Frequently Asked Questions - Wireless

FAQs - Wireless

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.

 xlrucr401 1

You will need a .050 inch allen wrench (Lectrosonics part number 35700). We will mail you one at no charge if you ask our service department at 800 821-1121 or

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.

 xlrucr401 2

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 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).

On the side of the newer units, on the blue metal strip, you should see a +10 dB marking indicating that these units have an increased gain compared to your older units. Here's what we said on RAMPS (See FAQ#021-WIRELESS).Though a little long it explains our rational to making the change and what some users were seeing as far as typical gain settings on the SM transmitter. We didn't make this change lightly because we knew it would cause some confusion. Below is the slightly edited version of the RAMPS thread. The actual thread is at Link to RAMPS thread. We kept the display at 0 to 44 due to memory limitations.

Larry Fisher Sep 6 2006
To the Group: 
After some 6 months or so of field experience with the SM transmitter, we are strongly considering increasing the overall gain of the SM and SM series transmitters by 10 dB. This would increase all input configurations including line level input. The display would now show 10 to 54 dB of gain rather than the current 0 to 44 dB. The same displayed numbers for gain would represent the same gain on either version, i.e., a setting of 30 dB would be the same on either version. Equivalent input noise, response, limiting and so forth would not change. 

From what I've read on RAMPS and various emails, indicates we are a little light on gain. Also, I think some users don't like running the gain at maximum levels even if that is the best setting in a given case. Any and all feedback from the real world would be appreciated. Best Regards, 
Larry Fisher 

Scott Farr Sep 6 2006, 9:27 am 
I run my SM transmitters at 38 on the gain setting never any higher and I am using TRAM TR50's 

Larry Fisher Sep 6 2006, 10:13 am 
Thanks Scott, 
You are within 6 dB of full current gain (44). You would still set the transmitter to 38. What is the lowest you remember setting the transmitter? 

Scott Farr Sep 6 2006, 11:10 am 
I think around 32

wyatt Sep 6 2006, 12:05 pm 
I am using 8 SM transmitters on my current production. I am using an assortment of lavs, and my gain settings varry accordingly. The lowest gain I have used to date would be 24 using a cos-11, outdoor scene, times square. the highest would be 44, indoors, using either a b6 (grey band) or a TR-50 (i dont quite recall which at the moment). My normal operating gain for a cos-11 has been between 29 and 31. I think a gain increase would a beneficial improvement, especially considering that you can get most of the lavs that we, as soud mixers, employ daily with attenuated output levels. I have yet go below 24db on my transmitter gain.
Wyatt Tuzo

Larry Fisher Sep 6 2006, 2:29 pm 
Thanks Wyatt, 
More good info. 

Scott Smiith Sep 6 2006, 8:20 pm 
This is something I have noticed as well (although the output of the mike used definitely plays into the equation). I would say at least 6 db would be helpful, and there is certainly nothing wrong with 10 db, as long as it doesn't risk overloading the front end preamp. Scott D. Smith C.A.S.

Larry Fisher Sep 7 2006, 12:13 pm 
Hi Scott, 
When the gain is set to minimum, even with the additional gain, the SM will still require 250 uA of peak current from the mic before the limiter even begins to engage. This would require a lavaliere that pulled 500uA of bias. This is higher than any pro mics we have measured. Another way of saying this is that at minimum gain, any known lavalliere will run out of bias (clip) before the limiter starts to limit let alone overdrive the preamp. Further, even at minimum gain there is still more than 30 dB of limiting before the limiter gives up and allows the preamp to overload. As I said earlier, I think we were being way too conservative on gain. Field experience seems to be bearing this out. 
Best Regards, 

LaFayette Sep 8 2006, 3:20 am 
Greetings Larry,
Would this be an upgrade mod on existing units or only for new versions? 

I've set mine from 30 w/ Sankens outdoors to 38 w/ Sonotrims indoors. It has been suggested to go w/ red dot Sankens since the regular ones tend to be hot w/ SM's. Although, I also hear that the Sankens wired specifically for the SM sound better anyway, more low end. Should I save my money on new Sankens and just buy the upgrade on the SM? Cheers, S.L.

