Part15

License Free, legal, low-power radio broadcasting

Need Advice

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Got a really nice power transformer but have no clue how to set the primary side for 115VAC. Here’s what I mean.

Got a really nice power transformer but have no clue how to set the primary side for 115VAC. Here’s what I mean.

The primary is capable of 115 or 230 VAC. The primary side has four solder terminals with two separate windings that are not connected together.

The box the transformer came in shows only one primary winding and a picture of a totally different transformer, so it’s no help. The website at Jameco.com at least has a correct picture of the two side-by-side primary windings, but the next line says “No data sheet available.”

I have thought of two possibilities. Either I only need to drive one of the windings with 115 VAC, or the two windings need to be wired in parallel for 115 VAC.

The secondary will be 12.6 VAC when it’s working correctly.

Just hooking it up probably won’t hurt it, but I’d rather get good advice.

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Comments

  1. Never Mind
    I hooked 115 VAC to the first of the two primary windings and measured an exact 12.6 VAC on the secondary. Case closed.

    Is Part15.us o.k? Not long ago it was busy with activity coming and going all day and night, but ever since the nuclear meltdowns things seem abandoned here on the site. Days go by with not much happening.

    • Let’s hope folks are outside, working on their antennas!
      Our comment volume comes and goes and is definitely affected by the time of year, holidays and similar family and personal influences. A check of our brother and sister boards out there seems to indicate that the summer slowdown is pretty wide spread.

      Hopefully, we’ll start getting progress reports as stations get their summer tune up 🙂

      No question that past board bullying had some folks turtle up – after all, who likes to get their head bitten off for a simple question or observation? That indicates the need for a heavier hand in moderating going forward…

      As always, scwis is easy to reach at scwis at yahoo dit com

    • Transformer wiring
      For 115 VAC input, both of the 115 VAC windings are supposed to be connected in parallel. For 230 VAC input, the two 115 VAC windings are supposed to be Connected in series. Connecting only one of the two 115 VAC windings will give you the correct secondary voltage, but will limit the maximum secondaey current.

      • Important to Know
        Many thanks Ermi for letting me know, as I haven’t been able to find this information elsewhere.

        I notice that using only one winding also causes the transformer to get rather hot, which must be a sign of the current situation you describe.

        You have contributed to The Big Talker shortwave transmitter project and your name goes on the design credits.

        • I’m Feeling Out Of Phase
          After hooking the two primary windings in parallel, if you get no or very little output one of the windings is connected backward. Simply reverse the leads of one of the primary windings.

  2. ANTENNAS….SIGNALS…..LAND CONTOURS????
    Hey all!

    Who has some insight on best way to improve signal range or reach to areas with contours or trees?

    Fortunately, we are broadcasting from hill top – however – our line of sight has some tree hurdles. How much extending of the antennas vertically can be done?

    Thanks.

  3. Starter Kit
    Hello RAW radio

    After several years of experimentation here is the experience I will share.

    I am located half-way up a hill. The front yard is downhill, the backyard is uphill. EVERT antenna I have ever built ALWAYS sends a fine signal downhill. NOT ONE of my antenna experiments has EVER sent a signal uphill.

    HOWEVER, I am now putting a good signal up to the top of the hill. How? I buried a ground wire from the transmitter over 100-feet up to the top of the hill. NOW the signal is good up there.

    Under Part 15 Rules you are limited to no more than 10-feet of vertical antenna. But of course everyone experiments with longer antennas. I tried a 20-foot vertical for one afternoon. The range of the transmission was more or less the same. Why? On AM/MEDIUM WAVE radio the quarter wavelength is over 100-feet high, and until you get near such a tall and long length, the distance is not much improved.

    Good Luck to RAWradio

    • To Reach or Not to Reach (with antennas)
      Carl Blare,

      thanks for the prompt response. According to earlier posts about tree blockage, a 1/2 mile signal reach is about the most expected from an AM transmitter (i.e. Rangemaster or Procaster). Does this mean that a 1-1/2 mile distance from the target area is NOT a good base for the transmitter?

      The FM transmitter based on a 2nd story or roof top has more reach – however – an elevated antenna has not been added yet.

      When raising the antenna, should more reach even be expected from either the AM or FM transmitter?

      Thanks!

      • AM vs. FM
        Heh … well, there really isn’t much “vs.” Part 15 FM transmission has one overriding restriction …

        Any unlicensed 88 to 108 MHz broadcasting with a signal strength greater than 250 µV/m at a distance of 3 m from the antenna is punishable by law and confiscation of all broadcast equipment.

        … so there ya go. You can’t expect much more than 300′ with a good receiver, probably less with an ordinary receiver with unmatched antenna. And it is mostly Line-Of Site.

        Of course AM radio is in an entirely different band, i.e., much longer wavelengths (center band wavelength is about 600′ long), which work on ground wave during daylight hours. Therefore, Line-Of-Sight is not the main factor, but best possible ground is. This is why all the old-time AM towers have, on average, 120 buried ground radials at 100′ each fanned about the center of the antenna. You usually see them in the middle of a fair-sized field.

        Trees and foliage tend to absorb ground wave, so getting above them with higher elevation will help, but that’s the reason. You STILL need superior ground to get your signal out.

        Most of the Earth’s land formations are rather rocky. Rocks and sand do not make good antenna ground, somewhere between about 4 – 30+ mHo’s/meter. Rich damp soil is better if you can get it, the sea is really good, about 5000 mHo’s/meter.

        In almost every case I can think of, AM has better range per watt than FM, albeit more susceptible to RFI from wideband sources, especially at night when stuff in that band does skywave. Otherwise, it will follow the terrain on the ground.

