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About LarryF

  • Birthday 12/11/1943

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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

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  1. It is actually a lot more complicated than a simple 3, 4,or 5 Volt level. The recommended 5 Volt spec is with a resistor of 4.8k as used in some popular wireless. The actual voltage at the DPA mic is only 1.5 Volts and that voltage is fairly well fixed by the DPA circuitry, a compound FET and bipolar transistor circuit. The resultant current draw with that 4.8k resistor and 5 Volt setup is slightly less than 1 mA. The servo bias circuit on the Lectro units was chosen to maintain about 4 Volts across the more common single FET mics. Since the servo bias circuit is trying to maintain 4 Volts and the DPA mic is trying to maintain about 1.5 Volts, large, noisy, current arguments ensue. This is perfectly resolved with the recommended resistor value shown in our wiring recommendation. The full audio Voltage swing is available with that choice. Why does DPA recommend 5 Volts? Because with the internal resistors in some transmitters, it requires 5 Volts to get the optimum current (700uA) to the DPA mic. In an imperfect world, when the user has to use lower voltages, the user could just substitute a lower value internal resistor to keep the current at 0.7 mA (700uA). The downside is you would need to be able to get to the internal transmitter resistor. However, it is rarely a problem, since the DPA mics are very tolerant of various current values. Best Regards, Larry Fisher
  2. The pilot tones were chosen by the hex switch setting on the much older equipment (200 and 400 series). If the two 16 position switches were set at A-12 on any block, the pilot tone for A-12 was chosen. To be specific A-12 on block 21 would have the same pilot tone frequency as A-12 on block 22. This didn't cause problems because the carriers of the blocks were separated by at least 25.6 MHz. Choosing the pilot tone based on the hex switch settings saved lots of memory, which early on was in short supply. Block 470 introduced problems since identical carrier frequencies on overlapping blocks had different hex switch settings. With newer Lectro gear covering multiple blocks this became a "Gotcha". Today with new processors with LCD displays and more memory, we wouldn't have done it that way. I do think we could have made better decisions about block 470 even with the old gear. However, once we screwed up, continuing compatibilty forced us into living with it. "RTFM" is not really really an excuse for a poor decision but there you have it. Best Regards, Larry Fisher
  3. My error. I've mixed them up. The DSQD is in production, not theDSR4. We are going to need more foam. LEF
  4. An aluminum shortage was holding up delivery of extrusions for the front panels. Mind you, aluminum is one of the most common elements on the face of the Earth but deliveries were almost a year late. We've had to mount some sound absorptive foam to the production manager's wall. Not to quiet his frustrated screams but to prevent a concussion when he pounds his head against the wall. A quantity of aluminum finally came in and just today a small quantity of units have been given to shipping. There is a substantial backlog but the Damn dam has burst. Best Regards, Larry Fisher
  5. One of the more subtle ones. Lef
  6. https://www.lectrosonics.com/april-press-releases/11-lectrosonics-introduces-wa520-wireless-antenna.html?highlight=WyJhbnRlbm5hIl0=
  7. If an amplifier is used for gain, both the desired signal + any noise present are both gained up by the amplifier. Some receivers look at the noise level to make diversity decisions and squelch decisions. Excess amplifier gain can upset those systems. There is a place for amplifier gain for such things as balancing out losses in long cables (after the amplifier) or balancing out losses in splitters (after the amplifier). Trying improve performance by wildly amplifying signal and noise is a loser. Introducing loss and then trying to amplify it back up is also too late. Directional antennas have gain for the desired signal with no increase in noise. There is no reason to attenuate this stronger signal as the noise level is low. The stronger signal can overcome cable and splitter losses and still have a good signal to noise ratio at the receiver input. FM and Digital Hybrid systems are immune to desired signal overload. You can have a transmitter right on top of a receiver antenna with no overload. Full digital systems are not quite as bullet proof but good designs have variable gain amplifiers in the RF or IF signal path to overcome the strong transmitter RF signal problem. So in sum, keep RF amplifier gain before all the lossy cables or splitters and within a few dB of the losses. For directional antenna gain with no noise gain, it should never be a problem. Best Regards, Larry Fisher
  8. Mini 8 is an improved .250" cable and is only slightly better than RG-58. The larger 9913F is .400" and is much lower loss. (The F suffix is for "Flexible" as the center conductor is stranded. The stranding does lead to slightly more loss than the solid core 9913. Remember the "ironclad" rule of thumb, "If it is smaller, it has higher loss" Best Regards, Larry Fisher
  9. LarryF

    Noisy R1a?

    Yep. LarryF
  10. 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
  11. 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
  12. "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
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