FM Transmitter

Discussion in 'Tuners' started by musichal, Jun 18, 2018.

  1. Bill Ferris

    Bill Ferris Super Member

    Messages:
    1,416
    Location:
    NE. FL.
    I wouldn't/don`t locate electronics in a environment that I wouldn`t be comfortable in.
    Cold temperatures, usually no problem.
    Heat, well..

    What`s the issue with locating the XMTR in the house ?
    If you keep the power output low(less than a watt), you probably can even use a tack on the wall over the counter FM folded dipole.
    My first Ramsey (not the FM100B) drove a old back of the set twin rabbit ears from some old portable TV that I attached to a metal peanut can`s lid with some weight added to the can for stability, and I then adjusted the length and orientation of the telescoping rods for best received signal at the desired location`s receiver 50 ft. away.

    Of course, in my case, with no wife, I didn`t care what it looked like placed on my A/V rack, until I purchased the Ramsey FM 100B later on, and went with their outside PVC antenna, but both XMTR`s always lived inside on top of my A/V rack close to the FM XMTR`s audio input source.
    if I am comfortable temperature wise, so will be my electronics.
     
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  2. musichal

    musichal poet emeritus Subscriber

    Messages:
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    Location:
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    Exactly, that's what I've always felt - keep the electronics where I live. However, the lowest setting for this Xmitter is 1.9w, and it seems possible that it was over-modulating my tuners due to proximity. That garage antenna location would provide a bit more dx between the Xmitter and all my tuners, which might be desirable, given the previous round. Also, the garage location puts it on the opposite end of the house than my wireless router (which seems good to me), which I realize operates at a much higher frequency but thought maybe they could interfere RFI-wise, IDK??

    I'm a night owl, and probably night-time will be the right time for me to play, with heat less a factor. In addition to that, it would be the only place in the attic my wife's old bones will access - my old bones can't even climb the ladder's first rung. Literally can't, even with a gun to my head. Just shoot me. Anyway, that is the highest I could place the antenna. I can put it up there as far as possible from the door opener and front of garage and hope it works out. At this point that seems my best bet, and one I'd likely not attempt at all if I were paying for the unit, I admit.

    Obviously, I could buy a longer cable and locate the Xmitter somewhere inside but that gets into having to hire someone to run the cable, etc. With a brand new FM outdoor Yagi still new in the box after a couple years due to not finding an installer who can navigate the blown-in insulation of my tight attic space, well, you see the problem. Besides, our next hire-somebody project involves landscaping, including hardscape and some construction; we are contacting such services now for estimates.

    So I'm not interested in this Xmitter toy running into high costs, at all. A couple hundred bucks was fine to play with a new thing, and now admission has fallen quite a lot, it appears. It just isn't a high priority for more spending now - nor later, really.
     
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  3. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Bill, of course at this time we do not know if his first unit was defective.

    As musichal mentioned, lowest power setting it 1.9 watts.

    This will produce over 3 million microvolts of signal per meter, that is 3 volts of RF, at 3 meters from the transmitter's antenna, be it a vertical antenna or a dipole antenna,

    And it he used a 300 Ohm folded dipole antenna, he would need to us a 4 to 1 balun transformer to match the antenna impedance to the transmitter.

    And the balun would need to be able to handle the power of the transmitter, almost 2 watts. There is no guarantee that the common TV type baluns that we are familiar with will handle that much power, although some may.


    The voltage at the feed point of the antenna will be almost 12 million microvolts of RF, that is almost 12 volts of RF. Poor RF decoupling at the antenna feed point (poor RF ground plane and so on), causing unwanted common mode RF currents that can allow all of that RF to run amuck, go places and do things that can cause unwanted issues.

    Depending on the particular device used to receive the RF signal, there may be overloading of the RF front end.

    The RF may infiltrate the audio section(s) and cause issues.

    This picture below is an illustration It shows a dipole antenna but it would be the same with a poorly decoupled vertical antenna.. Note how the common mode RF current may flow right back to the transmitter on the outside of the shield of the coaxial cable. The coaxial cable is now acting as part of the antenna and may radiate the common mode RF. Since the transmitter may be located fairly close to the audio source and or the rest of a person's audio gear, this may be an issue.

    upload_2018-7-1_8-34-34.png

    Again, while not everyone may have unwanted issues, this general information is just an RF 101 heads up.

