The biggest difference between the SRa and SRb receivers is the use of a six layer printed circuit board rather than the original four layer board. This single change reduced internal interference (birdies) to the point that gain could be reduced in multiple amplifiers in the RF and IF stages. In fact, one IF stage was simply removed since it was now unnecessary to the design. In spite of the reduced gain, the sensitivity of the receiver improved overall. As you would expect, intermodulation and overload performance improved greatly with the reduced gain. This improved board was first used by exchanging customers' boards on Block 606 in England as they were having the most problems.
With what we learned on the Block 606 changes, we added the same general changes and the six layer board to all the SRa units without saying much about it for several months. These improved units seemed to work very well and tested much better in production. While shipping the improved units, we went back to the SRa RF board and spent several months re-matching every amplifier and filter in the RF and IF sections. This was necessary because of all the other changes that had already been made. Many small improvements were made at each stage leading to fairly impressive additional improvements overall. One of which was an improvement in sensitivity of more than 6 dB. The last major change was to relocate the two IF filters. We found an optimum location by making up 5 different prototype boards, with the IF filters located in various trial positions with different shields and ground plane configurations. The final result had one IF filter on the top of the PC board and one underneath with a solid ground plane and our usual shielding. This simple change improved out of band selectivity by a huge 30 decibels.
With the improved sensitivity, better out of band rejection, improved intermodulation performance, and the elimination of internal spurious responses we decided to advance the model designator from "a" to "b", thus the SRb. As a service to our customers with SRa units, we offered an upgrade for the difference in retail price between the SRa and the newer SRb. The change in model designator also indicates that we think this is a major improvement in the SR receiver and it encourages our customers to get the upgrade.
The output level is adjusted in the DSP and not by an output attenuator. Since the original design was seen as a "venue" (auditorium, etc.) unit originally, lower output levels were not seen a necessary or a desirable feature and would add cost to the user. The problem for sound mixers is that if the level were to be adjusted lower in the DSP, then the output D to A noise would become a problem.
The other thing is that we didn't realize was that some of the pro gear had a hole in their ability to handle input levels. It amazes me that line levels are so high and mic levels so low that they don't overlap.
As a band aid, we have a cable that has an attenuator at the mixer end to reduce ground loop noise and can be set for -20, -30 and -40 dB of attenuation.
The RM2 does not have an LCD readout and can not set the frequency of operation of the SM transmitter. The RM2 uses a potentiometer for the gain control setting of the SM where the RM has the LCD readout. This means that you can only set the gain to an approximate value where as on the RM it can be set exactly. The speaker on the RM2 is not quite as loud as on the RM so the maximum range is a few inches less. The lithium battery on the RM2 is inserted into a clip on the circuit board and requires removing the back cover to replace, though it should last for years.
Here is a RAMPS posting.
To the Group:
This post is in reply to an earlier post about "hot" SM transmitters. The SM puts out no more heat than a UM400; it just does it in a smaller volume. Since, despite the non stick finish, I'd never had any luck cooking omelets with an SM, I thought I'd run some crude tests.
I tested the temperature rise of an SMa transmitter, lying with its backside on a pad of paper with the temperature probe between the unit and the pad of paper. The air was fairly still with only the usual office air conditioning running. The pad blocked some air circulation to the backside and seemed to be equivalent to a unit on a belt. After 3 hours the temperature rise was 16 degrees, from 76 to 92 F. The battery was an Eveready lithium disposable, though the battery should make no difference. An SMQa (250 mW) under the same test rose 22 degrees from Seventy-four to Ninety-six degrees F.
I then firmly taped an SM transmitter to my leg with summer dress pants between the back of the unit and my leg. The probe was positioned between the pants material and the transmitter back. The unit was then covered in 6 layers of a Lectrosonics' jacket (polyester fleece) spread out over a 12 inch by 16 inch area around my leg. I think it is safe to assume that all the heat went into my leg. After the temperature stabilized with the transmitter off at 94 degrees F, I turned it on and at 45 minutes it was up to 104.5 degrees. At 66 minutes it was at 104.7 degrees and was effectively stable. The temperature rise (10 F) was smaller than the "belt" example (16 F) even though there was no heat loss to the air since heat was carried off by the circulatory system.
The 8 hr metal contact standard for Europe is 43 C or 109.4 F. and this correlates well with the fact that I never detected the smell of burning Larry. Another web tidbit was that oxygen gas sensors for neonatal units use a small metal plate warmed to 45 C (113 F) to increase the gas exchange rate from the skin of a baby to the detecting unit. These can be operated for up to 8 hours.