Larry Fisher Sep 8 2006, 4:42 am 
There is no downside to running the current SM at maximum gain or close to it. Performance of the current units at 44dB gain (wide open) will be exactly the same as the new units at 44 dB gain (10 dB left). So if you have sufficient gain now to handle the mics you have, then it is not necessary to change the units. This is not a necessary "upgrade" and won't be automatically done to units in for other repairs unless the customer requests it, unlike mandatory upgrades that we always make to repairs. Mandatory upgrades are due to a mistake we made and are done at no charge. 

Older units can be changed to the new gain structure and corresponding firmware. There will be a $70 charge to open, test and reseal the unit. This is the same as for the RM addition mentioned earlier on RAMPS. On the other hand, you can get both done at once for the same charge. Depending on the age of the SM you may also pickup a new emulation also.There is no charge for the firmware and new value resistor themselves; just the work involved in opening, closing, sealing and testing the unit. If we are already inside a unit for other reasons, there will be no additional charge for the gain change. As I said above, the customer must request the change since if they are happy with the current gain structure, we are very satisfied to leave it alone. 
Best Regards, 

morantzsound (Steve Morantz, C.A.S.) Sep 9 2006, 11:35 pm 
I was told when I bought my SM's anywhere form 24 to 30 was average. I usually stay around 27 or 28 and make adjustments at the board or Deva. It has worked pretty well for me, but will start experimenting with higher outputs. 
Steve Morantz C.A.S.

You can add a RF choke to each lead of the XLR in the Schoeps mic. We have helped several customers with an RF bead placed around all three wires at the XLR connector inside the mic. The Mouser part number is 623-2643000301. The Fair-Rite brand part number is 2643000301. Placing short leaded 100 pF capacitors between all the XLR pins and one to the ground lug might help also, but the chokes are most effective. Schoeps has a factory modification that is more elaborate, that works very well.

--Clearing up the Issue of Higher Transmitter RF Power and IM

For many years, Lectrosonics has built wireless transmitters that are higher-powered than those from other vendors. In addition, when we say a typical power of 100mW, we don’t mean that we had one engineering sample reach that power with a westerly wind. We center our production on 100mW with small manufacturing variations both up and down. We have built 100mW units for what we feel are four good reasons:

  1. Increased range
  2. Fewer dropouts
  3. Reduction of interference
  4. Better signal-to-noise ratio

There have been discussions about problems with higher powered units like ours, but the only real negative of higher power when properly implemented is a slightly increased drain on transmitter batteries. Since most of the battery power is used supporting digital processing in the Lectrosonics’ transmitters, the increased RF power is only a minor consideration. Another way of saying it is, if you have made the choice of digital processing in the transmitter, you might as well have increased RF power too, since it doesn’t change the battery life that much. The new generation of rechargeable batteries can reduce battery costs for all wireless systems and battery usage isn’t quite as important a consideration as it was several years ago.

--Design Considerations

Careful design has removed the two other problems that are sometimes discussed when higher power is considered. The possible problem of increased intermodulation (IM) in the output stage of the transmitters at higher power has been solved by using an output isolator in the antenna circuit. This prevents two transmitters that are physically close together from creating IM products. This isolator is unique to Lectrosonics’ transmitters and is in all transmitters except the LM series. Possible IM in the receivers has likewise been solved, because Lectrosonics’ receivers have always had higher power RF stages for substantially better IM rejection than competing receivers, so the increased transmitter power is no problem whatsoever. 

The technology used in the Lectrosonics products is all fine and good but the real question revolves around what happens in actual use. What about a real world situation with lots of transmitters on a stage? We’ve been hearing stories that 100mW transmitters are absolutely unusable in a stage environment and that 100mW systems will wipe out the wireless operations of theatres over city blocks, if not the entire Eastern Seaboard.

