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David Thomas

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    Rio Rancho, NM
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    Senior Design Engineer, Lectrosonics, Inc.

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  1. I'm sorry no one replied to you sooner. Naturally our Customer Service department would be happy to talk with you. So far as diagnosing the problem goes, if you have a block 25 transmitter or receiver, you might be able to set the transmitter and receiver as close as possible in frequency (only 25 kHz or 100 kHz away) and defeat the squelch (bypass the pilot tone) on the receiver. This wouldn't give you the lowest distortion, but it will still receive, and you'd be able to tell whether the static is still there.
  2. As Larry said, the best sounding (but not the most economical) solution would be a Digital Hybrid receiver and a headphone amp. In case you consider this option, the new LR receiver is small and portable and covers three blocks.
  3. I'm not sure what hatting is, so I hope I'm not doing it inadvertently, or if I am, I hope I can be good at it <grin>. In any case, the deal with the antennas and receivers is this. Both antennas always feed both receivers. In the RATIO case, the antenna combinations are fixed, nominally "in phase" for one of the receiver sections and "out of phase" for the other, so the likelihood of a drop-out affecting both receiver sections is minimized. In SWITCHED mode, each antenna phase combination switch is under microprocessor control, in an attempt to make preemptive switches before a drop-out gets noisy. Fanatically, David
  4. JCC, thanks for writing back. Those firmware versions are stable and mature, and matched to your hardware, so I'm left having to venture further afield in my guesses. [by the way I had to read your first serial number three times to convince myself it wasn't 65536. I see that number a lot, since it's 2 to the 16th power.] It might be interesting to try reversing the roles of receivers 1 and 2. Admittedly, there is a guideline that says the Rx2 frequency should be higher, but quoting Dr. Peter Venkman from Ghostbusters, "Actually, it's more of a guideline than a rule." The rule is that relationship 4.2 <= (Rx1 - Rx2) <= 4.8 (MHz) must be avoided. The easiest way to avoid it is to make sure that Rx2 is higher than Rx1, but you can also ensure that the difference doesn't fall within the 4.2 to 4.8 MHz range. In this case, 05 and A7 should present no problems either way. If system performance is markedly different with the roles reversed, the call is coming from inside the house... woops my movie quoting has gone into overdrive.. I mean the problem is provably internal to the receiver. If the performance is roughly the same with the roles reversed, we still can't eliminate possible external signals mixing with your transmitters, at least in theory. Either way we'll learn something useful. Oh, here is another question. With both the 05 and A7 transmitters switched off, what does a scan of the block look like (using the SRA's SCAN function)? If it's interesting, perhaps even post a photo if you can conveniently take one. Ooh ooh! Then turn on 05 and scan again, for comparison. That would be very interesting. Okay, cue the dancing girls and/or dancing lobsters. Fanatically, David
  5. This is most puzzling, in more than one way. First, it does seem odd that a transmitter on 05 should interfere with a receiver on A7, especially registering full scale on the meter (if that's what is meant by "sends a full signal"). My expectation would be that you'd have to have the antennas touching to have even a chance of that, as the IF filters are quite effective 16 MHz off frequency. [besides that, Larry F. pointed out to me just now that it is normally only necessary to use compatible frequencies when more than two units are in use.] Second, once the receiver is in RATIO mode, the two internal receiver sections are supposedly always tuned to the same (single) channel. The behavior described in this thread makes it sound as though the second receiver were still acting independently. Because I'm the firmware guy, and this sounds very much like misbehaving or mismatched firmware, I'd be very interested in the answers to these questions. 1. Is the unit marked on the housing as SR, SRA or SRB, and what is the serial number? 2. When the unit powers on, does the firmware say SR, SRA or SRB, and what version number is displayed? Also, it might be interesting to repeat the 05/A7 experiment, but with different frequencies, to see if the interference changes with channel 1 tuning, channel 2 tuning, or stays the same regardless of tuning. I'll monitor this thread eagerly for any more clues! Fanatically, David
  6. I might be mistaken but I seem to remember the known problem was that a setting of "1" would result in the level not being correctly reset at the next power-on. I thought a value of "0" was always okay. In any case, we certainly issued fixes for all such known problems. -DT Lectrosonics Firmware Fanatic