    Hopefully musichal's replacement transmitter will work fine and he will not have to worry about any of this.

    BTW even at a power level of 0.5 watts
    , the RF field strength at 3 meters will be about 1.7 million microvolts or about 1.7 volts and the voltage at the antenna terminals will still be about 6 million microvolts or 6 volts.
     
    Last edited: Jul 1, 2018
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  4. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Musichal, per your discussion of possibly putting your transmitter antenna in the attic, please note my post above. Without proper common mode RF decoupling at the antenna, the outside of the shield of the coaxial cable can act and both an antenna (radiating the common mode current) and a conduit for the common mode RF current. And that common mode RF current may end up right back at the transmitter and in the vicinity of your audio source and or the rest of your audio gear.

    Several common mode ferrite chokes, or looping the cable through a couple as shown in one of my previous posts, at the antenna would not be a bad idea.

    Again, we are all hoping that your replacement transmitter works fine, with no issues.

    Another BTW, that 1.9 watts of power, if fed to an antenna somewhat above ground, say in the attic, will likely cover a fair amount of territory. Be sure to choose a frequency that is not likely to step on another radio station.
     
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  5. Bill Ferris

    Bill Ferris Super Member

    Messages:
    1,416
    Location:
    NE. FL.
    I understand, your point & concerns I LIKE MUSIC,
    And could very well be mitigated with various method choke applications.
    While my Ramsey FM 100B wasn`t as RF hot as musichal`s model, even after cranking up the RF drive trimmer pot max, in which I think resulted in maybe a 50 microwatt output at the BNC connector, which even before I purchased Ramsey PVC encased a 300 ohm large ribbon folded dipole, with a beefy Balun, if I remember correctly, as it was constructed and installed nearly 18 years ago.
    No overload was detected on two Mac tuners that are fed via a passive/lossy 75 ohm splitter from a large outside 13 ft. long deep fringe Radio Shack TV/FM antenna ~ 20 ft. from the Ramsey PVC encased antenna at around the same height(36 ft.)

    Both tuner`s signal strength indicators full bars with full quieting on my XMTR`s channel, and no co channel interference/splatter noticed as received on the SS Mac tuners, and my tube MR 67 fed with a standard 300 ohm folded wall tacked dipole to that tuner`s 300 ohm ant. input ..
    I`m sure feeding the Ramsey XMTR output through 100 ft. of RS/Tandy branded RG 6 imparted some attenuation at my frequency of 103.3 Mhz. which was a clear channel at the time, plus a coax surge protector to help reduce nearby lightning EMP`s from eating my XMTR.

    Musichal might be able to find a power rated Balun on line, or see if Ramsey will sell him one of theirs reasonably priced ?

    The Ramsey FM 100B has a grounded power cord and, at least, in my case, was very low impedance grounded, due to my extensive multi bonded ground rod system, so looking at any of my unshielded Cat- 6 balun`ed 6 room whole house line level audio distributed feeds with a 100 Mhz. Tek. scope didn`t reveal any RF on both L/R audio lines, at the rack where the XMTR is located, nor at the end points, just a very little, as to be expected, audio circuit noise, as the scope`s gain was cranked up.

    Anyway, enough of noise from me about my "WBIL" Ramsey XMTR set up.

    Good luck Musichal, with whatever method that end`s up working out for you..

    Take care Sir.

    Kind regards, OKB
     
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  6. Watthour

    Watthour Electron Rancher - JS3600

    My antenna is in my garage attic. It's a 1/8 wave ground plane. The transmitter is also in the garage. The space is heated, but not cooled. It stays above 60° in winter, but often gets above 90° in summer, like today (it pushed 100 Friday and yesterday). I also have a PC in the garage, and a TV, and a Kenwood receiver. The heat hasn't killed any of them yet, but it's only been about ten years.
     
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  7. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Interesting...

    A 1/8 wave ground plane antenna, instead of a 1/4 wave? Was that done for physical size requirements? If so what type of feed point tuning or loading to bring the antenna to resonance and match the antenna's impedance to the feed line does it use, or do you just live with the mis-matches?
     
