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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

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 = 10Log₁₀(P_o /P_i)

Example:

A transistor has an output power of 50 watts with 10 watts input power. Its gain in dB is:

10Log₁₀(50 /10) = 10Log₁₀5 = 6.9897 ~ = 7.0 dB

and an attenuator that has an output of 25 watts with an input of 100 watts is:

10Log₁₀(25 /100) = 10Log₁₀0.25 = -6.021 ~ = -6.0 dB

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 ‘Pointy-Hair’ 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, ‘Pointy-Hair’ 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 f2-f1 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 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

– 100 = 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

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 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 IL

Current Power in to load is PL

For maximum power
RL=RS
You don’t believe us?

You are going to have to look at some calculus!
So if PL = IL2 RL
And for maximum power

And PL = IL2 RL = Vs2 RL (Rs+ RL)-2
Then

So: (Rs+ RL)-2 = 2RL(Rs+ RL)-3

1 = 2RL(Rs+ RL)-1
2RL = Rs+ RL
Rs= RL

All system impedances are 50 Ω.

A 50 Ω load is equal to a cable with a 50 Ω characteristic impedance infinitely long.

How do I find an equivalent to an ENI pulse amplifier?

E&I does not produce MRI pulse amplifiers.

What does P1dB mean?

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 you can run it at 100 Watts 24h hours a day, 7 days a week, in a continuous mode or any other mode your application may require.

Does E&I design amplifiers for HF, VHF, and UHF applications?

Yes, E&I’s broadband amplifiers cover all of these frequencies. Please refer to our Application pages for additional details on which models are best suited for specific applications.

What if my impedance doesn’t match that of the amplifier?

All E&I amplifiers have a charactertic impedance of 50 ohms. If the amplifier is driving a non 50 ohm load, this will create a mismatch resulting in certain amount of power being reflected back to the amplifier.
E&I’s amplifiers are designed to withstand 100% reflected power continuously without damage.The mismatched power, however will in turn affect the gain of the amplifier.

Check out our new line of impedance matching transformers.

Is there any protection built into E&I 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 voltage output of an E&I amplifier?

This will depend upon the impedance of your load. If you are unsure how to calculate this, please feel free to Contact Us for more information – we can provide you with a spreadsheet that calculates this for you.