Defining the RF Environment Part 1: Creating Frequency/Band Objects
WSM determines where and how to create carriers based on device properties like switching bandwidth/micro-range – as well as how spectrum space is defined by the user. In a very basic situation, a spectrum range might be “undefined“– that is spectrum usage has not been determined. On the frequency chart this is the default gray background area.
Chart showing undefined spectrum space:
Frequency & Band objects:
Frequency and Band objects are used to determine a specific spectrum range and how that spectrum might be used to assign carriers. There are two general approaches to define these spectrum ranges: as Discrete Frequency or Band objects.
Band objects are defined by a start frequency and an end frequency. This is useful where spectrum definitions start at a specific frequency and end at a specific frequency. For example, DTV channels and other spectrum usage, is often defined this way by licensing agencies.
Discrete Frequency objects are defined as a centre frequency and a “tolerance” range. The tolerance is simply bandwidth centered on the centre frequency. For example, a centre frequency of 500MHz with a 50 kHz tolerance means the resulting band starts at 499.975 MHz and ends at 500.025 MHz. A Discrete Frequency object can be visually identified in the chart by a vertical line centered in a green or red colored area…
Examples of Band and Discrete Frequency objects:
Both approaches can define spectrum ranges and can be used to either block carrier creation or prioritize their creation. How you use them is up to you. If you have a strong interference frequency it makes sense to use a Discrete Frequency object: determine its centre frequency and then set the tolerance to encapsulate the entire affected range. DTV makes the most sense as a Band object.
Once a Discrete Frequency or Band object is created, you must also determine its Priority. You can define whether an object is blocking in nature – or define a particular non-blocking priority for that range. There are three non-blocking priorities: High, Medium and Low.
Setting the priority for a Frequency/Band block:
Priorities help WSM understand what areas you most need carriers. WSW will attempt always place carriers in high priority areas before medium and low priority ranges. Defining blocked ranges is critical in more complex environments.
Noise level is an additional property that can be used along with scan data to define thresholds - where scan data can be used to automatically block a range based on thresholds. Details of this will be covered in a future article.
Creating Frequency / Band Blocks:
The WSM manual that is installed with the software covers creating each of the various types of objects. Objects can be manually created by using the Add Freq./Band… button in the Frequencies / Band tab, or by click-dragging horizontally on the chart, while using modifiers. The latter approach is interesting in that you can zoom into scan data and use that data to guide you in the area to click-drag.
Here are the keyboard shortcuts to create these objects directly on the chart:
||Usable Band object
||Un-Usable Band object (blocking)
||Usable Discrete Frequency object
||Un-Usable Frequency object (blocking)
The range that you click-drag determines either the start-stop frequency – in the case of a Band object… or the centre frequency/tolerance in the Frequency object. The modifier determines whether the band is blocking in nature – or is a Medium priority. Changing the priority from medium, to low or high, must be done manually by modifying the properties in the dialog box.
There are some interesting ways to create Frequency/Band objects automatically using the Regional Grid Bar or scan data. These will be covered in the next tutorial: Using the Regional Grid Bar.
Defining the RF Environment Part 2: Using the Regional Grid Bar
Earlier versions of WSM had internal settings to define the TV channel grid for different localities. During the development of the new chart tool for Professional Setup, it was determined that this data would no longer be embedded in the application, but defined via an external XML file.
Part of the motivation for this approach, is that a great part of the world’s UHF spectrum is going through significant changes. Those changes also added additional complexity as new wireless technologies were being deployed – and at an accelerated rate.
A separately maintained list, allowed for simpler maintenance of this changing data – but it also provided opportunities for enhancements that professional users might exploit: the ability to create detailed localized versions and along with scan data, provide additional functionality to automatically create blocked or prioritized ranges. These can be used to simplify coordination activities. This list is the RGB XML file located in the WSM installation path:
WSM installs different RGB files for country localizations and the first release 1 included USA, German and Canadian RGB’s. I will focus on the Canadian one for this article.
Preamble - The New WSM 4 Chart:
The new WSM chart (mock-up below) simultaneously shows an amplitude/frequency chart where high-resolution spectrum scans are shown along with various other displayed elements. Frequency/Band objects (green and red vertical rectangles), can define prioritized usable frequency ranges or blocked ranges. System Regions (horizontal blue-bars) and Device Ranges (horizontal dark grey bars) can be overlaid – as well as color-coded/labelled markers and of course device carriers.
