RF Power Amplifier Resource Center
Providing RF Expertise, Technical Resources and Tools
This section provides a variety of technical resources to help educate our customers on all aspects of our products and our industry. If you have any trouble finding the information you’re looking for, please don’t hesitate to Call Us at 5852140598.
Here you can find:
 Application notes and technical articles
 Useful RF formulae
 Specifications & terms defined and illustrated through examples
 Useful website links that support the markets and industries we serve
 FAQs section providing answers to some of the most common questions we receive
Application Notes
Piezo Crystals and Capacitive Loads
(PDF  147B)
Class A vs. Class AB
(PDF  308KB)
Choosing an Amplifier
(PDF  115KB)
Bias T
(PDF  136KB)
Useful RF Formulae & Tools

 Return Loss = 10Log10(Preflected/Pforward)
 Reflection Coefficient ρ (or G) = VR/VF
 Return Loss = 20Log10 ρ

 VSWR = (1+ρ)/(1ρ)
 ρ = (VSWR1)/(VSWR+1)
Specifications and Terms
1dB Compression
The term "1dB Compression" is defined and illustrated below with a working example.
Consider the primary transfer characteristic of an amplifier...
Assume:
 Linear Gain is 20 dB
 1 dB compression point, is where Pg = 19 dB
 119 W output at 1.5 W input = 19dB = 10Log(119/1.5)
Then:
1dB compression point is 119 Watts
Decibel (dB)
The term "Decibel (dB)" is illustrated through the below example:
A dB is a ratio that we use when we are talking about power
 P_{i}=Power Input
 P_{o}=Power Output
 X dB = 10Log_{10}(P_{o} /P_{i})
Example:
A transistor has an output power of 50 watts with 10 watts input power. Its gain in dB is:
10Log_{10}(50 /10) = 10Log_{10}5 = 6.9897 ~ = 7.0 dB
and an attenuator that has an output of 25 watts with an input of 100 watts is:
10Log_{10}(25 /100) = 10Log_{10}0.25 = 6.021 ~ = 6.0 dB
Q
The definition of Q, along with some helpful advice
When one thinks of Q one thinks of that upper class British technocrat explaining how the latest weaponry gadget works, to a disinterested James Bond. Who, himself, is more interested in contemplating how to uncover his next female spy. If you want more of that, I am afraid you will have to go elsewhere. We are not here to discuss what might impede fact or fictional relationships, but rather to discuss the real and imaginary relationships of impedances. Q: initially stood for ‘Quality Factor’. This was due to the fact that it was first used to describe the energy storage properties of a circuit in relation to its energy dissipation properties.
Now it is just Q, a dimensionless number. In fact one must be careful not to refer to it as ‘quality factor’ especially around management types. One could just imagine Dilbert proudly telling ‘PointyHair’ that he has just designed an amplifier circuit that has a very low quality factor and promptly getting fired! The next day, as if on a crusade, ‘PointyHair’ starts putting up motivational posters all around the engineering building: ‘Increase the quality factor of your circuit by 100%’. It would become part of management review and a strategic goal… Stranger things have happened.
But where Q really comes into its own is in terms of bandwidth. If bandwidth is f2f1 then:
Where f0 is the center frequency.
It is now obvious why we may want to design a circuit with a low Q. As we can see from the first equation (or elementary filter design rules) it will mean greater loss. However, for most circuits we want low Q.
(N.B. If we are talking about an element such as an inductor or capacitor we always want a high Q, as a low Q element would be indicative of parasitic resistance.)
Another useful way of looking at Q is on a Smith Chart.
The blue lines indicate a constant Q. If you want to have a circuit with a Q below a certain value, then you must ensure that the transformation does not go outside the Q circle.
dBm
dBm is an absolute measure of power.
 the m stands for milli watts
 to convert dBm to watts we divide by ten and then take the inverse log in base 10
 so 0dBm = 1 mW
– 0/10 = 0
– 10^{0} = 1
 10 dBm = 10 mW
 20 dBm = 100 mW
 30 dBm = 1,000 mW = 1 W
 using dBm is helpful when looking at power through circuits, as we can simply add the gain and subtract the attenuation in dB and end up with a final power number in dBm
 you can also use dBW
– where 0dBW = 1 Watt
Third Order Intercept
What are third order products?
 It is in the frequency domain. Third Order products are the intermodulation distortion products between the one of fundamental signals and the harmonic of the other signal.
 Consider the diagram below:
To plot the Third Order Response follow Steps 1 – 4 illustrated below:
A Good Match
A good match means that the output of one element is matched to the input of another to achieve maximum Power Transfer.
However, this is one place that one might help.
Consider the flow of water through a pipe...