The point here is that if the SM is not touching the skin, the heat rise exists but is moderate. If the surrounding air temperatures are very high or the unit is in the sun, the unit might be uncomfortable to touch but that is only if it is not in contact with a cooling device (human being) and if it isn't in contact then there isn't a problem. If it is in long term contact with a person, then the person will cool the unit so that there is only a small temperature increase. The skin on a healthy person is going to be less than 98 degrees to begin with or they've got much worse problems than the 0.75 Watt heat source of an SM.
In spite of all this, if the talent doesn't like the warmth, then a larger transmitter that spreads the heat out (UM400a) is one solution or a pouch or some thin foam between the transmitter and the talent.
As far as potential burns, the safe touch temperature for unpainted metal for 10 seconds is 132 F. Ten seconds is more than long enough to remove the offending object to a safe place. If they have a good arm, it can be removed 50 feet or so.
The SM weighs 60.5 grams (2.13 ounces). A lithium battery weighs 15.5 grams, an alkaline battery weighs 22.5 grams, and a NiMh battery wighs 28.8 grams. The SM with a lithium battery is a formidable lightweight with 6.5 hours battery life, 100 mW RF output and only weighing 76 grams (2.7 ounces).
Here is the way to correct the problem of the XLR insert sleeve coming loose and causing the battery door to "flop" around as shown below.
On the UCR401, push the XLR and sleeve until the sleeve face is flush with the battery door as shown below.Then tighten the allen screw. Don't overtighten.
The sleeves on the UCR201, UCR211, UCR411, and UCR411A are not flush. Push the XLR sleeve until the sleeve face sticks out 1/16 of an inch (approximately) as shown below and then tighten the allen screw. Don't overtighten.
Thanks to our service manager, Dean Slotness, for the pictures and explanation.
The range is not really limited by how loud the RM is or how the gain is set on the SM though these do have some affect. The limit on range is reflections from other surfaces. This effectively limits the range to 8 feet or less with maximum output on the RM and maximum audio gain on the SM. Even outdoors this short range is true since generally both the talent and the operator are standing on the ground and this is a reflective surface. The reflections cause the SM to receive echos of the transmitted tones so that the SM is trying to decode the proper sequence of tones and a delayed version of the tones. Amplifying the tones does no good at all since it is reflections that cause the failure of the decoding.
There is a positive aspect to this in that it is difficult for one RM to activate two transmitters at once which could lead to unintended results. More importantly, some prankster can't play the tones through the PA system and cause havoc. It is possible to to play the tones through a 2 way radio and allow very remote control. Cell phones don't work very well in this application due to the large amount of signal distortion (destruction?) that goes on.
If you are using VRpanel.EXE to control and monitor one or more Venue frames (VRM), you can take advantage of the software's "nickname" feature. This feature allows a name of your choosing to be associated with each receiver channel or diversity pair. The new name can be viewed or changed in the "Set Up VR dialog" and is displayed in the "Main Window" next to the faux LCD corresponding to the applicable channel or diversity pair.
If no nicknames are assigned, the default names "Rx 1" through "Rx 6" are used for single receivers, and "Rx 1 & Rx 2" through "Rx 5 & Rx 6" are used for diversity pairs.
Here's an internal email from DT (David Thomas) that describes this situatiuon and its fix
I just got a Venue master that apparently wouldn't power up for a dealer. On examining it, I found it to be intact, hardware-wise, but it had corrupted firmware, such as might happen during a botched upgrade attempt.
The wonderful thing is: THIS PROBLEM IS 100% FIELD RECOVERABLE!
It is easy to think that a unit that "won't power on" certainly isn't failing due to firmware, and even if it were, how can you upgrade if it "won't power on"? Well, actually, you can and I just did!
The way the Venue's power supply works, the micro always gets power, and it is in charge of turning the rest of the circuits on or off. If an upgrade attempt fails, it is possible that the program firmware won't work correctly, which can mean that the unit doesn't power on when the power button is pressed. Nonetheless, the micro has power.
The bootloader portion of the firmware is code protected at the factory, so that in theory, it will always be possible to recover from a botched upgrade. This case was no exception. I held down the two buttons to the left of the LCD and applied power, and the display lit up happily, displaying the word UPDATE. I was then able to load the correct firmware in from the PC, and the unit is now working!
So, word to the wise (and perhaps for the troubleshooting guide and FAQ list): a Venue that appears to have power supply problems may in fact just have bad firmware loaded. The way to check is to attempt a firmware update.
