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LarryF

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About LarryF

  • Birthday 12/11/1943

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    fisherlarry@gmail.com
  • Website URL
    http://lectrosonics.com

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  • Location
    Rio Rancho, New Mexico
  • Interests
    Classical music, fast cars and Maine Coon cats
  • About
    I have been chief janitor at Lectrosonics for 40+ years.
  • Interested in Sound for Picture
    Yes

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  1. Sorry but no such luck. There are internal balancing resistors that come into play when ports are unterminated or poorly terminated, i.e., not 50 Ohms. You still have a 3 dB loss with a single out but the input is balanced to 50 Ohms. Best Regards, Larry Fisher
  2. The MiniCircuit parts split the input power into two outputs, each having half the power. That is why the "insertion" loss is 3 dB or half the power. There is very little loss, it's just split in half (-3 dB). The single input to the MiniCircuit part remains at 50 Ohms even though you are outputing to two 50 Ohm devices so you have an excellent match to the 50 Ohm antenna. Also, the two output ports are isolated from each other by about 20 dB or more, so accidental garbage (local oscillator) on a receiver input doesn't interfere with the other receiver. The BNC "T" does none of these. The input impedance and output impedances are at best 25 Ohms, there is little isolation between ports to receivers and the losses will be greater than 3 dB. The fact that the antenna and receivers aren't seeing 50 Ohms, may shift passbands or filters of the antenna and receivers. Now the disclaimer: All these effects may be small (other than isolation) and totally unnoticeable in an environment with good signals. On the other hand, the 2 way MiniCircuit splitter is not very expensive and is the correct solution. However, if I were in a situation where one antenna had to drive two receivers and all I had was a BNC "T" , I'd use it in a microsecond. Best Regards, Larry Fisher
  3. "Now, I was told at my local retailer to definitely get a BSRF system, which they sell, because I lose 4dB gain in a distro wlsewise." and they would lose an expensive sale if you don't. Definitely go passive. If you are not running long cables and/or splitters with 10 dB or more loss, passive is the right choice. You will have no intermod in an amplifier (you don't have one), lower current draw, a system smaller and lighter, at lower cost. Furthermore, at 99% of your distances, you will have plenty of signal. By the way, MiniCircuits is a classic company and their products are so solid, Lectro resells them as an aid to our customers. Best Regards, Larry Fisher
  4. The final element in the RF filter at the RF output may be an inductor to ground (chassis) or an LC resonator to ground. Either case would measure zero Ohms to ground or chassis. Since it seems to work well, I wouldn't worry about it. Best Regards, Lawrence Fisher
  5. Then an attenuator is your most cost effective solution. Check with service at Lectro 800 821-2100 or 1-505-892-4501 for maybe a better opinion. Tell the nice human that answers, that you want service. Also, https://www.lectrosonics.com/contact-info-21.html Best Regards, Larry Fisher
  6. Check with service at Lectro for a quote. My guess is that will be too expensive, perhaps involving a new RF board. A simpler solution would be to use an SMS inline attenuator, then you could choose your power on an as needed basis. Battery life wouldn't improve though. You might also try swapping your 250 mW for a 100 mW unit. The 250 mW units are kind of rare now. Or sell the 250 mW and buy a 100 mW unit. Best Regards, Lawrence Fisher
  7. No degredation with the Lectro bias supply. You can have antenna power on or off, no diff. Best Regards, Lawrence Fisher
  8. Measure the resistance with a multimeter from the center pin of BNC to the metal shell of the BNC. If is an open circuit (or greater than 1000 Ohms) you are OK Best Regards, Larry Fisher
  9. Absolutely correct. Even with the best RF measuring equipment, it would be hard to distingwish a "10%" improvement. Making a radiated power comparison between a wire soldered to a PC board and an SMA antenna is difficult and the 1 dB difference that represents 10% of range, would be in the noise. Walking around and making a seat of the pants judgement about small differences in range is almost laughable. Best Regards, Larry Fisher
  10. Hi Matthew, You have good insight into the potential problems. There isn't much I can add, even as a designer of the systems. One area I can speak to, is that there are a few good multicouplers out there but many more that are, shall we say, under designed. Look for third order intercept specifications; if the product doesn't specify that number, look elsewhere. For instance, our service department has had too many cases where an inadequate multicoupler distrorted the AM component of digital modulation transmitters, leading to very short range. Best Regards, Larry Fisher
  11. The theoretical 1/4 wave length is calculated using an infinite ground plane with the antenna feedpoint just above that plane. With a body pack transmitter and a wire soldered to the PC board (original G3) the feedpoint is at the ground plane but the ground plane itself (transmitter case) is nowhere equivalent. When you add on an SMA connector, the feed point of the wire is raised away from the ground plane further changing the parameters. Rather than spending a week making models and simulations that probably would be wrong anyway, we hooked up a network analyser and just measured the best match. That is where our cutting chart comes from. You will note that the recommended lengths are not strictly proportional to the frequencies, i.e., twice the frequency is not half the length of wire. Theory and the real world are usually different. Again, getting the perfect length is a vanishingly small consideration when the transmitter mounted on a person. And a microscopic factor when a camera link is on your frequency. Best Regards, Lawrence Fisher
  12. "...since the Gx antennas have no external metal shielding (rubber coated only), does the metal of the pack effectively become the shield? Does that determine the "start point" of length of the antenna?" The simple answer is yes. Also, once the antenna is near or touching a warm bag of salt water (also known as talent), all length considerations are out the door. The antenna length is only correct for a transmitter in free space, a rare occurence. Best Regards, Lawrence Fisher
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