Get your questions answered

Many questions are: “How big does a heat sink have to be?”

Unfortunately this question couldn’t be answered in one sentence. However, the proverb “A lot helps a lot” is surely appropriate in this case. Amplifiers built up of semiconductors always works best at moderate ambient temperature due to the physical properties of the transistors. Exceeding the max. working temperature given by the manufacturer will cause the termination of the transistor. Furthermore the lifetime of semiconductors will detach enormously at high working temperature.

Here are some hints to mind helping you dimensioning and working with heat sinks:

What is the max. air temperature for a heat sink to work well? For example, in southern Spain the ambient temperature is much higher as in Norway.
Is the device continuously active or just for a short time? At short times of activity a smaller heat sink can be used as the device cools down during the off-time.
When using heat sinks with a profile and without additional cooling of a fan, it’s very important to assemble it vertically because the air must go unhindered through the cooling ribs.
Black anodized heat sinks will cause a better cooling effect as bright surfaces.
When using heat sinks out of doors, direct solar radiation should be avoided. This can lead to an exceedance of the max. working temperature of the amplifier even when it’s not operating.
RF power amplifiers usually will be supplied in aluminium or copper cases with a flat floor space. The mounting area of the heat sink should also be flat to enable best heat transfer.
The use of thermal paste improves the thermal resistance between the amplifier and the heat sink. Silver-bearing pastes like ARCTIC SILVER 5 have a better heat conductance value as common products.

Here is an example for dimensioning a heat sink:

Max. air temperature: Tair = 25°C


Power loss of the amplifier: Tv = 60W

(Power consumption of the amplifier minus output power)


Max. case temperature of the amplifier: Tcase = 50°C

Our bias-tees KU BT 6001 N/SMA are intended for voltage supply of Low Noise Amplifiers (LNA) and Low Noise Converters (LNC), but not for Power Amplifiers (PA). The KU BT 6000 N/SMA is specified for the following maximum RF power of 1 W. If there’s only one frequency band required we can probably offer you a special version with more RF power. Please specify the required power and the frequency.

Unfortunately we cannot offer conductive silver adhesive, please check out the web for CircuitWorks CW 2400 which is provided by many suppliers (Bürklin, Conrad, Voelkner, Farnell, Mouser, etc.).

Another (but expensive!) solution is the material EPO-TEK H20E which is supplied by the following company: www.jpkummer.com

An isolator protects the power amplifier in case of bad antenna matching as it prevents reflected RF to go back into the final stage. So if you have a good antenna situation where the VSWR is always fine, you really won’t need an isolator. But if there is the chance that the antenna might be forgotten or damaged it is really worthwhile to protect the power amplifier. Generally the VSWR of load is specified with 1.8:1 for all of our power amplifiers.

We strongly recommend the use of a sequence controller for your amateur radio system. Many coaxial relays have too low isolation between the ports during the changeover. If the power amplifier (in a transmit-receive system) is switched too early, this may lead to damage or destruction of the input transistor in the LNA or converter. With a sequence controller this trouble can be avoided. The sequence controller provides a control signal for the coaxial relay and it switches the voltage supply for the power amplifier. There is a time delay between the two signals to guarantee safe switching.
Our sequence controllers are intended to control a power amplifier and an antenna relay - not to control a transverter module. Your transceiver must provide a ‘PTT to GND’ signal to switch the transverter module into transmitting mode. If you don’t use a power amplifier it is not necessary to use a sequence controller.

Our modules are not designed for bi-directional applications and don’t include any coaxial relays. The switching between transmitting and receiving must be done externally by the customer – there’s no RF switching implemented! 

Most of our power amplifiers include a built-in directional coupler for detection of the forward output power. So the output power can be observed by a simple DC voltage - it is proportional to the RF power, but not calibrated and no linear function.

Generally the output power of our power amplifiers is specified for a single carrier CW signal. If you'd like to use them for COFDM / digital modulated signals you can expect an output power of about 10 ... 20 % of the CW power. This depends on the type of modulation you want to use and the required signal quality and specifications.

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