Clear Waves’ lockout feature allows you to manually lockout frequency ranges of your choosing. Frequencies within the locked-out regions are removed from consideration as potential candidates for a frequency set. This feature is accessed from the main menu by selecting Intermodulation > Lockout Frequency Ranges.
Reserved Frequencies
Reserved frequencies allows you to enter one or more frequencies into the coordination when a particular device is considered mandatory. For example, facilities or events often have a pool of existing equipment to which channels will need to be added. Also guest systems using preconfigured channels may have to be integrated and coordinated with resident systems.
Intermodulation Analysis
Intermod Settings
When performing calculations for intermodulation analysis, there are several settings that affect the size and stringency of the resulting frequency set. These include the following:
- Intermod Stringency / Compatibility Level
- Step Size
- Ignore Certain Intermod Products
Clear Waves calculates the 3 types of intermodulation products that happen to be closest to our fundamental frequencies. These are:
Number of Transmitters | Fundamental Frequencies |
---|---|
Two-Transmitter products | 3rd Order Components (2Tx 3rds) |
Three-Transmitter products | 3rd Order Components (3Tx 3rds) |
Two-Transmitter products | 5th Order Components (5Tx 5ths) |
When creating an intermodulation-compatible frequency set, any combination of these 3 tests can be applied in order to obtain the desired level of reliability. In fact, these three tests can be combined in different ways in order to generate frequency sets with 7 different levels of stringency:
Stringency | 2Tx 3rds | 3Tx 3rds | 2Tx 5ths |
---|---|---|---|
Strictest | YES | YES | YES |
Strict | YES | YES | |
Moderate | YES | YES | |
Lenient | YES | ||
Weak | YES | YES | |
Weaker | YES | ||
Weakest | YES |
What this means is that a frequency set created under ‘Strictest’ conditions is guaranteed to be free of intermodulation interference caused by 2Tx 3rd, 3Tx 3rd and 2Tx 5th intermodulation products. Similarly, a frequency set created under ‘Strict’ conditions is guaranteed to be free of intermodulation interference caused by 2Tx 3rd and 3Tx 3rd intermodulation products. And so on…
Ideally one would always want to use a frequency set created under ‘Strictest’ conditions because the frequencies within the set could be assigned to different transmitters and the level of reliability would be very high (since interference caused by intermodulation distortion would be eliminated for all intents and purposes). However, for practical purposes, it may not be possible to always create frequency sets of ‘Strictest’ stringency when you have many transmitters you need to assign channels to. Assuming that transmitter channels fall on 25 KHz boundaries, then for a particular frequency range (e.g. 470 MHz – 500 MHz) there are a limited number of intermodulation-free frequencies that can be computed. Furthermore, as the stringency is increased then the number of intermodulation-free frequencies that are available goes down. That is, the size of the frequency set is determined by (a) the frequency range, and (b) the intermod stringency or compatibility level.
For example — let’s take the frequency range of 470 MHz – 500 MHz and assume that transmitter channels fall on 25 KHz boundaries. The following results are approximations:
Stringency | Frequency Set Size |
---|---|
Strictest | 16 |
Strict | 17 |
Moderate | 22 |
Lenient | 32 |
As you can see, the number of transmitter channels you require will dictate the level of intermod stringency that can be applied in order to generate a frequency set of sufficient size to accommodate your needs. In this example, if we required 26 channel assignments then we would create a frequency set of “Lenient” stringency.
As a side note, when it comes to configuring audio equipment, at the very least your frequency set should be free of interference from 2Tx 3rd-order intermod products — i.e. be of “Lenient” stringency or higher — since these are the most destructive.
Near Hit Settings:
Related to ‘Stringency’ is the concept of ‘Near Hits’. This means that in order to qualify as a compatible frequency and be a member of a frequency set a candidate frequency must not match an intermod product nor be within a specified distance of an intermod product. A ‘Near Hit’ setting specifies the minimum distance a candidate frequency must be from an intermod product in order to qualify as a compatible frequency. If a candidate frequency is too close to an intermod product then it is disqualified. For example, by default, intermod-compatible frequencies must be at least 99 KHz from 2Tx 3rd-order products, 49 KHz from 3Tx 3rd-order products, and 89 KHz from 2Tx 5th-order products. As the ‘Near Hit’ distance is increased then the frequency set becomes more stringent, but that comes at a cost — fewer candidate frequencies will qualify as members of the frequency set and, hence, the frequency set will be smaller. We suggest you leave the ‘Near Hit’ settings at their default values.
Step Size
Most audio transmitters are designed to operate on channel frequencies that fall on 25 KHz boundaries — i.e. they are “tunable” in 25 KHz steps. Given a frequency range (e.g. 470 MHz to 500 MHz) and a step-size of 25 KHz, then only frequencies within that range and which also are multiples of 25 KHz are potential candidates to be included in the frequency set that Clear Waves generates (provided they also meet the stringency requirements described above). We suggest you leave the Step Size setting at its default value of 25 KHz.
