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Author Topic: RF Amplifier For DC Rx  (Read 412 times)

K3UIM

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RF Amplifier For DC Rx
« on: November 20, 2021, 08:25:02 AM »

Is there a fairly simple way to amplify the RF from the oscillator of a SA612AN in a DC receiver to power a digital readout circuit?
Charlie
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Charlie. K3UIM
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W1RKW

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Re: RF Amplifier For DC Rx
« Reply #1 on: November 20, 2021, 01:38:46 PM »

Charlie,  You would need 2 active devices at a minimum to make this work.  First stage would need to be a buffer of some sort so it does not pull the oscillator of the 612. A source follower as a buffer followed by a BJT should be as simple as it gets.
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K3UIM

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Re: RF Amplifier For DC Rx
« Reply #2 on: November 20, 2021, 04:02:48 PM »

RKW: Any circuit suggestions?
Charlie
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Charlie. K3UIM
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K3UIM

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Re: RF Amplifier For DC Rx
« Reply #3 on: November 20, 2021, 04:36:33 PM »

"AADE HF 20dB Preamplifier Kit - General Purpose Broadband Amplifier"
This is what I need, but they're temporarily out of supplies, or something. ...sigh...
I'll keep looking.
Charlie
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Charlie. K3UIM
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WB6BYU

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Re: RF Amplifier For DC Rx
« Reply #4 on: November 20, 2021, 08:29:04 PM »

Here's a simple example.

Q2 is an emitter follower to provide a high input impedance.
Q3 provides voltage amplification.


Of course, the required circuit depends on what the actual problem
is that you are having.  If the output voltage is too low, then some
sort of voltage amplifier is needed.  (The emitter follower gives power
gain, but not voltage gain.)

If the problem is just that the input to your counter pulls down the
VFO, then a common emitter stage may be sufficient.

Of course, a common source stage like the one shown here might
be even better.

Or this one.

G4AON

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Re: RF Amplifier For DC Rx
« Reply #5 on: November 21, 2021, 02:04:38 AM »

RKW: Any circuit suggestions?
Charlie
Spice circuit modelling software is your “go to” solution to checking out circuit designs, such as simple low power RF amplifiers. Modelling transformers can be awkward, as can adding obscure transistors, but in the main they are pretty straightforward to use and save a lot of time.

LTSpice is free and powerful, although it’s not as easy to use as Tina. There is a reduced functionality free version of the latter courtesy of Texas Instruments.

I mostly use version 12 of the student version of Tina, which costs $49.

https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html

https://www.ti.com/tool/TINA-TI

https://www.tina.com/

73 Dave

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G3RZP

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Re: RF Amplifier For DC Rx
« Reply #6 on: November 21, 2021, 04:45:57 AM »

Something like a 74HC06 hex inverter with two or even four inverters cascaded and a feedback resistor of abou a megohm or two will probably suffice up 20MHz.
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VK6HP

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Re: RF Amplifier For DC Rx
« Reply #7 on: November 21, 2021, 05:19:37 AM »

Charlie,

Here's a simple two-transistor (2N2222) VFO buffer and amplifier, courtesy AA8V:

https://www.frostburg.edu/personal/latta/ee/lm13/lm13bufferandxfmr/lm13bufferandxfmr.html

As I understand it, your DC receiver does not go beyond 14 MHz, so this circuit should be OK.

73, Peter.
« Last Edit: November 21, 2021, 05:23:57 AM by VK6HP »
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K3UIM

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Re: RF Amplifier For DC Rx
« Reply #8 on: November 21, 2021, 06:00:33 AM »

Thank you for your suggestions. I have some work to do! LOL
Charlie
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KB1GMX

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Re: RF Amplifier For DC Rx
« Reply #9 on: November 21, 2021, 02:42:54 PM »

most of the solutions presented are suitable for low impedance sources
and not friendly to the 612/602.

AADE is out of the business for many years now.  That used a
wideband OPamp and had a low input impedance.

The design needed most have a fet input for impedance low loading.
The first stage is best a (MPF102, 2n2210, J310)  source follower
as a start ,driving a 2n3904 or 2n2222 for gain.

FYI the Sa612/ne602 datasheet has a few ideas on how to drive a
counter from the oscillator on the chip. 

The oscillator in the 612/602 is very low power and loading it too
much will stop it.  So a buffered two stage high impedance input
amp is required. 

Allison
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KL7CW

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Re: RF Amplifier For DC Rx
« Reply #10 on: November 26, 2021, 11:03:33 AM »

some folks who use an SA612 choose to use a separate external oscillator for various reasons.  With a separate oscillator it may be easier to divide the output and, if necessary, amplify the counter output.    KL7CW
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