  7. As my coworker often says, "Why buy it when for $500 more I can build it myself?"
  8. I agree with jon: probably something conductive like sweat or salt water got onto the circuit board. Interestingly, it probably didn't simply short out the power switch, or the unit would act more normally. A flashing red LED can indicate low battery or power-off in progress. I don't see any code that calls for flashing amber in the current version of the firmware, so I wonder if the two sides of the LED are also somehow shorted together, and what you're seeing is an attempted flashing red, with a little color added. I'm sure our Customer Service folks can take care of it for you in any case. Fanatically, -DT
  9. I just thought I'd jump in because this is such an interesting discussion, especially with Professor Senator's mathematical treatment! From a "firmware guy" perspective, the SMQV and SMDB differ in terms of which compatibility modes and RF power levels are enabled. The SMDB is fixed at 50 mW, whereas the SMQV can be set for 50, 100 or 250 mW. The SMQV offers six compatibility modes: 100 Series, 200 Series, "Mode 3", Digital Hybrid (higher deviation version), IFB, and "Mode 6". If I remember correctly, the SMDB offers three compatibility modes: "Mode 3" (with enhanced limiter for European compliance), Digital Hybrid (lower deviation version), and IFB (also with enhanced limiter, if I remember correctly). The two versions of Mode 3 are compatible, as are the two versions of IFB mode, but the two versions of Digital Hybrid don't interoperate correctly, due to the different deviation levels. If you use a low deviation transmitter with a high deviation receiver, the result will be that the transmitter could be in limiting and the receiver is still not showing full scale on the meter. The other way is worse: if you use a high deviation transmitter with a low deviation receiver, the receiver could clip in situations where the transmitter gives no warning. I'm also not sure what the disparity in deviation levels might do to the character of the noise floor. Oh, and another subtle point about those different deviation levels: the high deviation Digital Hybrid mode does a better job of hiding the diversity switching "ticks" than the low deviation version. The SRb of course offers ratio mode, with no diversity ticks, but then you have a more expensive channel. Fanatically, -DT
  10. I've played the files now, and I definitely see what you mean about the "choppy" nature of the noise floor. It sounds like the SRb uncompanding is mistracking slightly in response to energy in the bass frequencies (such as HVAC noise or traffic noise). An interesting test might be to try the 200c into the SRb again without a microphone plugged in to the transmitter. My guess is that the noise floor would then be smoother, since there would be no mic to pick up those bass frequencies. Your request is very timely as I am just now revisiting some of our analog compatibility modes and trying to work out the subtle reasons why some receiver models decode 200 Series with a little more accuracy than others, despite the fact that the algorithm is supposedly the same. The differences can be due to the mathematical precision used in various DSPs, differences in the hardware itself, and just plain programming bugs. I'm not sure what the solution is yet, but with the bosses' approval, I'll try some 200 Series transmitters with various current receivers and see if some yield cleaner noise floors than others. If so, I'll try to figure out what's different; if not, I'll see about perhaps improving the algorithm. Thanks very much for posting. I have a strong preference for getting this stuff right! Fanatically Yours, -DT
  11. (smile) Thanks for the very nice introduction, Larry. I'll have to get our administrator to help me since soundcloud.com is blocked from internal company access. Once I get to listen, there's a good chance I'll have an opinion. Oh, it could be wrong, but I've been listening to these modes a lot lately, and pretty intently at that! I'll post again once I get my ears on the audio. Fanatically Yours, -DT
  12. I thought I'd jump in here. I'm the author of the firmware for the SMDB and many other Lectrosonics products. A quick look at the archives makes it appear that every production SMDB has the "pBAc" feature. I'd like to try to determine what firmware is running in your unit. Could you please tell me the version number reported during the power-up sequence? The screen in question looks roughly like this: b21r4.3 ("block 21, revision 4.3"). Also, does your unit have a backlight on the LCD, and does it report the RF output power during the power-up sequence (e.g. "Pr 50" for 50 milliwatts)? Once I know what firmware you're running, I can help figure out whether an upgrade, a repair, or simply a different procedure is needed to do what you want. Fanatically Yours, David Thomas
  13. You could be dealing with more than one source of the noise, I'm not sure, but you can test for RF pick-up in the mic cable or mic element by holding the mic cable a few inches from the end in one hand, and the transmitter in the other. If you slowly run the antenna along the length of the cable, you should hear no change in the noise floor in the received signal; if instead you hear hiss surge up and down and find "hot spots" along the cable, it's likely that RF is getting picked up by the mic cable or element. Swapping mics and/or adding capacitors at the mic connector can sometimes fix that problem. If there is no sensitivity to the position of the antenna relative to the mic, but slapping the antenna with the hand causes a whooshing or thumping noise, I've encountered that before, too. If this is a good description of your symptom, can you tell me the model numbers and blocks of the transmitters that are doing it? -DT
  14. It would be interesting to know whether it happens only on loud transients (i.e. the limiter might be involved) or on quieter ones as well. It would also be interesting to swap around different transmitters, receivers and frequencies, and see if the problem always tracks with a given piece of equipment. Digital Hybrid does a good job of hiding defects in the channel, which is nice for production work, but not so nice when you're trying to figure out what's wrong. I realize if it only happens once a year, this is a tall order, but if you were recording at the time, do you have a sound sample you can post or send privately to me?
  15. Hmmm I don't know of any double secret master reset, though there is a pong game (hold down the UP key while powering on). The menus did get a little more sophisticated as the product matured, so it's not alarming that the two receivers behave differently. You'll also notice that your v2.0 unit's backlight won't time out. It couldn't, due to a hardware limitation which was remedied in later revisions. If you want the latest firmware available for each unit, your v2.0 unit can be taken as far as v2.2, but I don't know that I'd bother. Version 2.0 has a small bug wherein the three very lowest channels (00, 01, 02) don't return correct signal strength while scanning for clear frequencies, and 2.2 has the fix. Your version 4.0 unit could likewise be upgraded to 4.2, but again, the improvement is tiny. In this case, the only change is that a keyboard shortcut was added for faster tuning (MENU+UP and MENU+DOWN tune in 16 channel increments). Thank you for your question. It's nice to look back over the firmware change log and see that this excellent product has seen relatively few changes over the years. I had wanted to have a DT-made-a-mistake firmware update port installed on the UCR201, but I'm happy that cooler heads prevailed, and that it didn't wind up being necessary!
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