433MHz module RF output amplification

Hello,

I would like to amplify my AUREL TX-SAW/s-Z module RF output by external amplifier (MMIC, MAX 2430 or AT41511 circuit) to reach RF output power 20dBm. According to datasheet AUREL module provides max. RF output power +10dBm when 5,5V power supply applied. I can identify component labeled "E2W" (which I consider to BFS17A transistor) on module PCB and I am able to measure voltage changes on its pin during transmittion. But no voltage I was able to measure on RF output pin what is confusing me because I expected it as input for my external amplifier. When antenna is connected to this pin broadcast coverage increases so it seems the RF output is OK. Do you have any explanation why I am not able to identify any voltage on module RF output pin? Just basic multimeter and PC souncard osciloscope (max. 20kHz) are available to me so I cann't do experiments with Spectrum analyzer and devices like this. Any ideas appreciated.

Many thanks,

RST

Hmmm.... let me see..... You are trying to measure 433,000,000 Hz with a soundcard having a 20,000Hz top limit and a multimeter that might manage a few hundred Hz at best.

Nope, I thought long and hard but I don't think that will work.

Brian.

betwixt: To be precise I don't want to discover voltage curve or precise voltage value at 433MHz. I just expected "some voltage changes" during transmition on RF output pin in line with changes on transistor that operates on the same frequency and which has been measured by the multimeter "that might manage a few hundred Hz at best". May be I can't see some crucical fact but your post haven't moved me forward. Nevertheless thank you for contribution. The question is the same: "Why I am able to find voltage changes on amlifier transitor and zero voltage on RF output?"

Thanks a lot

RST

---------- Post added at 23:54 ---------- Previous post was at 23:47 ----------

betwixt: To be precise I don't want to discover voltage curve or precise voltage value at 433MHz. I just expected "some voltage changes" during transmition on RF output pin in line with changes on transistor that operates on the same frequency and which has been measured by the multimeter "that might manage a few hundred Hz at best". May be I can't see some crucical fact but your post haven't moved me forward. Nevertheless thank you for contribution. The question is the same: "Why I am able to find voltage changes on amlifier transitor and zero voltage on RF output?"

Thanks a lot

RST

you cant measure RF voltages directly with a multimeter... as the other poster said... it aint gonna work
and forget about the sound card
If you want to measure the Rf voltage you must have a RF probe and the output of that probe can go to the multimeter

An RF probe is easy to build, google a cct for one and build it, then you will see the results you expected

cheers Dave
VK2TDN

Thanks for the backup Dave !

Bear in mind that even with an RF probe you will only see a few mV on your meter and it will be impossible to follow any modulation pattern.
Going back to your original topic, most modules have an output impedance at the antenna connection of 50 Ohms so if you are careful not to upset the matching, you can connect it to a MMIC or similar to boost the power. I would urge caution though, be sure there is a DC blocking capacitor on the antenna connection and also be aware that you might amplify harmonic outputs to unacceptable levels. Most modules are low enough in output power that spurious signals are not a problem but when you amplify them, they may become significant.

Brian .
GW6BWX

I agree. When I was a student I was trained to faultfind on all manner of RF comms equipment with just an AVO 8 meter and a homemade diode based RF probe. We made our own RF probes using a pair of diodes and a couple of capacitors on a tiny PCB.

It takes a few minutes to make one. I suppose that today there are better options, eg a broadband true RMS detector chip could be used to make accurate measurements in 50 Ohm systems but a simple diode probe is still very useful and it represents the bare minimum in terms of RF (hardware) tools that someone should have.

OK, I have done RF probe according to design published at Simple RF Measurement Probe and now I can see voltage changes on RF output pin during module broadcast. Thank you for your helpful comments.

Regards,

RST