Ignore Certain Intermod Products
Intermodulation products are calculated from either two transmitter frequencies (e.g. 2Tx 3rds, 2Tx 5ths) or three transmitter frequencies (3Tx 3rds). If you prefer that Clear Waves ignore 3Tx 3rd products generated by 3 frequencies where at least one of them is more than 40 MHz distant from the others, then enable this setting by checking the CheckBox. By checking the CheckBox you are telling Clear Waves to ignore certain intermodulation products, thereby decreasing the stringency of the frequency set.
Likewise, if you prefer that Clear Waves ignore any product where at least one of the transmitter frequencies is more than 100 MHz distant from the other(s), then enable this setting by checking the CheckBox. Again, by checking the CheckBox you are telling Clear Waves to ignore certain intermodulation products, thereby decreasing the stringency of the frequency set.
By default Clear Waves does not ignore any intermod products when generating a compatible frequency set. However, if you find yourself in a situation where you need to slightly increase the size of a frequency set, then you might consider checking one or both of these CheckBoxes. Interference from intermodulation distortion may be less of a problem when transmitters are operating in bands that are many MHz apart from one another.
Signal Bandwidth
This parameter controls the minimal distance between adjacent frequencies in the resultant frequency set that is computed. From a practical standpoint the distance between adjacent channel assignments should be sufficient to ensure transmitters do not interfere with one another. The recommended, default value of 299 KHz is on the conservative side. It is important to note this value has a direct bearing on the final size of the frequency set. The larger the signal bandwidth, the less chance adjacent transmitters will interfere with one another — but the smaller will be the frequency set. The smaller the signal bandwidth, the greater the chance adjacent transmitters will interfere with one another — but the larger will be the frequency set. So, if you need more channels then experiment with decreasing the size of the signal bandwidth. On the other hand, if you do not require lots of channels then you can use the default value or even increase that if you wish.
Results
When the computation has completed the intermod-compatible frequencies (that compose the frequency set) and white spaces are listed in the tables below the chart. These frequencies are guaranteed to be intermod-compatible based on the stringency applied during the intermodulation analysis. If channel bands are being used, then these are also indicated in the table.
Monitored Frequencies
This mode displays the RF signal strength that is detected at specific frequencies defined by the user. The user is alerted when the RF energy detected at one of those frequencies exceeds a threshold (here called the Alert Threshold). Up to 60 frequencies (within the frequency range supported by your analyzer) can be specified and monitored at one time. If the signal strength of an interfering transmitter were to rise above the Alert Threshold (specified by the user) then the corresponding bar for that frequency turns red (otherwise it appears green).
The purpose of this feature is to alert you in the event the ambient RF energy, measured at specific frequencies, were to rise above a threshold value — thereby posing a risk to using a specific frequency as one of the channels you assign to an audio transmitter. For example, in the setting of a live performance where it is important to monitor the channels that have been assigned to wireless audio devices, this feature can be used to ensure those channels are not being impacted by other sources of RF transmissions. Alternatively, if there are wireless devices that transmit at specific frequencies and you wish to monitor their transmissions, then this mode can be used to verify they are currently operating.
The frequencies being monitored are displayed across the horizontal axes according to their ID numbers (as opposed to their frequency in Hertz, as in the Spectrum Analysis views). For example, the green bar above the number 2 in the above screen capture represents the RF energy transmitted at whatever frequency the user defined the 2nd monitored frequency as, and this frequency may be either higher or lower than the frequency assigned to the ID number 3, depending entirely upon the user’s definition. When the RF signal strength as measured at a particular frequency exceeds the Alert Threshold then its corresponding bar appears red, otherwise it appears green.
To specify frequencies you wish to monitor select Tools > Monitored Frequencies… from the main menu. The Monitored Frequencies dialog box will then appear.
The check boxes in the leftmost column allow you to select which frequencies you’d like to monitor — if a check appears in the check box then that frequency will be monitored — otherwise, if unchecked, then it will be ignored. The second column (from the left) displays the frequency ID displayed in the chart, as mentioned above. The third column displays the user-defined frequency in MHz which corresponds to the ID number preceding it. Finally, the last column displays a description for this frequency or channel. Typically, the description will correspond to the device assigned to this channel.
The Alert Threshold can be adjusted using the slider control to the right of the Monitored Frequencies chart. If the signal strength at a monitored frequency exceeds the threshold, the bar above the corresponding ID number will turn red (otherwise it appears green).
As a side note, the Monitored Frequencies dialog box can not be accessed while the analyzer is actively scanning. That is, if the analyzer is scanning and you wish to make changes to the monitored frequencies then it is necessary to first press the Stop button.
Delta Trace
Used to view small (or large) changes in the RF spectrum over time. When scanning begins, the first trace is saved as a snapshot. For all subsequent scans, the snapshot trace is subtracted from the current trace and the difference, i.e. ‘delta’, is displayed. Plotting the data in this way makes it easy to detect RF changes in transmitted signals that occurred since the initial snapshot and is most useful in environments where RF transmissions change over time.