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LarryF

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Everything posted by LarryF

  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
  13. From lunchtime chats with Gordon (Lectro Pres), I understand we have received recent IFBlue shipments that catch us up on most backorders. Further, we are going to receive enough units in the next few days that will allow us to even put units on the shelf. The current global semiconductor supply chain shortages due to fires and Covid are playing Hell with delivery schedules. The positive way to look at it, is that the Black Plague was worse. Best Regards, Larry Fisher
  14. Those are rated in mWh not mAh. Since they are 1.5 Volts that would be 2000 mAh. All that aside, if they give you the times you need, then they are fine. Best, Lef
  15. In today's electronics, switching power supplies at the power input of the transmitter pull a fixed Wattage. Therefore, for a higher input voltage, less current is pulled. That means a lithium battery that maintains a higher output voltage over its life, will run at a lower total current draw, making it run longer. Alkalines start at 1.5 Volts and fall relatively rapidly to end of life at 0.8 Volts. NiMh start at a low 1.2 Volts and stay there until they suddenly die. Lithiums maintain 1.5 volts down to 1.2 Volts for a longer time. The current draw on a lithium is 20% less at the beginning than for a NiMh. Since most of the transmitters are current hogs, the higher current capabilities of a lithium mean the voltage stays higher, resulting in a lower current draw and longer life. Alkalines give up voltage early and result in higher current draws. All of this would be clearer if batteries could be rated in Watts. However, this would fluctuate with the load making things even more confusing. Interestingly, under very light loads such as 100 mA or less, alkalines have more competitve lifetimes since their current is now delivered at a higher, light load voltage. Under very heavy loads such as 4 to 5 amps, Ni-Mh are ideal since their output voltage is constant even at very high loads. For transmitters running middle of the road 5 to 8 hour discharge rates such as 500 mA, lithiums are the choice. Best Regards, Larry Fisher
  16. Hi Donald, My suggestion is as always; eleminate, then test and then add back until you find the guilty party. Try running the Lectros without the distribution device, i.e., the Lecros with just whip antennas. Do everything else the same with the A10's and see if the problem is now cleared up. The repair department has been reporting a number of RF overload and interference problems with distribution amps. If you've done this already, then it may be time to look at the output of the A10's with a quality spectrum analyser. Best Regards, Larry Fisher
  17. It's the middle connector that is the offender. Note the lower arm is going to the outside of the middle output connector which is connected mechanically to the box. There should still be a balun in the circuit. Best Regards, Larry Fisher
  18. L is 1/2 wavelength or 26" at 216 MHz. The individual arms would be about 13". The upper and lower connectors' outside shells are grounded to the case, though this has little to do with operation. The 200k resistor is to discharge static electricity and can be almost any value greater than 1k. What is not shown is a balun to convert the balanced arms of the dipole to the unbalanced shielded cable. Also, the way this is drawn, the case would have to be plastic or the lower arm is shorted to the case by the output connector. Look for an example on the web that uses a folded cable or a ferrite transmission line transformer at the output to form a balun. Best Regards, Larry Fisher
  19. My error in reading too fast. Those lithium AA batteries are even worse about charge detection. The internal LiPo battery in the AA's is running at 3.7 to 3.2 (?) Volts and an internal power supply knocks the voltage down to a regulated 1.5 Volts or thereabout until the internal battery dies. The regulator then shuts down quickly to protect the LiPo. Treat them the same as NiMh; only use the timer in the unit. Best Regards, Larry Fisher
  20. It is absolutely impossible to measure the voltage of a NiMh battery and derive its state of charge. Do as your audio guy suggested; fully charge the NiMh and then use the timer to determine how much time expended and/or left. The power light color is absolutely meaningless for NiMh be it green, red or purple, except to tell you that the transmitter is on. Best Regards, Larry Fisher
  21. Here's a test on some AA rechargeables after a year of use in solar lights, i.e., many charges and discharges. https://www.bing.com/videos/search?q=projectfarm+rechargeable+AA+Batteries&&view=detail&mid=12C4897AB10FFD02F03712C4897AB10FFD02F037&&FORM=VRDGAR&ru=%2Fvideos%2Fsearch%3Fq%3Dprojectfarm%2Brechargeable%2BAA%2BBatteries%26go%3DSearch%26qs%3Dds%26form%3DQBVDMH This projectfarm guy tests a little bit of everything, generally very thoroughly. He doesn't test the Eneloop black, which I found to be the best 5 years ago. But that was 5 years ago. Don't trust the ratings of off brand batteries; the measurements are dreamed up by the marketing depart after being threatend with unemployment if sales don't go up. Best Regards, Larry Fisher
  22. IMHO, I think the 4060 is the better choice. On loud signals, you can use "0" with no transmitter preamp problems. Make sure whoever builds the connector, uses the Lectrosonics recommended 1k resistor. Ignore the DPA recommendation of no resistor on the 4061. Set the gain according to the transmitter manual. Best Regards, Larry Fisher
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