This is cribbed from the UDR200C manual and it was written years ago but is still very true:
"A number of years ago, the problem posed to the design staff was to retain the RF reliability of the Lectrosonics’ fixed frequency designs but add the frequency flexibility of a frequency agile design. The universal (but not best) way to build frequency agile systems is to design a wide open front end that will pass any frequency within the tuning range of the system. This leads to compromised RF performance in the front end with the possibility of interference, forcing the user to switch frequencies in an attempt to sidestep the interference. This makes frequency agile receivers a self fulfilling system; you have to use the frequency agility to get away from the problems caused by the frequency agile design compromises. The problem of frequency agility is further compounded when you realize that frequency changes “on the fly” cannot be made on any type of wireless system. For example, if there is suddenly an interference problem with a system in use, on stage for instance, a frequency change cannot be made without interrupting the program. Basically, the show must go on. In multichannel applications, changing the frequency of one system will usually produce all kinds of new intermodulation problems with the other systems operating in the same location. Frequency agility is not the universal panacea for interference problems. It is only another tool and a limited tool at that. The first line of defense must be the system’s basic immunity to interference. That required a new look at frequency agile receiver design.
"FREQUENCY TRACKING FRONT-END
Our solution to the wide open front end problem was to design a selective front end that can be tuned to the frequency in use. Since we wanted this front end to be equivalent to our fixed frequency front ends, this was a daunting task. Lectrosonics has always used front ends with more sections and much more selectivity than any other wireless manufacturer. The final design consisted of a total of 12 transmission line resonators with variable capacitance applied to each resonator by a microprocessor. This allows each resonator to be individually tuned by the microprocessor for any user selected frequency in a 25 MHz band. This sophistication produced a front end that was as selective as fixed frequency designs, yet could cover the entire 25 MHz range.
"HIGH CURRENT LOW NOISE AMPLIFIERS
The gain stages in the front end use some rather special transistors in a feedback regulated high current circuit that combine three parameters that are generally at odds with one another. These are: low noise, low gain and relatively high power. It is easy to understand the advantages of low noise and high power capability but why is low gain desirable? The answer is that in a receiver, low gain allows the front end to handle stronger RF signals without output overload, which is “increased headroom,” so to speak. The result of a design that takes all three of these parameters into consideration at once, is a low noise RF amplifier with a sensitivity rating equal or better than the best conventional design with a hundred times less susceptibility to intermodulation interference. Combining the high power gain stages with the tracking front end produces a receiver that is unusually immune to single and multiple interfering signals close to the operating frequency and in addition strongly rejects signals that are much farther away."
The VRS is the (S)tandard receiver module for the Venue receiver system. The VRT is the more complex (T)racking front end receiver module for the Venue system. There are no other differences between the modules in either the RF sections or audio sections. If you are familiar with our other receivers, the VRS front end is similar to the UCR201 and the VRT front end is similar to the UCR411. For an explanation of what a tracking front end is see the following FAQ.
What is a tracking front end? (See FAQ What is a tracking front end?)
The UCR201, UCR211 and UCR411A (but not the UCR411 -- no room for the code) are equipped with a Pong game. To activate, hold down the UP button while powering on.
The Venue has the Whack-A-Mic game. To activate that, hold down button 1 while powering on.
The R400 doesn't have a game yet but we are thinking Asteroids, because all it requires is a rotation control and a fire button. Stay tuned.
The MM400B has a better seal between the battery compartment and the electronics compartment. You will notice a new line of screws in the middle of the cover. We were getting occasional leakage between compartments. The battery door now has a spring battery contact because the old solid door was putting too much pressure on the battery. The new spring door controls that pressure. The chain that was used to retain the battery door on most of the MM400A's was recently replaced with a stainless wire lanyard that is much stronger. That lanyard is carried over to the MM400B also.
The biggest change is a new off-on switch. The only way to turn off the older MM400A was to unscrew the battery door a turn or two. This could introduce moisture under wet conditions when all the user wanted to do was to shut the unit off. We added an easy to find, magnetic on-off switch on the side of the unit. The magnet activates a tiny reed switch on the inside of the case. Since this does not penetrate the case, the unit is just as weather proof as always. If you don't like the on-off feature the switch can be removed and the unit will stay on at all times. It can also be reprogrammed to become a mute switch. If this mode is programmed, the unit can still be turned off with the switch. You simply activate the switch three times to turn the unit off.
The MM400C replaced the SMA connected antenna with a permanet antenna for much better water sealing. About the same time as the C changeover, we went to a darker finish that tarnishes less.
