how to check an RF board?

Hi

If I make a RF circuit (for example a complete superhetrodyne receiver including several stages like as LNA,RF Amp, filter,mixer, PLL ,....) how to test each section of the circuit ? how can I get the signal of a stage with spectrum analyzer?

How you test your RF boards and its stages?

My problem is each stage is 50 ohm input and 50 ohm output,so I can not use a measurement device like as SA with 50 ohm input impedance for measurement.

if each stage is 50 ohm to 5o ohm u don't have a problem to measure the circuits

khouly

why?
for ex. the output of stage 1(50 ohm output) is connected to input of stage 2(50 ohm input),If I want to check the signal between stage 1 and stage 2 ,I can not add SA,because it is a load with 50 ohm,and stage 1 will have two 50 ohm load!

when i do this , i always , place a 0 ohm resistor , in serise between the blocks , so i can remove it , and connect a pig tail in the pads of the resistor so i have access to both circuits separated


khouly

Use active probe that has high input impedance

where can I find one on internet to see datasheet and buy?

what is "pig tail" ?Can I see its picture?Ca I buy it? or I have to make it myself.


How do you perform Internal node testing in RF circuits(between 50 ohm stages)?

http://cp.literature.agilent.com/lit...988-9889EN.pdf

In what frequency range are you working on?

If below 5GHz, you can make your own passive (or even active) high-z probe with some work. Don't go waste your money on agilent/tektronix probes right away...

the big tal is a semi rigid coax cable with open end and the other is SMA , the open end can be soldered to the board


and rfmw
can u send any link or tutorial how to make my own active probe , it will help me alot

khouly

@khouly

https://www.edaboard.com/viewtopic.p...=passive+probe

it has a broader frequency range now. DC-10GHz ;) and its active now ;)

rfmw: Please send yhe sch and photo of your probe if possible,is it active high impedance proble?

I saw your given link ,but I need more help and comment.

Thank you

The probe is basically taken from the (one of the) Black MAgic books from Howard JOhnson -> a resistor tip and coax. I had to choose the right resistor to get frequency independent response, well at least to 10GHz, that is. Then I compensated the resistors response with a MMIC amplifier to make it active. If I remember correctly, the active probe now has a -15dB response, instead of -30dB in the passive version.

I frequency needs is under 2GHZ.

What ebook of Black MAgic books did you use? what page?

for f<2GHZ,is there any need for Active probe? Is passive one enough?

I think first book of Black Magic is the one.

My probe has 500Ohm input impedance so it might be too low for your application. The load on a 50Ohm transmission line is still acceptable.

Whether you need a passive or active one depends upon your application/circuit. I'm using it for in-circuit measurements with DSO/DCA. However using the probe with spectrum analyzer is valuable too.

It is upon you to decide which one to choose, an active probe with high impedance (25kOhm || 0.2pF) or passive one with 200-1kOhm impedance.