    Last edited: Jul 1, 2018
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  8. Watthour

    Watthour Electron Rancher - JS3600

    ^ What ILM said.

    I have a ferrite loop on the AF feed line to limit interference:

    [​IMG]
     
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  9. Watthour

    Watthour Electron Rancher - JS3600

    Sorry, it's a ¼-wave. Center-fed, modified GP. This is the vendor's image - I'm not climbing into the garage attic to get one:

    [​IMG]
     
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  10. spicer

    spicer Well-Known Member

    Messages:
    987
    If it was on the up and up it is kind of cute. Wouldn't it be something if the replacement is everything one could hope for... It is interesting they, if it was them, are that concerned about a negative review. They must have some idea that something might have been wrong with the one you had... or maybe they'll send you one that received special attention on the assembly line to insure it performs without the issues you mentioned. This is a possible interesting turn of events...
     
  11. I LIKE MUSIC

    I LIKE MUSIC Super Member

    ^^^This.

    Who knows, he might receive a special edition 50 or 100 watt transmitter just to be sure his signal is strong enough.
     
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  12. spicer

    spicer Well-Known Member

    Messages:
    987
    That's funny... more power solves everything. That thinking does have it's place....
     
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  13. musichal

    musichal poet emeritus Subscriber

    Messages:
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    Location:
    Norman OK
    I believe it pretty much has to be them. Lots of folks mention Angela, and her persistence in making the customer happy, in several reviews. And the conversation was pretty much as I posted; I didn't have to dress it up. I was laughing at times. Angela actually watches the reviews, makes comments sometimes, answers questions. I guess Amazon is their primary market-place. But why she offered a free one beats me, except that if I do like it, I might feel guilty about not paying. Fortunately, I seem to have a fairly high tolerance for guilt. :D



    Its Place


    [​IMG]

     
  14. audiotemp

    audiotemp Well-Known Member

    Messages:
    513
    Don't worry about that, Angela will bail you out.
     
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  15. imral3

    imral3 Super Member

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    Location:
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    ROTFLMAO!!!
     
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  16. spicer

    spicer Well-Known Member

    Messages:
    987
    That's funny... I was thinking of being in the passing lane. And, of course, enough power would solve those personal detention issues too.
     
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  17. Bob@FM

    Bob@FM Active Member

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  18. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Not all attenuators will handle 2 watts of power.

    upload_2018-7-5_10-29-13.png

    In general if an attenuator does not have a power rating, its power rating will likely be fairly low. They are designed for line level attenuation.

    Some are available for higher power levels, but they can be somewhat pricey.

    upload_2018-7-5_10-22-40.png

    I took a look at the spec sheet for the recommended attenuator and it does not specify a maximum power level, so it is likely to be use for line level applications, rather than power attenuation applications.

    Note that they are listed for CATV use, not power attenuation.

    upload_2018-7-5_10-40-9.png

    To be clear, i have not used this particular brand, but I would be very cautious using general purpose, unrated (for power) CATV type attenuators for power attenuation application.
     
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  19. Bob@FM

    Bob@FM Active Member

    Messages:
    323
    Location:
    NE NY
    OK, good points. I also tried to look up the power rating for the inexpensive ones, none list it.
    Even the "power" rated ones from that brand only give a DC power passing voltage level, not the same thing.

    I suppose the cheapest way to do it is to make your own with 5W non-inductive (carbon) resistors, and shield it or use a little metal box. Here's the Pasternack site with a calculator for that
    https://www.pasternack.com/t-calculator-pi-attn.aspx

    Or buy the Pasternack ones, sometimes you can find them cheaper on Ebay. I know you can get nice used HP 50 to 75 ohm BNC in/out small modules for signal stereo generators that way.
     
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  20. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Just to be on the safe side, and satisfy my slight (or somewhat more) ODCness, I would likely build something like this, just in case the transmitter was set to 15 watts by mistake.

    upload_2018-7-5_14-6-52.png

    The resistor values are for a 50 Ohm impedance rather than 75 Ohms, but the idea is the same.

    The resistor values can be calculated for 75 Ohms.
     
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