Picking low noise amplifiers for my project

[Amish_Fighter_Pilot]

Hello everyone. I am looking for a low noise amplifier for two purposes. I first of all need one for a low frequency antenna(DC-to-500KHz spectrum) that I can use to give my antenna output some gain before the diode ring mixer. I am using an FG-200 function generator as my LO, so I need an amp that will give the antenna gain but won't output a stronger signal than the function generator is. Can anyone recommend specific mixers that would be suitable for this?

The other LNA I need is for the transmitter. I'm taking the same signal from the FG-200 and also sending it to the transmitter, and I need an amp for that purpose as well. I really don't know yet how much gain this amp will need, but it can be much greater maximum output.

It would be excellent if the LNA is inductorless. I'm trying to keep inductors out of my design except for the tx/rx antennas. Also, BNC connectors are a plus. Thanks.

[David Hess]

Atmospheric and ambient noise below the HF band is usually so high that a low noise preamplifier is not necessary and gain before the first mixer only lowers dynamic range.

At 500 kHz and below, I would implement some variation of a feedback amplifier using a current feedback operational amplifier for both cases, and noise could be low anyway.  An LT1210 or LT1206 could be used for a higher output power.

[Amish_Fighter_Pilot]

Thank you! I will look in to those! I should note that I'll be filtering out high frequencies that aren't within audio range of the target frequency. So if I'm aiming for 1KHz, then the filter will remove anything above 1.5Khz or so.

[David Hess]

Nothing prevents designing and building a class-a or class-ab discrete feedback amplifier operating into the 500 kHz range, but I assume you want something simpler to work with hence my recommendation of the LT1210 and LT1206.

[Amish_Fighter_Pilot]

The current strategy I have is to get a board made with the ADA2050(a class AB part) for the transmitter amplifier, but I worry that 5W minimum output already might be overkill to my TX antenna. I think it will be less work to get a premade board and just replace the RC filter with different values.

For RX I am still trying to figure out how much gain I will even need for the antenna because its output has to stay lower relative to the function generator. Given the very wide range this system will operate at: I probably will need more than one antenna to swap between.

For the mixer I am leaning toward the AD831 mixer, but I can't figure out what sort of loss I'll have at those frequencies. I'm assuming the mixer loss will necessitate an active antenna rather than a passive one, but I'm still learning here.

[qiongcao]

https://tejte.com/blog/bnc-connectors-overview-uses-and-adapters/
Here is everything about bnc

[jmelson]

I needed an ultra-low noise op amp in a precision regulator for a very sensitive circuit.  I found the AD706 is tested down to one milli-Hertz, so the 1/f corner frequency is REALLY pushed down.  I don't know if this will do what you are looking for, but you might take a look at their data sheet.

Jon

[TimFox]

Your RX amplifier spec has the bandwidth going down to DC.
What is the actual lowest frequency of interest in your signal?
Low-frequency low-noise amplifiers will have "1/f" or "pink noise" that "outshouts" the white noise at low frequencies, characterized by a "corner frequency" below which the pink noise dominates.
Typically, bipolar transistor amplifiers are chosen when low-frequency pink noise is important, and the data should be shown on an IC datasheet.
An important detail about 1/f noise is that once it is added to the signal, averaging the result does not reduce it in the same manner that averaging reduces white noise (e.g. thermal and shot noise).

[Terry Bites]

Ultra low noise opamp specs can only be achieved with specific input impedances.
You could just be chucking money down the drain if you don't analyse the circuit properly.
The small print is a killer.

I think going down to actual DC is not going to work out.
Static charge buildup on the antenna might just kill the front end if you go down to DC
Before any gain, some serious filtering is needed. 50/ 60Hz will swamp everything, no?
So bandpass and notch.

[TimFox]

The standard reference for low-noise stuff, especially good for the "audio" and "video" spectral regions is
C D Motchenbacher & J A Connely Low-Noise Electronic System Design John Wiley (1993), the revised version of Motchenbacher's Low-Noise Electronic Design (1973)
Terry Bites' comment about source impedance is imperative.

[GigaJoe]

Will a nearby lighting strike kill the antenna's input ?

[David Hess]

Will a nearby lighting strike kill the antenna's input?

Yes, but so can the static discharge associated with thunderstorms without a nearby strike.  There are various ways to protect against anything except a direct strike.

[mawyatt]

The standard reference for low-noise stuff, especially good for the "audio" and "video" spectral regions is
C D Motchenbacher & J A Connely Low-Noise Electronic System Design John Wiley (1993), the revised version of Motchenbacher's Low-Noise Electronic Design (1973)
Terry Bites' comment about source impedance is imperative.

Those are a couple of the best references available, we were fortunate to have Dr Motchenbacher as another Honeywell Fellow back in the day!!

BTW those books and a few discussions with Dr Motchenbacher guided us in the development of the Rate Compensated Preamp utilized in the MSP (MILES Signal Processor) which had to detect nanovolt signals in the presence of extremely high noise backgrounds down to 0.1Hz. The concept of "pushing the signal integration" right up on the input from the MILES cable outperformed any other signal processing techniques at the time, and handily won the fly off with a much larger, more power, complex and costly system (long story if interested on how we were supposed to lose the fly off, but didn't!!).

Best