 Water pressure is analogous to voltage
 Water volume is analogous to current
 Pipe diameter is analogous to resistance
 If you take the output of one pipe and put it against the input of one with a smaller diameter you will maintain your pressure but lose volume. If you put it against a pipe with a larger diameter you will not lose volume but you will lose pressure
For maximum power transfer the input and output impedances must be matched.
Now for some Maths (urrrgh)...
Consider the circuit below:
Now Current into the load is I_{L}
Current Power in to load is P_{L}
For maximum power
R_{L}=R_{S}You don’t believe us?
You are going to have to look at some calculus!
So if P_{L} = I_{L}^{2} R_{L}
And for maximum power
And P_{L} = I_{L}^{2} R_{L} = V_{s}^{2} R_{L} (R_{s}+ R_{L})^{2}Then
So: (R_{s}+ R_{L})^{2} = 2R_{L}(R_{s}+ R_{L})^{3}
1 = 2R_{L}(R_{s}+ R_{L})^{1}
2R_{L} = R_{s}+ R_{L}
R_{s}= R_{L}
The Basic RF Bench
All system impedances are 50 Ω.
A 50 Ω load is equal to a cable with a 50 Ω characteristic impedance infinitely long.
Industry Websites
FAQs
Below you will find answers to some of our most frequently asked questions. If you are unable to find an answer to your question, please don’t hesitate to Contact Us or give us a call at 5852140598
How do I find an equivalent to an ENI broadband RF linear amplifier?
E&I offers a range of amplifiers in which the performance specifications mirror the former ENI line. For a more in depth comparison, please refer to the table on our ENI Comparison page, or Contact us.
How do I find an equivalent to an ENI Pulse MRI amplifier?
E&I does not produce MRI Pulsed amplifiers. But, we know an excellent company that does: Stolberg HFTechnik. You can find them at http://www.stolberghf.com
Where can I find a product manual?
Product manuals can be downloaded from the E&I web site; each product page provides a link to download a PDF of the corresponding product manual.
Does E&I design products for HF, VHF and UHF applications?
Yes, E&I’s Broadband RF amplifiers cover all these frequencies. We have a range of HF amplifiers, VHF amplifiers and UHF amplifiers. Please refer to our Applications pages for more details on which units are best suited for specific applications.
Are linear amplifiers useful as RF test amplifiers?
RF linear amps are more suitable for RF test applications than non linear types as they do not alter the fidelity of the signal that they are amplifying.
How do I find out how much an amplifier costs?
A Request for Quote form can be submitted directly from our website; we will then send you a formal quotation, typically within one business day. You can also call our Sales Dept. at 5852140598 x 1.
What if I don't see an amplifier with the specifications I need?
In addition to our standard product line, we also specialize in designing custom amplifiers to meet each of our customers' specific application requirements. Please submit a Custom Request form or if you’d like to discuss your requirements feel free to give us a call at 5852140598 or send us an email; info@eandiltd.com Our product support and sales staff are available to help.
All products purchased from E&I include a three year warranty from the date of delivery.
What is the voltage output of an E&I amplifier?
This will depend upon the impedance of your load. Please Contact Us for more information  we would be happy to calculate this for you, or provide you with a spreadsheet that allows you to determine this information.
Does E&I support the old ENI amplifiers?
We offer service and repair on ENI amplifiers as well as E&I models that have been made obsolete. All repairs are completed utilizing original ENI schematics and approved components.
E&I rates all of its amplifiers at 1 dB compression – this is the point where the power gain is 1 dB below that of the linear range. When we say a unit is rated at 100 Watts, this means that you can run it at 100 Watts 24 hours a day, 7 days a week, in a continuous mode or any other mode your application requires.
What if my impedance doesn’t match that of the amplifier?
All E&I amplifiers have a characteristic impedance of 50 ohms. If the amplifier is driving a non 50 ohm load, this will create a mismatch resulting in a certain amount of power being reflected back to the amplifier. E&I’s amplifiers are designed to withstand 100% reflected power continuously without damage. However, the mismatched power will in turn affect the gain of the amplifier. E&I offers a solution to resolve this mismatch and also improve the power transfer; with its line of Matching Transformers. By placing a matching transformer in between the amplifier and the load, you are able to achieve maximum power transfer without the added cost in power output.
Is there any protection designed into E&I’s amplifiers?
E&I amplifiers are completely protected against damage due to load mismatch provided that the input RF level does not exceed 1.0 V RMS. The units are built to withstand input signals of +13 dBm without damage for all output load conditions including short and open circuits.
What is the difference between Class A vs. Class AB and how is it relevant to various applications
Most simply, the difference between Class A and Class AB is the point at which the transistors are biased. Our Class A amplifiers provide excellent linearity and they amplify the input signal with minimal distortion. With Class AB, however, some distortion is inevitable, but these units are more efficient. A more in depth explanation is provided in an application note;