Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
General purpose RF amp




 
The AM Forum
November 20, 2018, 07:28:48 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: General purpose RF amp  (Read 461 times)
0 Members and 1 Guest are viewing this topic.
PA0NVD
Member

Offline Offline

Posts: 366


Nico and Chappie (Chappie is the dog...)


« on: October 17, 2018, 03:58:44 PM »

It happens many times experimenting that you just need a bit more amplification somewhere. There are many IC nowadays that give you a certain amount of gain at low cost, but very few are adjustable. And, many times you just don't find them in the junk box. But transistors are always there...
So a small circuit attached. The amp has in input impedance set by R1. So for 50 Ohms, use 47 Ohms. The gain is set by R2, actually by R2/R1. So if you take 470 Ohms, you have 10 x voltage gain is 20 dB. Take a 1 k pot and you can adjust the gain. Take R5 zero and you have 0 Ohms output impedance, Take R5 47 Ohms and it is a 50 Ohms output impedance.
R4 should be selected for the current demand at the output. Low power RF amps, 220 Ohms will do fine. and your second transistor will take approx 2 1/2 mA. Take 100 Ohms and your second transistor takes approx 5 mA.
If you need some voltage swing, than you should put in R opt. If R opt is approx R2/2 (half the value of R2), your amp is able to swing approx 3 V tt Without R Opt approx 0,8 V tt
R3 depends upon the type of transistor and the upper frequency limit you need. For general purpose transistors like the BC546, 2.2K will do fine and you amp has a BW of approx 10 MHz Using RF transistors with an Ft of approx 2 GHz and R3 = 1k at  Vcc 12 V, you can expect approx 250 MHz BW
I used this amp to have a little more noise in my noise canceler, In a wide band noise generator wit a zener diode that give 0dBm from 1 to 500 MHz (used for bandfilter adjustment together with a spectrum alalyser of for adjusting bandfilters at max)
and many other projects and experiments. So I thought sharing it


* GP amp.JPG (377.4 KB, 2592x1944 - viewed 142 times.)
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 6948



WWW
« Reply #1 on: October 19, 2018, 08:43:40 PM »

Very Helpful! Thanks!
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
PA0NVD
Member

Offline Offline

Posts: 366


Nico and Chappie (Chappie is the dog...)


« Reply #2 on: October 26, 2018, 03:22:06 PM »

Here is the amp used for a wide band magnetic loop antenna. R1 is deleted, the loop needs zero ohms load.


* magnetic loop amp.JPG (2246.7 KB, 2592x1944 - viewed 47 times.)
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.061 seconds with 18 queries.