LarryF

Perfect. Lef

Wisycom quotes "Output" third order intercept (Oip3) rather than the more useful "Input" ip3. The output ip3 number always looks better and therefore is commonly quoted. For instance, a device with a 20 dBm output ip3 (good) and 30 dB of gain (bad design), has an input ip3 of -10 dBm (poor). Specifically, high gain, low noise gain stages can have a good output ip3 but a lousy input ip3. And input ip3 is the important spec. Having said all that, the Wisycom unit is low gain, moderate noise, and high current. Looking at the 7 dB of gain, fudging a few dB of filter loss and 7 dB of splitter loss the input ip3 is probably about 14 dBm. All in all, good numbers. I just wish they would quote the more descriptive numbers. Best Regards, Larry Fisher

The input third order intercept is only -5dBm (minus 5 dBm), according to their web specs of -35 dBm intermod products at -15 dBm two tone input. To convert to input third order intercept, subtract -15 dBm from -35 dBm for 20 dB difference. Add half of 20 dB to -15 dBm input and you have a -5 dBm third order input intercept. That isn't great in today's RF environment. Best Regards, Larry Fisher

For a quarter wavelength whip antenna, 16 cm would be 470 MHz. You can use the numeric length guide on Lectrosonics.com to get a reasonable approximation for your frequencies if you want to trim to your blocks. https://www.lectrosonics.com/downloads/category/1-accessories.html?download=22:amj Best Regards, Larry Fisher

To be a smart ass, there are 86,400 seconds in a day. Using three of them seems like a reasonable trade for not stepping on a mission critical transmitter. When you pick up an "off" transmitter, there is no way of knowing if it is clashing with an important channel. The "quick on, RF off" mode allows you to see what frequency it is on and adjust if necessary. And when you adjust the frequency you don't rip through a critical channel. As far as turning the feature off, that's fine 'till you forget that it's going to come on "hot". Finally, there needs to be some button combination that allows you to start up in RF off or RF on. A short press and a long press is a simple way to do that. Perhaps a shorter delay would be more palatable. A one and a half second delay would leave 86,398.5 seconds remaining. Best Regards, Larry Fisher

p.s. Either wiring is "correct".

There are two correct wirings for a COS-11. https://www.lectrosonics.com/lectrosonics-microphone-wiring/913-uhf-transmitter-5-pin-input-jack-wiring.html?highlight=WyJtaWMiLCJtaWMnIiwibWljJ2VkIiwibWljJ3MiLCJtaWMnZCIsIndpcmluZyIsIid3aXJpbmcnIl0= See Fig 5 (external resistor) and Fig 11(internal resistor) as shown in the above document. You may have two wired as Fig 11 (simpler) and one wired as Fig 5 (harder to do). The difference in gain between a 1k resistor in Fig 5 and the internal 2.7k in Fig 11 is 10 dB. Noise is reduced 10dB also, so gaining up the transmitter by 10 dB does not has zero ill effects. I always thought the 1k resistor was too low anyway. Best Regards, Larry Fisher

To the Group: The crew at Lectro has recently been getting a fair number of reported problems concerning performance issues with digital transmitters. In almost every case it has been traced back to amplified antennas or antenna distribution systems that have not followed good design principles. Typically, the system is being used in an environment that has strong local RF signals. To pinpoint the problem, we've asked the users to eliminate their amplified antenna or distribution amp and simply try a whip antenna to see if the transmitter and receiver are working properly. Full digital systems are particularly vulnerable to overload in the RF signal chain since the full digital modulation has both FM and AM components. If that RF signal passes through an overloaded amplifier, the AM part of the signal is compressed (clipped) and the AM information is distorted or lost. Antenna systems that may work satisfactorily with FM systems can fall apart when full digital signals are used in the presence of other strong RF signals. So what designs work properly? Those that do the following: 1. Use a band pass filter in front of the RF amplifier to remove strong out of band signals. 2. Use a high current, relatively high power amplifiers in the RF amp stages to handle high RF signals without overload. 3. Use low gain amplifiers in the RF amp stages to keep from overloading the output of that same amplifier. 4. Use only enough gain to overcome splitter losses and cable losses. This goes along with #3 above. Why wouldn't a designer follow these rules? 1. Bandpass filters add cost and reduce the theoretical sensitivity due to signal losses of the desired signal. 2. Higher cost of the amplifier plus associated power supply parts. 3. Low gain amplifiers typically have higher noise figures. Higher noise figures reduce the receiver sensitivity. It is difficult to satisfy both low gain, low noise and low cost. What can the user do? 1.Buy an antenna or antenna system with the minimum frequency range that will satisfy your needs. A system with response from DC to light is wrong for your purposes. 2. The addition of a passive filter just after the antenna can work wonders (such as Lectro PF25, PF50 or equivalent). This does restrict your frequency of operation but different filters can be swapped in or out as you work in different locations. 3. Stay away from low current/low power systems. The designer doesn't understand today's RF jungle. 4. Beware of systems that have fantastic noise figure specs like 0.8 dB or 1 dB. The design is probably built around a high gain, low current, low cost part. 5. Beware of systems that don't quote a third order intercept. The designer will not have taken digital signals and/or strong interfering signals into consideration. You as a user can help the situation by only using enough amplifier gain to overcome cable or splitter losses. Don't turn up the gain of an amplified antenna to greater than that necessary to overcome cable and splitter loses. Excess gain will also upset the automatic gain leveling stages that exist in most digital receivers. Gain in an antenna amplifier increases not only the desired signal but also noise and any interfering signals. As an aside, antenna gain is a different animal since a hi gain antenna is always directional and therefore rejects background noise and interfering signals. So, hi gain amps are bad except to overcome cable and splitter losses; hi gain antennas are good (pointed in the right direction). Best Regards, Larry Fisher