--Real World Numbers

Let’s first apply a little common sense and then run some numbers, first looking at general reception issues and then those specific to transmitters:

If intermodulation was really a consistent problem with 100mW transmitters then it would be only slightly less of a problem with 50mW transmitters, all things being equal. The only way to change from a supposedly “real” problem to a rare occurrence would be to make a radical change in transmitter power such as down to 5mW or less. A 3dB difference in power doesn’t mean much when typical signal levels on a stage are making 50dB swings as people move around. Just as an increase in power from 50mW to 100mW doesn’t solve all dropout problems and only extends effective range by 30%, reducing power from 100mW to 50mW won’t solve all IM and transmitter interference problems if there were any to begin with. In the same way, even a 3 to 1 change from 100mW to 30mW is insignificant when signal levels at the receiver can vary by 100,000 to 1, i.e., the previously mentioned 50dB.

To show why there shouldn’t be IM problems at either power level, let’s do the numbers. We will analyze the signals that would be present at a receiver from a 100mW transmitter in the worst possible situation and then in a real world situation. Even better, we will use published numbers from other manufacturers rather than our own measurements (even though they are about the same). We will do a third order analysis since it is accepted as being the worst case. Second and fourth order products are not a problem because they are totally removed by the receiver’s RF filters and fifth order and higher are at much lower levels than third order.

NOTE: The Firmware listing & information has moved to Wireless Firmware Lookup on the support site.

Click here to redirect to Firmware History and to lookup product firmware history

This posting about Lectro firmware has taken a while and has engendered a lot of discussion here at Lectro. The firmware version and update issue is rather confusing. Unlike computer software, where the latest version is always better, "it ain't necessarily so" when it comes to our products. The simple reason is this: the firmware is very secondary to the hardware. Most firmware "updates" are made because of hardware changes, some of which are forced on us by outside suppliers. Here is just one example of many. For the UM400 we have 3 branches of the firmware. The 2.x branch is for units using a Philips 7026 phase locked loop, the 3.x branch is for units with the Texas Instruments TI2050 PLL and the 4.x branch is for units with the National LMX2353 branch. Obviously the 3.x branch is not better than the 2.x branch and the 4.x branch is not twice as good as the 2.x branch. Almost all of our firmware revisions have to do with hardware changes and not improvements in the product. We have to do revisions when sometimes the only change is that a company has discarded one IC package for a different one that has more or fewer pins and more or fewer functions. Just as often, we are informed that a part is being dropped from production by an IC manufacturer because the 100 thousand a year that they sell to 4 or 5 companies is not enough to keep the part in production. So we find a similar part, change the PC board and revise the firmware to handle a new command set for the new part. We also do many revisions to make our manufacturing and testing simpler or simply better. It may be easier to put a correction factor for modulation at different frequencies into the firmware than to select varactors and resonators to make deviation uniform across a block. That doesn't mean that older firmware with select parts is better for the customer than standard parts and newer firmware with a correction factor. All this is to say, we've pared down the hundreds of firmware revisions to those that truly affect the end user. Some of these listed changes are the fixing of firmware bugs and some are added features. If the bug has never affected your system and/or if you never need the feature then it may not be worth your effort to "upgrade" the firmware. Further, adding new features may also require hardware changes that may not be possible or may be more expensive than it is worth.

To summarize, a higher firmware number by itself is meaningless. It does not mean a better product. We have listed changes by date of manufacture since serial numbers are not reliable indicators of firmware version. This is because our products are manufactured on many frequency blocks and serial numbers are assigned to units months before actual shipping. Our service department can help you with specific questions about your unit. Please have your serial numbers available so they can check the date of manufacture.

This is the same text as that engraved on the back of the UCR401 and UCR411a receivers.

Press all 3 keys simultaneously to either enter or exit the spectrum analyzer. MENU key to stop, zoom or start scan. Zoom is indicated by < > icons. In zoom, since  most data is off the screen, the cursor is  centered and the data scrolls. Use the UP  and DOWN keys to scroll. To save cursor  frequency, press all three simultaneously  and then select "use new". To clear  spectrum, turn power OFF briefly.

Step the menu key to the MAIN window.  Press the MENU and UP keys together for  b bypassed or p normal plot.