        Case in point: My station does poorly going over a hill on a paved road with sidewalks and a plethora of overhead and buried power lines, yet it wends its way over the same hill away from the pavement between houses and other buildings and down to a lagoon, especially after a rain, and the signal is almost as clear as it is downtown. I believe that’s because people have larger pieces of property and fertilize and water their lawns in that area.

        … Just some more things to ponder …

        • 3 miles max or 2 mile safety zone?
          Thanks Ken….

          So, for the record: FM is non-punishable so long as it does not exceed 3 miles in broadcasting?

          AM is legal as long as it does not surpass 2 miles?

          ANTENNA question: If the transmitter signal can be directed over the trees by the antenna….will a radio be able to get the signal about a 1 1/2 to 2 miles away?

          (PLEASE pardon the “elementary” technical questions)

          Thanks.

          • A quarter mile range is more like it
            Two or three miles is in your dreams only.

          • The FCC only speaks to us in terms of field strength
            The FCC doesn’t care about range, they measure field strength

            For FM, the permitted field strength is 250 micro-volts/Meter @ 3 Meters

            Another blog, Low Power Radio, reviewed FCC enforcement actions in the FM band here:

            http://tinyurl.com/FCC-FM-NOUOs

            For AM, it’s the constant 24000 divided by the Frequency to get the permitted field strength in micro-volts/Meter @ at 30 meters. AMers can also comply with a transmitter with less that 100 mW DC power input, a 3 meter antenna and a very short (< 6") ground lead to a subsurface ground. The Low Power Radio blog reviewed FCC enforcement actions in the AM band here: http://tinyurl.com/FCC-AM-NOUOs

            For compliant FM, “miles” is out of the question – think feet, like 200 feet, 400 feet, etc. For compliant AM, a portion of a mile (1/2 mile, etc.) in much more likely.

          • Wrong info
            “So, for the record: FM is non-punishable so long as it does not exceed 3 miles in broadcasting?”

            *** EDITED ***

            No sir … the “m” is for meters, not miles. FCC regulations use engineering data. Read it again … you can’t expect more than 200-300 feet from a Part 15 compliant FM signal because maximum field strength, which is the only regulatory factor and is a hard measurement on FCC standard field strength measuring equipment (which BTW most of us can’t afford), and is, again, 250 µV/m at a distance of 3 meters (39.37 inches) They usually take measurements at 30 meters (just shy of 100 ft.) and extrapolate.

            The only way to achieve more range is not with transmission (you can’t legally transmit at more than the allowed field strength), but with reception. The better the receiver, the better the reception.

            Range of coverage in the AM band is much better, based on a number of factors, especially as concerns AM broadcasting under Part 15. You are restricted to 3 meters of antenna length including transmission line and ground lead (the exact meaning of what constitutes those items is still under debate, seems different field agents have different interpretations), and 100 µW input to the final stage, but also there is a another set of field strength limits (not the same as FM). Field agents get to apply these as they see fit, AFICS..

            All-in-all, distance, or transmission range, is not a legal limitation, per sé, in either case (FM or AM) except as the result of the physics of the restrictions imposed by the rules. Back in, I think, ’96, the FCC issued a paper that said 200 feet is the expected range limit, but in the regulations themselves, no such limitation can be found.

            AM radio is more susceptible to interference (than FM) from various sources, even storms 50-100 miles away for such low power as we’re discussing, and especially at night when skywave interference can all but bury a Part15 signal, even at short ranges.

            As mentioned before, excellent ground is a major factor with AM radio.

            So, expect a maximum of about 300 feet for Part 15 FM, and maybe a mile or possibly two for perfectly-matched AM with superior ground.

            Also, the listening range is also governed by even more subjective premises, i.e., that of what a given listener considers to be listenable. For ham radio folks, lots of noise is acceptable if the voice or CW tones are easily understandable, but of course, listening to music is an entirely different thing … in that case noise become quickly fatiguing, and you’ll likely get tuned out.

            So, under Part 15, if you want range, AM is the best choice. And if you want more coverage, then place more stations where you can get the audio to them. If you use different frequencies, make sure they’re far enough apart in the band not to interfere with each other … or if on the same freq, you’ll have to set up near-absolute synchronization as shown on the Rangemaster website … several ways to accomplish it.

            Here, the only workable solution for same-freq application is microwave, i.e., sending the audio to crystal-controlled transmitters via microwave from a base station.

            BTW, as some of you may have discerned, this is how I would set up a LPFM licensed station. The outlying areas unreachable by the LPFM main signal and with no internet available, would get passed to Part 15 AM transmitters via Part 15 digital microwave links. True, they cannot get a stereo signal, but for things like important community meetings, it’s a better solution than none at all.

  4. Next Move – Procastor just arrived (hooray!!)
    Thanks everyone,

    The info about the signal range is great — it seems like a 1/2 mile or less is the best place for setting up the transmitters.
    (any range beyond a 1/2 mile is icing on the cake).

    QUESTION: There have been some videos and comments saying that Procasters can be set up on roofs (two stories or more above ground) — is this true? What about its effectiveness and limitations?

    Also, any tips for “simulcasting” on an FM channel?

    Some great tips about station set-ups have come from Jeff Gill at Liberty & Justice 1640.
    For those unaware of him, here is his link: http://www.libertyandjustice1640.com/signal.html

  5. STATION LAUNCH COUNTDOWN BEGINS…….
    The official launch for WMAS is scheduled for August 2011!

    We will be checking the signal ranges in our prospective broadcasting area this week,so, all advice during this process is welcomed.

    One technical question though: Is there much of a difference between using an R8 coax cable and an R6? Both chords seem to work well for producing a clear transmission.

    We will be testing the mast and antennas this week. Thanks for all the great advice!