want a LNA(fre:10-30MHz,NF<1.2dB,gain>15dB)

时间：04-09 整理：3721RD 点击：

Who knows where a LNA would be bought.The LNA is required as follows: operating frequency:10MHz to 30MHz, NF<1.2dB, gain>15dB.
In addition,if i want to design it by myself,what kinds of devices should i select?

google for PA0RDT miniwhip antenna. this has implemented two types of antenna amplification for short waves, and is a reputed design.

Sarma

Thank you, Sarma.
But the noise figure in that design downloaded from http://www.py2mg.qsl.br/Arquivos_PDF/pa0rdt%20whip.pdf is not mentioned.
Do u have other good suggestions for me?

Who knows the answer can contact me immediately by eamil: bigxu1979@163.com

Will you try
http://www.wantcominc.com/data%20Sheets/WEA101.pdf

The overal noise is greatly depend on the first amplifier which is J310 in your case and it has a NF of around 3dB. At these low frequencies it might be better but I have not checked the datasheet. So the total NF will be mainly calculated by the NF of the first transistor+ the NF of the second. see http://www.microwave.gr/content/casc...l_nf_calc.html for an online calculator to easy calculate the total NF.

if you use 2n7000, the NF will be improved i feel

It is hard to get the NF values from the data sheet of any vendor as the current BJT transistors are capable of operating at 4 to 6GHz.

It is the call you have to take that say ATF35143 which is based on GaAs has low NF around 0.5dB. But Data sheet is not indicating the NF at 10MHz range.
It might be true if we extend the NF curve to 10MHz.

In this case I will try ATF device and decide if it fails.
In my view it may not fail by 90% to meet the required NF

Is it really? I thought as a general rule that the NF pf any active device is lower at lower frequencies always.

having made a statement, let me take a little time either to get corrected or convince you, please.

I agree with mvs sarma that NF may increase at low frequency resulting extrapolation fail.
Then we need to know up to what frequency point the NF will decrease and then stars increasing?
We can not get this information from data and need to do the experimentaion and the same is explained above.
Certainly not that the NF will shoot below the frequency measured by the manufacturer.

while i am still studying the matter, I found that NF is related to collector current. thus the front end amplifiers need to run at low collector currents, adding additional stages if needed. BTW, GaAsFETs offer lowest NF. but will they offer needed gain at such low frequencies and are they cost worthy?

Sarma

Hi Sarma,
It is not always true that reduced collector or drain current will lead to NF. NF is like a well, until an optimum point we can decrease the current but less than that NF will again raise.
The same phenomena is applicable to frequency too.
Instead GaAs FET I recommend p-HEMT devices (ATF family mentioned above) which gives much lesser NF.
GaAs will give around 1dB NF but p-HEMP will be around 0.3dB.
Check the data sheets and process if you like to validate this.

Yes, the device I mentioned above will give the needed gain.

Thanks Kspalla,

Any device numbers and approx cost and availability. For info I am at Hyderabad in India.

want a LNA(fre:10-30MHz,NF&lt;1.2dB,gain&gt;15dB)

want a LNA(fre:10-30MHz,NF<1.2dB,gain>15dB)