I've had a lot of luck with the PGA-103 device for homebrew pre-amps from Minicircuits, which works well for both VHF and UHF: https://www.minicircuits.com/WebStore/dashboard.html?model=PGA-103%2B. The only downside is if you buy just the chips from them, the minimum order quantity is 20, at $1.99 a pop.  They also sell 'connectorized' version in a small package with SMA connectors for around $50.00.  Main features are 50 ohm input/output making impedance matching easy, sub 1.0 dB noise figure, high gain through UHF (greater than 20dB), and pretty high OIP3 for good linearity in the presence of strong signals.

Inspired by prior work done by hams (including a paper by WA5VJB), I did my own layout in Eagle CAD which can be found here:  https://github.com/zleffke/eagle_pga103.%C2%A0 Main features on my version are a built in 5V, low noise, regulator so that I can supply it with standard 13.8V.  The regulator also has an enable/disable pin that I use as a PTT control signal for TX/RX sequencing.

The form factor of the board was for a specific type of enclosure I happened to have, so you may want to do your own layout, but the basic schematic might be helpful to get you going (basically taken from WA5VJB's paper, with slight tweaks).  For the filtering part, I was targeting a specific chip level SAW filter for UHF applications, which can by 'bypassed' (little jumper on the board in place of the filter chip) for VHF applications (I have yet to find a SAW filter for VHF that I like that's readily available on digikey/mouser).  You could toss out my filtering chip piece and insert your own.  Minicircuits has detailed S parameters on their page to get the matching part fine tuned (though they do claim 50 Ohm impedance on both input/output across the range of operation).

I haven't done any rigourous testing of the three prototypes I built (impedance, gain, or Noise Figure measurements) yet, other than just getting on the air with them.  They seem to perform well enough for me.

The github link might not be perfect for your application, but might be a useful starting point for you.

Hope this helps, good luck!

-Zach, KJ4QLP

Research Associate Aerospace Systems Lab Ted & Karyn Hume Center for National Security & Technology Virginia Polytechnic Institute & State University Work Phone: 540-231-4174 Cell Phone: 540-808-6305

On 12/7/2018 10:09 AM, Ed Krome wrote:

Go to wa5vjb.com; search for preamp cookbook. All kinds of useful circuits.

Ed Krome K9EK

Sent from my iPhone

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On Dec 7, 2018, at 9:55 AM, "[email protected]" [email protected] wrote:

Hi to all!

In my club we are building a groundstation, and we want to make two LNA's one for VHF and other to UHF eggbeater antennas. Someone can share a circuit to do one for each band??? i can't find it in google (maybe i'm searching wrong).

Thanks in advance

Mati LU9CBL

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