The Regional Grid Bar in the example below is the numbered, two-tone gray horizontal bar near the top of the chart. Above it is the marker bar and an overview that can be used to zoom in and out of different areas. The grid bar below is using the Canada.xml example.
Chart showing the Regional Grid Bar - using the Canada.xml example:
The Canada.xml provides general spectrum definitions and utilization based on data provided by Industry Canada – the Canadian agency in charge of spectrum and licensing. In the example above you can see that the UHF-TV spectrum is a 6MHz grid – and that Ch. 37 is used for Radio-Astronomy.
I will be describing how to modify the Canada.xml file to create a more useful version for a specific locality – Toronto, Ontario: Canada’s most populous metropolitan area. First an over view of how the RGB is structured.
RGB Basic XML Structure:
The basic XML structure has three main sections. Each section‘s general purpose is as follows:
<WSM Bar Data>
... various attributes like Bar Name and Description along with Date and Version number.
...this area has numerous elements used to define the various types of spectrum usage. In some cases, the spectrum use is simply given a frequency range/width and a numeric label – like TV channels shown in the mock-up image above. In other cases, its carrier structure might be defined. An example of this is terrestrial analog television. Another example is defining uplink and downlink areas for LTE. An RGB will have multiple definitions for each type of spectrum use.
Below is an example for North American (ATSC) digital television:
The <Spectrum Definition> area can have as many entries as required in order to define whatever is used in a locality. This section must also contain all definitions that the >Band< section refers too. (See <Band> below.) If a band is defined that does not exactly refer to a <Spectrum Definition>, the XML will not validate and WSM cannot use it.
...this area has numerous elements used to define each of the ranges to be displayed in the WSM Grid Bar. The element <BandType> refers to the element <SpectrumID> in the Spectrum Definition area. This relationship is similar to a parent-child relationship in relational database design. The xml schema forces validation on this element.
The <BandType> and <BandStart> and <BandName> are non-optional elements.
This article is meant as a basic overview. For more detail on each section’s elements, the various properties, relationships etc., please refer to the PDF: Regional Grid Bar v1.19.pdf which is posted in the section called Related Files. This pdf includes the complete schema documentation.
The Canada.xml file, describes the general spectrum structure usage for the Canadian marketplace. This includes defined analog television which is still used for some rural areas, DTV, GSM and LTE ranges as well as speciality bands like Astronomy and Public Safety. These definitions are common to all of Canada. A partial example of the Canada.xml <Band> element definitions:
Below is an illustration on what this data will look like in the WSM chart:
Each country/region will include a similar xml file with the WSM installation package. Users that need to change their locality for a specific coordination can load any file included in the installation package; by right-clicking on the Regional Grid Bar and using the context menu to load a different xml file:
These xml files are easily modifiable. To make the Canada.xml file provide specific detail on the RF environment for Toronto, we can simply change the element of each parent, to something that is more appropriate…
The Toronto.xml file, uses Canada.xml as the base file. The easiest way to do this is to simply copy Canada.xml into a new file and then rename it to the desired locality. Then, re-label the DTV and other services to the RF environment for that specific locality. Here are the same channels of the earlier example modified for the Toronto region – for details see the attached xml file under Related Files - Toronto.xml:
<BandComment>Crossroads - 20 kW Transmitter from Hamilton, ON</BandComment>
<BandComment>6 MHz Bandwidth</BandComment>
<BandComment>ABC - 358 kW Transmitter from Colden - Buffalo, NY</BandComment>
Example 2: Named TV Channel Call Letters – DTV & Astronomy w/Blocked Freq/Band Objects
Defining Blocked Ranges:
The Toronto.xml file has the “Radio Astronomy” and “DTV” definition with the element set to 0 (zero) – which means WSM will block this area for device carriers.
The result is shown in Example 2 (above). This will block ranges defined as DTV and Radio Astronomy. Inspect the difference between Canada.xml and Toronto.xml for further clarification. (Links will load the XML files in a new page.)
