking tape type type medium for keeping similar value
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components together).
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The scariest moment for me was soldering in the 18 pin DIP socket that
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houses the heart of the kit, a ROHM stereo transmitter on a chip. We
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are talking TEENY TINY little pins separated by seeming microns.
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EGAD. After each dot of solder, I held the PC board a quarter inch
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from my eyeballs to make sure there were no solder bridges. And I
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measured all the components with the Digital meter a second time
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before installing each one. You probably won't take these
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extrordinary steps, which make the simple kit an all night project.
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But it was a FUN night. The scent of melting tin/led/rosin... The
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occaisional absolutely PERFECT joint... Kitbuilding is not only an
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art, it is positively a cosmic experience. It is relaxing, creative,
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and there is the anticipation of all the wonderful things you will do
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with your kit upon completion.
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3:25AM
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Ah. The moment of truth.
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Connect the nine volt battery, push the power switch, and TUNE around
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on the FM radio to find the carrier.
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And I found.......
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NOTHING.
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It did not work.
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Now this is where we separate the men from the boys. How well you
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manage not to throw the thing through the window.
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So I went back through the whole manual. checked EVERY joint.
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Eyeballed EACH component. I could find NOTHING wrong.
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Elaine came into the shack as I was holding the PC board. I hated to
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admit defeat. But I told her it did not work.... yet.
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She held the board and looked at it with wonder. She could not
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believe that I had placed each of the little parts in their places.
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She told me I would figure out what was wrong with it.
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The next day, I went through the manual again. I took voltage
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measurements, and found all the proper voltages on the chip and RF
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amplifier. I was stymied.
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Then I looked very closely at the OTHER side of the board. I stared
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at the ROHM chip, which Elaine had called a "train trestle". Hmmm. I
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wonder if I pushed on the chip if it would go in any farther.
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Push. Click. It snapped into place.
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I pushed the power switch, turned on the FM radio, and found a nice
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clean carrier at 102.3, with the stereo light blazing away in pure
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clear silence.
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Hot DAWG it WORKS!
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First thing I did was to move the frequency. Since it was
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transmitting on top of one of the local stations, this seemed in
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order. Ramsey's manual stresses the importance of selecting a clear
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channel so as not to bring the wrath of neighbors and the FCC. Up
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here in the boonies, there is a tremendous clear swath from about 98
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Mhz to 102 mhz. (I plan to pouplate it).
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The next thing required is adjustment of the subcarrier frequency and
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stereo balance. Surprisingly mine was already right on for the
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subcarrier adjustment, and I found out that this adjustment is
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actually pretty critical. There is a test point if you have a freq
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counter to get it exactly on 19khz, but it can be done by just turning
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the little variable capacitor until the stereo light goes on.
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The "stereo balance" control takes a bit of explaining. This is not a
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simple LEFT-RIGHT adjustment, but actually adjustment of the level of
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left MINUS right. It is more of a separation adjustment, and also
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seems to have a real effect on tonal quality. It took quite a bit of
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diddling to get it right, and there seems to be some interaction
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between the two controls, as the stereo light will go out just when
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you think you have the sound right... The end result is a surprising
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quality signal with amazing separation. However, one thing to make
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note of... The RM-10 is designed with NO audio level controls. This
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is a bit of an oversight, because when using it with components that
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have fixed level output, the unit is prone to overmodulation. You
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MUST be able to lower the audio level of whatever it is you are
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feeding to the tranmitter, as it is too sensitive with EVERY component
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I tried connecting direct. Once you get the level under control,
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though, it actually sounds better than many local FM stations because
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the signal is not run through all sorts of "Enhancers" that
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broadcasters use to be the loudest thing on the band. I did find
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though that adding an audio limiter (an old DBX 119) really helped
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tame the overmodulation problem.
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I finished the project by mounting it in the $12.95 Ramsey Kit
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cabinet. OK, this is where the Ramsey guys make a few bucks. It does
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give the kit a finished look, but I would have to say that this is a
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bit dear for a simple plastic case. I think the next one will be
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built into a VIDEOTAPE plastic case or other cheapo cabinet.
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One oversight is that there is no hole in the cabinet for the whip
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antenna which mounts to the circuit board. Ramsey suggests
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constructing a dipole or groundplane antenna, which I did initially in
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the final installation in my hamshack. I have since stopped using
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this antenna however (more on why later)
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OK NOW WHAT CAN I DO WITH THIS LITTLE GADGET
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Ramsey gives many practical applications in the manual. I found the
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unit handy for listening to MDS stereo TV on a little sony walkman in
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the wee hours without having to run headphone cords. Remote listening
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of ANYTHING on your main stereo system in any room in your home by
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just tuning the radio is just ONE thing the kit can be used for.
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My own application is a bit unique. I have the FM-10 in my ham/swl
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shack, and it is connected to a stereo mixer, to which I have several
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receivers patched in. I am a communications junkie and often in the
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shack I listen to several things at once. The only problem is that
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one can not stay in ones hamshack all day long. Well with the FM-10
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and a pocket stereo receiver, you can monitor whatever you wish in
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your home or yard. Now since the Ramsey Kit is a STEREO transmitter,
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you can do what I do (if you are insane enough) I have a 2 meter rig
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on the LEFT channel, scanner on the RIGHT channel, and the HF rig
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panned dead center. The ears and the brain manage to sort it all out.
