Today's wideband systems can easily overlap each other, which makes frequency band planning a necessity. In the US our wideband units cover 470 to 608 MHz; in Europe that goes up to 614 MHz. When working out of a bag, attention to avoiding frequency overlap between talent receivers and hop or IFB transmitters is doubly crucial, as these units sit in close physical proximity to each other. The goal is to keep different types of RF system spectrums separated from each other so that they don't cause interference and disrupt each other's range and performance. Proper band planning avoids overlap and interference issues.
Three general suggestions before you plan:
- Keep IFB and camera hop transmitters as far as possible physically from receivers. Some bags allow you to mount on the strap or place units in external pockets. Remember that doubling your distance reduces your signal by 6dB (the Inverse Square Law)
- Use external antennas for either transmitters or receivers. Lectrosonics offers the 4 foot long ACOAXTX, which has an SMA connector, is block-specific and works for both transmitters and receivers. If you're using a wideband transmitter, order the antenna in the middle of that band. Or you can make your own, as we showed you in Wire List #24. A common strategy is mounting the antenna on your harness strap and snaking it up the available length - the IFB antenna would run up the left strap and your camera hop transmitter antenna would run up your right strap.
- Smart Scan before set up, so you can visualize pockets of free frequency space within the spectrum.
A Scenario and Two Strategies for Band Planning:
Here are some examples of what good band planning might look like when using Lectrosonics equipment:
Example 1: You have a DCHT in your bag as a stereo camera hop. You also have 3 SRcs: Two on the A1 band for your four talent lavs and one for your two boom mics on the B1 band. Then, you’ve got an LT or SMQV transmitter on B1 as an IFB transmitter.
Option 1: Place the units into bands that do not overlap with the other devices. Leave room between your close transmitters and the receivers that are nearby. The closer in frequency and distance to each other they are, the more problems they will generate. This is an example of a workable set up. Scanning your local spectrum ahead of time will determine the specifics of how you allocate your units:
Option 2: Using the previous example, another strategy is to replace one of your A1 SRcs with a 941 Band unit. That will give you 300Mb between the top of the B1 band and the bottom of the 941 band. Looking further into the future, when you plan your equipment upgrades, give some thought to reducing possible overlap in the situations you work in most often. A 941 unit can give you additional open spectrum that the A1 and B1 units don’t offer.
What if you’re coordinating a huge system around others from many manufacturers? After you’ve done your spectrum scans of the local RF environment, the table below provides an example of pre-planning and frequency sweet spots for this type of scenario. Print a copy and keep it in your bag or your prep workbench for reference:
** Pay special attention to walkie talkies – they are just below block 470 and can cause interference if you don’t plan around them. If possible, have them reduce their transmit power to the lowest available.