Defining Usable Ranges With Priority:
With DTV we generally want to block the complete range. For ATV, we may want to use space between carriers for some prioritized carriers. (i.e.: carriers are placed in lower priority areas after higher priority areas are exhausted.) It is possible to create a definition that allows prioritized spectrum in a TV channel, while blocking areas where the luma, chroma and audio carriers exist:
Below is an example definition of NTSC analog television for this use-case:
<SectionName>NTSC Channel Space</SectionName>
Note that the NTSC Channel Space section (labelled S1 in the chart area), has the <SectionWidth> defined to 6MHz and the <SectionPriority> set to 1, (Low-Priority) and a <SectionBlockLevel> set to -70. All of the other sections (S2, S3 and S4) that define the ATV carriers have a <SectionPriority> set 0.
This means that the carrier areas will be blocked – however, for areas in between carriers and when scan data analysis returns a noise floor in between less that -70dbm, these areas will produce a Frequency/Band object with a low priority.
The is somewhat arbitrary since it depends on transmission power, distance from the tower, building isolation etc. Keep in mind that it is possible to create multiple definitions of the one listed above: one definition could be named “ATV – Strong (NTSC)” a second called “ATV – Medium (NTSC)” and a third called “ATV - Weak (NTSC)”. In each definition, the <SectionWidth> could be different – as well as the section priority in the channel space.
Then by assigning different SpectrumID’s to each <BandType> elements, a specific locality can have a very accurate representation of the RF environment and with the possibility of using the available spectrum as efficiently and safely as possible.
The WSM Regional Grid Bar xml files are easy to modify for some basic additional functionality – like labels. More advanced modifications can help streamline some coordination activities, allow for more efficient spectrum usage, as well as more professional reporting.
Defining the RF Environment Part 3: Making your own RGB's
The easiest way of creating your own RGB's is to take an existing one - perhaps one that has some information in common with the new RGB - and copy it and rename it accordingly. In this example, I'm going to create a new RGB for Belleville, Ontario.
The nearest locations that I have in the Canadian Cities chart is Peterborough and Kingston - Belleville is about 76 km south-east of Peterborough and about 73 km south-west of Kingston. Not much of a difference but I'll start with the Kingston RGB as the base:
STEP 1: Download the Kingston RGB file on to your computer. Copy it and rename the new file to: Belleville.ON.Canada.
The next step is to load the new file into a text editor - or even better - an XML editor. Since many people do not have XML editors, I will perform this using a simple windows text editor like Notepad:
STEP 2: Right-click on the Belleville RGB and select Open With: Notepad.
There are two sections of the RGB file that need to be modified. The first is the "header" information that stores basic, general information in the <WSMBarData> element: Name, Description, Owner, Date, Version.
STEP 3: Change the header data to something appropriate like:
WSMBarName="Belleville Grid Bar Data v1.0"
WSMBarDescription="Localized Belleville Spectrum Definitions for WSM"
WSMBarOwner="Rob Poretti - Sennheiser Canada"
Note: Careful to not modify the structure of the data file and remove or modify tags, (greater-than and lesser-than symbols) or quotation marks. (Which define string information.)
The second section that requires modification are the <Band> definitions. Scroll down past all of the <SpectrumDefinition> tags - probably about half-way down the window. We have to modify each band that defines DTV for the Belleville area - based on the data that we get from the TV Fool.com web-site. First a search on the site for Belleville:
STEP 4: Go to the TVFool.com web-site and search for Belleville, ON. About half way down you should see a list of TV stations similar to this:
These are all the channels that have significant levels of DTV from downtown Belleville. (I purposely did not select GREY channels which are quite low-level) Also, the stations that we're interested in is between 470 MHz (UHF 14) and 698 MHz (UHF 51). Ignore any other channels. Therefore, from the list above, we need to make sure that DTV is defined for 21, 26, 30 and 41.
STEP 5: Modify the <Band> definitions.
The Belleville RGB file still has the old Kingston <Band> definitions. Any bands defined as DTV stations that are NOT 21, 26, 30 and 41 - need to be changed to basic ATSC space. For example, channel 15 which in the original Kingston file was DTV, should be changed from this:
<BandComment>ION - 49 kW Transmitter 108.8km south of Kingston - north of Syracuse, NY</BandComment>
to something like this:
Keep in mind that you only need to modify the following:
<BandType> from DTV to ATSC,
<BandName> from the channel call letters back to a simple channel number - in this case from WSPX-TV 15 to just 15.
<BandComment> should be deleted completely - both the tag and the content. This tag is optional and is not necessary for just the ATSC definition.