The 400 series digital hybrid series transmiters and receivers will emulate other analog systems such as the Lectro IFB, 100, 195 and 200 series. Basically, we turn off the high level hybrid processing of the signal and just run the DSP as a dual band compander. We can also emulate any single band compander since that is a much simpler process but will choose those brands that have enough units in the field to make economic sense for us. At the moment we will only emulate two other brands and frankly we aren't going to heavily advertise the fact that we can do it. I don't want to get into a shoving match about whether the emulation is "correct" or not. Our dealers can simply make a recommendation of "try it and see". Interestingly, the single band emulation has most of the problems of the real unit in the areas of breathing, noise modulation and the dreaded "key test". The emulation gives only small improvements in these areas. We were hoping for much more since we could detect overload much more accurately but.... To be fair, the 200 series dual band emulation is no better or worse than a real 200 transmitter. One additional downside to the emulation is that you will have 1.5 ms of processing delay that you won't have with a real full analog system.
The emulation was created for three reasons: one is to sell a few more units by being compatible with a competitor's system, to have a reasonable upgrade path for users that have invested in 200 series systems and don't want to sell the farm to move to the 400 series and finally sometimes it is very handy on a movie set to be able to make a system imitate another when you are just one item short.
The big change was the way we indicated the onset of limiting in the transmitter. The LED was changed to green to warn our users that this was a different system than in the past. The previous red LED on the B version came on just before limiting and users were setting the gain too low on the transmitter and having noise artifacts from both the compander and RF link. On the C version, the green LED is turned on by the same matched FET as is used in the limiter itself so the LED comes on when you are in limiting and not before. Too many users were being "scared" by the previous limit LED even though the limiter is pretty smooth and IMHO, does little damage to the signal.
In scientific tests performed on anybody we could drag into engineering, we found that the gain on the C version is set about 10 dB higher by the average user than on the B version. What is really important though, is the questions and complaints from end users about low level noise, artifacts, etc. have dropped off by a factor of ten. In reality, if the gains are set the same on the B and C versions they will perform the same.
The biggest unseen change to the C transmitters is the addition of a circular isolator or circulator to the output stage of the transmitter. This is a magnetically polarized non linear ferrite device that has three ports, any of which can be used as input or output. What's black magic about this device, is power applied to port A goes to port B, but power applied to port B goes only to port C, and power applied to port C goes only to port A. What this does for a transmitter is this: the output stage is connected to port A of the circulator and the power is delivered to port B which is connected to the antenna. The transmitter acts just like a regular transmitter so far. However, if the antenna tied to port B picks up power from another transmitter such as a two way radio or more commonly another wireless , this power doesn't get back into the output stage that is connected to port A but gets transferred to port C. Port C is tied to a 50 Ohm resistor and the incoming RF is simply dissipated as heat. The circulator reduces intermodulation between transmitters by 30 to 40 dB. Intermodulation between transmitters is probably as common as intermodulation in receiver front ends and some interference attributed to the receiver may be really due to transmitter intermod.
A BIAST is used with the UFM50 antenna amplifier. It provides DC phantom power on the coaxial line to the UFM50 so a customer does not have to run a separate cable to power the UFM50. Some Lectrosonics receivers already have phantom power built in to the antenna connectors and don't need a bias T.
Using the bias T at the receiver with a CH-20 will put 12 VDC at up to 150 mA to power the UFM50. The internal polyfuse is a 300mA unit and should allow 150 mA under any temperature conditions. The UFM50 pulls 85 mA at 12 VDC. Good quality UHF cable, should allow several miles of length before resistance drops would reduce the available voltage. Since the amplifier can only compensate for 400 feet of Belden 9913, the lowest loss medium sized cable, this will never be a problem.
The bias T consists of a feed inductor to apply DC to the BNC that goes to UFM50 (the antenna side) and a blocking capacitor to keep DC off the receiver BNC side. The RF is connected directly from one BNC to the other with only the blocking cap in series. A locking power jack connects to the CH-20, the recommended power supply. A series diode and the polyfuse are in the circuit for protection against reverse voltage and shorts.
The Bias T is effective from 60MHz to 950 MHz with less than 1 dB of loss. From 150 MHz to 850 MHz the loss is less than .5 dB. The unit is labled for customer ease of operation.
RAMPS is an acronym for "rec.arts.movies.production.sound". This is a news group for sound mixers in the film and video industry as well as others that have similar interests in field recording of sound. There are a number of very helpful pros that support the group and there is a lot for anyone to learn. You will need a news reader to access the group. You can use the link below to access RAMPS using Google Groups. Go to RAMPS group