[amsat-bb] LNA Circuit for VHF and UHF homebrew

[Zach Leffke]

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.  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
>
>> On Dec 7, 2018, at 9:55 AM, "lu9cbl at gmail.com" <lu9cbl at gmail.com> 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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