On the other hand, <Band> definitions for channels 21, 26, 30 and 41 need to correspond to data collected for the Belleville locale. The TVFool image above, shows the channel number, station call letters, power and distance. If you want more information for the <BandComment> element, click on the radio button next to a station and the map will give it to you. Here is an example for TVOntario transmitter - the strongest for the Belleville area:
Modify each band for active DTV (21, 26, 30 and 41) and save your file. Below is an example of what channel 26 should look like:
<BandComment>TVO - 13kW Transmitter 21.9km north-east of Belleville, ON</BandComment>
Preparing for a Multi-City Canadian Tour - Part 1
This last tutorial describes how WSM might be used to create a frequency coordination for a short tour in southern Ontario: Toronto, Peterborough, Belleville and Cornwall. The procedures and approach can be used in much larger tours - the principles are the same. Here are the locations in Google Maps:
STEP 1: Go to your RGB repository and select the four cities you need. CTRL-C for copy - and paste them in a Tour project folder... I like setting up a project folder that looks like this:
STEP 2: Launch WSM and create a New Configuration. The system should be in "off-line" mode: that is, it should not be connected to devices. (I assume that the gear is on a truck somewhere en-route to the first event location. For my example, I will have the following wireless devices in my configuration:
- 8 channels of Evolution G3 - Range A
- 4 channels of Evolution G3 - Range G
- 4 Channels of Evoultion G3 IEM - Range B
- 1 Telex BTR700 Base Station - Range B4
- 4 Telex BTR700 Belt-packs - Range B4
When complete, your expanded Devices tab should look something like this:
Note: If you don't want to create your own, the custom Telex device file can be found here.
STEP 3: Load the RGB.
Start for the most difficult event site: Toronto. This is done by right-clicking on the grid bar - a menu appears that shows the current RGB as well as an option to change it:
A open dialog box will appear. Look for the Toronto RGB in your RGB repository - or you can get it here.
STEP 4: Create Frequencies/Band objects using the Analyze Frequency Spectrum button.
Without scan data, the Analyze Frequency Spectrum function will use only the RGB data to create blocked and prioritized ranges ranges. The end result should look something like this:
Note that I have trimmed the graphic and slimmed it down to show the frequency bar, the grid bar - and enough of the F/B objects to see where there is spectrum available... and clearly where there isn't any!
STEP 5: Defining Spares.
Spare frequencies should always be defined in advance, so that in the event that some local interference pops up, you have a fall-back frequency or two. I usually generate 10-20% additional spares for a device-group total. For example, with 8 Range A mics, I'll include 1 extra spare. In my configuration I have spares for each range:
STEP 6: System Regions - Optimizing coordination parameters.
A review of the Device Range bars on the chart above will show that the Toronto coordination might be challenging. However, the devices can be organized into two logical groups, with enough spectrum between the two that would allow independent IM calculations of those two groups. WSM allows this by using something called System Regions. For this project, I set-up the microphones and Telex Base Station in one Region and the IEM system and Telex belt-packs in another region:
Note the check mark on "Independent". This tells WSM to coordinate carriers for these two regions without calculating IM products between them This can only be done if sufficient spectrum is in between the two areas. The general rule of thumb is that there should be about twice the spectrum between each region, then is being used by any region. In my example, I'm seriously stretching this concept - so you must keep an eye on IM products. However, there is about 10 UHF channels between the two regions, so it is a possible strategy when space is at a premium.
The System Regions and Spare allocation should produce the following chart:
Summary: We have created our wireless device list for our tour. We have defined the number of spares that we need - and tried to optimize the coordination results by limiting the device ranges in order to make independent IM calculations for those two regions. We are ready to start the coordination process and saving results for each city.
Preparing for a Multi-City Canadian Tour - Part 2
STEP 7: Start Coordination
On the Coordination pane click on the Start Coordination button. This directs WSM to start calculating carrier frequencies for your devices. On the left hand side, WSM will create a "result". Each result is a potential coordination with frequencies for some/all of your devices. The table shows how many high, medium, low or undefined frequencies are created - and most importantly, if there are some "unusable" devices. Unusable means that WSM could not create a usable frequency for a device. We want to make sure that a result has 0 (zero) in the "unusable" column. Each result is rated and the idea is to select one with a high rating. Below is an example with this coordination:
The result selected (#11) has an 82% rating (pretty good) and has 0 unusable - in other words, I have all the carriers I need 21 plus 4 spares = 25 carriers. On the right are the individual frequencies calculated along with various properties... each carrier also has a rating and most importantly the carrier spacing and IM spacings - and if the device carrier spacings is not safe) based on the device properties) it is marked in red:
No RED = EXCELLENT! However, very often you will get red items - review the safety requirements, the spacing specified and see it is acceptable. Often 3Tx IM products are not a concern where 3 transmitters are never in close proximity. After a coordination result is selected, switch to the Allocation tab.
