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black Beauty MAX 160 COMMON MODE CHOKE
Optimized for 160 meters
Best for single band 160 meter antennas.
This choke has been optimized for the highest possible common mode rejection on the 160 meter band. It incorporates two stacked cores, has negligible Inherent Loss, 55 dB of common mode attenuation, and can be used with full legal limit power of 1500 Watts on all modes, including FT8/4. No compromises here.
All of our products are fully characterized
We measure and publish the performance our chokes. They are fully characterized, like any other important electronic component or subsystem. A spec sheet is included below and performance curves are provided throughout.
Common Mode Rejection Ratio (CMRR)
This choke provides the most common mode attenuation possible on 160 meters with a single winding choke. The common mode attenuation has been measured at 55 dB. This means only 0.0032% (32 ppm) of the common mode current generated by your antenna system makes it through the choke and flows onto the coax shield. This is unmatched by any other choke. There is further discussion of this below.
Choking Impedance
This choke confronts common mode current with an impedance of more than 13 kΩ, of which 12.7 kΩ is resistive. This exceeds any other choke by a hefty margin. It means that very nearly ALL common mode current is choked off and will not flow through the choke onto the shield of the coax feedline. A commonly used rule of thumb (per G3TXQ et al) is that the choking impedance should be at least 1 or 2 kΩ. With more than 13 kΩ of choking impedance, this is the best choice possible for high performance on 160 meters. See the impedance curve and related discussion below.
Insertion Loss
Insertion Loss has two components: Inherent Loss, which is dissipative, and Mismatch Loss, which is not dissipative. Inherent Loss is the loss of power as the signal passes through the choke to the antenna. The Inherent Loss of this choke is only 0.02 dB (on 160 meters). This is so small that it has a completely negligible effect on signal strength, either transmitting or receiving.
Power Handling
This choke is designed to handle full legal limit power of 1500 Watts PEP on the 160 meter band.
It is not possible to determine precisely the maximum amount of transmitted power that a Common Mode Choke can handle based only on the characteristics of the choke and the amount of power transmitted. This is because the antenna system in which the choke is used determines how much of the applied power comes back to the choke as common mode current.
The components we use can handle 2600 Watts of transmitted power without any problems. However, the temperature of the ferrite core will actually limit the amount of power you can use without damaging the choke. That temperature is a function of the choking impedance of the choke, the magnitude of common mode current generated by the antenna system, the SWR of the antenna, and the location of the choke along the feedline relative to the standing wave current peaks. These are specific to each installation and so cannot be completely determined in advance.
Some portion of the common mode current generated by the user's antenna system is dissipated in the choke due to core loss. The more common mode current that a particular antenna system generates, the greater the power that will be dissipated by the choke. You can think of it as "how hard the choke has to work" to suppress the common mode current.
The amount of power that a Common Mode Choke can handle is almost always limited by how hot it gets. This, in turn, is greatly influenced by how well the enclosure can get rid of heat. This characteristic is called "thermal resistance". It is expressed as the number of degrees that the temperature will rise inside the enclosure for each Watt of power that the choke must dissipate.
For this reason, Watts Engineering chokes are ventilated. This allows air to flow over the ferrite core, cooling it dramatically. This ventilation allows our chokes to dissipate about 80% more power than comparable chokes in sealed enclosures. Notice the 7/8 inch diameter ventilation holes along the bottom of our chokes. Screens keep the bugs out.
How much power can our chokes handle? About 80% more than anybody else's!
The bottom line on power handling is the temperature of the ferrite core in the choke. Measure this temperature by looking up through the ventilation holes on the bottom of the enclosure with an IR temperature measuring device, such as an IR temperature gun or an IR camera. If the temperature inside the choke exceeds 180F, reduce power or make some changes to the antenna system to mitigate common mode current and/or reduce SWR.
Learn more about Power Handling ability of Common Mode Chokes
Common Mode Rejection (CMRR)
This choke is optimized for the 160 meter band and provides >55 dB CMRR
The purpose of an inline Common Mode Choke is to reduce, or eliminate, common mode current flowing on the shield of coax feedline. It does this by presenting a high impedance to the common mode current, which "encourages" that current to flow into the antenna instead of back along the coax shield. How well it does this is measured as the Common Mode Rejection Ratio (CMRR).
This choke has about 55 dB CMRR on 160 meters. This means that only 0.00032% of the common mode current will be allowed through the choke onto the feedline shield. Which is outstanding.
Common mode current flows on the coax shield because the shield is connected directly to one "leg" of the antenna. Placing a Common Mode Choke at the feed point "breaks" that connection and stops the common mode current from flowing on the coax shield. The choke isolates the feedline from the antenna.
Connecting the shield directly to one "leg" of the antenna also makes the shield part of the antenna. This affects the efficiency and pattern of the antenna. A Common Mode Choke placed at the feed point preserves the antenna's "native" characteristics.
In addition, some of your transmitted signal is picked up by the coax shield, inducing common mode current on the feedline between the feed point choke and the rig. This current will make its way to the rig and can also cause RFI. Placing another Common Mode Choke near the rig, perhaps just before the coax enters the Radio Shack, will block this common mode current and further reduce RFI and received noise.
RFI and Noise
Common mode current on the coax shield is undesirable because it causes RFI - your signal interfering with other electronic devices.
It is also undesirable because local noise (EMI) picked up by the coax shield becomes common mode current flowing on the shield which, without a choke, is conducted directly onto the antenna. This raises the noise level during reception.
This noise will also be conducted directly to the shack and the rig on the coax shield, and some portion of it will show up as received noise. The cure is to place a second Common Mode Choke in the feedline near the rig.
Common Mode Chokes stop RFI and reduce received noise - sometimes quite dramatically.
Choking impedance
This choke confronts common mode current with a very high choking impedance, more than 13 kΩ
A Common Mode Choke reduces common mode current flowing on the shield of the coax feedline by presenting that current with a high impedance. This forms a resistive divider between this impedance and the impedance presented to common mode current by the antenna. The higher the choking impedance, the less common mode current flows through the choke.
This choke presents a measured impedance of 13.2 kΩ to common mode current, which is a very large impedance compared to any other choke. The resistive portion of that impedance is 12.7 kΩ. Steve Hunt, G3TXQ (SK), who is often cited as a reliable source of information concerning chokes, says a choking impedance should be at least 1.2 kΩ. By all existing measures, this choke provides truly outstanding choking impedance. Steve says, "Remember, a good choke will be high impedance and Resistive over the frequency range of interest." This choke meets that requirement perfectly.
Steve's work has been very influential. But time has shown that his estimate is optimistic. Many antenna need higher choking impedance. Black Beauty MAX 160 meets that need.
The choking impedance of a broadband choke is, by necessity, a compromise. It will peak at some frequency and fall off above and below that frequency. Since this choke was designed for maximum performance on just one band, 160 meters, it is able to provide very high impedance on that band.
This is the advantage of the MAX 160 choke: it is designed specifically for 160 meters and provides greatly superior performance on that band.
Resistive vs Reactive choking impedance
The reactive portion of an impedance can, conceivably, be partially cancelled by the reactive component of the impedance an antenna presents of common mode current.
Think of the source of the common mode current being a voltage source in series with a source impedance. That impedance will be in series with the impedance of the choke. The reactive components add. If one is inductive and one is capacitive they can cancel one another, at least to some degree.
For this reason it is commonly accepted that the best choking impedance should have a large resistive component and a small reactive component.
MAX 160 certainly meets this requirement. Of the 13.2k of choking impedance, 12.7k is resistive. It is not going to be compromised by your antenna's impedance.
