RF components needed for small project

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,655
Hello...

I need to know about which referencies I can purchase for RF components for the following:

Diodes
OpAmps
MOSFETS
Signal Generators

Desired frequencies can be anything from 27Mhz up to 400Mhz or even more! This is supposed to build a VSWR simple testing device. I actually have some RF components here but I'm looking to improve the circuit even if I have to spend some money on better components.

Actually I'm using:

Diodes - AO91 (or AO90, can't be sure)
OpAmps - MCP6002
AD9850 as signal generator but I guess it has not enough power for the circuit!
 

danadak

Joined Mar 10, 2018
4,057
What are you trying to measure ?

Over what power/voltage range ?

What is desired freq range ?

What is done with the signal ? Display on PC ?

Regards, Dana.
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,655
What are you trying to measure ?
Already answered but I'm trying to measure VSWR.

Over what power/voltage range ?

Very low Power but a signal generator module using AD9850 is not enough.

What are you trying to measure ?
What is desired freq range ?
Up to 470Mhz or so.

What is done with the signal ? Display on PC ?
VSWR is measured and shown in an LCD by means of a uC.
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,655
I have my "thing", so to speak, built but I think I might need to improve it so that I can get better results.

I'm using a signal generator module (but not enough power), a couple of 1% tolerance resistors for a resistive bridge, AO90 (or AO91) diodes, and caps for peak detection, then I use 2x MCP60001 amplifiers to amplify the signal coming from the bridge and lastely I use AtMega328p ADCs to read those values and convert them into "readable" values that are shown in an LCD.

Problem is that this diodes are like "injecting" quite some non-linearities into the circuit and results might suffer with that. I will try to use software correction to try to filter out at least some of those non-linearities, but if I can get better components, I'll try to use them instead. Also, if I can amplify the DDS output signal which is very low to make the circuit work, it would be ideal for me!
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,655
Hello,

The non-linearity might be a problem of the construction of the measuring bridge.
In the given PDF's there are some ideas for the measuring bridges.

Here is an other page with the construction of an UHF bridge:
http://vk5ajl.com/projects/swrmeter.php

Bertus
Ok, from what I see in that link, my small academic project as a more simple concept. But probably it's roughly the same but that one should be way better.
The base I used for my circuit was this:
https://ludens.cl/Electron/swr/swr.html

Then I used a couple of filters and OpAmps at the bridge output. That's all. The rest is for reading and converting values (uC ADC) and LCD to show them and a few lines of code. Not much more. But I struggled because I started building this on a breadboard which might raise some problems due to frequency, despite the fact that initially I was using low frequencies such as 1Mhz, 10Mhz up to 30Mhz and only used resistive load for testing purposes. Now I'm porting this to a copper clad board and I would like to use slightly better components in order to decrease error from hardware and possibly correct more of the errors with software! That's why I asked for some references of RF components suitable for this range of frequencies up to 400 Mhz or 500 Mhz. That way I can eventually use one of my school lab antennas to make a real measurement!
 

RichardO

Joined May 4, 2013
2,271
Look for some transistors that have an F_t of several GHz. Use very low capacitance diodes in your bridge. Use all surface mount parts. Use a good ground and power plane with very short traces on your PCB. Bypass, bypass, bypass -- at all frequencies.

I like the high frequency transistor arrays such as the HFA3127, HFA3096 and the like. The HSMS2822, HSMS282P, etc. series of Schottky diodes is probably better in place of a germanium diode like the Ao90.
 

ian field

Joined Oct 27, 2012
6,536
Hello...

I need to know about which referencies I can purchase for RF components for the following:

Diodes
OpAmps
MOSFETS
Signal Generators

Desired frequencies can be anything from 27Mhz up to 400Mhz or even more! This is supposed to build a VSWR simple testing device. I actually have some RF components here but I'm looking to improve the circuit even if I have to spend some money on better components.

Actually I'm using:

Diodes - AO91 (or AO90, can't be sure)
OpAmps - MCP6002
AD9850 as signal generator but I guess it has not enough power for the circuit!
Germanium diodes are probably OK for the high end of the SW radio bands, but you're looking to wander about in the same ball park as TV tuners. some TV tuners use a mixer diode and that might be as good a place to look as any.
 
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