STEP 8: Allocation
Manually allocate frequencies to devices - or press the "Allocate Automatically..." button. Allocation moves your coordinated frequencies on the left to the device list on the right. It is a "virtual" assignment process - ie: frequencies are assigned to devices - but devices are offline, so devices are not yet programmed. When allocation is complete, all carriers on the chart change form straight lines to dotted lines. It should look something like this:
STEP 9: Create a Report - Save Your project.
To create a report, click on the document icon on the chart - next to the magnifying glass. This will create an XML file with various resources, including a jpeg snapshot of the chart. Set the zoom level and position of the chart as you would like to see it in the report - including the filter area to show or hide the various elements.
Finally, close the Professional Setup window and save the project. For example, in this case I would save as "Toronto Event" - or something similar. This is the final step in create the first coordination. As you will see in the final part of this tutorial, creating the additional coordination's for the other locations will be quite simple.
Preparing for a Multi-City Canadian Tour - Part 3
STEP 10: Create a New Project.
We have prepared a coordination for the first stop in our tour: Toronto, Ontario. Now we have to do the same for the next three stops. We start with the currently opened project by performing another Save As... - this time we will save it as "Peterborough Event". After the files has been saved we make some simple modifications. Re-open the Poofessional Set-up window...
STEP 11: Load the New Environment (RGB File)
In Peterborough we have a completely different RF environment. This means that the Frequencies/Bands objects create with the Toronto RGB needs to be deleted. Select all items in Frequencies/Bands pane and press the Delete button. It will first ask if you're sure about the object dletion - and then a second wanting saying that the current coordination is no longer valid... or course this is fine, since we will be re-coordinating with a new environment. Next right-click on the RGB bar and load the Peterborough.ON file. You can find the file here.
STEP 12: Create new Frequencies/Bands objects
Click on the Analyze Frequency Spectrum Button... this will create a new set of F/B objects from the Peterborough environment.
STEP 13: Start the new Coordination
Go to the Coordination pane and click on the Start Coordination button. As with the Toronto coordination, review the results and select a coordination. Peterborough should be much easier to coordinate for compared to Toronto.
STEP 14: Perform the new Allocation
Go to the Allocation pane and select Allocate Automatically,,,
STEP 15: Create a Report
Click on the Report button on the chart name the report for the new city... save.
STEP 16: Close the Professional Setup Window and Save the Project.
After saving the project, you are ready to coordinate the next stop of the tour. Repeat steps 10-16. In step 1, re-save as the next city stop... Belleville, and then finally Cornwall. Make sure you name the reports accordingly - and save the project in (this) Step 16, before re-saving for the next location.
At the end, you should have a single project folder, with 4 project files, 4 RGB files, and 4 reports. When you are on-location with devices connected, its a matter of loading the project configuration file for the relevant city, and go back to the allocation pane and click on the button: Send to Connected Devices... All Sennheiser Receivers and IEM transmitters will get their correct frequencies. Synchronize the transmitters and IEM belt-packs.
The reports are used for the Telex intercom - which require manually programming the devices with the coordinated frequencies.
Summary: By storing a configuration of devices and re-loading the RGB file, it can be very quick to assess a multi-city tour's requirements in advance. RGB's do not replace location scans to determine the RF environment, but often it is difficult to get scans - and scans also age and become less relevant with time. Only a recent scan can give you a high probability of what a situation might be. You should always take a scan during staging or sound check and cross reference it with the RGB and F/B objects created to make sure they match. If you find that on site there is some new DTV - or some other interference, its is relatively easy to re-coordinate, allocate and send to devices.
On a tour where a city is so congested that you require a different complement of devices to give you more spectrum range flexibility, simply add those devices for that particular city. If this requires renting RF gear then often the local rental companies' RF expert can help with the environment with recent scans of specific venues.
If you have comments or questions regarding this tutorial, feel free to connect with me at: porettirATsennheiserDOTca