How to choose the right elements for your wattmeter or line section power monitoring setup.

Selecting the right element for your power measurement application requires that you take the following details into consideration:

• Frequency range - Because there is not "one size fits all element", you will need to determine what frequency range or ranges you will be working with. 
• Power levels - Additionally, you will need to have a good approximation of how much forward power you are expecting to encounter when transmitting so the element you opt for can handle it. Similarly, you may also be concerned with measuring reflected power and using this information to help you determine if you have a good match by way of the VSWR level. To measure reflected power, it is Bird's recommendation to acquire an element that will handle 1/10 the power of what your forward power element can handle. 
• Line section size - The larger line section sizes will be more capable of delivering high power, so you can expect elements with higher power to accommodate those larger sections
• Quick contact connector style - Most wattmeter models will include a 7/8" line section that accepts the quick contact (QC) connectors. While your primary interest is getting your hands on the right element(s), you will also want to think about the QC type your wattmeter has installed and whether or not it is the best option for the frequency + power combination you are attempting to measure. 

Probably the most straightforward means of getting the answer for the right element is to start on the Bird website, navigate to the landing page for your wattmeter model, then using the element table options provided. Let's walk through a couple examples you illustrate how this might be done. 

Example 1: Locate an element that will help measure 180 W forward power

at 25 MHz using a Model 43

Go to birdrf.com then find the Model 43 product landing page using either the search bar or by navigating through to Products->RF Wattmeters and Elements->CW Wattmeters->Portable CW Wattmeters then click on the link for the 43 that is provided.       

                                         

Scroll down on the page to the "Compatible Devices" section and click on the "View More+" button to expand and show all options.   

                                       

Note that when the element table options are all shown, each will indicate the size of the line section that these types can accommodate which is also what is installed in the Model 43. If you are unsure where to start, the Table 1 - Standard Elements often helps cover a majority of power measurement needs. 

You can then use the provided table to match up to your forward power needs. In this case, you can see that the 250H element will cover up to 250 W from 2 to 30 MHz, meeting your measurement needs.

Using the Bird guidance of selecting a reflected power element at 1/10 of the forward power, you can see that the 25H would be the logical option. 

The base Model 43 comes configured with Type N(f) QC connectors. For the power & frequency in this case, there should be little worry that we have the right connectors for the job, however, we recommend verifying this just to be sure, and you can do so using guidance in the article Average Power Handling for QC Connectors.

Example 2: Locate an element that will help measure 5600 W forward power at 180 MHz using a 3127A Wattcher series wattmeter. 

Go to birdrf.com then find the 3127A landing page using either the search bar or by navigating through to Products->RF Wattmeters and Elements->CW Wattmeters->Wattcher Series RF Monitors then click on the link for the 3127A that is provided.   

                                       

Scroll down on the page to the "Compatible Devices" section and click on the "View More+" button to expand and show all options.   

                                       

Note that when the element table options are all shown, each will indicate the size of the line section that the elements can accommodate and note how they are dependent on line section size. Click on the option that aligns with the line section you are using - in this case, let's say you are using a 3-1/8" line section. 

You can then use the provided table to match up to your forward power needs. In this case, you can see that the 10KC3 element will cover up to 10 kW from 100 to 250 MHz, meeting your forward measurement needs.

Using the Bird guidance of selecting a reflected power element at 1/10 of the forward power, you can see that the 1000C3 would be the logical option.