Step menu key to SETUP/EXIT window.  Step SEL UP key to SETUP/TONE  window. Press TONE (MENU) key. Press  TONE (UP) key. Step LVL (UP/DOWN)  keys to set tone level. Press MENU key to  stop and EXIT tone.

Press and hold the MENU  key for 5 seconds.

Press and hold MENU and DOWN key together  for one second.

The best way is to use three 2-way splitters on 3 of the outputs from your 4 way multicoupler and run the last output as usual for a total of 7 outputs. You will have a 3 dB+ loss on the split lines. If you are working at relatively close distances (under 100 feet) and/or in a RF noisy environment, you will not notice any change in performance. The reason is that if you are close you have plenty of signal and a small loss won't be noticeable. If you are in an RF noisy environment, the splitter will drop the signal and the noise both by 3 dB and the signal to noise ratio at the input remain the same. This is true until the attenuated external noise is less than the front end input noise of the receiver. I would try the passive splitters and save the money. Plus, splitters are always handy things to have around even if you eventually get a UMC16B.

Here's a reply to a problem with range on RAMPS. The test described can be done with any of our UHF receivers.

I didn't get into the thread before, because I wanted to make some distance versus RF display measurements before I started mouthing off. What we wanted to determine was a setup such that a user could make a simple, repeatable measurement to check our equipment for proper operation. This "test" should show the proper operation (or not) of a Lectro transmitter and a Venue receiver. Here's the setup:

  1. Two vertical right angle whip antennas, type A500RA, are on the back of the Venue receiver.
  2. The Venue receiver is about 1 meter above the ground with no large metal objects close to the antennas other than a metal or plastic cart surface under the Venue and the metal case of the Venue itself.
  3. The UM or SM transmitter is held by the metal case at arm's length away from the body with the antenna vertical.
  4. Line of sight between the transmitter and the Venue.
  5. All done outdoors.

We are not trying to duplicate a real use case here but we are trying to eliminate all variables such as body and clothing absorption (15 dB), antenna gain factors (0 to 5 dB), defective antenna amplifiers (30 dB), bad cabling (60 dB), reinforcement from room walls (6 dB), etc. Under our simplified but repeatable conditions, whether you have RF interference or not, the Venue RF display for a good system will be full scale at a separation of 100 meters. You may get dips due to multipath but moving a foot or more in any direction should get you out of the multipath. Again, the maximum reading is the correct one for this test since multipath will rarely increase the signal more than 6 dB but can decrease the signal by 30 dB.

We did this test in our parking lot with a clear line of sight between a UM400 100 mW transmitter and a block 26 Venue receiver. To double check the real world against theory we did a path loss calculation. Here's the path loss formula:
The formula for path loss between two 0dBd antennas given a separation D and a wavelength y with y=0.461 meters at 650 MHz is
Path Loss in dB = 22 + 20 Log (D/y).

For 650 MHz at 100 meters separation the Path Loss = 69 dB. Since a 100 mW transmitter power level is is 20 dBm then the signal at the Venue antenna is 20 dBm - 69 dB = -49 dBm. Full scale on the Venue is 1000 uV or -47 dBm. (Remember 0 dBm at 50 Ohms is 0.224 Volts not .775 Volts as in a 600 Ohm audio system.) In any case, the -47 dBm at full scale is scarily close to the theoretical path loss result of -49 dBm. Ground bounce reflections can add 6 dB to the numbers and diversity antenna addition can add 3 dB. In any case, with some hand waving, the actual measurements seem very valid.

As long you have line of sight between the transmitter and Venue, it doesn't make any difference what kind of ground surface you are on. Interference, even at high levels will only increase your RF readings on the Venue scale. The European 50 mW units will shorten the 100 meter readings to 70 meters. The LM would be about 70 to 90 meters depending on the particular LM. The SMq, UM250 and UM450 250 mW units will increase the full scale range to 160 meters.

