Considerations when using high-gain LNAs

s-l1600

Some of our LNAs provide in excess of 40 dB of gain and operate over a wide frequency range. The primary application of these products is to amplify weak signals by increasing the signal-to-noise ratio at the receiver.

One important consideration when using these LNAs is that they amplify everything across their frequency range of operation. If your receiver does not have any front-end filtering, you might find yourself having to deal with a large assortment of strong unwanted signals. Most software-defined radios are wideband and therefore susceptible to these strong signals. A strong signal present at the input of a receiver can cause it to saturate and produce garbage at the output.

When using these high gain LNAs we recommend using a bandpass filter for your frequency range of interest. We have a number of such filters for GPS, 426, 433 MHz, 915 MHz and 2450 MHz bands: http://stores.ebay.com/gpiolabs/Bandpass-Filters-/_i.html?_fsub=28020158018

and we are looking to add new filters. If you would like to see us develop a filter for your application, get in touch.

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9 thoughts on “Considerations when using high-gain LNAs

  1. Hi where should the band pass filter 162 Mhz be set, before the LNA or after the LNA ? to receive best quality signal and distance on the AIS reciver ?

  2. The challenge with that is if you’re trying to feed LNA supply voltage up the coax. The filter trailing the amp will block the supply current.

    I have another question, this regarding the 2 10-2000 MHz 0.5 dB LNAs that I recently purchased. I started out feeding the +5 vdc supply externally, because I didn’t have any 10 uH chip inductors to allow feeding up the coax. Yesterday, I picked up some Coilcraft 10 uH 0805 chips and soldered one on the two pads right there by the output SMA. The low frequency (less than 200 MHz) performance went to heck, and I’d swear there’s a little oscillation now. Are you certain that it’s a 10 uH inductor that is necessary? When I removed the inductor, everything returned to normal.

    1. Can you please post the data sheet or part number for the inductor? Also when you say oscillation, did you see a reduction in gain at 200 MHz or lower? Or what do you mean by oscillation?

  3. Hi there –
    All I can say is that the inductor is part of the Coilcraft C-12 kit. My friend Doug uses this kit for a variety of RF projects. I can’t find the actual details on the 10 uH part he provided me. I’ll keep looking. However, since I’m using your FM BCB blocking filter behind the LNA, I can’t supply current up the coax so the setup is working well for me. That is one awesome amp.
    Cheers and 73 – Jon N7UV

  4. Good evening –

    I was wondering what you estimate is the current draw of the 100 kHz to 2 GHz LNA. On two of them I’ve measured between 160 and 180 mA at 5.0 vdc. On the Minicircuits data sheet, it indicates that the nominal current at 5.0 vdc is 97 with a max of around 120 mA. Certainly the LED pulls a little current, but I’m not sure it’s worth 80 mA or more. Any ideas?

    Cheers and 73 – Jon N7UV

  5. Hi there – I am using the +5 vdc pad on the board. I am measuring current using an HP Harrison 6224B power supply set at 5.0 vdc. I will check the current reading independently.

  6. Ok that makes sense. That is the current into the regulator. Our design uses a regulator to ensure that the LNA sees a fixed voltage as the output from a USB supply can deviate from 5V.

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