10.7MHz amplifier - Page 1
Forum section: electronics / beginners

author: Brian2003
author_rank: Newbie
timestamp: December 07, 2023, 04:59:05 pm
content: hi,I'm trying to build 40dB 10.7MHz amplifier with opamp. I found a couple of LMH6628 and I thing with 3 stage I can reach 40dB anyone tried something similar.That is not to easy I need to use single 5V supply. Any comment on the circuit below?

author: TimFox
author_rank: Super Contributor
timestamp: December 07, 2023, 05:11:36 pm
content: In simulating that circuit, you should add a resistor after the voltage source to represent its output impedance, make sure your op amp model includes its capacitances, and possibly add some "stray" capacitance to represent the circuit board capacitances.Check for oscillation/stability: you may need to add a very small capacitor across the feedback resistor.In construction, you need to be paranoid about coupling backwards across three amplifier stages at high forward gain: probably should include series resistance or inductance in the power-supply decoupling at each stage.

author: David Hess
author_rank: Super Contributor
timestamp: December 07, 2023, 05:55:57 pm
content: You can definitely do that, but keep in mind that high gain will require good isolation between the input and output to prevent oscillation. 40dB total gain is possible but will require some care in layout.

author: iMo
author_rank: Super Contributor
timestamp: December 08, 2023, 04:35:48 pm
content: The 10.7MHz amplifiers are usually not made of opamps (assuming you want to build an IF amplifier). There are IF RF chips for that, or discrete transistor amps, with some impedance matching and selectivity as well..

author: David Hess
author_rank: Super Contributor
timestamp: December 08, 2023, 05:52:28 pm
content: Linear Technology published a couple of examples of current feedback operational amplifiers in IF applications.Besides cost, I think the major disadvantage is inherently higher noise, but in most IF applications noise is not a limitation.

author: iMo
author_rank: Super Contributor
timestamp: December 08, 2023, 06:01:18 pm
content: 40db gain at 10.7MHz with 3 opamps - a good exercise to try, but nobody would do that in real life, imho..

author: Brian2003
author_rank: Newbie
timestamp: December 08, 2023, 08:17:57 pm
content: I know the device which works in real life with 3x TSH110 opamp exactly with 40dB gain and after that AGC.I will try with OPamp too to see in the realIf any can suggest any useful IC for IF ampliers I will be very grateful as I found yet many of them is obsolete MC1350, CA3028.

author: MarkT
author_rank: Frequent Contributor
timestamp: December 08, 2023, 10:00:50 pm
content: These days I guess you'll have to find a generic low power broadband RF amp and add IF filters on input and perhaps output. Or go to the SDR approach (which its lower selectivity). Analog RF modulation is dying out fast.

author: David Hess
author_rank: Super Contributor
timestamp: December 08, 2023, 11:49:58 pm
content: Quote from: iMo on December 08, 2023, 06:01:18 pmWhere they would do it is a video or baseband application where instead of 10.7 MHz it is DC to 10.7 MHz.

author: vk6zgo
author_rank: Super Contributor
timestamp: December 09, 2023, 12:15:01 am
content: Quote from: David Hess on December 08, 2023, 11:49:58 pmYes, the OPs schematic looks a lot like a video amplifier.Over time, we have had quite a few Beginners complaining that their clever Op Amp tuned RF amplifier simulated perfectly, but oscillated in real life, thus learning an interesting lesson about Op Amps, & the similarity of the effect to that which made the old school "Tuned Plate, Tuned Grid" oscillator work.I tend to wonder what the application is, as 10.7MHz is usually used for IF stages which are required to be selective.If this thing is fed from conventional LC tuned circuits & outputs to similar circuitry, it will almost certainly oscillate.