The NP-50 batteries will have a temporarily higher voltage right off the charger but that voltage falls quickly to a "normal" value. Li-ion batteries only lose 2% of their charge per month (!) unlike some high capacity NiMh batteries that can lose 15% or more in a day after being fast charged. All this to say, you can charge a Li-Ion NP-50 and use it a week later with almost unmeasurable capacity loss. Best Regards, Larry Fisher

At high sound levels, the 1k resistor reduces the distortion from 7% to less than 1%. The resistor provides large quantities of negative feedback which reduces distortion. This also reduces the "gain" of the mic but that is easily compensated for in the transmitter. I highly recommend the 1k (1k to 4k) resistor. Best Regards, Larry Fisher Going to pin 5 substitutes an internal resistor in the transmitter for the 1k, accomplishing the same distortion reduction. It is not universal wiring of course. Best Regards, Larry Fisher

Maybe not the laugh of the day but a definite grin. LEF

The fact that the whips on the SRc's worked makes me believe something was going on with the PSC Four Pack. The Betso Bowties are just wideband dipoles and should act no differently than a whip that is the correct length for the frequency. The Bowties won't overload in and of themselves. This leaves the cables and the PSC as possible problem areas. It may be the TV and cell towers with their strong RF signals were overloading the amp in the PSC. The problem with trying to analyze it later, is that the RF environment is probably absent. If you could get back to the same location, try the setup with and without the PSC along with your other tests. Best Regards, Larry Fisher

Exactly what I would have said. And as Doug said, you must match the =>exact<= frequency. M185 or M187 will work with those receivers. LEF

We were able to get a little more out (+7dBm) of the DCR822. And our general statement of running receivers wide open when you can is the theoretical best operating point. But here's a case when you have a solid reason not to run the DCR822 wide open; to match the SRc receiver. The +5 dBm level is so close to wide open, I'd run it at +5dBm and cut down on downstream confusion. Any level above -20dBm gives you full SNR. Levels above -20 dBm help suppress ground loops and electrical noise induced in the cables. Best Regards, Larry Fisher

Too true. It is a Catch-22 problem. Roads are built for cars (SUVs) because there are few bike commuters. People won't ride bikes because they don't want to end up in the grill of a Chevrolet Suburban. Bike commuting will only influence infrastructure if more people commute. On a positive note, with Covid influencing peoples' travel habits and modes of exercise , bicycle sales and Ebike sales are at an all time high. Best Regards, Larry Fisher

Very interesting, Paul. LEF

Somebody must have changed the page in the site upgrade. This works at the moment: https://www.lectrosonics.com/press-releases/1261-lectrosonics-introduces-the-smwb-and-smdwb-wideband-transmitters-in-the-941-mhz-frequency-band.html Best Regards, Larry Fisher

+1. Also check with Lectro service. I'm sure they have run into this before. Best Regards, Larry Fisher

Another advantage: cycling at 12 MPH for an hour, burns off 800 (!) calories. Best Regards, Larry Fisher

I haven't seen this posted before. Interesting analysis on Digg, particularly the bit about Nolan mixing only for excellent theatre sound systems not for run of the mill, smaller theatre systems. Also that the mix for home viewing is different from the mix for theatre viewing and that leads to different opinions about the sound: https://digg.com/video/the-reason-why-you-can-barely-hear-the-dialogue-in-tenet Best Regards, Larry Fisher p.s. Makes you wonder about 48k vs 96k

+1

Ok. I went to the current Fox site and searched for the word "tuna" and didn't find anything. I just checked and it's still not there. The corrected link does bring up the older page. Thanks for the correction. Best Regards, Larry Fisher

Fox news pulled the article. It very well may have been fake news and the Fox lawyers didn't want to fight with the Subway lawyers. LEF

Probably because of a lawsuit that claims DNA testing shows no tuna in their tuna sandwiches. Somebody trying to short the stock? https://www.foxnews.com/lifestyle/subway-accCused-selling-fake-tuna-footlong-fraud-lawsuit Best Regards, Larry Fisher

If we put it in a book, it would rival "War and Peace" in length. For Europe it would be a two volume set. LEF