This test only checks the power level of the transmitter and the RF operation of the receiver; it does not address any added factors such as interference in the area or the rest of your setup. It does give you a starting point for diagnosing problems but it is only valid under the 5 conditions above. If you perform the above test and the results are good, then you can start adding antennas and cabling to the system. The remote antennas, cables, amplifiers, etc., should give at least the same distance results as this right angle whip test or there is something wrong. Before I get buried in replies that say full scale at 100 meters is impossible, reread the 5 strict requirements above; this is a very special test setup.

If you get the correct readings for RF level, then the next most probable cause of short range is interference. Then the Venue scanning function should find the problem.

Best Regards,
Larry Fisher

This was a posting to RAMPS about "Calculating Intermod Frequencies".

Here's a chance for a 40 page dissertation that I'm not going to take. In the interest of keeping it simple and easy to remember, I'll make some general statements that are 99% true, i.e., errors are 40 dB down and good enough for sound mixers. ;-)

Intermod is calculated in exactly the same way by all the programs and has little or nothing to do with i.f. frequencies.

Odd order intermod (3rd, 5th, etc.) is much more of a problem than even order intermod (2nd, 4th, etc.) because with odd orders it is possible to generate interference that is very close to the receiver frequency. This interference can therefore pass straight through the receiver front end filters. Of the odd orders, third order intermod is of greatest concern because the interference is always at a much higher level than 5th or 7th.

Second and 4th order are of lesser concern because the carriers that generate them cannot be close to the receiver frequency and will be filtered out by the front end. (Our IFB receiver is one of the few receivers for which this statement is not true. The IF is so low, 70 kHz (!!), that the image at 140 kHz from the operating frequency can be generated by 2nd order intermod.)

Intermod due to wireless transmitters getting into the receiver is not a factor if the transmitters are all, repeat ALL, 20 feet or more away from a good quality receiver. Intermod between a transmitter and a TV station does not follow the 20 foot rule for the TV station component obviously, or for two TV stations.

Intermod generation between transmitters is more of a problem in most situations particularly if the transmitters have standard output stages and are closer than 5 feet apart. The intermod frequencies are exactly the same as in receivers and any intermod program will catch them. I have seen fairly strong 5th and 7th order when transmitters are only a few feet apart.

A quick discussion of image frequencies is appropriate here since most programs also calculate images and this is where different brands do have differences. The knowledge of the i.f. frequency is critical in determining where the image frequencies will lie. A first low i.f frequency says the image frequency will be a small distance from the receiver operating frequency. Most modern receivers have a high first i.f. such as 244 MHz. This puts the image at 2 x i.f = 488 MHz away from the tuned frequency. Almost 500 MHz away means the front end filters can strongly suppress it. Generally, with modern i.f.'s, other wireless transmitters don't cause image problems. It's from other high power transmitters in the environment.

If the above is the Reader's Digest version of intermod stuff, here's the Cliff's notes:

  1. Third order intermod is the biggie.
  2. Any program will calculate third order.
  3. Third and higher order between transmitters is usually the main problem.
  4. You only need to worry about intermod if the transmitters are close to the receivers (less than 20 feet) or each other (less than 5 feet) or in other words, always.

Since the original question was "Mathematical formula in finding Intermodulation free frequencies" here it is:
1.Find the difference between two transmitter frequencies. 
2.Subtract the difference from the lower frequency and add it to the higher frequency. Those will be the two interfering frequencies, so don't have a receiver on those frequencies.

Example: Transmitter A=525.000 MHz, transmitter B=550 MHz. Difference is 25 MHz. Don't have a system on 500.000 (525-25MHz) or on 575.000 (550+25MHz). Note that you can't screw up the math. Doing it wrong such as 525 +25 and 550-25 gives you the original starting frequencies. Also note that two systems don't have intermod problems. It takes two transmitters to generate garbage on a third frequency and you have to have a third system in order to have something to interfere with. TV stations do count as a transmitter, however, if the signal is strong at the receivers, i.e., equivalent to a wireless transmitter at 20 feet or less.

Well at least I managed to keep it to only one full page (if you use a small font).
Best Regards,
Larry Fisher