RF probe for 434Mhz

Anyone know of a decent RF probe for use at 434Mhz, that will give a DC voltage level reading even for signals around the 100mV area.

I would very much like a 500Mhz Scope, but they aint cheap, not in my price range.

A simple, well screened, RF probe would do. Buy or DIY.

I need to measure the effectiveness of screening, grounding and PCB layout on a module using a 434Mhz transmitter.

I already have a digital 30MS/s scope, and multimeters down to 0.1mv resolution.

You can make one look here:
http://www.qsl.net/n9zia/wireless/appendixF.html#22

OR see if you can get one of these:
http://www.analog.com/en/rfif-components/detectors/products/index.html

Which are pretty well calibrated already and respond pretty quickly.

Talk to manuka? ....

Here's one:

http://www.seeedstudio.com/depot/rf-explorer-433m-p-784.html?cPath=174

Hi,
I,m wondering, do you mean uV? If you just want a dc voltage, use a microwave diode or similar, and use an op amp.

Regards John

I tried the RF probe mentioned in post #2, and did get an indication, but I am thinking that this probe needs a few hundread mV to work.

I dont need to go down to uV, say more like a 20mV and higher.

The Analogue devices things look like they are capable, a worked example would be good.

Oh, and the intention would be to fit the probe in a metal tube (like a probe really), steredent or cigar tube for instance.

A metal tube is definitely the way to go. Sealing up the circuit in metal will help give you more consistent measurements.

Once the signal has been rectified to DC, any low-power, single supply op-amp can be used to jack up the voltage to a useable value.

While not cheap at $9.50 US, the AD8361 looks pretty versatile.

It does indeed, the application note suggests its not difficult to setup. Sample layout for a PCB too.

0.25db linear response 0-2.5Ghz !

I love the Analog devices IC's - they really take a lot of headache out of these types of measurements

This RF probe has a 50 ohm impedance. I don't know what you are measuring, but 50 ohms might load down the circuit if you are using it like a scope probe. It should be sensitive into the microvolt range, but noise might swamp the signal. Also, this might be a negative detector, so make sure you are looking for negative voltages.

You could probably include a 4:1 transformer to get the impedance to 200 ohms and not load the circuit so much.

Hi,
If you think how a 430MHz swr meter works, for forward power just a diode, resistor and a cap.
Depends how complicated you want it..

Regards john

john hauton said:

Hi,
If you think how a 430MHz swr meter works, for forward power just a diode, resistor and a cap.
Depends how complicated you want it..

Regards john

Click to expand...

They work sure, but a passive SWR does not work generally for such very low powers. Granted I have not hooked up a mV meter across the SWRs own meter terminals, but does not the SWR need a minimum power to make the diode conduct ?

I might find my SWR meter and do an experiment.

A good SWR meter will have the min/max power listed. Readings made on a passive SWR meter with less than the minimum driving power will not be accurate.

John

Someone elsewhere pointed out this device,

http://www.lessemf.com/probe.html#rf

Which looks ideal, but its expensive to get sjhipped from the US.

Wonder whats inside the probe ?

Anyone seem something similar this side of the pond ?

Could be something like

http://sound.westhost.com/project74.htm

using a "special" diode from, for example

http://www.modecomponents.co.uk/

http://www.jabdog.com/semi-diode.htm

e

I have some IN34 diodes on the way, they seem to be the standard for this sort of thing.

Also a 1/4" Metal jack plug to house the probe.

We shall see how it performs .......