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I feel sorry for any of the neighbors who happen to tune in when in
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this configuration (when I am in my active monitoring mode).
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No Code, No License, No Kidding It's LEGAL
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Now speaking of neighbors, lets focus for a moment on the LEGALITY of
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using this kit under part 15 of the FCC rules. In 1989, the FCC
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revised part 15, changing the way the measurements are taken to
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determine if a device is legal. The new standard is: 250 microvolts
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per meter. A calibrated Field Strength Meter is needed to make sure
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the signal complies with this regulation (FCC rule 15.239). Beyond
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this, part 15 requires that the unit produce no interference to
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licensed stations. Basically those are the rules. What you put on
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the device is YOUR business. It comes under the same type of
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regulation as cordless phones, baby monitors, and walkie talkies. the
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only difference is that this unit operates in a BROADCAST band rather
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than a semi-hidden part of the spectrum like the others.
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The Ramsey manual has a chart that shows that even if one complies
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FULLY with this measurement, the transmitter has a surprising range.
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Doing the math of the inverse square law, we find that there is still
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.41 microvolts at 5000 feet from the transmitter, nearly a mile.
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Since the Ramsey kit has a FINAL AMPLIFIER, it is much more powerful
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than a similar kit sold by another manufacturer which uses the chip
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output only (that one can be heard well within only 20 feet). I found
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that the kit with a dipole antenna cut to the operating frequency has
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TOO MUCH range for my own use. Those who wish to "Play DJ" might be
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interested in running the recommended dipole antenna (making CERTAIN
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they make the Field Strength Measurement) to get the maximum range out
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of the unit. I found that just a small piece of wire gives me all the
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coverage in my home that I need.
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For someone interested in providing a broadcast type service, to a
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college dorm, appartment complex or local neighborhood (Legally the
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signal can be quite loud over a quarter mile away) It can be legally
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done under part 15 of the present FCC rules (as ammended in June of
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1989) by simply adding a mixer, microphone, and sound sources to the
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Ramsey Kit.
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An application I am considering is connecting the audio output of my
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new satellite system and tuning it to the BBC audio feed and just
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leave it run that way when I am not using the dish for other purposes.
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This way I can enjoy BBC in FM quality and so can my immediate
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neighbors. Now before the flames begin, please remember that
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copyrights, etc, do not apply to part 15 transmissions. You can put
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on ANYTHING you want. Just as if you were listening on closed circuit
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speakers. The only difference is that your immediate neighbors CAN
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also enjoy the transmissions as well.
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FCC RULE 15.215(a) Says: "Unless otherwise stated, there are no
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restrictions as to the types of operations permitted under these
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sections." This general provision *APPEARS* to leave you free to use
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the fm transmitter for just about ANY type of operation you desire,
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including becoming a "legal low power broadcaster".
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Now the nitty Gritty:
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RAMSEY FM-10 FM STEREO TRANSMITTER KIT
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Price: Circuit Board and Components -- $29.95
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Cabinet (black plastic) -- $12.95
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Shipping add 6%.
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Ramsey Electronics
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793 Canning Parkway
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Victor, NY 14564
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(716) 924-4560 (Voice)
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(716) 924-4555 (FAX)
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o Operates from internal 9 volt battery
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o Choice of onboard whip or external antenna
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o Stable output, from 88 to 108 MHz
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o Left and Right channel RCA line audio input jacks
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o Use with Mixers, cassette or CD decks etc.
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o Clear, step-by-step assembly instructions
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o Helpful information on FCC rules included
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TYPICAL USES:
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o Extension of home stereo system without wires
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o Student-operated school radio station
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o Home or neighborhood radio station
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o College dorm favorite music broadcast service
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o Listening aid for auditoriums, churches
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NOTE1: I am in NO WAY affiliated with Ramsey Electronics other than
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being one of their very satisfied customers.
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NOTE2: If you plan to use the kit as a "broadcasting" service, I would
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STRONGLY SUGGEST you have the output level CERTIFIED by an
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engineer assertaining for SURE it is no more than 250
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microvolts per meter. This kit has an almost amazing range,
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and I imagine it could very easilly exceed LEGAL SPECIFICATIONS
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if you are not careful.
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=============== WB8EOH = The Eccentric Old Hippie = WB8EOH ================
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X-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-X
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Another file downloaded from: NIRVANAnet(tm)
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& the Temple of the Screaming Electron Jeff Hunter 510-935-5845
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Burn This Flag Zardoz 408-363-9766
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realitycheck Poindexter Fortran 510-527-1662
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My Dog Bit Jesus Suzanne d'Fault 510-658-8078
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New Dork Sublime Demented Pimiento 415-864-DORK
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The Shrine Tom Joseph 408-747-0778
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"Raw Data for Raw Nerves"
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X-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-X
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