problems in adding power amp to a rf module
I connected the output of TXM-433-LR RF TX Module from LINX technologies company to input of RA07H4047M (7W RF power amp from mitsubishi)
according to datasheets.
But in output of RF power amp I have 5 carrier frequecy with 47MHZ spacing centered around 433MHZ. and the highest power carrier is 481MHZ with 37dbm.
I do not know why one 433Mhz carrier is converted to 5 carrie?
do you have any help for me?
Is there a way to solve the problem?
May PA have effect on RF module?
how can I remove these spur unwanted frequencies?
sounds like you've made a nice power oscillator.
I would look at grounding and shielding (even just mounting of the PA module). I'm not familiar with the LINX modules you're using, but they may not be shielded enough (or at all) to prevent the high power output from getting back into them.
I'm not sure it is such a good idea to bring one of those modules up to several watts anyway!
Lance
Well, that's pretty cool. But nothing we haven't seen before!
Things I would try:
1) put a 3 db pad between the Linx and power amp and see if problem goes away.
2) Put a (high power) pad at the output of the power amp and see if the problem goes away.
3) Put a scope probe on all the bias points of the power amp module while it is running, and see if there is any 47 MHz sine wave riding on top of the DC. If so, try bypassing with big (47 uF) tantalum caps.
Then let us know what you see.
I placed 10W 20db power attenuator at output of PA but problem exist!
I placed a RF amp block between LINX module and PA but problem exist!
I removed LINX module and used a POS-535 VCO tuned at 434MHZ and apply its signal to PA input,but problem exist!
I also replaced PA module by another one but problem exist!
I want to test supply and gate lines.
Hi, The problem is most likely from your powersupply connections to the PA module. First ONLY use tantalium capacitors and ceremic 100nF// 10nF//1nF//100pF capacitors nothing else. // means parallel. Do not use electrolitic types !.
Between the power module and you VCC put a ferrite beat and use the above given capacitors and connect the close to your module. The module should be mounten on a heatsink and directly connected to a PCB so NO wires for VCC, GND or RF !.
Things to test: Connect a 50 Ohm resistor at RF in to ground and see if you still get something out of the module if so your harware setup is NOT for RF and you should read about RF before you continue !.
Paul.
I agree. It sounds like your power amp wants to oscillate at 47 MHz, and that is mixing with the 433 MHz you want to be amplified. Could be power supply bypassing. There is a slim chance it is the supply or voltage regulator that is providing the DC. Myabe try a different power supply or battery power. Also, make sure there is some isolation between the various bias points so there is no RF feedback along the bias lines from the output fet of the amplifier to the input fet.
How I connect module heatsink(module casie) to RF PCB ground plane? (bottom layer of PCB is GND plane).
Do you have any photo for such circuit(mitsubishi modules) that works without any problem?
I have used SMA connector for RF-In and RF-Out,Is this ok?